CS220299B1 - Method of producing 1-phenyl-4,5-dichloro-6-oxo-1h-pyridazine - Google Patents

Abstract

The process for producing 1-phenyl-4,5-dichloro-6-oxo- 1H-pyridazine by reaction of mucochloric acid and phenylhydrazine in a dilute medium hydrochloric acid] mole ratio of hydrogen chloride to phenylhydrazine 2.2 to 2.5: 1.

Description

The present invention relates to a process for the preparation of 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine.

1-Phenyl-4,5-dichloro-6-oxo-1H-pyridazine is the starting product in the manufacture of herbicidal compositions (U.S. Patent 120,858).

Hitherto, methods for preparing 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine from mucochloric acid and phenylhydrazine in an organic solvent environment have been known, wherein the water formed by the reaction is removed from the reaction medium as an azeotrope (DAS 1086 238). Podlá čsl. aut. The reaction of mucochloric acid and phenylhydrazine is carried out in a mixture of an organic nonpolar solvent and water. Other known methods are based on the reaction of mucochloric acid and phenylhydrazine hydrochloride in an aqueous medium. According to U.S. Pat. No. 2,628,181, the reaction of mucochloric acid and phenylhydrazine hydrochloride in water in the presence of sodium carbonate is isolated and the resulting phenylhydrazone mucochloric acid product is isolated and boiled in 1-glacial acetic acid to 1-phenyl-4,5-dichloro-6-oxo H-pyridazine. Another known process is carried out by reacting mucochloric acid and phenylhydrazine in dilute hydrochloric acid (British Patent No. 881616). As is evident from the example section of this patent, the patent does not capture the fact that high yields of reaction of phenylhydrazine with mucochloric acid can only be achieved in a strictly defined molar ratio between phenylhydrazine and hydrogen chloride. Thus, by way of example, the reaction carried out between phenylhydrazine and mucochloric acid, in hydrochloric acid, at a reaction time of three hours and at a reaction temperature of 90 to 100 ° C yields only 78.5% yield of 1-phenyl-4,5-dichloro-6. oxo-lH-pyridazine.

It has now been found that for optimum yield as well as influencing the reaction rate in the preparation of 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine by reacting mucochloric acid and phenylhydrazine in the same molar ratios in dilute hydrochloric acid environment, the most important the factor is the relative ratio of hydrogen chloride to phenylhydrazine.

The principle of the invention is that the relative molar ratio of hydrogen chloride to phenylhydrazine is 2.2 to 2.5: 1.

A major advantage of the process for preparing 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine is the high yield of 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine in a relatively short reaction time.

Effect of the relative molar ratio of hydrogen chloride (HCl) to phenylhydrazine (FH) on the yield of 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine (PCC) in the reaction of mucochloric acid and phenyilhydrazine in equimolar ratios at reaction temperatures of 90-95 ° C for 10 minutes is shown in the following table.

Molar ratio HCl: FH

1.02 l; 05

2.0

2.2

2.5 3,0

3.5 4,0

PCC yield (%)

81.9 83.4

86.9 90.8 90.8 86.1 85.0 83.4

The following examples illustrate but do not limit the invention.

Example 1

A flask equipped with a stirrer and a reflux condenser was charged with 36.3 g of 93% mucochloric acid, 400 ml of water and 52.4 g of 32% hydrochloric acid. Then, 21.6 g of phenylhydrazine was added with stirring and the reaction mixture was heated to 90-95 ° C and held at this temperature for 30 minutes. After cooling to 20 ^° C, the product was isolated by filtration. 47.1 g of 1-phenyl-4,5-dichloro-6-oxo-1H-pyridazine of 98.4 percent purity were obtained. Yield 96.05% of theory.

Example 2

187 kg of 93% mucochloric acid and 300 L of water were charged to the boilers. While stirring, 212.6 kg of a 7% aqueous phenylhydrazine hydrochloride solution and 136 kg of 36% hydrochloric acid were added. The reaction mixture was heated to 95-100 ° C and held at this temperature for 45 minutes. After cooling the mixture to 20-25 ° C, the solid product was filtered off. 247 kg of technical 1-phenyl-4,5-dichloro-6-oxo-pyrid-pyridazine having a purity of 96.7% were obtained.

Yield 96.2% of theory.

Claims (1)

A process for preparing 1-phenyl-4,5-dichloro-6-oxo-ΙΗ-pyridazine by reacting mucochloric acid and phenylhydrazine in dilute hydrochloric acid, characterized in that hydrochloric acid and phenylhydrazine are used in a molar ratio of 2.2 to 2, 5