CS233447B1 - Process for preparing 2-chlorobenzothiazple - Google Patents

Abstract

The invention relates to the preparation of 2-chlorobenzotlazole by the reaction of 2-mercaptobenzothiazole with gaseous phosgene in an inert solvent at 0°C, with subsequent thermal decomposition of the resulting adduct, using dimethylformamide as a catalyst. The catalyst is added to the reaction mixture just before the thermal decomposition of the formed addition compound of 2-mercaptobenzthiazole with phosgene. Said compound serves as an intermediate in the preparation of pesticides.

Description

The present invention relates to the preparation of 2-chlorobenzothiazole by reacting 2-mercaptobenzothiazole with phosphine in an inert organic solvent in the presence of N-substituted acid amides. These serve as intermediates in the production of pesticides.

Methods for the preparation of 2-chlorobenzothiazole by chlorination of 2-mercaptobenzothiazole with some chlorinating agents are known in the literature. J. Am. Chem. Soc. 1966 (1946) discloses the preparation of 2-chlorohenzothiazole by chlorination of 2-mercaptobenzothiazole with chlorine gas in an acetic acid medium at a temperature of up to 45 ° C, producing a considerable amount of by-products.

US Pat. No. 1,878,699 (1932) discloses the preparation of 2-chlorobenzothiazole by coupling phosphorus pentachloride to 2-mercaptobenzothiazole in the presence of thiophosphorus pentachloride in an organic solvent and US Pat. 2,043,948 (1936) the same solvent-free production episode. U.S. Pat. No. 2,469,697 (1949), 2-chlorobenztlazole is produced by adding 6 moles of sulfenyl chloride per mole of 2-mercaptobenzothiazole at 25 ° C. The product is isolated in chloroform, after addition of ice and water to the reaction mixture, to decompose the excess sulfenyl chloride. NSR pat. 1164 413 (1964) starts from the preparation of 2-chlorobenzothiazole from 2-mercaptobenzothiazole to which it is treated in chloroform solution in the presence of a catalytic amount of dimethylformamide with phosgene gas at 0 ° C. After heating the reaction mixture for 1 hour at reflux temperature, with a slight addition of phosgane, the product is isolated from the reaction mixture in 81% yield.

It has now been found that it is possible to prepare 2-chlorobenzothiazole by reacting 2-mercaptobenzothiazole and phosgene gas in an inert solvent at 0 ° C, followed by thermal degradation of the resulting adduct, using dimethylformamide as the epfisob catalyst of the invention.

The invention is based on the fact that the dimethylformamide is added to the reaction mixture only before the thermal degradation of the 2-mercaptobenzothiazole-phosgene addition product formed.

The reaction proceeds according to the reaction scheme:

, /

C-S-CO-Cl e

Cl heating catalyst 11jC-Cl + COS + HCl. The method of the present invention increases the yield of 2-mercaptobenzothiazole by about 6-8%.

<,

The following examples illustrate but do not limit the scope of the invention.

EXAMPLE

66.8 g of 2-mercaptobenzothiazole and 200 g of chloroform were metered into a reaction flask equipped with a stirrer, a thermometer, a reflux condenser and a gas inlet. To the mixture cooled to 0 ° C was added 40 g phosgane with stirring. The reaction mixture was then stirred for 1 hour without addition of phosgane so that the temperature rose to 10 ° C. 0.3 g of dimethylformamide was then added to the reaction mixture, and the reaction mixture was heated at reflux (about 67 ° C) for 8 hours, while a gentle stream of phosgane was bubbled through the reaction mixture. After stopping phosgane addition, the volatiles were distilled from the reaction mixture at atmospheric pressure, and the residue was distilled under vacuum.

60.7 g of distilled product, b.p. 133 DEG C./0.6 mbar, containing 99.2% of 2-chlorobenzothiazole, were obtained. The yield was 88.9% calculated for 2-mercaptobenzothiazole.

