CS273077B1 - Method of 2-phenyl-4-chloro-5-methoxy-3 (2h)-pyridazinone preparation - Google Patents

Abstract

The invention concerns a method of preparing 2-phenyl-4-chloro-5-methoxy-3(2H)-pyridazinone by the reaction of 4,5-dichloro-2-phenyl-3(2H)-pyridazinone with methanol in the presence of alkaline metal hydroxide for 3 to 4 hours at reflux temperature and a molar ratio of 4,5-dichloro-2-phenyl-3(2H)-pyridazinone and alkaline metal hydroxide of 1:1 to 1.1. The resulting reaction mixture is mixed with the water residue and the crystalline product is isolated in the usual way. The invention can be used in the chemical industry.

Description

(57) Solution 3a relates to a process for the preparation of 27-phenyl-4-chloro-5-methyl-3 (2H) -pyridine

by reacting 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone with methanol in the presence of an alkali metal hydroxide for 3-4 hours. at a reflux temperature and a molar ratio of 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone to an alkali metal hydroxide of 1: 1 to 1.1. The resulting reaction mixture is mixed with excess water and the crystalline product is isolated in a manner known per se.

The solution can be utilized in the chemical industry.

CS 273 077 B1

The present invention relates to a process for preparing 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone by reacting 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone with methanol in the presence of an alkali hydroxide.

2-Phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone is known as a herbicide (Symp. New Herhioides, 2 nd, Paris 1965, 171-186). It is known to prepare it in 85% yield by reacting 4 ' 5-dichloro-2-phenyl-3 (2H) -pyridazinone with sodium methylate in anhydrous methanol while boiling in an autoclave under a nitrogen atmosphere (DE 1 210 241). refluxing a mixture of the above reactants at atmospheric pressure (J. Heterocyclic Chem. 2 (4-), 1965, 463-472; Chem. Pharm. Bull. 12 (2), 1964-, 176-182). The disadvantages of the known methods for the preparation of 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone are the difficulty of working with sodium methylate, the long reaction time required to achieve an average yield and possibly the need for autoclaving. 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone is formed in small amounts in addition to 2-phenyl-5-hydroxy-4-chloro-3 (2H) -pyridazinone even when hydrolyzing 4,5-dichloro-2-phenyl- 2-phenyl-3 (2H) -pyridazinone with excess potassium hydroxide in methanol medium as a by-product of the reaction (Chem. Rum. 19 (5), 1965, 403-412).

It has now been found that 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone can be prepared in high yields by reacting 4,5-dichloro-2-fepyl-3 (2H) -pyridazinone with methanol in the presence of alkali metal hydroxide according to the invention. SUMMARY OF THE INVENTION The reaction is carried out at a molar ratio of 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone to an alkali metal hydroxide of 1: 1 to 1.1 at reflux for 3 to 4 hours, resulting in the reaction mixture is mixed with excess water and the crystallized product is isolated in a known manner.

The main advantages of the process according to the invention over the known processes are that they eliminate the difficulty of working with sodium methylate, the reaction has a rapid and unidirectional process, while achieving high yields of 2-phenyl-4-chloro-5-methoxy-3 (2H). -pyridazinone, which is easily and freely recovered in crystalline form from the resulting reaction mixture after mixing with excess water. If desired, the product thus obtained can be further recrystallized from organic solvents such as ethanol, ethyl acetate, methanol and others.

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

Example 1

A mixture of 24.1 g of 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone, 4.0 g of sodium hydroxide and 100 ml of methanol was heated at reflux temperature for 3 hours with stirring. The reaction mixture was then poured into 500 ml of water, the solid was filtered off with suction, washed with water and dried. 22.0 g (93.2% of theory) of 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone, m.p. Mp 160-161 ° C. After crystallization from ethanol, the product was obtained in the form of colorless needles having a purity of more than 99.8% (determined by gas chromatography method).

Example 2

A mixture of 24.1 g of 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone, 6.2 g of potassium hydroxide and 150 ml of methanol was heated at reflux temperature for 4 hours with stirring. Thereafter, the reaction mixture was cooled and mixed with excess water, the solid was filtered off with suction, washed with water and dried. 20.7 g (87.7% of theory) of 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone, m.p. Mp 160-161 ° C. Crystallization from methanol gave the desired product with a purity of more than 99.8% (determined by gas chromatography).

Claims (2)

OBJECT OF THE INVENTION A process for the preparation of 2-phenyl-4-chloro-5-methoxy-3 (2H) -pyridazinone by reacting 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone with methanol in the presence of an alkali metal hydroxide, characterized in that the reaction is carried out at a molar ratio of 4,5-dichloro-2-phenyl-3 (2H) -pyridazinone to an alkali metal hydroxide of 1: 1 to 1.1 for 3 to 4 hours. at the reflux temperature of the reaction mixture, the resulting reaction mixture is mixed with excess water and the crystallized product is isolated in a known manner.