The present invention relates to a process for preparing haloalkanesulfonic acids from sulfur trioxide and a haloalkane, particularly to a process for preparing tri- fluoromethane sulfonic acid from sulfur trioxide and trifluoromethane, in which SO3 and an haloalkane are contacted with each other in the presence of a sol vent, said solvent does not constitute a superacid and the combination of said solvent with one or more of the reactants also does not give rise to a super acid.

Haloalkanes, also known as halogenalkanes or alkyl halides, are a group of chem ical compounds structurally derived from alkanes by replacing one or more hydro gen atoms by halogen atoms. They are widely used as flame retardants, fire ex- tinguishants, refrigerants, propellants, solvents and pharmaceuticals. By replacing a hydrogen atom of a haloalkane by a sulfonic acid group SO3H, haloalkanesulfonic acids can be derived. Said haloalkanesulfonic acids are also formally derivable from alkanesulfonic acids by replacing hydrogen atoms by halogen atoms.

Among the haloalkanesulfonic acids, trifluoromethanesulfonic acid (TFMS), which is also known as triflic acid and has the chemical formula CF3SO3H, is of particular technical importance. At room temperature TFMS is a hygroscopic, clear and col orless liquid, soluble in polar solvents. Notably, TFMS is a super acid and with a pKa value of -14.7 one of the strongest known acids. Trifluoromethansulfonic acid is widely used as a catalyst for esterification, and isomerization, among other re actions. Triflic acid's conjugate base CF3SO3- is called triflate and is a well-known protection group in organic chemistry. On an industrial scale, trifluoromethanesul fonic acid is particularly used in the polymer, fuel, pharmaceutical and sugar in dustry. On an industrial scale, trifluoromethanesulfonic acid is produced by electro chemical fluorination of methanesulfonic acid (T. Gramstad and R. N . Haszeld- ine, J. Chem. Soc., 1956, 173). In theory, trifluoromethanesulfonic acid could also be prepared by the direct reaction of trifluoromethane (CF3H) and sulfur trioxide.

CF3H is a strong greenhouse gas with a global warming potential of 15,000 times more than one molecule of carbon dioxide. It was formerly used as a refrigerant, although this application should now be avoided. Trifluoromethane is still pro duced, however, as an undesirable side-product in a number of industrial pro cesses, e.g., in the production of polytetrafluoroethylene (PTFE), also known as teflon. There is thus need to eliminate excess trifluoromethane, preferably by transforming it into some useful and harmless substance. The reaction with sul fur trioxide might yield TFMS, which is considered to be an environmentally friendly acid.

Mukhopadhyay et al. (S. Mukhopadhyay, A. T. Bell, R. V. Srinivas, G. S. Smith, Org. Proc. Res. Dev. 2004, 8, 660) describe the direct synthesis of trifluoro methanesulfonic acid from trifluoromethane and sulfur trioxide employing hy drogen peroxide - urea and RhC as catalyst in fuming sulfuric acid. The yield, however, is small and the method is not economically feasible.

Therefore, there is still need for a process, which can transform trifluoromethane to trifluoromethanesulfonic acid in an efficient and economically feasible way. Such a process could provide both an efficient route to trifluoromethanesulfonic acid and a new method to eliminate trifluoromethane by converting it to a useful and harmless substance.

It is thus the object of the present invention to provide an improved process for the preparation of haloalkanesulfonic acids from the respective haloalkane and sulfur trioxide. Particularly, a process for the preparation of trifluoromethanesul- fonic acid from trifluoromethane and sulfur trioxide should be provided.

Surprisingly, it was now found that stable reaction conditions can be obtained when working under non-superacid conditions. Thus, the solvent has to be se lected extremely carefully. It was now found that selecting an appropriate sol vent helps to provide improved reaction conditions. According to the classical definition, a superacid is an acid with an acidity greater than that of 100% pure sulfuric acid, which has a Hammett acidity function (Ho) of -12. Accord ing to the modern definition, a superacid is a medium in which the chemical potential of the proton is higher than in pure sulfuric acid. Consequently, the pK _a value is negative.

