The present invention relates to novel uses of organic peroxoacids comprising functional groups as catalysts in the preparation of alkanesulfonic acids from alkanes and sulfur trioxide, methods for the production of alkanesulfonic acids employing said catalysts as well as reaction mixtures comprising said catalysts. The invention particularly relates to the production of methanesulfonic acid from methane and sulfur trioxide employing organic peroxoacids comprising functional groups as catalysts.

Alkanesulfonic acids are organic acids that can reach a similar acid strength as that of inorganic mineral acids, for example, sulfuric acid. However, in contrast to usual mineral acids such as sulfu- ric and nitric acids, the sulfonic acids are non-oxidizing and do not give off vapors that are harmful to health, as can be observed with hydrochloric and nitric acids. Further, many sulfonic acids, for example, methanesulfonic acid, are biologically degradable. The applications of sulfonic acids are many, for example, in cleaning agents, surfactants, galvanic and electronic industry, as catalysts, and in organic synthesis, pharmaceutical chemistry, for example, as protective groups. The salts of sulfonic acids are employed, for example, as surfactants, for example, sodium dodecylsulfonate, or in the electroplating industry, especially as tin, zinc, silver, lead and indium, but also other metal, alkylsulfonates. Furthermore, organic salts are employed in pharmaceutical chemistry. The very high solubility of alkyl sulfonates plays an important role, in particular. Further, no harmful gases are formed in electrolysis, and the use of toxic compounds, for example, cyanide, which is common in many cases, is dispensed with.

The structurally simplest representative of alkanesulfonic acids is methanesulfonic acid.

US 2,493,038 describes the preparation of methanesulfonic acid from SO ₃ and methane.

US 2005/0070614 describes further methods for preparing methanesulfonic acid, and its applica- tion. The methods known in the prior art are in part complicated, cost-intensive, and lead to unde- sirable products because of the harsh reaction conditions.

The reaction conditions in conventional processes of alkanesulfonic acid production can result in undesirable side products, which even manifest themselves as disturbing inhibitors in the produc- tion of alkanesulfonic acids. This may lead to termination of the actual reaction for preparing the alkanesulfonic acid, but also to impurities, formation of side products and poor yields, based on sulfur trioxide and methane.

WO 2007/136425 A2 discloses the use of the compound di(methanesulfonyl) peroxide (DMSP), which must be prepared by a complex electrolysis and, in addition, is a crystallizable highly explo- sive solid, as an initiator in a reaction in which methanesulfonic acid is formed from sulfur trioxide and methane.

WO 2015/071365 A1 and WO 2015/071455 A1 both describe processes for the sulfonation of alkanes. The main steps are:

1 ) Synthesis of an initiator/initiator-solution. 2) Preparation of a sulfur trioxide-solution (oleum) by dissolving sulfur trioxide in an inert sol- vent (e.g. sulfuric acid)

3) Reaction of oleum with the corresponding alkane after or during addition of the initiator/ initiator- solution in a high-pressure-reactor.

4) Quenching of non-reacted starting material

5) Purification (e.g. distillation, crystallization etc.)

6) Recycling of the inert solvent (e.g. sulfuric acid).

According to said prior art, the initiator is particularly prepared by reacting an alkanesulfonic acid ALK-SO3H, i.e. the desired product, with hydrogen peroxide in order to form an initiator- precursor ALK-SO2-O-OH. Said initiator-precursor is then reacted with SO3 yielding initiator compounds such as ALK-SO2-O-O-SO3H. The cited prior art therefore requires some amount of the desired product to form an initiator.

It is thus the object of the present invention to provide novel catalysts for the preparation of al- kane sulfonic acids, especially methane sulfonic acid (MSA). Particularly, it is the object of the invention to provide catalysts that do not require the desired product itself to be present as an initiator-precursor. Further, requirements for sulfurtrioxide and alkanes should be of no rele- vance, meaning that not only absolute pure raw materials might be used, but that impurities do not affect negatively the reaction.