Example 2

To a flask with a stirrer, a thermometer, a reflux condenser and a gas inlet was weighed 66.8 g of 2-mercaptobenzothiazole, 160 g of toluene was added, and 4 ° g of phosgene was introduced with vigorous stirring at 0 ° C. Phosgene feed was stopped and the reaction mixture was stirred for an additional 1 point below 10 ° C. 0.3 g of dimethylformamide in 2 g of toluene was then added to the reaction mixture. A very gentle stream of phosgene was passed through the reaction mixture while the contents of the flask were heated to reflux (ca. 105 ° C) for 6 hours. The phosgene stream was then stopped and the volatiles were removed from the reaction mixture at atmospheric pressure. 154.8 g of toluene were obtained and the residue was distilled under vacuum.

Distillation yielded 61.9 g of product, boiling point 136-136.5 ° C / 50 mm Hg, containing 95.2% 2-chlorobenzothiazole. The yield was 86.97%, calculated for 2-mercaptobenzothiazole.

Example 3

200.4 g of 2-mercaptobenzothiazole, 600 g of toluene were charged to a 2 L reaction flask and 120 g of phosgene was introduced at 0 with vigorous stirring. The mixture was stirred for 1 hour at less than 10 ° C without phosgene introduction. Then 0.9 g of dimethylformamide in 6 g of toluene was added to the flask and the reaction mixture was heated to 65 ° C with vigorous stirring _and under a low phosgene flow for 8 hours. After stopping the phosgene stream, toluene was distilled off from the reaction mixture under reduced pressure at a water bath temperature of 65 ° C. The residue was distilled under vacuum.

190.0 g of distilled product having a boiling point of 133 to 133.5 ° C / 2.660 kPa containing 96.0% of 2-chlorobenzothiazole were obtained. The yield was 87.16% of theory calculated on 2-mercaptobenZ-thiazole.

Claims (1)

EXAMPLE 2 66.8 g of 2-mercaptobenzothiazole were weighed into a flask with a stirrer, a thermometer, a low-temperature refrigerant and a gas inlet, 160 g of toluene were added and 4 g of phosgene was poured in at 0 DEG C. with vigorous stirring. The phosgene feed was stopped and the mixture was stirred for a further 1 h at 10 ° C. Then dimethylformamide (0.3 g) was added to the reaction mixture in 2 g of toluene, the very mixture of phosgene was passed through the reaction mixture and the contents of the flask were heated to reflux (ca. 105 ° C) for 6 hours. Then, the pro-phosgene was stopped and the volatiles were distilled off from the reaction mixture at atmospheric pressure. 154.8 g of toluene were obtained and the residue was distilled under vacuum. Distillation yielded 61.9 g of product, b.p. 136-136.5 ° C (3.325 kPa), containing 95.2% 2-chlorobenzothiazole, 86.97% of theory, calculated with 2-mercaptobenzothiazole. EXAMPLE 3 200.4 g of 2-mercaptobenzothiazole were metered into a 2 l reaction flask, 600 g of toluene was loaded with &amp; at 0 with vigorous stirring of 120 g of phosgene. The mixture was stirred for 1 hour at a temperature below 10 ° C without phosgene decanting. Thereafter, 0.9 g of dimethylformamide in 6 g of toluene was added to the flask and the reaction mixture was heated with vigorous stirring and weakly fed phosgene for 8 hours at 65 ° C. After stopping the phosgene flux, toluene was distilled from the reaction mixture under reduced pressure at a water temperature of 65 ° C. The residue was pre-distilled under vacuum. 190.0 g of distilled product were obtained, b.p. 133-133.5 ° C (2.660 kPas) containing 96.0% 2-chlorobenzothiazole. The yield was 87.16% of the theory calculated for 2-mercaptobenzothiazole. DETAILED DESCRIPTION OF THE INVENTION The preparation of 2-chlorobenzothiazole of formula I by reacting 2-mercaptobenzothiazole with phosgene gas in an inert solvent at 0 ° C, followed by thermal decomposition of the resulting adduct, using dimethylformamide as catalyst, characterized in that the dimethylformamide is added to the reaction mixture prior to thermal decomposition. 2-mercaptobenzothiazole addition phosgene.