GB1578909A

GB1578909A - Process for the electrolytic production of sulphones

Info

Publication number: GB1578909A
Application number: GB25733/77A
Authority: GB
Original assignee: Kernforschungsanlage Juelich GmbH
Current assignee: Forschungszentrum Juelich GmbH
Priority date: 1976-06-30
Filing date: 1977-06-20
Publication date: 1980-11-12
Also published as: DE2629320B2; DE2629320A1; FR2356743B2; FR2356743A2; BE856190A; DE2629320C3; JPS535137A

Description

(54) PROCESS FOR THE ELECTROLYTIC PRODUCTION OF SULPHONES (71) We, KERNFORSCHUNGSANLAGE JÜLICH GESELL SCHAFT MIT BESCHRANKTER HAFTUNG, of 5170 Jiilich, Federal Republic of Germany, a Body Corporate organized according to the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a process for the electrolytic production of sulphones, and is an improvement in or modification of the inventions of our Patent Specification No. 1,471,186 and our co-pending Application No. 882/76 (Patent Specification No. 1,528,217).

Sulphones have many applications in technology. For example, they serve as additives in textile processing, as intermediates in the preparation of dyestuffs, and as plasticisers for plastics, and notably as therapeutically active substances.

Our Patent Specification No. 1,471,186 describes and claims a process for the preparation of a sulphone or a mixture of sulphones including the steps of forming SO2- ions by electrolysis of a sulphur dioxide solution and reacting the SO2- ions so formed and an organic compound or mixture of compounds to substitute SO2 groups for one or more atoms or groups in the organic compound or compounds, thereby to form a sulphone or sulphones. Amongst other embodiments the invention of that patent provides a process which can be very economically carried out, and which resides in electrolysing (with direct current) the solution of an organic halogen compound and sulphur dioxide in an aprotic solvent. In a variant of this process the organic halogen compound may be added to the electrolysed sulphur dioxide solution.A tetraalkylammonium salt may be added to increase the conductivity.

This process is carried out in an electrolytic cell which is subdivided into a cathode chamber and an anode chamber by means of a diaphragm or an anion exchange membrane. The current is passed into the anode chamber by migration of anions X which are liberated in the cathodic process, and the anions are oxidised at the anode. The sulphone is formed in the cathode chamber. It is either separated from the solution by distillation or extracted therefrom. For the extraction, there is employed a solvent, for example such as chloroform, in which the salt added to promote the conductivity is insoluble.

As described in our co-pending Application No. 882/76 (Patent Specification No. 1,528,217) the production of sulphones may be carried out by electrolysing sulphur dioxide in an aprotic solvent and (before or after the electrolysis) adding to the solution a salt which forms halogen ions, as well as sulphuric acid or sulphonic acid esters which form with the halogen ions of the salt an organic halogen compound. The organic halogen compound from which the sulphones are produced is then derived from reaction between the halogen ions of the salt employed, and the ester.

According to the present invention there is provided a process for the production of sulphones wherein a solution of sulphur dioxide in an aprotic solvent is electrolysed, and there is added to the solution a salt forming halogen ions and a phosphoric acid triester. Addition may be before, during, or after electrolysis. The invention widens the choice of starting materials, which may enable a more economical production of sulphones. The process of the present invention may be carried out in the same manner as mentioned above in connection with the invention of our Patent Specification No. 1,471,186.

In this invention the sulphone formation is due to the reaction between the sulphur dioxide anions SO2- which are formed in the electrolysis by cathodic reduction of sulphur dioxide, and the molecules of the organic halogen compound denoted by RX in the equation below which are formed in the solution with dealkylation of the phosphoric acid triester by the halogen atoms thus:

It is advantageous that-as is disclosed in "Methoden der organischen Chemie/Houben-Weyl", published by E. Muller, Stuttgart 1964, Volume XII/2, part 2, pages 256 to 258-the reactivity of the reactants can be greatly influenced by the choice of the two non-participating alcohol radicals (R'O-) and thus the triester suited to the particular manner in which the process is desired to proceed.

The process according to the invention allows sulphones (R-S02-R) to be produced with alkyl radicals (R-) from starting compounds other than those which have hitherto been considered suitable, namely the phosphoric acid triesters.

