EP1244618A1

EP1244618A1 - Method for treating a reaction mixture containing a sulphinic acid salt whereof the bearing carbon sulphur is perfluorinated

Info

Publication number: EP1244618A1
Application number: EP01905851A
Authority: EP
Inventors: Virginie Pevere
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 2000-01-04
Filing date: 2001-01-04
Publication date: 2002-10-02
Also published as: WO2001049659A1; HUP0204013A2; CA2396433A1; FR2803295B1; AU3382701A; FR2803295A1

Abstract

The invention concerns a method for treating a perfluorinated sulphinic acid on the carbon bearing sulphur, or one of the salts thereof, comprising a step which consists in extracting said acid by contacting it with a liquid basic organic phase.

Description

PROCESS FOR TREATING A REACTION MIXTURE

CONTAINING A SULFINIC ACID SALT OF WHICH THE SULFUR CARBON IS PERFLUOROUS

The subject of the present invention is a method of treatment, in particular of enrichment and purification of salts of a sulfinic acid whose carbon carrying sulfur is perfluorinated. It is known according to the European patent application published under the

No. EP 0 735 023 A1 to prepare acid salts of the perfluoroalkane-sulfinic type.

In general, these salts are formed in water-miscible polar aprotic solvents which it is then difficult to remove since their affinity for the salts, and in particular the alkaline or alkaline-earth salts, is such that one finds them. always, even after distillation, significant proportions in reaction products, all the more so since the anions corresponding to perfluoroalkanesulfinic acids are extremely little complexing and very dissociated. As examples, and even more precisely of paradigms, of these solvents strongly complexing alkaline and alkaline-earth salts, mention will be made of peralkylated amides and especially DMF (dimethylformamide) which, subsequently, will completely represent the complete class of these aprotic solvents polar hard to remove. These solvents are commonly used for the synthesis of sulfinic acids, and in particular perfluoroalkanesulfinic acids, whether by the technique referred to above or by other techniques such as those described in patent EP 237 446 A.

It should be recalled the importance of perfluoroalkanesulfinic acids and in particular of its first member, namely trifluoromethanesulfinic acid sometimes called triflinic acid.

This acid serves, on the one hand as a precursor of trifluoromethanesulfonic acid and, on the other hand, constitutes the source of a triflinyl radical (CF ₃ -SO-) which plays an important role in many derivatives useful in pharmacy and in agriculture. To graft the triflinyl radical, or its equivalents, it is often useful to go through the acid halide of sulfinic acid; for reasons that are not fully understood, the purity of triflinic acid or its salts plays an essential role in the synthesis of the acid halide, in general bromide, and especially chloride.

It can also be indicated that the synthesis of chlorides of perfluoromethanesulfonic acids, and more generally of perfluoroalkanesulfonic acids require high purity to obtain significant yields.

This is why one of the aims of the present invention is to provide a process for treating the reaction mixture which makes it possible to obtain triflinic acid, or one of its salts, with good purity. Another object of the present invention is to provide a process for treating any perfluorinated sulfinic acid on carbon carrying the sulfinic function, or its salts, so as to obtain a sulfinic derivative of good purity.

Another object of the present invention is to provide a process of the above type which makes it possible to avoid the presence of polar aprotic solvents, especially when they are water-soluble, in significant proportion in the purified product (that is to say soluble in water at least 50% of the water body).

Another object of the present invention is to provide a process which makes it possible to avoid the presence of halides in high proportion in the final sulfinic derivative obtained.

Another object of the present invention is to provide a process of the above type which makes it possible to obtain a level of heavy halides, that is to say in the context of the present invention of bromide or iodine-iodide particularly low ; in particular, to obtain a molar ratio between the sum of heavy halides, on the one hand, and the sulfinyl radical considered, on the other hand, of at most 2%, advantageously at most 1% (the percentages are expressed as percentages of equivalents).

These aims and others which will appear subsequently by means of a process for the treatment of a perfluorinated sulfinic acid on the carbon carrying sulfur, or one of its salts, which comprises a step of extraction of said acid. , or of said salt, by bringing said acid into contact with a basic organic liquid phase.

Said sulfinic acid, or its salts, can in particular be: ° either in the form of a crude reaction mixture or after distillation, in particular resulting from the processes described in the European patent applications specified above;

_° either in the form of an impure dry cake of salts of said sulfinic acid; ° or, finally, in the form of an acidic aqueous solution containing this sulfinic acid; ° either in the form of a mixture of sulfinic acid and an impurity.

