GB2235923A - Preparation of arylalkylsulfones - Google Patents

Abstract

Arylalkylsulfones are obtained in good yield and purity by reacting an arylsulfinic acid or a salt thereof with a halocarboxylic acid or a salt thereof in the presence of a water-soluble iodide as catalyst, and subsequently decarboxylating the reaction product. <IMAGE>

Description

1-17742/=/BSQ Process for the preparation of arvlalkvlsulfones The present

invention relates to a novel process for the preparation of arylalkylsulfones.

A number of processes for the preparation of these intermediates for dye synthesis have already been described, for example the reaction of arylsulfinates with alkyl halides and the alkylation of arylsulfinic acids with dialkyl sulfates or dialkyl alkanephosphonates. The principal shortcomings of these processes, which are particularly evident in production on an industrial scale, are to be found in the formation of ether and alcohol as byproducts of the alkylation reaction, thereby resulting in serious safety problems. Further, the use of dialkyl sulfates as alkylating agents leads to pollution of the wastewater with the environmentally problematical monoalkyl sulfates. Finally, aggressive alkylating agents such as alkyl halides and dialkyl sulfates require the observance of special safety measures. It is taught in US patent 19 39 416 that arylalkylsulfones can be obtained from the corresponding arylsulfonylcarboxylic acids by elimination of carbon dioxide. These arylsulfonylcarboxylic acids can be obtained by reacting arylsulfinates with halocarboxylic acids (q.v. R. Otto, Chem. Ber. 18, 154-162). While this route of synthesis for preparing arylsulfonylcarboxylic acids does not give rise to problems comparable to those described above, it is unsatisfactory as regards the yield and purity of the products.

It is the object of the present invention to provide a technically simple process for the process of arylalkylsulfones, especially one which can be carried out on an industrial scale, which process substantially rules out safety and environmental problems and leads to the desired products in high yield (95 to 100 %, based on the arylsulfinic acid used) and purity (greater than 90 %, based on the product).

This object is achieved in the practice of this invention by carrying out the reaction of arylsulfinates with halocarboxylic acids described in Chem. Ber. 18, 154-162, in the presence of a water-soluble iodide as catalyst and decarboxylating the reaction product.

Accordingly, the present invention relates to a process for the preparation of arylalkylsulfones by reacting an arylsulfinic acid, or a salt thereof, with a halocarboxylic acid, or a 1 salt thereof, in aqueous solution, and subsequently decarboxylating the reaction product so obtained, which process is carried out in the presence of a water-soluble iodide as catalyst.

Further ob ects of the invention are the arylalkylsulfones obtained by the above process, in j particular 4-chlorophenylethylsulfone, and the use of said sulfones as intermediates for the synthesis of dyes, especially acid dyes and metal complex dyes.

In the process of this invention, the aryIsulfinic acid and halocarboxylic acid, or a salt of each, are reacted in aqueous solution. The ratio of arylsulfinic acid to halocarboxylic acid is preferably 1: 1 to L2. In principle, the halocarboxylic acid may be added to an aqueous suspension of the arylsulfinic acid or the arylsulfinic acid may be added to the halocarboxylic acid. The reaction temperature is preferably in the range from 20 to 1001C. Below 2WC the reaction rate may be too slow for the reaction to be carried out economically. In the temperature range above 60 to 1OWC, the hydrolysis of the halocarboxylic acid may reach such proportions that substantial losses in yield of arylalkylsulfone occur. In this event, an excess of halocarboxylic acid can then be used to reduce these losses. The pH is preferably kept in the range from 3 to 7.

The arylsulfonylcarboxylic acid derivative obtained in this reaction is decarboxylated, without isolation, by heating the reaction mixture to a temperature in the range from preferably 80 to 1 100C. The decarboxylation must therefore be carried out under normal pressure or under elevated pressure. During the elimination of carbon dioxide, the pH will preferably be kept at that value to which it was adjusted in the above described reaction of an aryIsulfinic acid with a halocarboxylic acid.

The catalyst used in the process of the invention is a water-soluble iodide, preferably an alkali metal iodide such as sodium or potassium iodide. It is convenient to use 0.01 to 0.05 mol of catalyst per mol. of halocarboxylic acid. The use of such a catalyst in the reaction of an arylsulfinic, acid with a halocarboxylic acid increases the yield as well as the purity of the arylalkylsulfone obtained.

Normally the arylalkylsulfone obtained is precipitated after the decarboxylation as an oil. This oil will usually contain only insignificant amounts of impurities, so that it can mostly be further processed direct to a dye (or dye precursor). The arylalkylsulfones can be obtained in great purity by extraction with an organic solvent, for example toluene, and recrystallisation of the extracted product from a suitable solvent such as ethanol.

1.

The aryIsulfinic: acid used in the process of this invention is preferably a compound of formula RI,, J S02M R2 wherein R, and R2 are each independently of the other hydrogen, alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 atoms, halogen, nitro, hydroxy, - C024 wherein Z is hydrogen or alkyl, sulfb, amino, alkyl or dialkylamino or -NHCOY, wherein Y is alkyl, and M is hydrogen, ammonium, an alkaline earth metal or an alkali metal, and the halocarboxylic acid is a compound of formula Rr-TH-COOH X wherein R3 is hydrogen or alkyl of 1 to 4 carbon atoms, and X is chloro or bromo.

The process of this invention is particularly suitable for the preparation of 4-chlorophenylethylsulfone. Accordingly, a preferred embodiment of this process comprises reacting 4-chlorophenyl- I -sulfinic acid with 2-chloroor 2-bromopropionic acid, in aqueous solution at a pH value of 5 to 6 and in the temperature range from 40 to SOT, in the presence of potassium iodide as catalyst, and subsequently decarboxylating the reaction product so obtained in the temperature range from 100 to 1 10T. The 4-chlorophenylethylsulfone obtained as an oil is sufficiently pure for further processing to, for example, 4-chloro-3- nitrophenylethylsulfone, another precursor for the synthesis of dyes.