In a first embodiment, the object underlying the present invention is therefore solved by a method for producing haloalkane sulfonic acid, in which SO3 and an haloalkane are contacted with each other in the presence of a solvent, wherein said solvent does not constitute a superacid and the combination of said solvent with SO3 and/or the haloalkane sulfonic acid does not give rise to a superacid.

In a preferred embodiment, the solvent further comprises compounds stabiliz ing SO3 as additive.

In a further preferred embodiment, the method is a method for the production of triflic acid.

In another preferred embodiment, the method is a method as disclosed in WO 2018/096138 A1 with the proviso, that pure SO3 is used as one of the educts and one of the solvents according to the present invention is used. In one preferred embodiment, the present inventions provides for a method for manufacturing haloalkane sulfonic acids, especially triflic acid, comprising the following steps:

a. Providing sulfur trioxide SO3;

b. Providing an haloalkane, especially trifluoromethane;

c. Providing a solvent, wherein said solvent does not constitute a super acid and the combination of said solvent with SO3 and/or the haloalkane sulfonic acid does not give rise to a superacid;

d. Bringing into contact SO3, haloalkane and the solvent in a high-pressure autoclave or laboratory reactor;

e. Setting a pressure of from 1 to 200 bar;

f. Adding a compound which is able to initialize the reaction between SO3 and haloalkane at the described reaction conditions;

g. Controlling the temperature of the reaction mixture at 0 °C to 100 °C; h. Letting react the compounds so that the haloalkane sulfonic acid, espe cially triflic acid, is formed.

In the following, the present invention will be described in more detail. Fea tures mentioned for one embodiment can be also used in other embodiments, even if not explicitly mentioned.

The present invention for the first time shows that direct sulfonation of trifluo romethane or any other haloalkane is possible not only under super acid con ditions but also under non super acid reaction conditions. The solvent accord ing to the present invention is selected such that the solvent alone does not constitute a super acid. It may be, that in the reactor, in which the educts and the solvent react with each other, the solvent and SO3 react with each other in any kind or interact with each other. Also, such a reaction or interaction of the solvent with SO3 does not give rise to a super acid according to the present in vention. The same is true for the combination of the solvent and the haloal kane sulfonic acid which is formed during the reaction in the reactor. Thus, the solvent alone does not constitute a super acid. Also, the combination of the solvent and SO3 does not give rise to a super acid. Further, the combination of the solvent and the haloalkane sulfonic acid does not give rise to super acid. Also the combination of the solvent with SO3 and the haloalkane sulfonic acid does not give rise to super acid within the meaning of the present invention.

A super acid is an acid with an acid strength stronger than that of pure H2SO4. Therefore, in the meaning of the present invention a super acid means an acid with a pK _a value less -3.

Direct sulfonation of haloalkane with SO3

The method of the present invention is suitable to produce different kinds of haloalkane sulfonic acids. Preferably, the haloalkane which is used as educt and from which the respective haloalkane sulfonic acid is formed, is a short chain haloalkane with 1 to 10 C atoms which can be linear or non-linear. Pref erably, the haloalkane is an haloalkane with 1 to 5 C-atoms, where at least one, preferably at least two, particularly at least three H-atoms are replaced by a halogen. The halogen may be F, Cl, Br, I, especially it is F. It is within the meaning of the present invention that all H-Atoms of the alkane a replaced by one or more halogens. Preferably, the haloalkane is trifluoromethane so that the haloalkane sulfonic acid being formed according to the method of the pre sent invention is triflic acid.

The reaction between SO3 and the haloalkane in the present solvent usually takes place in a high-pressure autoclave. Thus, the pressure at which SO3 and haloalkane are contacted with each other is preferably in a range of from 1 bar to 200 bar, especially from 50 bar to 150 bar, preferably from 80 bar to 120 bar.