In a first embodiment, the object of the present invention is solved by the use of a compound comprising an organic peroxoacid or a salt thereof, wherein the organic peroxoacid comprises a peroxoacid group and at least one additional functional group, as a catalyst in the preparation of alkane sulfonic acids from alkanes and sulfur trioxide, especially in the preparation of methane sulfonic acid from methane and sulfur trioxide. Particularly, methane, ethane, propane, butane, isopropane, isobutane or a higher alkane can be reacted with sulfur trioxide to form the corre- sponding alkane sulfonic acid.

Surprisingly, it has been found that organic peroxoacids comprising functional groups show a similar catalytic activity as peroxoacids derived from the desired alkane sulfonic acids. There- fore, not only peroxoacids derived from the desired alkane sulfonic acid, which comprise no functional groups other than the persulfonic acid group itself, may be employed as catalysts in the preparation of alkane sulfonic acids from alkanes and sulfur trioxide and the desired product is not required as a precursor of the catalyst. In principal, any organic peroxoacid comprising functional groups can be employed according to the invention. Such organic peroxoacids or their corresponding oxoacids or derivatives thereof are cheaply available from commercial dis tributors.

Preferably, the peroxoacid is used as a catalyst in a condensed-phase homogeneous process. The peroxoacid catalyst is solved in the same phase as the reactants, i.e., an alkane and sulfur trioxide. In the following, the assumed catalytic cycle is exemplary described for the employment of me- thane as alkane. The same catalytic cycle is assumed to apply to other alkanes. In general, the peroxoacid according to the invention can be described by the formula R-O-O-H. Without the intention of being bound by theory, it is assumed that the peroxoacid acts by activating sulfur trioxide towards the reaction with an alkane.

In a first step, the peroxoacid reacts with sulfur trioxide upon which an activated form of sulfur trioxide is formed:

R-O-O-H + S0 ₃ — > R-O-O-SOsH (R1 )

In a second step, said activated form is able to react with methane in order to form methanesul- fonic acid upon which the peroxoacid is regenerated:

R-O-O-SOsH + CH ₄ — > H3C-SO3H + R-O-O-H (R2)

In what follows, the present invention is described in its preferred embodiments. The description is meant to be exemplary and not to limit the scope of the invention.

In a preferred embodiment the peroxoacid comprises at least one organic peroxoacid of sulfur, phosphorus, silicon, boron, nitrogen or carbon. Any suitable peroxoacid of said elements can be used. The peroxoacids are typically derived from the corresponding oxoacid of the respective element.

Preferably, the peroxoacid used as catalyst according to the invention comprises a peroxoacid group corresponding to -E(=X) _m (-YZ) _n -0-0-Z, wherein E is selected from the group consisting of S, P, Si, B, N and C, wherein X and Y may be the same or different and are selected from the group consisting of O and S, wherein m is an integer of from 0 to 2, wherein n is an integer of from 0 to 2, and wherein Z is H, Li, Na and/or K.

In a preferred embodiment of the invention, the peroxoacid group is selected from the group consisting of -SO2-O-O-X, -CO-O-O-X, -P0(0H)-0-0-X, PS(0H)-0-0-X, wherein X is H,

Li, Na and/or K. Surprisingly, it has been found that said preferred peroxoacids are particularly suitable as catalyst in the preparation of alkanesulfonic acids from alkanes and sulfur trioxide

According to the invention, the organic peroxoacid comprises at least one additional functional group. The additional functional group may particularly be selected from the group consisting of carbon double bonds, carbon triple bonds, aryl groups, heteroaryl groups and functional groups comprising heteroatoms, especially functional groups comprising O, S, N, P, Si, B, Se, Te, F, Cl, Br, I, Mg or Li atoms.

Particularly preferred are aryl groups, halogen atoms, such as F, Cl, Br, I, and siloxane groups. The functional groups, particularly aryl groups, may be further derivatized and may contain fur- ther functional groups. Examples of functional groups according to the invention comprise par- ticularly phenyl groups, carbonyl groups, ether groups, thioether groups, thioketone groups and halide groups.

Examples of suitable organic peroxoacids according to the invention are peroxybenzoic acid and trifluoroperacetic acid. Any of the aforementioned examples may be derivatized and/or sub- stituted with side chains, particularly with alkyl groups, aryl groups or halogen atoms.

