Field of the invention The present invention refers to a process for the preparation of a bis(acyl)phosphinic acid silyl ester of the general formula I,

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl; as well as the bis(acyl)phosphinic acid silyl ester and the bis(acyl)phosphinic acid obtained by the process.

Background of the invention

Bis(acyl)phosphine oxides (BAPOs) are well established and are extremely efficient photoinitiators for the industrial curing of pigmented or clear coatings, adhesives, inks, photoresists, printing plates, and dental applications. The most prominent commercial product of this class is Omnirad 819, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, formerly known as Irgacure 819. Since long, there is a high demand for liquid and / or water soluble BAPOs. Many efforts have been undertaken to get to such compounds, most of the processes consist expensive or laborious procedures. For example, WO 2012/012067 A1 discloses the synthesis of alkyl bis(mesitoyl)phosphinates starting from dialkyl hydrogen phosphites. Only n-butyl bis(2,4,6-trimethylbenzoyl)phosphinate was given as an example but without any information on yield or product properties. It is to be noted that the example could not be reproduced in the applicant's lab and does not seem to be reliable.

A water-compatible form of Irgacure 819 is available as a water dispersion but a stable BAPO solution in water is not yet available on the market. Such formulations are highly desirable for potential ink-jet and LED applications. In WO 2014095724 A1 , and

G. Muller, M. Zalibera, G. Gescheidt, A. Rosenthal, G. Santiso-Quinones, K. Dietliker, and H. Griitzmacher, Macromol. Rapid Commun. 2015, 36, 553, a synthetic procedure for a water-soluble BAPO derivative, the so-called BAPO-OH (bis(mesitoyl)phosphinic acid), is described. Many interesting photoactive derivatives, including lithium, sodium, potassium and ammonium salts as well as other water-soluble organic derivatives can be synthesized starting from the parent compound. However, the only known synthetic procedure for BAPO-OH suffers from severe limitations, rendering its synthesis costly, inconvenient or time-consuming. More precisely, the synthesis method for BAPO-OH makes use of metalation of white or red phosphorus or halogen-metal exchange of phosphorus trichloride. Even though the reaction proceeds with good to moderate yield, handling of white phosphorus is extremely dangerous due to its physical and

toxicological properties. When starting from red phosphorus or phosphorus trichloride, the yields are significantly lower. A complexing solvent is imperative, causing extra costs compared to standard solvents. In addition, an alkali metal is required, thus necessitating the corresponding special equipment for industrial scale production.

Therefore, there is a continuous need in the art for providing a process for the preparation of bis(acyl)phosphinic acids. Furthermore, it is desirable to provide a process for the preparation of an intermediate compound which avoids elaborate processing steps for obtaining the desired bis(acyl)phosphinic acids. Furthermore, it is desirable that the intermediate product can be easily prepared. In addition thereto, it is desirable to provide a process for the preparation of bis(acyl)phosphinic acids which avoids the use of metallic sodium or lithium in combination with undesirable phosphorus compounds such as an allotrope of phosphorus, e.g. white or red phosphorus, phosphorus trichloride, alkyl or aryl phosphine, or dialkyi or diaryl phosphine because of their volatility, bad smell, toxicity and susceptibility to air and fire. Furthermore, it is desirable to provide a process which allows for the preparation of bis(acyl)phosphinic acids which are not easily prepared by the processes of the prior art.

Accordingly, it is an object of the present invention to provide a process for the preparation of a compound which can be further converted into bis(acyl)phosphinic acids. It is an even further object of the present invention to provide a process for the preparation of this intermediate product and the bis(acyl)phosphinic acid without elaborate processing steps for obtaining the compounds. It is an even further object of the present invention to provide a process for the preparation of bis(acyl)phosphinic acids which avoids the use of metallic sodium or lithium in combination with undesirable phosphorus compounds such as white phosphorus, red phosphorus, phosphorus trichloride, alkyl or aryl phosphine, or dialkyl or diaryl phosphine. It is another object of the present invention to provide a process which allows for the preparation of bis(acyl)- phosphinic acids which are not easily prepared by the processes of the prior art.

Summary of the invention

The foregoing and other objects are solved by the subject-matter of the present invention.

According to a first aspect of the present invention, a process for the preparation of a bis(acyl)phosphinic acid silyl ester of the general formula I is provided,

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl, the process comprising the steps of

a) heating ammonium hypophosphite with a silylating agent for obtaining a

bis(silyl ether)phosphine, and

b) reacting the bis(silyl ether)phosphine obtained in step a) with a compound of the general formula I la and/or Mb,

wherein Ri , R2, R3, R4 and R5 and/or R ₇ , Rs, R9, R10 and Rn are as defined above; Z is halogen.

The inventors surprisingly found out that such a process is suitable for the preparation of a bis(acyl)phosphinic acid silyl ester which can be easily converted into bis(acyl)phosphinic acids and avoids elaborate processing steps for obtaining the bis(acyl)phosphinic acid silyl ester and the desired bis(acyl)phosphinic acids.

Furthermore, the process allows the preparation of the bis(acyl)phosphinic acids without the use of metallic sodium or lithium in combination with undesirable phosphorus compounds such as white phosphorus, red phosphorus, phosphorus trichloride, alkyl or aryl phosphine, or dialkyl or diaryl phosphine. In addition thereto, the process allows the preparation of bis(acyl)phosphinic acids which are not easily accessible by the processes of the prior art. Advantageous embodiments of the inventive process are defined in the corresponding sub-claims.

According to one embodiment, Ri , R3 and R5 and/or R ₇ , R9 and Rn are the same. According to another embodiment, Ri , R3 and R5 and/or R ₇ , R9 and Rn are the same and are selected from linear or branched Ci-C2o-alkyl, preferably linear or branched Ci- Ci8-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci- Cs-alkyl. According to yet another embodiment, R2 and R ₄ and/or Rs and R10 are the same, preferably R2 and R ₄ and/or Rs and R10 are different from Ri , R3 and R5 and/or R ₇ , R9 and R11.

According to one embodiment, R2 and R ₄ and/or Rs and R10 are the same and are H.

According to another embodiment, Z is selected from chloro, bromo and iodo, preferably chloro.

According to yet another embodiment, step a) is carried out under an inert gas atmosphere and/or without the addition of a solvent.

According to one embodiment, the bis(silyl ether)phosphine obtained in step a) is mixed with an organic solvent, preferably an aprotic organic solvent, before process step b) is carried out. According to another embodiment, the bis(silyl ether)phosphine obtained in step a) is subjected to process step b) without purification and isolation of the silylated product obtained in step a)

According to yet another embodiment, step a) is carried out at a temperature in the range from 100 to 130 °C, preferably in the range from 105 to 125 °C and most preferably in the range from 1 10 to 120 °C and/or step b) is carried out at a temperature in the range from -78 to +50 °C, preferably in the range from 0 to 40 °C, more preferably in the range from 0 to 30 °C, and most preferably in the range from 0 to 25 °C.

According to one embodiment, step b) is carried out in that the equivalent weight ratio of the compound of the general formula I la and/or Mb to the ammonium hypophosphite of step a) [I la and/or llb:P-compound] is in the range from 3.5:1 to 1 .5:1 and preferably in the range from 2.5:1 to 1 .8:1 .

