DE1643385A1 - Process for the production of thiophenols - Google Patents

Description

Process for the preparation of thiophenols The invention relates to a new process for the production of thiophenols by reducing aromatic ones Sulphonic acid chlorides with red phosphorus in the presence of catalytic amounts of iodine hydrogen in phosphoric acid.

Numerous methods have already been described (cf. e.g. Houben-Weyl, Methods of Organic Chemistry, 4th Edition, Vol. IX, page 29), according to those sulfonic acid chlorides with zinc dust in an acidic, organic or aqueous Medium can be reduced to thiophenols. In one process (Organic Syntheses, Coll. Vol. 1, page 504) the implementation is carried out in two stages, with the first part goes on at 0 ° C and then the mixture to reflux temperature brings.

The sudden, very breathless reaction makes the implementation of technical approaches impossible. The simultaneous addition of sulfochloride and acid to form a hot, aqueous zinc dust suspension according to the USA patent 3,326,981 leads, contrary to the information given there, only to yields of os. 70% of the Theory. All zinc reduction processes also have the disadvantage of containing zinc To deliver sewage from which there.

Heavy metal must be removed because of toxicity.

Werner is known that sulfochlorides with hydriodic acid in glacial acetic acid or acetone can be reduced to disulfides (P.T. Cleve, reports of the Germans Chemical Society, Vol. 20, page 1534; Vol. 21, page 1099; Vol. 23; Page 962; A. Ekbom ibid, vol. 24, page 335; Vol. 35, page 651; r. Challinger, Journal of the Chemical Society (London), 1948, p. 769; E. Gebsuer-Fülnegg and F. Riesenfeld, Monatahefte für Chemie, Vol. 47, page 185; Vol. 49, page 41; A. Perret and R. Perrot, Bulletin de la Société Chimique de France s, vol. 1, page 1531). This reaction can also be done with red phosphorus in the presence of catalytic amounts of iodine (K. Kawahara, Journal of the Pharmaceutical Society of Japan, Vol. 77, p. 959; Chemical Abstracts Vol. 52, Page 2791). It is also known from the literature that thiophenols are used from aromatic sulfonic acid amides by reduction with hydriodic acid in the presence of phosphonium iodide (E. Fischer, reports of the German Chemical Society, Vol. 48, page 93) and by reducing sulfochlorides with phosphorus in the presence catalytic amounts of potassium iodide (K. Miescher and J.R. Billeter, Helvetica Chimica Acta, Vol. 22, page 601). The latter authors received 4-thiocreool in 82 % yield by using the mixture of 4-toluenesulfonyl chloride (1/10 mole), potassium iodide and heat red phosphorus in 90% phosphoric acid until the reaction is very violent entered. The latter is so stormy that larger than 1/10 molar batches are not without it Danger can be carried out. Another, well-known, avoids this disadvantage Procedure (A. W. Wagner, Reports of the German Chemical Society, Vol. 99, Page 375) after which a mixture of red phosphorus and iodine in Glacial acetic acid was initially introduced and the sulfochloride was slowly added dropwise at the reaction temperature will. The thiophenols are isolated by subsequent steam distillation of the reaction mixture, but acetic acid passes over and this in the sump is diluted so much that it can no longer be used for the next batch is.

Finally, a method of reducing sulfonic acids by means of white phosphorus is known in the presence of catalytic amounts of iodine. Prerequisite for this However, it is essential that the sulfonic acid is completely free of water in the first stage Reduction to the disulfide. Another disadvantage is the need for use the easily flammable and poisonous phosphorus because of the associated technical effort and the necessary safety equipment.

All of the above-mentioned methods are therefore so far - only to laboratory dimensions ßstab has been carried out.

It has now been found that thiophenols are obtained on a teöhnischem scale in a simple manner if a mixture of phosphoric acid, red phosphorus and hydriodic acid is heated to 90 to 1600 C and the aromatic sulfonic acid chloride in question and the water required for the reaction according to the equation below are simultaneously in the The extent to which the heat of reaction can be dissipated and, after the reaction has ended, the thiophenol formed is driven off with steam or isolated by extraction with an organic solvent, In the above equation, R denotes a halogen atom or a lower alkyl group, preferably chlorine or methyl, while the index n has the value zero, 1, 2 or 3, preferably zero, 1 or 2.

When carrying out the process according to the invention, aqueous phosphoric acid is used in a concentration of 50 to 95%, preferably 80 to 90%, as the reaction medium etched. The phosphoric acid formed on the basis of the above equation can be looked up completed steam distillation from the reaction vessel; it can lead to fertilizers are processed. The remaining phosphoric acid is used after the spent phosphorus and hydriodic acid, the next analysis is carried out.

A preferred embodiment of the method according to the invention is carrying out the steam distillation at the boiling point of the corresponding concentrated phosphoric acid, the concentration of which remains unchanged. the Use of phosphoric acid is therefore likely to use acetic acid, its recovery Difficulty being preferable.

Red phosphorus is related to the above reaction equation into a. Excess # of 10 to 15 * used. The excess phosphorus eich collects on the surface and stands after the drainage of those formed during the reaction Phosphoric acid (bottom drain) available for the next approach.

Instead of the hydriodic acid used as a catalyst, a salt of the same or elemental iodine can be used.

2 to 10, preferably 3 to 4 g of iodine are used per mole of sulfochloride a.