The temperature during the reaction is preferably within a range of from 0 °C to 100° C, especially from 15 °C to 80° C, especially preferred from 20 °C to 70° C, preferably from 35 °C to 60° C. Therefore, in a preferred embodiment, the temperature at which SO3 and haloalkane are contacted with each other is below 70 °C, especially below 65 °C, preferably below 60 °C and especially preferred below 55 °C. If the temperature is around 0 °C or 10 °C, the reac tion time increases tremendously so that for an economically process the tem perature is preferably 20 °C or above, especially 25 °C or above, especially preferred 30 °C or above.

If the preferred reaction conditions are used, the pressure being from 1 bar to 200 bar and the temperature is controlled to be between 0 °C to 100 °C, the solvent used in a method according to the present invention is liquid under the respective conditions. Usually, SO3 is provided as liquid so it is homogenously distributed in the solvent. Alternatively, the SO3 can also be provided as gas. The haloalkane is added either as a gas or as liquid depending on the length of the C chain. For haloalkanes with low boiling point, the use of a pressure reac tor is therefore usually necessary. For pentane or higher haloalkanes, a com mon laboratory reactor is sufficient. In case of gaseous haloalkanes, for exam ple trifluoromethane, a pressure of 1 bar to 100 bar is set.

At the interphase between liquid and gas or in the complete reactor in case of sufficient mixture of the reaction mixture the reaction takes place so that in the reactor there remains a mixture of SO3, haloalkane, solvent as well as the formed haloalkane sulfonic acid. According to the present invention so that this stage of the reaction, the conditions inside the reactor are non-super acid.

Solvents

Suitable solvents which may be used in a method according to the present in vention are selected from the group consisting of CO2; carbonates; linear or non-linear, aromatic or aliphatic, substituted or non-substituted Ci-20 alkanes; substituted or non-substituted oligomers of alkanes with a chain length of up to C200, ionic liquids as well as mixtures of two or more of these. The advantage of using CO2 is that it does not give rise to a super acid together with any of the other compounds beeing present in a reactor. The CO2 is liquid under the conditions at which SO3 and haloalkane are contacted with each other. After the reaction is finished, the pressure is usually reduced in the reactor to remove non-reacted haloalkane, in case the haloalkane is gaseous. This leads also to a removal of CO2 from the reactor, as this will become gaseous as well.

According to the present invention it is possible to remove, in a preferred em bodiment where CO2 is used as solvent, the CO2 completely from the reaction mixture together with a non-reacted haloalkane. In such a case, only SO3 and the formed haloalkane sulfonic acid remain the reactor. This reaction mixture can be purified e.g. by distillation. In such a case, SO3 will be destroyed usually with water or an alkohol prior to distillation. The thus obtained mixture of sul fonic acid (where water is used to destroy SO3) and haloalkane sulfonic acid can be purified by distillation.

In another embodiment where CO2 is used as solvent, CO2 is not or not com pletely removed from the reactor together with the non-reacted haloalkane but remains in the liquid phase. The liquid phase is afterwards separated so that no more non-reacted haloalkane is part of this phase. Subsequently, the remaining gas phase - which comprises CO2 as well as non-reacted haloalkane - is set under higher pressure so that the haloalkane and the CO2 can easily be sepa rated. The CO2 can then be used again in a reaction according to the present invention as solvent.

Also, in cases where the CO2 is removed in a gas phase together with the non- reacted haloalkane, it is possible to separate the haloalkane and CO2. This can be done by pressurizing the gas phase as described for the other embodiment above. Alternatively, other separating methods in the gas phase are known in the prior art, which can be used also in the present invention for recycling of CO2.