In a preferred embodiment, the organic peroxoacid is part of or bound to an organic or inorganic polymer. Any suitable polymer may be chosen. The polymer backbone may constitute the addi- tional functional group, particularly in cases where the polymer backbone comprises heteroa- toms. Particularly preferred polymers comprise polysiloxanes, polyolefins, vinyl polymers, poly- ether, polyester, polyamides and polyurethanes. The peroxoacid group may be bound to the polymeric backbone or may be contained in a polymeric side chain. Particularly preferred are polymers comprising -SO ₂ -OOH groups.

The polymer may have any suitable structure. Particularly, homopolymers, copolymers, block copolymers, graft copolymers or comb copolymers may be employed. The polymers may have a dendrimer structure.

The organic peroxoacid used as a catalyst according to the invention may be obtainable by a reaction of the corresponding oxoacid with a peroxide. More preferably, the peroxoacid may be obtainable by a reaction of the corresponding oxoacid with hydrogen peroxide or a salt thereof. Without the intention of being bound by theory, the reaction of an oxoacid with hydrogen perox- ide can for example be described by

-EO _x (OH)y-OH + H2O2— > -E0 _c (0H) _g -0-0H + H ₂ 0 (R3)

In an alternative embodiment, the object of the invention is therefore solved by the use of a mix- ture comprising a peroxide and an organic oxoacid or a derivative thereof, wherein the oxoacid comprises at least one additional functional group, as catalyst in the preparation of alkanesul- fonic acids from alkanes and sulfur trioxide, especially in the preparation of methanesulfonic acid from methane and sulfur trioxide. Optionally the mixture may comprise a solvent. Prefera- bly, hydrogen peroxide or a salt thereof is employed as peroxide compound. Suitable salts of hydrogen peroxide particularly comprise alkaline metal peroxides or alkaline-earth metal perox- ides, such as sodium peroxide (Na ₂ 0 ₂ ).

The oxoacid used in the mixture according to the invention must be suitable to yield a stable peroxoacid upon the reaction with a peroxide. In this alternative embodiment, the catalyst corn- pound is produced in situ in the reaction mixture.

The additional functional group may preferably be selected from the group consisting of carbon double bonds, carbon triple bonds, aryl groups, heteroaryl groups and functional groups corn- prising heteroatoms, especially functional groups comprising O, S, N, P, Si, B, Se, Te, F, Cl, Br, I, Mg or Li atoms. Particularly preferred are aryl groups, halogen atoms, such as F, Cl, Br, I, and siloxane groups. The functional groups, particularly aryl groups, may be further derivatized and may contain fur- ther functional groups. Examples of functional groups according to the invention comprise par- ticularly phenyl groups, carbonyl groups, ether groups, thioether groups, thioketone groups and halide groups.

In a preferred embodiment, the organic oxoacid is part of or bound to an organic or inorganic polymer. Any suitable polymer may be chosen. The polymer backbone may constitute the addi- tional functional group, particularly in cases where the polymer backbone comprises heteroa- toms. Particularly preferred polymers comprise polysiloxanes, polyolefins, vinyl polymers, poly- ether, polyester, polyamides and polyurethanes. The peroxoacid group may be bound to the polymeric backbone or may be contained in a polymeric side chain. Particularly preferred are polymers comprising -SO2-OH groups.

The polymer may have any suitable structure. Particularly, homopolymers, copolymers, block copolymers, graft copolymers or comb copolymers may be employed. The polymers may have a dendrimer structure.

In a preferred embodiment, the organic oxoacid is an oxoacid of sulfur, phosphorus, silicon, boron, nitrogen or carbon or a derivative thereof, especially an acid halide.

In an alternative embodiment, the object of the invention is solved by a process for the prepara- tion of alkanesulfonic acids from alkanes and sulfur trioxide comprising the steps of i) providing sulfur trioxide;

ii) reacting the sulfur trioxide with an alkane, especially methane, in a high-pressure auto- clave or laboratory reactor;

iii) setting a pressure of from 1 to 200 bar;

iv) introducing an organic peroxoacid, comprising at least one additional functional group, or a salt thereof;

v) controlling the temperature of the reaction mixture at 0 °C to 100 °C;

vi) if necessary purifying the reaction product, for example, by distillation or extraction.