According to another embodiment, process step a) and/or step b) is repeated one or more times.

According to yet another embodiment, the process comprises a further step c) of hydrolyzing the bis(acyl)phosphinic acid silyl ester obtained in step b) such as to obtain a bis(acyl)phosphinic acid of the general formula III

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl,

C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OH.

According to one embodiment, step c) is carried out at a temperature in the range from - 78 to +50 °C, preferably in the range from 0 to 40 °C, more preferably in the range from 0 to 30 °C, and most preferably in the range from 2 to 28 °C.

According to a further aspect of the present invention, a bis(acyl)phosphinic acid silyl ester of the general formula I,

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl, obtained by a process, as defined herein, is provided.

According to another aspect of the present invention, a bis(acyl)phosphinic acid of the general formula III,

wherein Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OH, obtained by a process, as defined herein, is provided.

In the following, the details and preferred embodiments of the inventive process for the preparation of the bis(acyl)phosphinic acid silyl ester of the general formula I as well as the bis(acyl)phosphinic acid of the general formula II will be described in more detail. It is to be understood that these technical details and embodiments also apply to the inventive products, as far as applicable.

Detailed description of the invention

A process for the preparation of a bis(acyl)phosphinic acid silyl ester of the general formula I is provided. It is appreciated that a bis(acyl)phosphinic acid silyl ester of the general formula I is prepared,

wherein Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl.

As regards Ri , R2, R3, R4 and R5 in the general formula I, it is to be noted that they can be the same or different. Preferably, Ri , R2, R3, R4 and R5 are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring.

The term "linear or branched Ci-C2o-alkyl" in the meaning of the present invention refers to a linear or branched chain a Iky I group having 1 to 20 carbon atoms, and includes, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec. butyl, tert. butyl, n- pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 1 ,1 ,3,3-tetramethylbutyl, n-heptyl, 2,4,4 trimethylpentyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl. The term "linear or branched C2-C8-alkenyl" in the meaning of the present invention refers to a linear or branched chain alkenyl group having 2 to 8 carbon atoms, and includes, for example, ethenyi, propenyl, butenyl, triisobutenyl, pentenyl, hexenyl, heptenyl and octenyl, preferably ethenyi or propenyl. The term "alkenyl" in the meaning of the present invention includes the cis and trans isomers.

The term "Ci-Ce-alkoxy" in the meaning of the present invention means that the alkoxy moiety has a linear or branched chain a Iky I having 1 to 8 carbon atoms, and includes, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tertiary butoxy, pentyloxy, hexyloxy, heptyloxy and octyloxy.

The term "C2-C8-alkenyloxy" in the meaning of the present invention means that the alkenyloxy moiety has a linear or branched chain alkenyl having 2 to 8 carbon atoms, and includes, for example, ethenyloxy, propenyloxy, butenyloxy, triisobutenyloxy, pentenyloxy, hexenyloxy, heptenyloxy and octenyloxy.

The term "Cs-Cs-cycloalkyl" in the meaning of the present invention refers to a cyclic a Iky I having 3 to 8 carbon atoms, and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl, preferably cyclopentyl and cyclohexyl.

The term "C6-Ci2-aryl" in the meaning of the present invention refers to a group containing one or more 6-membered unsaturated hydrocarbon ring(s), wherein the unsaturation is represented formally by conjugated double bonds and which may optionally be substituted at one or more carbon atoms of such ring(s) by independently selected alkyl groups, and includes, for example, phenyl, naphthyl, methylphenyl, dimethoxyphenyl, 5-isopropyl-2-methylphenyl, methylphenyl and t-butylphenyl, preferably naphthyl.

The term "Cs-Cs-cycloalkoxy" in the meaning of the present invention means that the cycloalkoxy moiety has a cyclic alkyl having 3 to 8 carbon atoms, and includes, for example, cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, cyclohexyloxy, and

cycloheptyloxy, preferably cyclopentyloxy and cyclohexyloxy. The term "C7-Ci2-arylalkoxy" in the meaning of the present invention means that the alkoxy moiety has a linear or branched chain alkyl having 1 to 8 carbon atoms, preferably 1 or 2 carbon atoms, which is connected to C6-Ci2-aryl. The term "Cg-Cis-alkenylarylalkoxy" in the meaning of the present invention means that the alkoxy moiety has a linear or branched chain alkyl having 1 to 8 carbon atoms, preferably 1 or 2 carbon atoms, which is connected to C6-Ci2-aryl, preferably C6-aryl, which is further connected to linear or branched C2-C8-alkenyl, preferably C2- alkenyl. Preferably, the alkoxy and alkenyl moieties are connected in para-position of the aryl moiety.

The term "C6-Ci2-arylsulfonyl" in the meaning of the present invention refers to a sulfonyl moiety having a C6-Ci2-aryl. The term "4-alkylarylsulfonyl" in the meaning of the present invention refers to a sulfonyl moiety having a C6-Ci2-aryl, which is connected to a linear or branched Ci-C2o-alkyl. The alkyl moiety is connected in para-position of the aryl moiety.

The term "halogen" in the meaning of the present invention refers to chioro, bromo or iodo.

Preferably, Ri , R2, R3, R4 and R5 are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci- Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, Cs-Cs-cycloalkoxy, C7-C12- arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4-alkylarylsulfonyl, Ci- C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring.

In one embodiment, Ri , R2, R3, R4 and R5 in the general formula I are the same or different and are independently selected from H, halogen, linear or branched C1-C20- alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl and C6-Ci2-aryl. Preferably, Ri , R2, R3, R4 and R5 are the same or different and are independently selected from H, halogen and, linear or branched Ci-C2o-alkyl. Most preferably, Ri, R2, R3, R4 and R5 are the same or different and are independently selected from H and, linear or branched Ci-C2o-alkyl.

Thus, it is preferred that one or more of Ri, R2, R3, R4 and R5 is/are H.

Additionally or alternatively, it is preferred that one or more of Ri, R2, R3, R4 and R5 is/are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, one or more of Ri, R2, R3, R4 and R5 is/are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that one or more of Ri, R2, R3, R4 and R5 is/are Ci- or C2-alkyl, e.g. Ci-alkyl. Preferably, Ri, R3 and R5 are the same. In this embodiment, Ri, R3 and R5 are preferably selected from H, halogen, linear or branched Ci-Cs-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8- cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4- alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHRi2 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. For example, Ri, R3 and R5 are the same and are selected from linear or branched Ci-Cs-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs- alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6- membered heterocyclic ring.

In one embodiment, Ri, R3 and R5 are the same and are linear or branched C1-C20- alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci- Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, Ri, R3 and R5 are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C4-alkyl, e.g. linear Ci-C4-alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that Ri, R3 and R5 are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl. In one embodiment, Ri , R3 and R5 are the same and are SR12, NHR12 or NR12R13 with R12 and Ri3 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl. In one embodiment, R2 and R ₄ are the same. In this embodiment, R2 and R ₄ are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8- cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4- alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHRi2 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. Preferably, R2 and R ₄ are selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, C9-C15- alkenylarylalkoxy and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. For example, R2 and R ₄ are the same and are selected from H, linear or branched C1-C20- alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. In one embodiment, R2 and R ₄ are the same and are H.