Among the impurities that should be considered, in addition to the polar aprotic solvent, mention should be made of the starting product of the reaction mixture, namely in the case of the process described in European application 0 735 023, a carboxylic acid of formula Ea-CF -COOH or one of its salts, where Ea has the same values as those defined in said European application.

Said basic organic phase comprises either a weak base, optionally and even advantageously salified, or else the cationic part of a strong base. Among the relatively weak bases, there may be mentioned amines, imines including intra-cyclic such as pyridines, phosphines and in general all bases whose pKa of the associated acid is less than 12, preferably less than 11. This pKa is advantageously greater than 4. For bases for which it is difficult to define an associated acid but whose donor index is measurable and has a meaning, this excludes highly protic compounds such as alcohols; reference should therefore be made to the donor index. This index is advantageously at least equal to 15, advantageously 20.

Among these bases, particular mention should be made of oxygenated bases which have a donor index close to that of TPP (DN = 23 kcal / mole) and that of TOPO. By neighbor is meant a value which differs only by at most 30% from the reference value.

For the definition of the donor number, we can refer to the work of Christian Reinhardt Solvents and Solvents Effects in Organic

Chemistry, page 19, 1988, work in which the negative of the enthalpy (ΔH expressed in kcal / mol) of the interaction between the solvent and antimony pentachloride in a dilute solution of dichloromethane is found as a definition.

Among the oxygenated solvents, particular mention should be made of these basic compounds which constitute the oxygenated derivatives of pentavalent phosphorus. These compounds can be expressed by the general formula I: wherein R _{1 f} R ₂ and R ₃ represent identical or different hydrocarbon radicals; they advantageously correspond to formula II:

RO _m -

- where m is zero or 1,

- where R represents an aliphatic radical (the connecting carbon is sp ³ ), including cycloaliphatic, aromatic (the connecting carbon is sp ² ) and / or aliphatic.

The term “hydrocarbon radical” should be understood to mean a radical comprising hydrogen and carbon. These hydrocarbon radicals can in particular be alkyls (taken in the etymological sense of an alcohol from which the OH function has been removed), including aralkyls or aryls, including alkylaryl. Among the phosphorus products that have just been mentioned, it is worth mentioning more specifically the esters of phosphoric acid such as tributyl phosphate (sometimes designated by its English acronym of TBP) and phosphine oxides such as , for example, trioctylphosphine oxide (sometimes referred to by its English acronym of TOPO).

In the vast majority of implementations of the present invention, it is desirable that the above compounds be liposoluble. To be liposoluble and not very miscible with water, these compounds must have a total of at least 8 carbon atoms, preferably at least 12. Among the other basic compounds, mention should be made of the relatively heavy amines, ie - Say having at least 8 carbon atoms, preferably at least 12 carbon atoms. As examples of amines capable of being used by the present invention, mention may be made of tributylamine, tri IsoOctylAmine (sometimes designated by TiOA) and tri n-OctylAmine (TOA). Mention may also be made, as basic compounds, of the derivatives of nitrogen heterocycles which cannot be considered as amines, and in particular the derivatives of pyridine. In this case too, it is preferable to use pyridines or substituted quinoleines to have at least 8 carbon atoms, preferably at least 12, and even at least 15 carbon atoms.

The basic compounds specified above and which act as fat-soluble bases can be as heavy as desired as long as they remain liquid or soluble in a solvent. However, to avoid having to handle too large quantities of solvents, it may be desirable to limit the number of carbons reduced to the basic function to a value at most equal to 50, preferably at most equal to 35.

Among the basic compounds capable of serving as "liposoluble bases", particular mention should be made of phosphoniums and especially quaternary ammoniums. These compounds form a base when associated with a hydroxide ion and have the ability to extract the sulfinates according to the present invention, but the elution is more difficult. These quaternary ammoniums or phosphoniums advantageously have a number of carbons at least equal to 12, preferably 15.

Said basic organic phase advantageously comprises a solvent little miscible with water, that is to say a solvent whose solubility in pure water is less than 5% by mass, preferably 2% by mass. These solvents, or diluents, are advantageously chosen from those which are usually used in liquid-liquid extraction used in a field other than that of organic chemistry, namely extractive metallurgy in aqueous mode. Mention may in particular be made of aromatic hydrocarbons, such as benzene, optionally substituted, aliphatic hydrocarbons such as hexane, cyclohexane, halogenated hydrocarbons such as halogenated and in particular chlorinated derivatives of benzene and petroleum fractions such as those sold under the Solvesso brand or those of the kerosene type. The ratio between the diluent and the compound serving as a lipophilic base is generally between 1.5 and 10 by mass. These diluents are chosen according to their boiling points with a view to possible distillation, in particular of said polar solvents and / or of an alkanoic acid including fluoroalkanoic, to prevent them from boiling at the same time as other compounds; they are chosen so that they have higher boiling points than those of the compounds to be removed.