The inventive process differs from similar processes from the prior art in that in step iv) an or- ganic peroxoacid, comprising at least one additional functional group, is added as catalyst. Said peroxoacid corresponds to the abovementioned organic peroxoacids with additional functional groups, which may be used as catalysts.

Sulfur trioxide may be provided in the form of oleum, i.e., a solution of sulfur trioxide in sulfuric acid. Instead of oleum also pure sulfur trioxide can be employed. This avoids the preparation of sulfur trioxide solutions. The reaction conditions are here without added solvents. Further, non- reacted sulfur trioxide can evaporate, avoiding the necessity of quenching it. In a further embodiment, sulfur trioxide is used in a form of oleum with a trioxide content of 50 % (w/w) or less, or 65 % (w/w) or more. Surprisingly it has been found that for the processes of the present invention also oleum with a sulfur trioxide content of 65 % (w/w) or more, especially of 70 % w/w or more can be used without negatively affecting the inventive process. Even pure sulfur trioxide (100 % (w/w) sulfur trioxide) may be used.

The temperature during the reaction is preferably within a range from above 0 °C to 70 °C, es- pecially from 10 °C to 65 °C, preferably from 20 °C to 60 °C. Surprisingly the formation of side products was lower at lower temperatures. If the temperature is around 0 °C or 10 °C, the reac- tion takes place but needs a longer time so that for an economically process the temperature is preferably 20 °C or above, especially about 40 °C to 55 °C.

The pressure is set to be within a range from 1 to 200 bar, preferably from 50 to 150 bar, espe- cially from 80 to 120 bar.

Due to the advantages being connected with the use of pure sulfur trioxide mentioned above, the use of pure sulfur trioxide is preferred in the process for manufacturing alkane sulfonic acids according to the present invention. As contrary to the prior art, a circulation of solvent is not necessary, alkanes comprising higher amounts of impurities compared to the prior art can be used. Impurities usually are enriched in the solvent leading to a reduced yield of alkane sulfonic acids. By avoiding solvents and thus a circulation of them, impurities originating from the al- kanes are not negatively influencing the production of alkane sulfonic acids when pure sulfur trioxide is employed.

Sulfur trioxide, especially pure sulfur trioxide is reacted with an alkane in a reactor. For alkanes with a low boiling point, the use of a high-pressure reactor is necessary. For pentane and higher alkanes, a common laboratory reactor is sufficient. In the case of gaseous alkanes, for example, methane, a pressure of 1 to 200 bar gas pressure is set.

Subsequently, the peroxoacid catalyst according to the present invention is added. The catalyst may be provided in pure form or solved in a suitable solvent. Preferably, the initial molar ratio between the catalyst and SO ₃ is in the range of 1 :50 to 1 : 10000, more preferably 1 :100 to 1 :500, particularly 1 :150. The catalyst may be provided in a solvent, particularly in sulfuric acid.

After the reaction has taken place, the reaction mixture contains essentially of the respective al- kane sulfonic acid, especially methane sulfonic acid, as well as sulfuric acid. This mixture of alkane sulfonic acid, especially methane sulfonic acid (MSA), and H2SO4 might afterwards be used as the respective mixture. The combination of an alkane sulfonic acid, especially methane sulfonic acid, and sulfuric acid provides a strong acid in which even gold might be dissolved enabling different fields of technical applicability.

Alternatively, the alkane sulfonic acid, especially MSA, might be separated i.e. the method of the invention comprises the optional step of the purifying the reaction product, which might be done by distillation or extraction. But also alkane sulfonic acids, and specially methane sulfonic acids, might be used in different technical fields, i.e. as cleaning agent (cleaning comprising the area of cleaning and caring, home care as well as industrial and institutional cleaning of hard and soft surfaces, i.e. in dishwashing, commercial laundry, cleaning and sanitation, vehicle and transportation care, concrete cleaning, membrane cleaning, and others), for regeneration of ion exchange resins, in galvanic proceedings, in the area of oil, gas, mining, treatment of metals and/or their surfaces, in different areas of phar- maceutical, chemical and agro-chemical industry or in the production of biodiesel. MSA might also be used in galvanization process of plastics, the broad area of batteries, such as lead battery recy- cling and recycling in general, such as metal recycling, as well as borane generation are further possible areas of application.