Alternatively, carbonates and especially dimethyl carbonate can be used as sol vent. Again, this solvent enables non-super acid conditions in a method accord ing to the present invention. Surprisingly, the reaction is faster if the conditions are non-super acid compared to reaction conditions described in the prior art where sulfuric acid is used as solvent and thus, super acid conditions are con stituted.

Further suitable solvents according to the present invention are alkanes. Exam ples of suitable alkanes are short length alkanes with a carbon chain of 1-20 carbon atoms. These could be linear or branched, aromatic or aliphatic, substi tuted or non-substituted.

Substituted alkanes within the meaning of the present invention means that in a C-H-group hydrogen is replaced by another atom or functional group. Prefer ably, the substitution is with fluorine and/or a nitro group and/or sulfonic acid group. It is possible, that not only one hydrogen is replaced by a substituent but that two or more hydrogens are substituted. Also, within the invention it is possible that the alkane comprises only one substituent so that a suitable sol vent within the meaning is e.g., a fluorinated aliphatic alkane with a C-chain length of 1-20. Alternatively, an also suitable solvent is a linear or branched aliphatic alkane with 1-10 C atoms with NO2 as substituent. Also, alkanes com prising fluorine as well as nitro group and/or sulfonic acid group as substituents are within the scope of the present invention. Suitable example for a nitrated solvent is nitro methane. The alkane can be aliphatic or aromatic. In case the alkane is aromatic, it can be substituted as described above for the aliphatic alkanes either with fluorine or nitro group or sulfonic acid group with two or all the three of them. Other preferred solvents are oligomers of alkanes with a C-chain length of up to 200. Also, these oligomers can be unsubstituted or substituted. In case they are substituted, the substitution is especially with fluorine and/or nitro group as described for the aliphatic short chain alkanes above. The oligomers are usually oily or high viscous liquids and are non-reactive so that the educts do not react with the solvent.

An ionic liquid within the meaning of the present application is a salt in which the ions are poorly coordinated, which results in these solvents being liquid also below 100°C. Examples include compounds based on the l-Ethyl-3-methylim- idazolium (EMIM) cation and include: EMIM :CI, EMIM dicyanamide, (C2H5)(CH ₃ )C3H ₃ N ⁺ 2-N(CN)-2, that melts at -21 °C (-6 °F); and l-butyl-3,5- dimethylpyridinium bromide which becomes a glass below -24 °C (-11 °F).

The solvent further comprises in a preferred embodiment an additive in an amount of 2 ppm to leg (equivalent), the amount referring to the amount of S0 ₃ in the solution. This additive is suitable to stabilize S0 ₃ . Such stabilizers are present in a very low concentration but help to handle S0 ₃ in the reaction. The additive is preferably selected from the group comprising dimethyl sulphate, dimethyl ether, diethyl ether, amines as well as mixtures of these. Suitable amines are for example trimethyl amine, which is known to help for the handling of S0 ₃ . The amount is preferably within the range of from 5 ppm to leq, or 10 ppm to 1 eq. If the additive is added to avoid the polymerization (i.e., dimethyl- sulphate) of S0 ₃ , few ppm are sufficient. If the additive forms an adduct with S0 ₃ (i.e. amines), the additive should be present in equivalent amounts as the S0 ₃ is.

Initiator/catalyst

In a very preferred embodiment, the method of the present invention comprises the following steps: a. Providing sulfur trioxide SO3;

b. Providing an haloalkane, especially trifluoromethane;

c. Providing a solvent, wherein said solvent does not constitute a super acid and the combination of said solvent with SO3 and/or the haloalkane sulfonic acid does not give rise to a superacid;

d. Bringing into contact SO3, haloalkane and the solvent in a high-pressure autoclave or laboratory reactor;

e. Setting a pressure of from 1 to 200 bar;

f. Adding a compound which is able to initialize the reaction between SO3 and haloalkane at the described reaction conditions;

g. Controlling the temperature of the reaction mixture at 0 °C to 100 °C; h. Letting react the compounds so that the haloalkane sulfonic acid, espe cially triflic acid, is formed.