It is appreciated that R2 and R ₄ are preferably different from Ri , R3 and R5. Thus, if R2 and R ₄ are different from Ri , R3, and R5, R2 and R ₄ are preferably the same and are H and Ri , R3 and R5 are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, R2 and R ₄ are the same and are H and Ri , R3 and R5 are the same and are linear or branched C1-C6- alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ - alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that R2 and R ₄ are the same and are H and Ri , R3 and R5 are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl. In one embodiment, R2 and R ₄ are the same and are H and Ri , R3 and R5 are the same and are SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and C3-Cs-cycloalkyl. As regards R ₇ , Rs, R9, R10 and Rn in the general formula I, it is to be noted that they can be the same or different. Preferably, R ₇ , Rs, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-C12- aryl, C3-Cs-cycloalkoxy, C ₇ -Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring. More preferably, R ₇ , Rs, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C ₇ -Ci2-arylalkoxy, C9-C15- alkenylarylalkoxy and an O-, S- or N-containing 5- or 6-membered heterocyclic ring.

In one embodiment, R ₇ , Rs, R9, R10 and Rn in the general formula I are the same or different and are independently selected from H, halogen, linear or branched C1-C20- alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, C3-Cs-cycloalkyl and C6-Ci2-aryl. Preferably, R ₇ , Rs, R9, R10 and Rn are the same or different and are independently selected from H, halogen and, linear or branched Ci-C2o-alkyl. Most preferably, R ₇ , Rs, R9, R10 and Rn are the same or different and are independently selected from H and, linear or branched Ci-C2o-alkyl.

Thus, it is preferred that one or more of R ₇ , Rs, R9, R10 and Rn is/are H.

Additionally or alternatively, it is preferred that one or more of R ₇ , Rs, R9, R10 and Rn is/are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, one or more of R ₇ , Rs, R9, R10 and Rn is/are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that one or more of R ₇ , Re, R9, R10 and Rn is/are Ci- or C2-alkyl, e.g. Ci-alkyl.

Preferably, R ₇ , R9 and Rn are the same. In this embodiment, R ₇ , R9 and Rn are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8- cycloalkoxy, C ₇ -Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4- alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHRi2 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. Preferably, R ₇ , R9 and Rn are selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs- alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C ₇ -Ci2- arylalkoxy, Cg-Cis-alkenylarylalkoxy and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. For example, R ₇ , Rg and Rn are the same and are selected from linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered

heterocyclic ring. In one embodiment, R ₇ , Rg and Rn are the same and are linear or branched C1-C20- alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci- Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, R ₇ , Rg and Rn are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that R ₇ , Rg and Rn are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl.

In one embodiment, R ₇ , Rg and Rn are the same and are SR12, NHR12 or NR12R13 with R12 and Ri3 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl.

In one embodiment, Rs and R10 are the same. In this embodiment, Rs and R10 are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8- cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4- alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHRi2 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. Preferably, Rs and R10 are selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, C9-C15- alkenylarylalkoxy and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. For example, Rs and R10 are the same and are selected from H, linear or branched C1-C20- alkyi, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring.

In one embodiment, Rs and R10 are the same and are H. It is appreciated that Rs and R10 are preferably different from R ₇ , R9 and Rn . Thus, if Rs and R10 are different from R ₇ , R9 and Rn , Rs and R10 are preferably the same and are H and R ₇ , R9 and Rn are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, Rs and R10 are the same and are H and R ₇ , R9 and Rn are the same and are linear or branched C1-C6- alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ - alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that R ₈ and Ri ₀ are the same and are H and R ₇ , R9 and Rn are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl .

In one embodiment, Rs and R10 are the same and are H and R ₇ , R9 and Rn are the same and are SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs- cycloalkyl.

As regards Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn in general formula I, it is to be noted that they can be the same or different. Preferably, Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and R11 are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, C3-Cs-cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, C9-C15- alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci- Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring.

In one embodiment, Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn in the general formula I are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl and C6-Ci2-aryl. Preferably, Ri , R2, R3, R4, R5, R7, Re, R9, R10 and R11 are the same or different and are independently selected from H, halogen and, linear or branched Ci-C2o-alkyl. Most preferably, Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and R11 are the same or different and are independently selected from H and, linear or branched Ci-C2o-alkyl.

In one embodiment, Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn in general formula I are the same. In this embodiment, Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn are preferably H. Alternatively, Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn in general formula I are different.

It is preferred that one or more of Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn in general formula I is/are H.

Additionally or alternatively, it is preferred that one or more of Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and R11 in general formula I is/are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, one or more of Ri , R2, R3, R4, Rs, R7, Rs, R9, R10 and Rn is/are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C4-alkyl, e.g. linear Ci-C4-alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that one or more of Ri , R2, R3, R4, R5, R7, Rs, R9, R10 and Rn in general formula I is/are Ci- or C2-alkyl, e.g. Ci-alkyl. Preferably, Ri , R3, R5, R7, R9 and Rn in general formula I are the same. In this embodiment, Ri , R3, R5, R7, R9 and Rn are selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, Cs-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, C9-C15- alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci- Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. Preferably, Ri , R3, R5, R7, R9 and Rn are the same and are selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, Cs-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, C9-C15- alkenylarylalkoxy, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. For example, Ri , R3, R5, R7, R9 and Rn are the same and are selected from linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-C8- alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered

heterocyclic ring.

In one embodiment, Ri , R3, R5, R7, R9 and Rn in general formula I are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. For example, Ri , R3, R5, R7, R9 and Rn are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ - alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that Ri , R3, R5, R7, R9 and Rn are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl.

In one embodiment, R2, R4, Rs and R10 in general formula I are the same. In this embodiment, R2, R4, Rs and R10 are selected from H, halogen, linear or branched Ci- C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs- cycloalkyl, C6-Ci2-aryl, Cs-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs- alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and C3-C8- cycloalkyl, and an O-, S- or N-containing 5- or 6-mennbered heterocyclic ring. Preferably, R2, R4, Rs and R10 are selected from H, halogen, linear or branched C1-C20- alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, C3-C8- cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. For example, R2, R4, Rs and R10 are the same and are selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, C3-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring. In one embodiment, R2, R4, Rs and R10 are the same and are H.

It is appreciated that R2, R4, Rs and R10 are preferably different from Ri , R3, R5, R7, R9 and R11. Thus, if R2, R4, Rs and R10 are different from Ri , R3, R5, R7, R9 and Rn , R2, R4, Rs and R10 are preferably the same and are H and Ri , R3, R5, R7, R9 and Rn are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched C1-C18- alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs- alkyl, e.g. linear Ci-Cs-alkyl. For example, R2, R4, R ₈ and Ri ₀ are the same and are H and Ri , R3, R5, R7, R9 and Rn are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C4-alkyl, e.g. linear Ci-C4-alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that R2, R4, R ₈ and R ₁₀ are the same and are H and Ri , R3, R5, R7, R9 and R11 are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl.