It is possible to use halogen compounds (RX) which have hitherto been less readily available.

As is also the case with the invention described in our earlier specifications mentioned above polymeric and cyclic sulphones can also be prepared by the process of the invention.

The formation of polymeric sulphones follows the equation: 2nX-Z-X+ 2NS02 +4ne-Z-SO2Z-SO2-)+4nX- where Z is a bivalent organic radical and X a halogen. For the formation of the molecules X-Z-X which participate in the reaction, there may be used, for example, a bifunctional alcohol doubly esterified with phosphoric acid.In this case, the reaction proceeds in accordance with the equation:

For the preparation of cyclic sulphones there is used an ester with a bivalent radicals denoted by Z in the foreging equation-such that there is present between the two bonds a chain of a length which, in the terminating reaction, leads to a substantially strain-free ring-shaped sulphone

Between the bonds, the chain in Z then preferably contains from four to six members, for example C-atoms.

In the operation of processes embodying the invention, a very high sulphone yield has been achieved.

Example For the production of dibenzyl sulphone, there was employed an electrolytic cell in which the anode and cathode chambers were separated by an anion exchange membrane. There was used as the anode a vitreous carbon electrode, the cathode consisted of platinum and had a surface area of 9 cm2. As solvent, there was emploved acetonitrile, to which there was added as the salt increasing the conductivity and at the same time forming halogen atoms tetraethylammonium iodide having a concentration of 0.2 mol/litre. This solution was introduced into the anode and cathode chambers. Sulphur dioxide was introduced into the cathode chamber until saturation (i.e. in this solution about 0.5 mol/litre at an operating temperature of 70 C).

As phosphoric acid ester capable of reacting with the iodide ions in the solution to form an organic halogen compound there was added phosphoric acid tribenzyl ester in a concentration of 0.1 mol/litre.

The electrolysis was carried out with a current density of 40 mA/cm2 at a temperature of 70"C. After a charge quantity of 1500 coulombs had been passed through, the electrolysis was terminated. The solvent was distilled off from the reaction solution present in the cathode chamber. The residue was brought into solution by treatment with water and chloroform. On evaporation of the chloroform from the chloroform phase thus formed, dibenzyl sulphone was obtained as the product of crystallisation. The chemical yield, calculated on the quantity of phosphoric acid triester employed, was 61% of the theory; the current yield was 420/, of the theoretical value.

Similar results were obtained when using tetraethylammonium bromide as the salt forming halogen ions.

WHAT WE CLAIM IS: 1. A process for the production of sulphones wherein a solution of sulphur dioxide in an aprotic solvent is electrolysed, and there is added to the solution a salt forming halogen ions and a phosphoric acid triester.

2. A process according to claim 1 wherein one of the alcohol radicals in the ester is different from the other two.

3. A process according to claim 1 wherein the triester is provided by a bifunctional alcohol doubly esterified with phosphoric acid.

4. A process according to claim 1, claim 2 or claim 3 wherein the salt is a tetraalkyl ammonium halide.

5. A process for the production of sulphones substantially as herein described in the Example.

6. A sulphone or mixture of sulphones produced by a process according to any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. chamber until saturation (i.e. in this solution about 0.5 mol/litre at an operating temperature of 70 C). As phosphoric acid ester capable of reacting with the iodide ions in the solution to form an organic halogen compound there was added phosphoric acid tribenzyl ester in a concentration of 0.1 mol/litre. The electrolysis was carried out with a current density of 40 mA/cm2 at a temperature of 70"C. After a charge quantity of 1500 coulombs had been passed through, the electrolysis was terminated. The solvent was distilled off from the reaction solution present in the cathode chamber. The residue was brought into solution by treatment with water and chloroform. On evaporation of the chloroform from the chloroform phase thus formed, dibenzyl sulphone was obtained as the product of crystallisation. The chemical yield, calculated on the quantity of phosphoric acid triester employed, was 61% of the theory; the current yield was 420/, of the theoretical value. Similar results were obtained when using tetraethylammonium bromide as the salt forming halogen ions. WHAT WE CLAIM IS:

1. A process for the production of sulphones wherein a solution of sulphur dioxide in an aprotic solvent is electrolysed, and there is added to the solution a salt forming halogen ions and a phosphoric acid triester.