As already mentioned, the implementation according to the method is carried out at temperatures from 90 to 160 ° C, preferably at the boiling point of the corresponding concentrated Phosphoric acid carried out and expediently over the entire heat of reaction drained a reflux condenser. For safety reasons, the sulfochloride feed can eo be switched that it falls below the required reaction temperature is interrupted. This reports that a mixture capable of reaction is accumulating, which reacts explosively when heated.

The process according to the invention provides the products in excellent quality Purity with yields of 80 to 90% of theory, in some cases even up to almost 100 *.

The thiophenols obtainable according to the process are valuable intermediates for the production of plant protection products and pharmaceutical preparations. The decisive factor for the use of thiophenols for this purpose is a simple, technically easily feasible manufacturing method like that represents the claimed method.

The following examples explain the invention in more detail: Example 1: A mixture of 25.0 liters of 80% phosphoric acid, 0.65 liters of 57% hydroiodic acid (or 0.65 kg of iodine) and 8.5 kg of red phosphorus is heated. to boiling (temperature approx. 1400C) and with the heating switched off, 35.3 kg of benzenesulphonyl chloride and 10.0 l of water from two feed vessels are added simultaneously to the reaction mixture in such a way that the latter continues to boil by itself, but not too violently. The addition of benzene sulfochloride and water can also alternate in 6 to 8 servings. take place. After the addition is complete, the batch is refluxed for a further 1/2 hour, then the thiophenol formed is driven off with steam, the reaction vessel always being heated to 140-145 ° C. and finally the thiophenol being separated from the water. The product obtained in this way has a purity content of 98 to 99 * and is almost colorless. The yield is 95 to 98 ff of theory.

Than draws from the phosphoric acid remaining in the reaction vessel 18.0 @ through the floor drain or riser pipe. After adding 7.5 kg of red phosphorus and 0.65 l of hydriodic acid, the next batch can be carried out.

Example 2: The procedure described in Example 1 is followed and 42.2 kg of 2-chlorobenzenesulfochloride and 12.0 l of water are added dropwise to the reaction mixture.

After steam distillation at 140 to 14506, 26 to 27 kg (90 to 93% of theory) 2-chlorothiophenol obtained.

Example 3: The procedure described in Example 1 is followed, and 42.2 kg of molten 4-chlorobenzenesulfochloroad (melting point 530C) and 12.0 l of water are added dropwise to the reaction mixture. To avoid incrustations from 4-chlorothiophenol crystallizing out in the cooler, 2.0 l of chlorobenzene are added to the mixture. The product is isolated by steam distillation at 140 ° to 1450 ° C. with the gradual addition of approx. 50.0 l of ethylene chloride in order to avoid clogging of the condenser. The organic phase is separated off from the distillate. The solvent is drawn off and 26 to 27 kg (90 to 93% of theory) of pure, crystallized 4-chlorothiophenol with a melting point of 530C are obtained.

Example 4: A mixture of 24.0 liters of 90% phosphoric acid, 2.0 liters of 57% hydroiodic acid and 8.5 kg of red phosphorus is heated to the boil (temperature about 150 ° C.) and 49.1 kg are added dropwise as described in Example 1 3,4-dichlorobenzenesulfochloride and 10.0 l of water to the mixture. After the reaction has ended, the reaction mixture is cooled and extracted twice with 10.0 l of toluene each time. The toluene extracts are evaporated, the residue is distilled under reduced pressure and in this way 30 kg of C84% of theory pure, color-pseudo 3,4-dichlorothiophenol (boiling point 10: 112 to 1150 ° C.) are obtained.

Example 5: The procedure described in Example 4 is followed, but instead of 3,4- @ 2,5-dichlorobenzenesulfonyl chloride in the form of a melt (melting point 40 ° C.), 31 kg (86% of theory) of pure, colorless 2, 5-dichlorothiopheno with a boiling point of 110 to 13 ° C, which crystallizes on cooling (melting point 25 to 27 ° C).

Example 6: The mixture of 25.0 l of 75% phosphoric acid, 1.5 kg of sodium iodide and 8.5 kg of red phosphorus is heated to the boil (temperature about 130 ° C.) and 38.1 kg are added dropwise in the manner described in Example 3 molten 4-toluenesulfonyl chloride (rp. 680C) and 13.0 l of water to the reaction mixture. The product is isolated as in Example 3. 22 to 23 kg (89 to 92% of theory) of 4-thiocresol (melting point 41 to 430 ° C.) are obtained.

Claims (5)

Patent claims 1.) Process for the production of thiophenols thereby characterized in that one is a mixture of phosphoric acid, red phosphorus and hydriodic acid heated to 90 to 1600C and an aromatic sulfonic acid chloride and that for reaction required water at the same time in the mass in which the heat of reaction is dissipated can be, indicates and after completion of Umsetsuq the thiophenol formed with steam drives off or isolated by extraction with an organic solvent. 2.) The method according to claim 1, characterized in that the The reaction is carried out in 50 to 95%, preferably 80 to 90%, phosphoric acid. 3.) Method according to claim Ir and 2), characterized in that the reactin is carried out at the boiling point of the mixture. 4.) Method according to claim 1) to 3), characterized in that the steam distillation is carried out at the boiling point of the phosphoric acid. 5.) Method according to claim 1) to 4), characterized in that instead of hydriodic acid, its salts or elemental iodine are used.