In one embodiment, the bis(acyl)phosphinic acid silyl ester of the general formula I is a bis(acyl)phosphinic acid silyl ester, in which Ri , R3, R5, R7, R9 and Rn in general formula I are the same and R2, R4, Rs and R10 are the same. Preferably, Ri , R3, R5, R7, R9 and R11 in general formula I are the same and are Ci-alkyl and R2, R4, Rs and R10 are the same and are H. Alternatively, Ri , R3, R5, R7, R9 and Rn in general formula I are the same and are H and R2, R4, Rs and R10 are the same and are Ci-alkoxy.

Alternatively, Ri , R3, R5, R7, R9 and Rn in general formula I are the same and are H and R2, R4, Rs and R10 are the same and are chloro.

Alternatively, the bis(acyl)phosphinic acid silyl ester of the general formula I is a bis(acyl)phosphinic acid silyl ester, in which Ri , R3 and R5 in general formula I are the same, R ₇ , R9 and Rn are the same, R2 and R ₄ are the same and Rs and R10 are the same. In this embodiment, Ri , R3 and R5 in general formula I are different from R ₇ , R9 and R11 and R2 and R ₄ are different from Rs and R10. It is thus appreciated that a mixed bis(acyl)phosphinic acid silyl ester of the general formula I can be prepared by the process of the present invention.

It is appreciated that R6 in the general formula I is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl. It is appreciated that Ri ₄ , R15 and R16 can be the same or different. Preferably, Ri ₄ , R15 and R16 are the same, For example, Ri ₄ , R15 and R16 are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl. Preferably, Ri ₄ , R15 and R16 are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl. It is especially preferred that Ri ₄ , R15 and R16 are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl.

Alternatively, Ri ₄ , R15 and R16 are the same and are phenyl or methylphenyl, preferably phenyl.

In one embodiment, R6 in the general formula I is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being Ci- or C2-alkyl, e.g. Ci-alkyl. That is to say, R6 in the general formula I is preferably trimethylsilyloxy.

Thus, it is appreciated that the process of the present invention results in the

preparation of the bis(acyl)phosphinic acid silyl ester of the general formula I.

It is appreciated that the bis(acyl)phosphinic acid silyl ester of the general formula I is prepared by a specific process, namely a process allowing the easy preparation of an intermediate product suitable for the conversion into bis(acyl)phosphinic acids.

In particular, the process is characterized in that it comprises the steps of a) heating ammonium hypophosphite with a silylating agent for obtaining a bis(silyl ether)phosphine, and

b) reacting the bis(silyl ether)phosphine obtained in step a) with a compound of the general formula I la and/or Mb,

wherein Ri , R2, R3, R4 and R5 and/or R ₇ , Rs, R9, R10 and Rn are as defined above; Z is halogen.

Accordingly, in a first step ammonium hypophosphite is heated with a silylating agent. It is to be noted that this step preferably results in the quantitative reaction of the starting materials to the corresponding bis(silyl ether)phosphine. Thus, very high yields and purities and very high conversions are achieved within a few hours, and thus this step advantageously provides a bis(silyl ether)phosphine with high purity for the following process step b).

The silylating agent can be every silylating agent well known in the art. However, in order to obtain advantageous yields in the further process, the silylating agent is preferably a compound of the general formula Va and/or Vb

A-SiRi Ri ₅ Ri6 Va, wherein Ri ₄ , R15 and R16 are the same or different and are independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl, and A is selected from halogen, triflate (OSO2CF3), cyanide, azide and 1 -imidazolyl.

Ri ₆ Ri5Ri4Si-B-SiRi Ri ₅ Ri6 Vb, wherein Ri ₄ , R15 and R16 are the same or different and are independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl, and B is selected from O, NH, NCH3, OC(CH ₃ )=N, OC(CF ₃ )=N, NH(C=O)NH, and NH(C=O)O.

With regard to the definition of the Ri ₄ , R15 and R16 in general formula Va and/or Vb and preferred embodiments thereof, reference is also made to the statements provided above when discussing the technical details of the bis(acyl)phosphinic acid silyl ester of the general formula I, and especially R6, obtained by the process of the present invention.

Preferably, the silylating agent is selected from the group comprising

hexamethyldisilazane, trimethylsilyl chloride, trimethylsilyl bromide, trimethylsilyl iodide, triethylsilyl chloride, triethylsilyl bromide, tri-n-propylsilyl chloride, triisopropylsilyl chloride, t-butyldimethylsilyl chloride, bis(trimethylsilyl)acetamide,

N,N-bis(trimethylsilyl)methylamine, and mixtures thereof. More preferably, the silylating agent is selected from the group comprising hexamethyldisilazane,

N,N-bis(trimethylsilyl)methylamine, trimethylsilyl chloride and mixtures thereof. Most preferably, the silylating agent is hexamethyldisilazane and/or trimethylsilyl chloride. For example, the silylating agent is hexamethyldisilazane or trimethylsilyl chloride, preferably hexamethyldisilazane. Alternatively, the silylating agent is a mixture of hexamethyldisilazane and trimethylsilyl chloride. It is appreciated that step a) is preferably carried out under an inert gas atmosphere. This is advantageous in order to drive out the only by-product of step a), i.e. ammonia, and thus increases the purity of the bis(silyl ether)phosphine obtained in step a). The inert gas atmosphere may be an argon, helium or nitrogen atmosphere. It is one requirement of the present invention that the reaction between ammonium hypophosphite and the silylating agent is carried out under heating for accelerating the reaction. Preferably, step a) is thus carried out at a temperature in the range from 100 to 130 °C. For example, step a) is carried out at a temperature in the range from 105 to 125 °C and most preferably in the range from 1 10 to 120 °C.

It is preferred that the equivalent weight ratio of silylating agent to ammonium

hypophosphite [silylating agent:ammonium hypophosphite] is from 10:1 to 1 :1 , more preferably from 8:1 to 1 :1 , even more preferably from 6:1 to 1 :1 and most preferably from 5:1 to 1 .5:1 .

Step a) can be carried out with or without the addition of a solvent. If step a) is carried out in a solvent, the solvent is preferably an organic solvent, more preferably an aprotic organic solvent. For example, the organic solvent, more preferably the aprotic organic solvent, is selected from the group comprising dichloromethane, tetrachloroethylene, tetrahydrofuran, 1 ,4-dioxane, toluene, benzene, xylene, and mixtures thereof. Most preferably, the organic solvent, more preferably the aprotic organic solvent, is

dichloromethane.

Preferably, step a) is carried out in the absence of an organic solvent. More preferably, step a) is carried out in the absence of a solvent. Process step a) is preferably carried out under mixing the components, i.e. the silylating agent, ammonium hypophosphite and an optional organic solvent. The skilled man will adapt the mixing conditions (such as the configuration of mixing tools and mixing speed) according to his process equipment. If step a) is carried out in the absence of a solvent, i.e. after the preparation of the bis(silyl ether)phosphine, an organic solvent, more preferably an aprotic organic solvent, is preferably added before process step b) is carried out. As outlined above, the organic solvent, more preferably the aprotic organic solvent, is selected from the group comprising dichloromethane, tetrachloroethylene, tetrahydrofuran, 1 ,4-dioxane, toluene, benzene, xylene, and mixtures thereof. Most preferably, the organic solvent, more preferably the aprotic organic solvent, is dichloromethane.