Accordingly, a compound is added which initializes or catalyzes the reaction be tween SO3 and the haloalkane at the described reaction conditions (see step f) above). This compound may be provided in pure form or solved in a suitable solvent with the proviso that this solvent again does not constitute a super acid and the combination of said solvent with SO3 and/or the haloalkane sulfonic acid does not give rise to super acid. Preferably, in cases this compound is added together with the solvent, this solvent is the same as used in the reaction as a whole. If such a compound is added, the initial molar ratio between this com pound and SO3 is in the range of 1 : 50 to 1 : 10000, preferably 1 : 100 to 1 : 500, particularly 1 : 150.

The compound added at step f) of the method according to the above preferred embodiment may be a compound being known to initialize the reaction between an haloalkane and SO3 to form alkene sulfonic acid under super acid conditions. The compound added during step f) of the inventive procedure is thus a com pound comprising a heterolytically or homolytically cleavable bond. Suitable compounds with homolytically cleavable bonds are organic or inorganic peroxo- compounds. The compound can be an inorganic peroxoacid or an organic peroxoacid. Organic or inorganic peroxo compounds without acidic function are suitable.

The compound added to initialize the reaction between SO3 and haloalkane may be activated either in the reactor or prior to adding it into the reactor. Such an activation may be possible by irradiation with UV light or the addition of transi tion metals. Suitable transition metals are any metals of the d-block of the pe riodic table. Preferred are Pt, Pd, Rh, Ir, Ag, Au, Fe, and others. Such activation enables a higher reaction speed or the need of lower temperature to obtain the same reaction speed as at higher temperatures.

The compound added at step f) is preferably selected from the group consisting of organic or inorganic peroxides being stable at room temperature, compounds with a heterogeneously or homogenously cleavable bond, as well as mixtures of two or more of them. Suitable compounds are for example disclosed in PCT/EP2017/080495, EP 18157127.4, EP 18196493.3, EP 18196498.2, and EP 18196520.3, the content of which is enclosed herein in its entirety. Further suit able compounds are for example hydrogen peroxide, benzoylperoxide, cumolhy- droperoxide, lauroylperoxide, peroxo acetic acid, tert-butylhydroperoxide, Caro's acid, Marhall's acid, or DMSP (dimethyl sulfoyl peroxide). All of them may be used alone or in mixture. Preferably, only one compound is used in a reaction.

Especially, preferred, a compound is added according to the following formula (I) :

ALK-SO2-O-O-X (I) wherein ALK is a branched or unbranched alkyl group, especially a trifluoromethyl, or a higher haloalkyl group with 2 to 10 C-atoms, and X = hydrogen, zinc, aluminium, an alkali or alkaline earth metal. Higher alkyl group within the meaning of the present invention means an alkyl group with 1 to 10 carbon atoms. Prefer ably, ALK is trifluoro methyl. X is preferably hydrogen, alkali or alkaline earth metal. Particularly, X is hydrogen. Thus, in a very preferred embodiment, the compound added to initialize the reaction between SO3 and haloalkane is CF3-SO2- O-O-H.

Alternatively, the compound added in step f) of the preferred embodiment is an organic peroxoacid which, where appropriate, comprises functional groups. In general, the peroxoacid according to the invention can be described by the for mula 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 haloalkane. 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 typ ically 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 se lected 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 0 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 prep aration of haloalkanesulfonic acids from haloalkanes and sulfur trioxide According to the invention, the organic peroxoacid comprises at least one addi tional functional group. The additional functional group may particularly be se lected from the group consisting of carbon double bonds, carbon triple bonds, aryl groups, heteroaryl groups and functional groups comprising heteroatoms, especially functional groups comprising 0, 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 further functional groups. Examples of functional groups according to the invention comprise particularly phenyl groups, carbonyl groups, ether groups, thioether groups, thioketone groups and halide groups.