Advantageously, their boiling point under atmospheric pressure is at least equal to 100 ° C., advantageously 150 ° C.

Said sulfinic acid to be treated as seen above can be brought into contact with said liquid basic organic phase, either in the form of a mixture of salts, or in the form of an aqueous solution, or in the form of an aqueous suspension, or finally in the form of a solution in a polar aprotic solvent.

Except in the case where the basic compounds are chosen from oniums, it is desirable that during the process said basic organic phase be in contact with said sulfinic acid when the latter is in the form of a solution or a suspension. in an aqueous phase whose pH is at most equal to 2, advantageously to 1.

According to the present invention, the recovery of sulfinic acid or sulfinate is carried out by bringing said basic organic phase into contact with an aqueous phase. This contacting can be carried out in any device known for liquid-liquid exchanges and in particular in decanter mixer systems.

This counter-extraction, or elution, can be carried out co-current but it can advantageously also be carried out against the current. This latter implementation makes it possible to obtain concentrations of acids or salts of sulfinic acid of high concentration, while limiting the volume of aqueous phase and ipso facto the amount of organic product (s) in the aqueous phase (triple effect: salting out due to the saline nature, volume of the aqueous phase, density of the aqueous phase allow a more complete decantation).

According to the present invention, the aqueous phase used for the elution, or against the extraction, can contain high concentrations of water-soluble bases. As water-soluble bases, mention may be made of alkaline earth metals of low atomic weight such as magnesium, and especially alkali metals and water-soluble amines, that is to say the amines whose total number of carbons is reduced to the function amino and at most equal to 6, advantageously to 4.

When ammoniums or quaternary phosphoniums are used in place of the hydroxide anion, anions having a particular affinity with quaternary ammoniums can be used.

Prior to the step of bringing said basic organic phase into contact with sulfinic acid, it may be appropriate to subject the materials containing sulfinic acid, or one of its salts, to contact with a solvent insoluble in water, or sparingly soluble in water, and relatively polar. As types of solvents capable of meeting these constraints, mention may in particular be made of alkyl esters such as ethyl acetate, ethers which are not soluble in water such as ethyl ether, chlorinated and hydrogenated solvents which they are aromatic or they are aliphatic such as, for example, methylene chloride or dichlorobenzene.

This contacting makes it possible to better eliminate, on the one hand, the polar aprotic solvent which may be present and, on the other hand, the alkanoic acids which may be present in the reaction medium.

The present invention can be implemented according to numerous implementations and, in particular, the implementations specified below.

Depending on the implementation which is the subject of the rheogram of the single figure, one can easily follow the path of the different reagents by referring to this rheogram. The reaction mixture 1 is introduced into a distillation device, optionally under vacuum, where the polar aprotic solvent is removed as much as possible, generally partially.

Following this step A, the reaction mixture (to which an aqueous phase will generally have been added) which comprises a liquid phase and a solid phase, is filtered in a step B before or after the addition of acids, in general a strong mineral acid. This filtration gives, on the one hand, a solid residue which is rejected and which is represented by a double line and, on the other hand a liquid phase, which is subjected to a step C of liquid-liquid extraction by means of a water-immiscible but semi-polar diluent such as methylene chloride. During this extraction step C, the rest of the polar solvent and the various alkanoic or fluoroalkanoic acids are extracted and pass into the organic phase ΦO2. This organic phase can undergo an elution step by means of the aqueous phase ΦA2. This ΦA2 phase to facilitate the elution, or counter-extraction, of the alkanoic acids may contain basic compounds. This elution can be carried out in one or more stages and, advantageously, against the current in order to be able to recover the fluoroalkanoic acids which were used as raw material for the synthesis of sulfinic acid.

