CS253347B1 - Process for preparing 2,6-dichlorothiobenzamide - Google Patents

Abstract

A method for preparing 2,6-dichlorothiobenzamide by thioamidating 2,6-dichlorobenzonitrile in a dimethylformamide environment with an aqueous solution of ammonium sulfide at a temperature of 40 to 50 °C and adding an aqueous solution of ammonia at the end of the reaction period, whereby the mother filtrate after separation of the product is used in the following operation to precipitate 2,6-dichlorothiobenzamide and dimethylformamide is regenerated by distillation from the newly obtained mother filtrate, or the mother filtrate is simply drained and used as a batch of dimethylformamide in the following operation.

Description

The present invention relates to a process for the preparation of 2,6-dichlorothiobenzamide which, under the name PREFIX (Chlorthiamide), is used in agriculture as an effective herbicide to prevent the growth of oat, pea, diabetes, flax and the like.

The preparation of 2,6-dichlorothiobenzamide is usually associated with the introduction of dry hydrogen sulfide into a mixture of 2,6-dichlorobenzonitrile or 2,6-dichlorobenzaldoxime in pyridine, methanol, isopropanol or ethanol under catalysis of NH (C2Hg) 2, ^N * ^{C 2H} s'3 ^ane b ° ethanolamine at about 60 ° C and a reaction time of 4-6 hours.

It has now been found that 2,6-dichlorothiobenzamide of formula csnh ₂

Cl

Cl is prepared very advantageously according to the invention.

The process for the preparation of 2,6-dichlorothiobenzamide according to the invention is characterized in that it is thioamidated

2,6-dichlorobenzonitrile is carried out in dimethylformamide with an aqueous solution of ammonium sulfide at a temperature of 40 to 50 ° C, and by addition of an aqueous ammonia solution, the starting 2,6-dichlorobenzonitrile is reacted at the end of the reaction time.

The actual synthesis of 2,6-dichlorothiobenzamide is carried out by dissolving 2,6-dichlorobenzonitrile with stirring at 50 ° C in the present dimethylformamide and then adjusting the temperature to about 40 ° C by partially cooling the mixture. At a batch temperature of about 40 ° C, dosing of an aqueous solution of ammonium sulfide is started. In the first phase about 1/3 (NH 4 S) is introduced and in the course of 3 to 4 hours the remaining amount of ammonium sulphide is added. The progress of the reaction is monitored by thin-layer chromatography.

2,6-dichlorobenzonitrile. After completion of the reaction, the reaction mixture was cooled to 15 ° C and poured into ice water. The resulting white precipitate was stirred and then filtered on suction. The product on the suction was washed with cold water and then dried at ca.

The mother filtrate and the first wash water were combined and used to precipitate 2,6-dichlorothiobenzamide from the reaction mixture in a subsequent preparation operation. From the resulting mother filtrate of this second operation, water is first distilled off and then dimethylformamide is distilled under vacuum, or this dewatered filtrate is used directly (without regeneration) as a batch of dimethylformamide in the following, i.e., third operation. The use of the dewatered filtrate may only be a one-time use, since repetition of this process may result in the accumulation of colloidal sulfur in the product.

Compared with previously published methods for the preparation of 2,6-dichloro-thiobenzamide, the new process is characterized by higher yields (over 85%), thioamidation uses a technologically more advantageous aqueous solution of ammonium sulfide, using dimethylformamide as solvent eliminates the use of ethylamines as catalysts. solvents from the aqueous filtrate.

The preparation of 2,6-dichlorothiobenzamide can be carried out in conventional batch reactors equipped with a duplicator. Filtration and washing of the product on the flint does not cause problems.

The following examples illustrate embodiments of the invention.

Example 1

172 g (1 mol) of 2,6-dichlorobenzonitrile and 516 g of dimethylformamide are introduced into a 21-liter Keller flask and dissolved with stirring at 50 ° C. The batch temperature is then adjusted to about 40 ° C and the dosing of aqueous ammonium sulfide solution is started. First, 150 ml (NH 4 O 3) is added and then the remaining 300 ml (NH 4 O 3) are added over a period of 3 to 4 hours. The reaction is checked by chromatography in benzene: acetone (6: 1). The reaction mixture is cooled to about 15-20 ° C and poured into 3 liters of ice-cold distilled water. The precipitate of 2,6-dichlorothiobenzamide is filtered off and washed with 2x 300 ml of distilled water. 2,6-dichlorothiobenzamide (m.p. 151-153 ° C), i.e. 83.95 4.

Example 2

2,6-Dichlorothiobenzamide was prepared in a similar manner to Example 1, the reaction mixture was cooled to about 15 ° C and then poured into 3 liters at about 15 ° C of the cooled mother filtrate from the previous operation. The crude 2,6-dichlorothiobenzamide precipitate was filtered off and the product on the filter was washed with 2 x 500 ml cold water. Yield: 177 g of 2,6-dichlorothiobenzamide (m.p. 152-153 ° C).

The mother filtrate is placed in a distillation unit digester and water is distilled off under atmospheric pressure and a stream of nitrogen (0.5 l / min), and then regenerated dimethylformamide is collected under a vacuum of 27 kPa. The recovery efficiency of dimethylformamide is about 75 4. The distillation residue is disposed of by incineration.

Claims (1)

SUBJECT OF THE INVENTION A process for the preparation of 2,6-dichlorothiobenzamide characterized in that thioamidation of 2,6-dichlorobenzonitrile in dimethylformamide with an aqueous solution of ammonium sulfide is carried out at a temperature of 40 to 50 ° C and at the end of the reaction time an aqueous ammonia solution is added. The product was used in the following operation to precipitate 2,6-dichlorothiobenzamide, and dimethylformamide was recovered from the newly obtained mother filtrate by distillation, or the mother filtrate was only dewatered and used as a batch of dimethylformamide in the next operation.