Examples of suitable organic peroxoacids according to the invention are perox- ybenzoic acid and trifluoroperacetic acid. Any of the aforementioned examples may be derivatized and/or substituted 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 additional functional group, particularly in cases where the polymer backbone comprises heteroatoms. Particularly preferred pol ymers comprise polysiloxanes, polyolefins, vinyl polymers, polyether, polyester, polyamides and polyurethanes. The peroxoacid group may be bound to the pol ymeric backbone or may be contained in a polymeric side chain. Particularly preferred are polymers comprising -SO2-OOH groups.

The polymer may have any suitable structure. Particularly, homopolymers, co polymers, block copolymers, graft copolymers or comb copolymers may be em ployed. 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 peroxide can for example be described by

-EOx(OH)y-OH + H2O2 -> -E0x(0H)y-0-0H + H2O. (R3)

If such an organic peroxoacid is used as compound, it is only suitable if it does not give rise to superacid conditions in the reactor at which the reaction takes place. This may be controlled by selecting the compound carefully or by using it in only small amounts.

In a further preferred embodiment, the compound is an inorganic peroxoacid or a salt thereof, wherein the peroxoacid is stable at room temperature. Stability at room temperature is particularly to be understood as stability in a reaction solvent comprising sulfur trioxide and an haloalkane, especially trifluoro- methane. This solvent may be sulfuric acid. The peroxoacid according to the invention must be stable enough in order to act as catalyst in the production of haloalkanesulfonic acids and not to decompose. Said decomposition may par ticularly take place by the release of reactive oxygen species such as superoxide anions (02-). In this sense, stability of the peroxoacid catalysts of the present invention for example means the absence of the release of reactive oxygen spe cies such as superoxide anions.

In a preferred embodiment the peroxoacid comprises at least one peroxoacid of boron, silicon, phosphorus, carbon, nitrogen or sulfur. 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 a catalyst according to the invention is ob tainable by a reaction of the corresponding oxoacid with a peroxide. More pref erably, the peroxoacid is obtainable by a reaction of the corresponding oxoacid with hydrogen peroxide. Without the intention of being bound by theory, the reaction of an oxoacid with hydrogen peroxide can for example be described by

EOx(OH)y-OH + H2O2 -> E0x(0H)y-0-0H + H2O. (R3)

In a preferred embodiment, the peroxoacid used according to the invention comprises a polyprotic acid. Particularly, the peroxoacid may consist of one or more polyprotic acids. Said polyprotic peroxoacid comprises one or more peroxy groups, which can be described by -O-O-X, wherein X may be hydrogen and/or an alkaline and/or alkaline-earth metal. More preferably X is hydrogen, lithium, sodium and/or potassium. Most preferably, X is hydrogen.

Preferably, if a polyprotic acid is used, the peroxoacid comprises one or more hydroxyl groups in addition to the one or more peroxy groups. Said hydroxyl groups may be present in form of a salt, i.e., the groups can be described by - O-X, wherein X may be hydrogen, an alkaline metal and/or an alkaline-earth metal. Most preferably X is hydrogen. The replacement of hydrogen with an alkaline-(earth) metal, however, may be particularly necessary to stabilize the peroxoacid as required by the invention.

In a preferred embodiment of the invention, the reaction product of phosphoric acid (H3PO4) with hydrogen peroxide, the reaction product of boric acid (H3BO3) with hydrogen peroxide and/or potassium or sodium peroxomonosulfate (KHSOs or NaHSOs) is used as stable inorganic peroxoacid according to the invention. Surprisingly, it has been found that said preferred peroxoacids are particularly suitable as catalyst in the preparation of haloalkanesulfonic acids from haloal- kanes and sulfur trioxide. If such an inorganic peroxoacid is used as compound, it is only suitable if it does not give rise to superacid conditions in the reactor at which the reaction takes place. This may be controlled by selecting the compound carefully or by using it in only small amounts.