In one embodiment, the bis(silyl ether)phosphine obtained in step a) is thus dissolved in an organic solvent, more preferably an aprotic organic solvent, before process step b) is carried out.

If the bis(silyl ether)phosphine obtained in step a) is mixed with an organic solvent, more preferably an aprotic organic solvent, before process step b) is carried out, the bis(silyl ether)phosphine obtained in step a) is preferably cooled down to a temperature in the range from -5 to 50 °C, preferably in the range from 0 to 40 °C, more preferably in the range from 0 to 30 °C, and most preferably in the range from 0 to 25 °C, e.g. from 0 to 10 °C, before the organic solvent, more preferably the aprotic organic solvent, is added.

The bis(silyl ether)phosphine obtained in step a) is subjected to process step b).

Preferably, the bis(silyl ether)phosphine obtained in step a) is subjected to process step b) without purification and isolation of the silylated product obtained in step a). In one embodiment, process step a) is repeated one or more times. For example, process step a) is repeated one or two times, e.g. one time.

Preferably, process step a) is carried out in one step and thus is not repeated. It is appreciated that process steps a) and b) can be performed in a one-pot-reaction. That is to say, the bis(silyl ether)phosphine is prepared in situ, without isolation or purification, and the compound of the general formula I la and/or Mb is added to the bis(silyl ester)phosphine in the same reactor. The following process step b) is carried out in that the bis(silyl ether)phosphine obtained in step a) is reacted with a compound of the general formula I la and/or Mb,

wherein Ri , R2, R3, R4 and R5 and/or R ₇ , Rs, R9, R10 and Rn are as defined above; Z is halogen.

With regard to the definition of the Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn in general formula lla and/or Mb and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the

bis(acyl)phosphinic acid silyl ester of the general formula I obtained by the process of the present invention.

As regards Z in in general formula lla and/or lib, it is appreciated that Z is a halogen. Preferably, Z is selected from chloro, bromo and iodo, more preferably chloro and bromo. Most preferably, Z is chloro.

Thus, in one embodiment the compound of the general formula lla is a compound wherein Ri , R2, R3, R4 and R5 are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci- Ce-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl and C6-Ci2-aryl and Z is chloro.

Preferably, Ri , R2, R3, R4 and R5 are the same or different and are independently selected from H, halogen and, linear or branched Ci-C2o-alkyl and Z is chloro. Most preferably, Ri , R2, R3, R4 and R5 are the same or different and are independently selected from H and linear or branched Ci-C2o-alkyl and Z is chloro.

Thus, it is preferred that one or more of Ri , R2, R3, R4 and R5 is/are H and Z is chloro.

Additionally or alternatively, it is preferred that one or more of Ri , R2, R3, R4 and R5 is/are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyI, e.g. linear Ci-Cs-alkyI and Z is chloro. For example, one or more of Ri , R2, R3, R4 and R5 is/are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci- C3-alkyl, e.g. linear Ci-C3-alkyl, and Z is chloro. It is especially preferred that one or more of Ri , R2, R3, R4 and R5 is/are Ci- or C2-alkyl, e.g. Ci-alkyl, and Z is chloro. Preferably, Ri , R3 and R5 are the same and Z is chloro. In this embodiment, Ri , R3 and R5 are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, C3-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring, and Z is chloro. For example, Ri , R3 and R5 are the same and are selected from linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring, and Z is chloro.

In one embodiment, Ri , R3 and R5 are the same and are linear or branched C1-C20- alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci- Ci2-alkyl and most preferably linear Ci-Cs-alkyI, e.g. linear Ci-Cs-alkyI, and Z is chloro. For example, Ri , R3 and R5 are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C4-alkyl, e.g. linear Ci-C4-alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl, and Z is chloro. It is especially preferred that Ri , R3 and R5 are the same and are Ci- or C2-alkyl, e.g. Ci- alkyl, and Z is chloro. In one embodiment, R2 and R ₄ are the same and Z is chloro. In this embodiment, R2 and R ₄ are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-C12- aryl, Cs-Cs-cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring, and Z is chloro. For example, R2 and R ₄ are the same and are selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring, and Z is chloro.

In one embodiment, R2 and R ₄ are the same and are H, and Z is chloro.

It is appreciated that R2 and R ₄ are preferably different from Ri , R3 and R5. Thus, if R2 and R ₄ are different from Ri , R3, and R5, R2 and R ₄ are preferably the same and are H and Ri , R3 and R5 are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl, and Z is chloro. For example, R2 and R ₄ are the same and are H and Ri , R3 and R5 are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl, and Z is chloro. It is especially preferred that R2 and R ₄ are the same and are H and Ri , R3 and R5 are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl, and Z is chloro.

Alternatively, if R2 and R ₄ are different from Ri , R3, and R5, R2 and R ₄ are preferably the same and are Ci-Cs-alkoxy, preferably Ci-C ₄ -alkoxy, more preferably Ci-C2-alkoxy, e.g. Ci-alkoxy, or halogen, preferably, chloro, bromo or iodo, more preferably chloro or bromo, e.g. chloro, and Ri , R3 and R5 are the same and are H, and Z is chloro. It is especially preferred that R2 and R ₄ are the same and are Ci-alkoxy and Ri , R3 and R5 are the same and are H, and Z is chloro. Alternatively, R2 and R ₄ are the same and are chloro and Ri , R3 and R5 are the same and are H, and Z is chloro. As regards R ₇ , Re, R9, R10 and Rn in the general formula Mb, it is to be noted that they can be the same or different. Preferably, R ₇ , Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched C1-C20- alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, C3-C8- cycloalkyl, C6-Ci2-aryl, C3-Cs-cycloalkoxy, C ₇ -Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-Ci2-arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs- alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and C3-C8- cycloalkyl, and an O-, S- or N-containing 5- or 6-membered heterocyclic ring, and Z is chloro.

In one embodiment, R ₇ , Re, R9, R10 and Rn in the general formula Mb are the same or different and are independently selected from H, halogen, linear or branched C1-C20- alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, C3-Cs-cycloalkyl and C6-Ci2-aryl, and Z is chloro. Preferably, R ₇ , Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen and, linear or branched Ci- C2o-alkyl, and Z is chloro. Most preferably, R ₇ , Re, R9, R10 and Rn are the same or different and are independently selected from H and, linear or branched Ci-C2o-alkyl, and Z is chloro.

Thus, it is preferred that one or more of R ₇ , Re, R9, R10 and Rn is/are H and Z is chloro.

Additionally or alternatively, it is preferred that one or more of R ₇ , Re, R9, R10 and Rn is/are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl, and Z is chloro. For example, one or more of R ₇ , Re, R9, R10 and Rn is/are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci- C3-alkyl, e.g. linear Ci-C3-alkyl, and Z is chloro. It is especially preferred that one or more of R ₇ , Re, R9, R10 and Rn is/are Ci- or C2-alkyl, e.g. Ci-alkyl, and Z is chloro.