4-Chlorophenylmethylsulfone can also be readily obtained by the process of this invention. This compound can be converted, for example, into 3amino-4-hydroxyphenylmethylsulfone, which is also an important precursor for dye synthesis.

The process of this invention can be simply carried out in conventional apparatus and, in contradistinction to certain prior art processes, does not require any special safety measures. The by-products formed are mainly only salts such as sodium chloride, and also carbon dioxide and hydroxycarboxylic acid, for example the unproblematical lactic acid in the reaction with 2-halopropionic acid.

The invention is illustrated by the following Examples.

Example 1: 0.2 mol of 4-chlorophenyl-l-sulfinic acid are suspended in 70 mI of water. Then 0.04 mol of potassium iodide and 0.5 g of an antifoam based on octanol are added, and the pH is adjusted to 5.0-5.5. The temperature of the reaction mixture is raised to 45-SOIC and 0.4 mol of 2chloropropionic acid is added dropwise over 3 hours, while keeping the pH at 6 by addition of sodium hydroxide. The reaction mixture is thereafter refluxed for 45 hours. 4-Chlorophenylethylsulfone precipitates from the cooled reaction mixture as a yellowish-brown oil. This product can then be isolated in 95 % yield and 92 % purity. It is sufficiently pure in this form for further processing, for example to 4-chloro-3nitrophenylethylsulfone.

Example 2: The procedure of Example 1 is repeated, using 2-bromopropionic acid in place of 2-chloropropionic acid, to give 95 % of the oily product in 90 % purity.

Example 3: 394 ml of water are put into a 2 mI glass beaker. With stirring, 339.7 g of chloroacetic acid are added over 10 minutes. A clear, colourless solution forms, to which 281.8 g of aqueous sodium hydroxide are added dropwise over 15-20 minutes. With good stirring, 500.0 g of toluene-4-sulfinic acid are added over 10-15 minutes, the temperature rising to ca. 45C Then 4.9 g of potassium iodide are added and the reaction mixture is heated to 75C over 30-60 minutes and from 75'C to reflux (104'C) over 30-60 minutes and refluxed for 40 hours. 4Methylphenylmethylsulfone is obtained as an oil in 93 % yield.

Example 4: 394 mI of water are put into a 2 mI glass beaker. With stirring, 339.7 g of chloroacetic acid are added over ca. 10 minutes. A clear, colourless solution forms, to which 281.8 g of aqueous sodium hydroxide are added dropwise over 15-20 minutes. A temperature of 30C is not exceeded by cooling with ice. The pH is adjusted to 7.0 by the slow addition of ca. 13.3 g of sodium hydrogencarbonate. With good stirring, 565.5 g of 4-chlorobenzene-1-sulfinic acid are added over 10-1 5 minutes. Then 4.9 g of potassium iodide are added and the reaction mixture is heated to 7ST over 30-60 minutes and from 7ST to reflux (104T) over 30-60 minutes, refluxed for 20 hours, and then cooled to 40T over ca. 2 hours, whereupon sugar-like crystals of 4-chlorophenylmethylsuifone t fl precipitate.

The product is sufficiently pure for further processing to, for example, 4-chloro-3-nitrophenylmethylsulfone.

Claims (10)

What is claimed is:

1. A process for the preparation of arylalkylsulfones by reacting an aryIsulfinic acid, or a salt thereof, with a halocarboxylic acid, or a salt thereof, in aqueous solution, and subsequently decarboxylating the reaction product so obtained, which process is carried out in the presence of a water-soluble iodide as catalyst.

2. A process according to claim 1, wherein the aryIsulfinic acid is a compound of formula R, S02M R2 wherein R, and R2 are each independently of the other hydrogen, alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 atoms, halogen, nitro, hydroxy, - CO2Z, wherein Z is hydrogen or alkyl, sulfb, amino, alkyl or dialkylamino or -NHCOY, wherein Y is alkyl, and M is hydrogen, ammonium, an alkaline earth metal or an alkali metal, and the halocarboxylic acid is a compound of formula RS1H-COOH X wherein R3 is hydrogen or alkyl of 1 to 4 carbon atoms, and X is chloro, or bromo.

3. A process according to claim 1, wherein the reaction is carried out in the temperature range from 20 to 1OWC, and the decarboxylation is carried out in the temperature range from 80 to 1 100C.

4. A process according to claim 1, wherein the pH is kept in the range from 3 to 7 during the reaction and decarboxylation.

5. A process according to claim 1, wherein the catalyst is an alkali metal iodide.

6. A process according to any one of claims 1 to 5, which comprises reacting 4-chloro- phenyl- 1 -sulfinic acid with 2-chloro- or 2-bromopropionic acid, in aqueous solution at a pH value of 5 to 6 and in the temperature range from 40 to 50PC, in the presence of potassium iodide as catalyst, and subsequently decarboxylating the reaction product so obtained in the temperature range from 100 to 1 100C.

7. An arylalkylsulfone obtained by the process as claimed in claim 1.

8. 4-Chlorophenylethylsulfone prepared by the process as claimed in claim 6.

9. Use of an arylalkylsulfone as claimed in claim 7 as intermediate for the synthesis of dyes.

10. Use of 4-chlorophenylethylsulfone as claimed in claim 8 as intermediate for the synthesis of dyes.

Publ shed 1991 at The Patent Office. State House. 66171 High Holborn, London WC] R 417. Further copies may be obtained from Multiple Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by x techniques lid, St LlarY Cray, Rent.