In another embodiment, the compound is a compound comprising a heterolytically cleavable bond between an atom selected from the group consisting of nitrogen, phosphor sulfon oxygen and an atom selected from the group consisting of nitro gen, phosphor and sulfur.

A heterolytically cleavable bond in the sense of the present invention is espe cially a chemical bond -X-Y- between two atoms X and Y, which may be bro ken in such a way that the remaining fragments are not two radicals with un paired electrons. Particularly, the electrons of the bond are unequally parti tioned between atoms X and Y upon cleavage of the bond. The atoms X and Y of the heterolytically cleavable bond may additionally be bound to the same or different radicals. The bond between X and Y may be polarized. Polarization of the bond may enable or favor heterolytical cleavage of the bond. Polarization may, for example, be accomplished by choosing two different elements for at oms X and Y, especially elements with different electronegativities. Polariza tion of the bond may also be accomplished by choosing different radicals, to which atoms X and Y are additionally bound. These measures may be com bined, when X and Y are different and bound to at least two different addi tional radicals. In principal, any compound comprising heterolytically cleavable bonds in the aforementioned sense can be employed according to the inven tion. Such compounds are cheaply available from commercial distributors.

Heterolytic cleavage of the bond of the inventive catalyst preferably generates a cation and/or an anion. If the cleavage of the bond is catalyzed by an acid, particularly H ⁺ , the anion may formally react with the acid upon cleavage. In this case, only a cation and a neutral compound are generated.

In yet another embodiment, the compound added at step f) is a cation being stable under acid or super acid conditions as catalyst in the preparation of haloalkane sulfonic acids from haloalkanes and sulfur trioxide, especially in the preparation of trifluoromethane sulfonic acid from trifluoromethane and sulfur trioxide, said cation being able to react with the haloalkane to form an alkyl cation. The alkyl cation will afterwards react with sulfur trioxide forming the haloalkane sulfonic acid. Particularly, trifluoromethane, or a higher haloalkane can be reacted with sulfur trioxide to form the corresponding haloalkane sul fonic acid. Higher haloalkane within the meaning of the present application are straight or branched haloalkanes with 20 C-atoms or less. If the cation is sta ble, stability in this context means that it is able to react with the haloalkane but does not decompose within 24 h at room temperature (20 °C), i.e. the half-life time ti/2 at room temperature is at least 24 h, preferably at least 30 h, especially at least 48 h.

Stable cations are formed prior to their use, i.e. prior to their addition into the reactor in which the reaction between haloalkane and sulfur trioxide takes place. Preferably, one type of cation is used alone and not together with an other type of cation.

Alternatively, the cation is produced in situ during the production of the haloal kane sulfonic acid. In such cases a compound is added to the reaction and the cation is formed according to the above shown reaction (R2). Suitable com pounds to be used are halogens, especially I2 and Br2, inter halogen com pounds, especially I-Br, or solid elements of the 15 ^th or 16 ^th group of the peri odic table of elements, especially S, Se, Te, P, As, Sb. The present invention is exemplarily further disclosed in the following exam ple:

100ml methane sulfonic acid were cooled with an ice baths and 20 ml of hy drogen peroxide were added dropwise under extensive cooling to obtain an in itiator solution.

In a 1 gallon (3.75L) high pressure laboratory reactor equipped with a gas-in- jection-stirrer 400g of pure sulfur trioxide (SO3) were dissolved in 1 kg super critical carbon dioxide as solvent. The temperature of the reaction mixture was set to 50°C and the autoclave was pressurized with fluoroform. Afterwards the initiator-solution was added dropwise. Everytime the pressure droped for more than 5 bar the reactor was re- pressurized with fluoroform. The reaction is finished after 12h and was worked up by adding distilled water to quench the unreacted sulfur trioxide.

After releasing the gas, the purification using a distillation-unit yields to the pure product (79%).