Preferably, R ₇ , R9 and Rn are the same and Z is chloro. In this embodiment, R ₇ , R9 and R11 are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, C3-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring, and Z is chloro. For example, R ₇ , R9 and R11 are the same and are selected from linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring, and Z is chloro.

In one embodiment, R ₇ , R9 and Rn are the same and are linear or branched C1-C20- alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci- Ci2-alkyl and most preferably linear Ci-Cs-alkyI, e.g. linear Ci-Cs-alkyI, and Z is chloro. For example, R ₇ , R9 and Rn are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl, and Z is chloro. It is especially preferred that R ₇ , R9 and Rn are the same and are Ci- or C2-alkyl, e.g. Ci- alkyl, and Z is chloro. In one embodiment, Rs and R10 are the same and Z is chloro. In this embodiment, Rs and R10 are preferably selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, Cs-Cs-cycloalkyl, C6-C12- aryl, C3-Cs-cycloalkoxy, C ₇ -Ci2-arylalkoxy, Cg-Cis-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring, and Z is chloro. For example, Rs and R10 are the same and are selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl, Ci-Cs-alkoxy, C2-Cs-alkenyloxy, C3-Cs-cycloalkyl and an O-, S- or N-containing 5- or 6-membered heterocyclic ring, and Z is chloro.

In one embodiment, Rs and R10 are the same and are H and Z is chloro. It is appreciated that Rs and R10 are preferably different from R ₇ , R9 and Rn . Thus, if Rs and R10 are different from R ₇ , R9 and Rn , Rs and R10 are preferably the same and are H and R ₇ , R9 and Rn are the same and are linear or branched Ci-C2o-alkyl, preferably linear or branched Ci-Cis-alkyl, more preferably linear or branched Ci-Ci2-alkyl and most preferably linear Ci-Cs-alkyl, e.g. linear Ci-Cs-alkyl, and Z is chloro. For example, Rs and R10 are the same and are H and R ₇ , R9 and Rn are the same and are linear or branched Ci-C6-alkyl, e.g. linear Ci-C6-alkyl, preferably linear or branched Ci-C ₄ -alkyl, e.g. linear Ci-C ₄ -alkyl, and most preferably linear or branched Ci-C3-alkyl, e.g. linear Ci-C3-alkyl, and Z is chloro. It is especially preferred that R ₈ and Ri ₀ are the same and are H and R ₇ , R9 and Rn are the same and are Ci- or C2-alkyl, e.g. Ci-alkyl, and Z is chloro.

Alternatively, if Rs and R10 are different from R ₇ , R9 and Rn , Rs and R10 are preferably the same and are Ci-Cs-alkoxy, preferably Ci-C ₄ -alkoxy, more preferably Ci-C2-alkoxy, e.g. Ci-alkoxy, or halogen, preferably, chloro, bromo or iodo, more preferably chloro or bromo, e.g. chloro, and R ₇ , R9 and Rnare the same and are H, and Z is chloro. It is especially preferred that Rs and R10 are the same and are Ci-alkoxy and R ₇ , R9 and Rn are the same and are H, and Z is chloro. Alternatively, Rs and R10 are the same and are chloro and R ₇ , R9 and Rn are the same and are H, and Z is chloro.

In one embodiment, the bis(silyl ether)phosphine obtained in step a) is reacted with a compound of the general formula I la (or lib), wherein Ri , R3 and R5 (or R ₇ , R9 and Rn ) are the same and R2 and R ₄ (or Rs and R10) are the same and Z is chloro. Preferably, Ri , R3 and R5 in general formula I la (or R ₇ , R9 and Rn in general formula Mb) are the same and are Ci-alkyl and R2 and R ₄ (or Rs and R10) are the same and are H and Z is chloro. Alternatively, Ri , R3 and R5 in general formula I la (or R ₇ , R9 and Rn in general formula Mb) are the same and are H and R2 and R ₄ (or Rs and R10) are the same and are Ci-alkoxy, and Z is chloro. Alternatively, Ri , R3 and R5 in general formula I la (or R ₇ , R9 and R11 in general formula Mb) are the same and are H and R2 and R ₄ (or Rs and R10) are the same and are chloro, and Z is chloro. It is appreciated that this embodiment specifically results in the corresponding symmetric bis(acyl)phosphinic acid silyl ester of the general formula I, i.e. Ri , R3, R5, R7, R9 and Rn are the same and R2, R4, Rs and R10 are the same. Alternatively, the bis(acyl)phosphinic acid silyl ester obtained in step a) is mixed with a compound of the general formula I la and MB, in which Ri , R3 and R5 in general formula I la are the same, R ₇ , R9 and Rn in general formula Mb are the same, R2 and R ₄ in general formula I la are the same and Re and R10 in general formula Mb are the same and Z is chloro. In this embodiment, Ri , R3 and R5 in general formula I la are different from R ₇ , R9 and Rn in general formula Mb and R2 and R ₄ in general formula I la are different from Rs and R10 in general formula Mb and Z is chloro. It is thus appreciated that a mixed bis(acyl)phosphinic acid silyl ester of the general formula I is obtained if compounds of the general formula I la and MB are added in step b) of the present process.

Step b) of the process of the present invention can be carried out over a wide temperature range. Thus, process step b) is preferably carried out at a temperature in the range from -5 to 50 °C, preferably in the range from 0 to 40 °C, more preferably in the range from 0 to 30 °C, and most preferably in the range from 0 to 25 °C.

The compound of the general formula I la and/or Mb is preferably added dropwise to the bis(silyl ether)phosphine obtained in step a). The dropwise addition of the compound of the general formula I la and/or Mb is preferably carried out at a temperature in the range from 0 to 25 °C, e.g. from 0 to 10 °C.

It is preferred that the reaction of the compound of the general formula I la and/or Mb with the bis(silyl ether)phosphine obtained in step a), i.e. after the addition of the compound of the general formula I la and/or Mb, can be carried out at a temperature above the temperature used for adding the compound of the general formula I la and/or Mb. Thus, the reaction of the compound of the general formula I la and/or Mb with the bis(silyl ether)phosphine obtained in step a), i.e. after the addition of the compound of the general formula I la and/or Mb, is preferably carried out at a temperature in the range from 0 to 25 °C, e.g. from 10 to 25 °C. In one embodiment, the reaction of the compound of the general formula I la and/or Mb with the bis(silyl ether)phosphine obtained in step a), i.e. after the addition of the compound of the general formula I la and/or Mb, is carried out at about room temperature, i.e. 21 °C ± 2 °C. In view of the statements provided above with regard to process step a), it is appreciated that step b) is preferably carried out in the presence of an organic solvent, preferably an aprotic organic solvent, e.g. dichloromethane. It is appreciated that the compound of the general formula lla and/or Mb is preferably added in step b) in an excess to the ammonium hypophosphite of step a), based on the equivalent weight ratio.

