CS272012B1 - The process for the preparation of 1- (4-chlorophenyl) -3- (2,6-difluorobenzoyl) urea - Google Patents

Abstract

The insecticidal agent 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea of formula I is prepared by the reaction of 1-isocyanato-4-chlorobenzene and 2,6-difluorobenzamide at a temperature of 90 to 130 ° C. The resulting crystalline difluorobenzofuron is separated by filtration, washed with chlorobenzene, hexane and dried to constant weight.

Description

The invention relates to a process for the preparation of 1- (4-chlorophenyl) -3- (2,6-difluorobenzoyl) urea or Diflubenzuron (Dimilin) by the reaction of 1-isocyanato-4-chlorobenzene and 2,6-difluorobenzamide in a chlorobenzene medium:

For the preparation of the insecticide Diflubenzuron, two possible variants of the synthesis of the final preparation are mentioned in the literature:

1. Preparation of Diflubenzuron by addition of 2,6-difluorobenzoyl isocyanate (DPBIK) with 4-chloroaniline, DPBIK being prepared by reacting 2,6-difluorobenzamide with oxalyl chloride or phosgene.

2. Preparation of Diflubenzofuron by reaction of 1-isocyanato-4-chlorobenzene (IKCB) with 2,6-difluorobenzamide, wherein the IKCB is prepared from 4-chloroaniline by phosgenation in an aromatic solvent.

Because Diflubenzuron is a substance which is difficult to obtain because it requires the preparation of fluorinated intermediates.

The major starting material for the synthesis of Diflubenzuron in both of the above variants is 2,6-difluorobenzamide, which can be prepared either from 2,6-difluorobenzoic acid by chlorination with thionyl chloride and then reaction with ammonia, optionally by transamidation of 2,6-difluorobenzoic acid ester, or selective by hydrolysis of 2,6-difluorobenzonitrile. 2,6-Difluorobenzonitrile is most readily available from amoxidizing 2,6-dichlorobenzonitrile by exchanging chlorine for fluorine at high temperatures and in a suitable environment.

It has now been found that Diflubenzuron is preferably prepared by the process of the invention by reacting a chlorobenzene solution of 1-isocyanato-4-chlorobenzene with an anhydrous suspension of 2,6-difluorobenzamide in chlorobenzene at 90-130 ° C. Preferably, 1-isocyanato-4-chlorobenzene can be used directly in the form of a chlorobenzene solution, the preparation of which is described in MS. author's certificate No. 262295 and also 2,6-difluorobenzamide prepared according to MS. No. 264496. Crystalline Diflubenzofuron precipitates by combining the above components, which is separated by filtration and, after washing with chlorobenzene and finally hexane, dried in a vacuum oven.

The actual synthesis of Diflubenzuron is carried out by passing a chlorobenzene solution of IKCB to a dewatered suspension of 2,6-difluorobenzamide in chorbenzene and heating the resulting mixture to 90 ° C. The reaction is carried out at 90 to 105 ° C for 4 hours and then reacted at 126 to 130 ° C for two hours. The reaction mixture was then cooled to 50 ° C and the difluenzuron was filtered off. Isolation of the product is completed by washing with chlorobenzene and finally with hexane. The product is dried in a vacuum oven at 70-75 ° C. Hexane and chlorobenzene are recovered from the individual filtrates by rectification.

The synthesis of Diflubenzuron described in this way is characterized by high yields of intermediates and the final preparation in the declared quality. The advantage of this process is the simpler technology compared to variant 1, which requires distilled 2,6-difluorobenzoyl isocyanate. The lower technological complexity and simplicity of our procedure is also evident in relation to the data of the 2nd variant published so far. Use of chlorobenzene

CS 272012 B1 of the new IKCB solution without its separation by rectification makes it possible at the same time to significantly reduce the possibility of endangering the operator due to the infiltration of IKCB vapors from the distillation apparatus.

The example below illustrates an embodiment of the invention.

Exemplary embodiment

111.02 g (0.70659 mol) of 2,6-difluorobenzamide and 400 ml of chlorobenzene were introduced into a 1 liter flask, and then the suspension was dewatered by distilling off 125 ml of chlorobenzene. The DFBA suspension thus obtained is then introduced into a 1.5 l reactor and 995 g of a 12.3% strength by weight solution of 1-isocyanato-4-chlorobenzene in chlorobenzene (0.797 mol of IKCB) are passed from the measuring cup with stirring. After mixing the raw materials, the batch is then slowly heated to 90 ° C. The reaction mixture first darkens at 50 ° C and turns light brown at temperatures above 90 ° C. * The progress of the reaction was monitored by TLC.

The reaction was carried out for 4 h at 90-102 ° C and then for a further reaction, 2 h at 126-130 ° C. The reaction mixture was then cooled to about 50 ° C and the crude Diflubenzuron suspension was filtered off. The crude dififenzenzuron on the nut was washed first with 2 x 150 ml of chlorobenzene and then with 2 x 300 ml of hexane. 225.44 g of Diflubenzuron paste were thus obtained, which was then dried in a vacuum oven at 70-75 ° C to give 200 g of product which was chromatographically uniform by TLC, m.p. 210-222 ° C (last crystal melted at 230 DEG C.). ° C) fully complied with the specification of the commercial preparation given in Farm Chemicals Handbook 87. Yield of Diflubenzuron 90.9%.

The hexane filtrate was worked up by distillation to obtain about 2 g of distillation residue. From the mother chlorobenzene filtrate, a smaller amount of unreacted 2,6-difluorobenzamide contaminated with Diflubenzuron can be obtained by vacuum concentration of the filtrate to about 15% of the original volume and crystallization, and the remaining 2nd portion of chlorobenzene can be obtained from the mother filtrate thus obtained by regeneration.

Claims (1)

OBJECT OF THE INVENTION Process for the preparation of 1- (4-chlorophenyl) -3- (2,6-difluorobenzoyl) urea of structural formula by reacting 1-isocyanato-4-chlorobenzene with 2,6-difluorobenzamide, characterized in that a chlorobenzene solution of 1-isocyanato-4-chlorobenzene is admitted to an anhydrous suspension of 2,6-difluorobenzamide in chlorobenzene, the reaction taking place at a temperature of 90 to 130 ° C and the precipitated product are separated. .