In stage D, the aqueous phase resulting from stage C is subjected to the action of an organic phase ΦO3: usually, this basic organic phase comprises an amine, or even a substituted pyridine. When using an amine or substituted pyridine, it may be useful to provide a preliminary stage of protonation of said amine or pyridine so that the aqueous phase does not undergo any change in pH during extraction D, which allows better regulation of the system. This step D, like step C, can be carried out in one or more stages. However, it is preferable that this step D comprises at least two stages so as to better exhaust the aqueous phase and to better charge the organic phase with sulfinic derivatives. The organic phase ΦO3 can be subjected to an elution by means of an aqueous phase ΦA3. This elution can be carried out in one or more stages if a high concentration is desired, it is desirable to bring it in several stages. This aqueous phase ΦA3 is advantageously when using amines and pyridines loaded with basic compounds capable of releasing the amine.

Before elution, the organic phase ΦO3 can be subjected to a washing step using a concentrated sulfinic salt so as to avoid the presence of acidic impurities such as residual alkanoic acid after step C. The phase aqueous from step D, phase 4, constitutes the spent aqueous phase which can either be used to make sulfuric acid from an oleum or be recycled as an aqueous phase before step C liquid-liquid extraction. In this case, a purge should be provided to avoid the accumulation of mineral matter in the aqueous phase. According to a second implementation of the present invention, it is possible to use instead of an amine or a pyridine an ammonium, or even a phosphonium, quaternary in the organic phase ΦO3. In these cases, there is no need to provide a protonation step; elution may well understood to be carried out by a strong base in aqueous medium, soda, potash, but it can also be carried out by means of an anion having a good affinity for quaternary ammoniums.

Furthermore, according to this use, if a quaternary ammonium is used, the acidification by means of sulfuric acid needs to be less complete, and the amount of acid must be just necessary for the elimination of organic acids. alkanoic type so as to make them neutral for step C of liquid-liquid extraction.

According to another implementation of the present invention, the same rheogram can be used by using as basic organic compound in the ΦO3 phase an oxygenated compound and, in particular, a phosphorus compound of the tributylphosphate or trioctylphosphine oxide type. In this case, very little aqueous phase should be used and a large amount of strong acid, advantageously sulfuric, should be introduced. More precisely, in step D, it is advisable to extract aqueous phases whose pH is at most equal to 0, advantageously to - 0.5.

According to another implementation of the present invention, the basic compound is brought into direct contact with the reaction mixture before or after distillation of a polar aprotic solvent which may be present. Once the phosphorus compound has been added, the reaction mixture is then subjected to distillation to remove the non-acidic organic compounds. Once these compounds have been removed, it is possible to add a medium acid or a quantity of strong acids just sufficient to release any alkanoic acids, including fluoroalkanoic acids, present in the reaction medium. Once this addition has been carried out, the distillation can be resumed to remove the various volatile alkanoic acids under the operating conditions. The acids which can be used in this second step are advantageously acids of medium strength such as the second acidity of sulfuric acid or the first acidity of phosphoric acid (pKa between -1 and 2, preferably about 1). These acids are advantageously non-volatile mineral acids. Obviously, sulfuric acid can be used in a substantially equimolecular mixture with one of its salts so as to form the bisulfate which will serve as a medium acid. Once the distillation is complete, the reaction mixture, consisting of the basic organic phase loaded after optional filtration, is eluted by means of an aqueous phase optionally loaded with basic compounds such as sodium hydroxide and potassium hydroxide, or amine. This latter implementation is particularly advantageous for treating reaction mixtures essentially consisting of salts. In the latter case the basic use concentrated is not preferred on the other hand an elution against the current in several stages, the east.

The reaction mixtures exemplified in the various processes for the synthesis of sulfinic acid are essentially reaction mixtures giving salts. When the sulfinic acid is not in the form of one of its salts but is in the acid form, the present techniques can easily be transposed by eliminating the step of releasing the acid by adding acids, especially sulfuric.

The process according to the present invention can easily be transposed to sulfonic acids carrying the same fluorinated radical as the radical sulfinic acid which corresponds to the following formula:

R _f - SO ₂ - in which R _f corresponds to the formula:

EA - (CX ₂ ) _P - - where the X, similar or different, represent a chlorine, a fluorine or a radical of formula C _n F ₂ n ₊₁ with n integer at most equal to 5, preferably 2, with the condition that at least one of the X is fluorine;

- where p represents an integer at most equal to 2;

- where EA represents an electro-attractor group whose possible functions are inert under the conditions of the reaction, advantageously fluorine or a perfluorinated residue of formula C _n F _{2n + 1} , with n integer at most equal to 8, advantageously 5, the total number of carbon of R _f being advantageously between 1 and 15, preferably between 1 and 10.