It is preferred that the equivalent weight ratio of the compound of the general formula lla and/or lib to the ammonium hypophosphite of step a) [lla and/or llb:P-compound] is in the range from 3.5:1 to 1 .5:1 and preferably in the range from 2.5:1 to 1 .8:1 .

Process step b) is preferably carried out under mixing the components, i.e. the silylating agent, the of the general formula lla and/or Mb and the optional organic solvent. The skilled man will adapt the mixing conditions (such as the configuration of mixing tools and mixing speed) according to his process equipment.

In one embodiment, process step b) is carried out without the addition of further additives.

Alternatively, process step b) is carried out in the presence of further additives. For example, trimethylamine can be added in order to increase the reactivity of the silylating agent. It is appreciated that process step b) can be repeated one or more times. Preferably, process step b) is repeated one or two times, e.g. one time.

Accordingly, process step b) can be carried out in a one step procedure, i.e. without repeating the addition of the compound of the general formula lla and/or Mb, or in a stepwise procedure, repeating the addition of the silylating agent followed by the compound of the general formula lla and/or lib. If process step b) is carried out in a stepwise procedure, process step b) is thus repeated, preferably two times. It is appreciated that the stepwise procedure is especially advantageous for a controlled preparation of a bis(acyl)phosphinic acid silyl ester of the general formula I in high yield as the total stoichiometrically required amount of the silylating agent is not added at once. Furthermore, the stepwise procedure allows the preparation of a defined mixed bis(acyl)phosphinic acid silyl ester of the general formula I. That is to say, the stepwise procedure is preferred if a bis(acyl)phosphinic acid silyl ester of the general formula I is prepared, in which Ri , R3 and R5 are the same, R ₇ , R9 and Rn are the same, R2 and R ₄ are the same and Re and R10 are the same. Furthermore, Ri , R3 and R5 in general formula I are different from R ₇ , R9 and Rn and R2 and R ₄ are different from Rs and R10.

In one embodiment, the stepwise procedure allows the preparation of a

bis(acyl)phosphinic acid silyl ester of the general formula I, in which Ri , R2, R3, R4, R5, R6, R7, Rs, R9, R10 and Rn are the same or different. Preferably, process step b) is carried out in an one step procedure, i.e. without repeating the addition of the compound of the general formula I la and/or Mb.

It is appreciated that the bis(acyl)phosphinic acid silyl ester obtained in step b) may be further treated by

i) separating the obtained bis(acyl)phosphinic acid silyl ester of the general formula I from by-products and/or educts and/or solvent, and/or ii) washing the obtained bis(acyl)phosphinic acid silyl ester of the general formula I. Additionally, the bis(acyl)phosphinic acid silyl ester of the general formula I obtained in step b) may be subjected to a drying step.

Thus, the process of the present invention may comprise further steps for isolating and/or purifying the obtained bis(acyl)phosphinic acid silyl ester of the general formula I

Such steps are well known in the art and will be adapted by the skilled person according to the process conditions and equipment used for carrying out the process of the present invention. In one embodiment, the process comprises a further step c) of mixing the

bis(acyl)phosphinic acid silyl ester obtained in step b) with ethanol such as to obtain a bis(acyl)phosphinic acid of the general formula III

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OH

With regard to the definition of the Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn in general formula III and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the bis(acyl)phosphinic acid silyl ester of the general formula I obtained by the process of the present invention.

It is appreciated that the bis(acyl)phosphinic acid of the general formula III is prepared by a specific process, namely a process avoiding the use of metallic sodium or lithium in combination with undesirable phosphorus compounds such as white phosphorus, red phosphorus, phosphorus trichloride, alkyl or aryl phosphine, or dialkyl or diaryl phosphine. Furthermore, the bis(acyl)phosphinic acid of the general formula III can be easily prepared from the bis(acyl)phosphinic acid silyl ester of the general formula I.

For obtaining the bis(acyl)phosphinic acid of the general formula III, subsequently to step b), the bis(acyl)phosphinic acid silyl ester obtained in step b) is hydrolysed. It is appreciated that hydrolyzing of the bis(acyl)phosphinic acid silyl ester obtained in step b) can be achieved by using water and/or an alcohol, such as methanol, ethanol, propanol. Preferably, step c) is carried out by adding ethanol. If the process of the present invention comprises step c), it is appreciated that process steps a), b) and c) can be performed in a one-pot-reaction. That is to say, the bis(silyl ether)phosphine is prepared in situ, without isolation or purification, the compound of the general formula I la and/or Mb is added to the bis(silyl ester)phosphine in the same reactor, without isolation or purification, and the obtained bis(acyl)phosphinic acid silyl ester is hydrolysed in the same reactor.

Step c) of the process of the present invention can be carried out over a wide

temperature range. However, for avoiding the formation of unwanted by-products, step c) is preferably carried out at a temperature in the range from -5 to 50 °C, preferably in the range from 0 to 40 °C, more preferably in the range from 0 to 30 °C, and most preferably in the range from 2 to 28 °C. For example, process step c) is carried out at a temperature in the range from 5 to 25 °C.

Subsequent to process step c) of mixing the bis(acyl)phosphinic acid silyl ester obtained in step b) with ethanol, the process may comprise further steps for isolating and/or purifying the obtained bis(acyl)phosphinic acid of the general formula III.

For example, the process may further comprise a step of

i) separating the obtained bis(acyl)phosphinic acid of the general formula III from the solvent, and/or

ii) washing the obtained bis(acyl)phosphinic acid of the general formula III.

In one embodiment, the process further comprises the steps of

i) separating the obtained bis(acyl)phosphinic acid of the general formula III from the solvent, and

ii) washing the obtained bis(acyl)phosphinic acid of the general formula III.

Additionally, the process may further comprise a step of drying the obtained

bis(acyl)phosphinic acid of the general formula III. Such steps are well known in the art and will be adapted by the skilled person according to the process conditions and equipment used for carrying out the process of the present invention. In one embodiment, the process comprises a further step d) of halogenating, preferably chlorinating, the bis(acyl)phosphinic acid of the general formula III obtained in step c) for obtaining a compound of the general formula IV

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is halogen, preferably selected from chloro, bromo and iodo, more preferably chloro.

With regard to the definition of the Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn in general formula IV and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the bis(acyl)phosphinic acid silyl ester of the general formula I obtained by the process of the present invention.

Such halogenation reactions resulting in the halogenation of the bis(acyl)phosphinic acid of the general formula III are well known in the art and can be adapted by the skilled person according to the specific reaction and equipment used for carrying out the process of the present invention. In another aspect, the present invention refers to a bis(acyl)phosphinic acid silyl ester of the general formula I,

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OSiRi ₄ RisRi6 with Ri ₄ , R15 and R16 being independently selected from linear or branched Ci-C2o-alkyl or C6-Ci2-aryl. The bis(acyl)phosphinic acid silyl ester of the general formula I is preferably obtained by the process of the present invention.

With regard to the definition of the process, Ri , R2, R3, R4, R5, R6, R7, Re, R9, R10 and R11 in general formula I and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the process as well as the bis(acyl)phosphinic acid silyl ester of the general formula I obtained by the process of the present invention.