In an alternative embodiment, the object of the invention is solved by a process for the prepara- tion of alkane sulfonic acids from alkanes and sulfur trioxide comprising the steps of i) providing sulfur trioxide;

ii) reacting the sulfur trioxide with an alkane, especially methane, in a high-pressure auto- clave or laboratory reactor;

iii) setting a pressure of from 1 to 200 bar;

iv) introducing an organic oxoacid, comprising at least one additional functional group, or a salt thereof, wherein the oxoacid is optionally solved in a solvent, and a peroxide, wherein the oxoacid and the peroxide are introduced sequentially or simultaneously; v) controlling the temperature of the reaction mixture at 0 °C to 100 °C;

vi) if necessary purifying the reaction product, for example, by distillation or extraction.

The process according to this embodiment of the invention differs from the aforementioned em- bodiment of the inventive process in that the catalyst is employed by introducing an oxoacid with an additional functional group and a peroxide rather than an organic peroxoacid. The peroxoacid is thus formed in situ in the autoclave or laboratory reactor in which the reaction of sulfur trioxide and the alkane takes place.

Any suitable oxoacid which can be used in a catalyst mixture in the preparation of alkane sul- fonic acids as defined above can be employed. Accordingly, the oxoacid needs to be capable of forming a stable peroxoacid.

Preferably hydrogen peroxide or a salt thereof, such as sodium peroxide (Na ₂ 0 ₂ ), may be em- ployed as peroxide. Any peroxide as described above may be used.

Both the oxoacid and the peroxide are added to the reactor. They can be added in a mixture, optionally with a solvent. Suitable solvents comprise sulfuric acid or a liquid alkane sulfonic acid, e.g. methane sulfonic acid. The oxoacid and the peroxide may also be added separately but simultaneously. If both compounds are added separately, each may optionally be solved in a solvent, for example sulfuric acid. In yet another alternative, both compounds may be added sequentially, wherein each compound may be added as the first or the second compound.

Preferably, the oxoacid and the peroxide are added in a molar ratio of 1 :5 to 5:1 , more prefera- bly in a molar ratio of 1 :2 to 2:1 , most preferably in a molar ratio of 1 :1. The initial molar ratio between the oxoacid and the SO3 is preferably in the range of 1 :50 to 1 :10000, more preferably in the range of 1 :100 to 1 :500.

In an alternative embodiment, the object of the invention is solved by a mixture comprising an alkane, sulfur trioxide, an organic peroxoacid, comprising at least one additional functional group, and optionally a solvent. The inventive mixture is capable of producing an alkane sulfonic acid. Particularly, if the mixture is set at a pressure of 1 to 100 bar and held at a temperature of 0 to 100 °C, an alkane sulfonic can be produced in an efficient way. The organic peroxoacid acts as a catalyst.

In a preferred embodiment, the alkane is methane. Such a preferred mixture is capable of form- ing methane sulfonic acid.

In an alternative embodiment, the object of the invention is solved by a mixture comprising an alkane, sulfur trioxide, an organic oxoacid, comprising at least one additional functional group, a peroxide, especially hydrogen peroxide or a salt thereof, and optionally a solvent, wherein the oxoacid is capable of forming an organic peroxoacid as defined above. The inventive mixture is capable of producing an alkane sulfonic acid. Particularly, if the mixture is set at a pressure of 1 to 100 bar and held at a temperature of 0 to 100 °C, an alkane sulfonic can be produced in an efficient way. The organic oxoacid and the peroxide react to in situ form an organic stable peroxoacid, which is capable of acting as catalyst.

In a preferred embodiment, the alkane is methane. Such a preferred mixture is capable of form- ing methane sulfonic acid.