The following nonlimiting examples illustrate the invention:

Example 1

1,956 g of an aqueous solution composed of 263 g (1.53 mol) of potassium trifluoromethanesulfinate, 68.8 g (0.45 mol) of potassium trifluoroacetate and 126 g of dimethylformamide is acidified with 1 18 g 98.7% sulfuric acid (about 1.2 mol).

This solution is extracted seven times with 1,800 g of dichloromethane. For each extraction, the O / A ratio was 1,800/2,000, or 0.9.

The dimethylformamide content of the resulting aqueous phase is 0.1%. This aqueous phase is then subjected to a liquid-liquid extraction operation using 425 g of tributylamine (2.3 mol) dissolved in 500 g of toluene. The toluene phase is treated with an aqueous potassium solution corresponding to 8.7 g of potassium.

After extraction, the resulting aqueous phase is dehydrated by azeotropic entrainment with toluene to lead, after filtration to 250 g of a white solid composed of 233 g of potassium trifluoromethanesulfinate

(yield 0.89) and 7 g of potassium trifluoroacetate. The other impurities are in trace amounts.

Example 2

Obtaining trimethylammonium trifluoromethanesulfinate: 400 g of a reaction medium composed of 10.6 g of potassium trifluoroacetate and 27.7 g of potassium trifluoromethanesulfinate in solution in dimethylformamide is concentrated under reduced pressure so as to obtain 80 g of solution.

This medium is diluted with 160 g of water after addition of 27.7 g of concentrated hydrochloric acid. Seven extractions of the aqueous phase are carried out with 100 ml of dichloromethane each time (O / A = 120/260 = 0.46). The residual aqueous phase then contains a DMF level of less than 0.5% and a trifluoroacetic acid content of less than 0.5 g. The aqueous phase is then extracted with 29.8 g of tributylamine in solution in 55 ml of toluene. The toluene phase is eluted with 22.7 g of a 45% aqueous solution of trimethylamine. The resulting aqueous phase after removal of the water under reduced pressure leads to 25.8 g of a white solid of trimethylammonium trifluoromethanesulfinate. The content of methylammonium trifluoroacetate is less than 0.2 g. The other impurities are only present in trace amounts. Example 3

50 g of a solution of 8.9 g of potassium trifluoromethanesulfinate and 1.2 g of potassium trifluoroacetate in dimethylformamide is diluted with 30 g of tributyl phosphate (TBP) and 30 g of orthodichlorobenzene.

Dimethylformamide is removed by distillation under a reduced pressure of 15 mbar at 60 ° C. The organic phase thus obtained is extracted twice

30 ml of water. The aqueous phases are combined and contain 8.3 g of potassium trifluoromethanesulfinate and 1.1 g of potassium trifluoroacetate.

The other impurities are present in trace amounts.

Claims

1. Process for the treatment of a perfluorinated sulfinic acid on the carbon carrying sulfur, or its salts, characterized in that it comprises a step of extraction of said acid by bringing said acid into contact with a basic organic liquid phase .

2. Treatment method according to claim 1, characterized in that said basic organic phase comprises a liposoluble base.

3. Treatment method according to one of claims 1 or 2, characterized in that said basic organic phase comprises a diluent can be miscible with water.

4. Method according to claims 1 to 3, characterized in that the said acid is in the form of a solution or a suspension whose aqueous phase has a pH at most equal to 2, advantageously 1.

5. Method according to claims 1 to 4, characterized in that said basic organic liquid phase is previously put into cationic form, in particular by contacting with a strong acid solution.

6. Method according to claims 1 to 5, characterized in that it further comprises a step of elution of sulfinic acid from said basic phase.

7. Method according to claims 1 to 6, characterized in that said elution step is carried out by bringing the organic phase charged with sulfinate ion into contact with an aqueous phase.

8. Method according to claims 6 and 7, characterized in that said elution step is carried out by means of an aqueous phase which is either basic or has an anion easily extractable by said base.

9. Method according to claims 1 to 8, characterized in that it comprises, prior to said extraction step, an extraction step of said sulfinic acid by means of an organic phase comprising a solvent advantageously immiscible with water.

10. Method according to claims 1 to 9, characterized in that said sulfinic acid is in the form of a reaction mixture and that it comprises the following steps: a) optional distillation of the reaction solvent b) acidification by means of a strong acid, advantageously sulfuric c) extraction of the solution or suspension by means of a water-immiscible diluent d) extraction of the solution resulting from step c) by means of said basic organic phase e) elution