It is appreciated that the bis(acyl)phosphinic acid silyl ester of the general formula I obtained by the process of the present invention is preferably used for the preparation of bis(acyl)phosphinic acids.

In a further aspect, the present invention refers to a bis(acyl)phosphinic acid of the general formula III,

wherein Ri , R2, R3, R4, R5, R7, Re, R9, R10 and Rn are the same or different and are independently selected from H, halogen, linear or branched Ci-C2o-alkyl, linear or branched C2-C8-alkenyl, Ci-Cs-alkoxy, C2-C8-alkenyloxy, Cs-Cs-cycloalkyl, C6-Ci2-aryl, C3-C8-cycloalkoxy, C7-Ci2-arylalkoxy, C9-Ci5-alkenylarylalkoxy, nitro-, C6-C12- arylsulfonyl, 4-alkylarylsulfonyl, Ci-C2o-alkylcarboxy, Ci-Cs-alkoxycarbonyl, SR12, NHR12 or NR12R13 with R12 and R13 being independently selected from H, linear or branched Ci-C2o-alkyl, linear or branched C2-Cs-alkenyl and Cs-Cs-cycloalkyl, and an O-, S- or N- containing 5- or 6-membered heterocyclic ring; R6 is OH . The bis(acyl)phosphinic acid of the general formula III is preferably obtained by the process of the present invention.

With regard to the definition of the process, Ri , R2, R3, R4, R5, R6, R7, Re, R9, R10 and R11 in general formula III and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the process as well as the bis(acyl)phosphinic acid silyl ester of the general formula I and the

bis(acyl)phosphinic acid of the general formula III obtained by the process of the present invention. It is appreciated that the bis(acyl)phosphinic acid of the general formula III obtained by the process of the present invention is preferably used in a photopolymerizable composition together with at least one photopolymerizable unsaturated compound.

A further aspect of the present invention thus refers to a photopolymerizable

composition comprising the bis(acyl)phosphinic acid of the general formula III and at least one photopolymerizable unsaturated compound.

It is appreciated that any photopolymerizable unsaturated compound that is typically used in the articles to be prepared and is well known can be used as the at least one photopolymenzable unsaturated compound. For example, the at least one

photopolymenzable unsaturated compound can be a compound as described in WO 2004/099262 A1 which is thus incorporated herewith by reference. The photopolymenzable composition may also contain optional additives and/or optional further photoinitiators and/or coinitiator. The optional additives and/or photoinitiators and/or coinitiator are not limited any include any additive and/or photoinitiators and/or coinitiator typically used in the articles to be prepared and are well known in the art. For example, the additives and/or photoinitiators and/or coinitiator can be one or more compounds described as additives (C) and/or photoinitiators and/or coinitiator (D) in WO 2004/099262 A1 which is thus incorporated herewith by reference.

The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the invention and are non-limitative.

EXAMPLES

Example 1 : Synthesis of Bis(2,4,6-trimethylbenzoyl)phosphinic acid, stepwise procedure

Ammonium hypophosphite (20.0 g, 0.241 mol, 1 eq) was suspended in 68.04 g (0.422 mol, 1 .75 eq) 1 ,1 ,1 ,3,3,3-hexamethyldisilazane and stirred at 1 10-120 °C until ammonia evolution ceased and the ammonium hypophosphite was completely dissolved. The reaction mixture was cooled down to 5 °C in an ice bath and diluted with 200 ml_ of dichloromethane. 44.44 g (0.243 mol, 1 .01 eq) 2,4,6-trimethylbenzoyl chloride was added dropwise and the reaction mixture stirred overnight at room temperature. The flask was again cooled down in an ice bath and another 68.04 g (0.422 mol, 1 .75 eq) of 1 ,1 ,1 ,3,3,3-hexamethyldisilazane were quickly added. After three hours of stirring at 5 °C, 44.44 g (0.243 mol, 1 .01 eq) 2,4,6-trimethylbenzoyl chloride was added dropwise and left overnight with stirring at room temperature. The reaction mass was then cooled down to 0-5°C and hydrolyzed by dropwise addition of 200 ml_ ethanol, so that the temperature did not exceed 15 °C. After filtration, the residue was thoroughly washed with ethanol and the filtrate evaporated to dryness. To the yellow viscous oil was added TBME : hexane 1 :1 . After the product had crystallized, the slightly yellow solid was filtered, washed with cold hexane and dried.

Yield: 53.8 g of a pale yellow solid, 62% of theory

1H-NMR (400.13 MHz; CDCIs): δ (ppm) = 2.13 (s, 12 H), 2.26 (s, 6 H), 6.77 (s, 4 H), 9.53 (bs, 1 H)

³¹ P-NMR (161 .89 MHz; CDCIs): δ (ppm) = -3.67

¹³ C-NMR (100.62 MHz; CDCIs): (ppm) δ = 19.25, 21 .15, 128.70, 135.15, 136.23 (d, ³ J _PC 45.5 Hz), 140.23, 216.80 (d, ¹ J _PC 101 .2 Hz)

The total formula was confirmed by elemental analysis. The elemental analysis was carried out by a standard procedure.

Example 2: Synthesis of Bis(2,4,6-trimethylbenzoyl)phosphinic acid, one-step procedure

Ammonium hypophosphite (20.0 g, 0.241 mol, 1 eq) were suspended in 136.07 g (0.843 mol, 3.5 eq) 1 ,1 ,1 ,3,3,3-hexamethyldisilazane and stirred at 1 10-120 °C until ammonia evolution ceased and the ammonium hypophosphite dissolved completely. The reaction mixture was cooled down to 5 °C in an ice bath and diluted with 200 ml_ of

dichloromethane. 90.19 g (0.494 mol, 2.05 eq) 2,4,6-trimethylbenzoyl chloride was added dropwise and the reaction mixture was stirred overnight at room temperature until ³¹ P-NMR showed complete conversion. Subsequently, the reaction mass was cooled to 0-5 °C and hydrolyzed by dropwise addition of 300 ml_ ethanol so that the temperature did not exceed 25 °C. After filtration, the residue was thoroughly washed with dichloromethane : ethanol 1 :1 and the filtrate evaporated to dryness. The residue was dissolved in ethyl acetate and washed twice with dilute hydrochloric acid. The organic phase was dried and evaporated. The crude solid product was recrystallized from a mixture of heptane : toluene 1 :4 filtered, washed with heptane and dried to give bis(2,4,6-trimethylbenzoyl)phosphinic acid as a pale yellow solid.

Yield: 62.1 g pale yellow solid, 72% of theory

¹ H-NMR (400.13 MHz; CDCIs): δ = 2.13 (s, 12 H), 2.32 (s, 6 H), 6.97 (s, 4 H), 12.65 (bs, 1 H) ³¹ P-NMR (161 .89 MHz; CDCIs): δ = -2.97

¹³ C-NMR (100.62 MHz; CDCI3): δ = 19.14, 21 .27, 128.79, 135.26 (d, ² JPC 46.5 Hz), 135.46, 140.67, 213.72 (d, ¹ J _PC 98.7 Hz) Correct elemental analysis was obtained. The elemental analysis was carried out by a standard procedure.