Method for producing 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinon

Details Method for producing 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinon Method for producing 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinon

1981-04-16

1984-06-12

Berch, Mark L.

Organic compounds -- part of the class 532-570 series

Organic compounds

Four or more ring nitrogens in the bicyclo ring system

C07D23722, C07D23714

Patent

active

044543182

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method for producing 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone from 4,5-dichloro-2-phenyl-3(2H)-pyridazinone and ammonia.
4-Chloro-5-amino-2-phenyl-3(2H)-pyridazinone is a selectively acting herbicide, especially for the use in sugar beet areas. Sugar beets show specific resistance against this compound. 4-Chloro-5-amino-2-phenyl-3(2H)-pyridazinone has hitherto been produced from mucochloric acid via reaction with phenyl hydrazine for the preparation of the dichloropyridazinone derivative (4,5-dichloro-2-phenyl-3(2H)-pyridazinone) which is thereafter reacted with ammonia under pressure and at elevated temperature for the preparation of the desired 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone. In this last reaction step, about 10-20% of the isomeric compound, 4-amino-5-chloro-2-phenyl-3(2H)-pyridazinone, which has only half the herbicidal effect of 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone, is produced.
German Pat. No. 1,105,232 discloses the preparation of 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone from 4,5-dichloro-2-phenyl-3(2H)-pyridazinone and ammonia. 4-Chloro-5-amino-2-phenyl-3(2H)-pyridazinone is isolated in a 64% yield from the reaction product together with a 10% yield of the isomeric product.
German Offenlegungsschrift No. 2,100,685 states that the crude reaction product from the reaction described in German Pat. No. 1,105,232 contains 80% of 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone and 20% of the isomeric compound and gives directions for isolating pure 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone from this mixture by extraction with certain solvents.
Czechoslovakian Pat. No. 158,843 discloses the preparation of 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone by passing ammonia into molten 4,5-dichloro-2-phenyl-3(2H)-pyridazinone at 208.degree.-220.degree. C. A 93% pure product is obtained in a 71% yield.
No way of carrying out the reaction of 4,5-dichloro-2-phenyl-3(2H)-pyridazinone with ammonia giving pure 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone in high yield is known.
The present invention provides a method by which 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone is produced in high yield and substantially free from 4-amino-5-chloro-2-phenyl-3(2H)-pyridazinone. The method of the invention comprises reacting 4,5-dichloro-2-phenyl-3(2H)-pyridazinone with aqueous ammonia in the presence of a catalyst which is capable of selectively exchanging the 5-chlorine atom in 4,5-dichloro-2-phenyl-3(2H)-pyridazinone with a leaving group of such a nature that the resulting intermediate compound is capable of alkylating ammonia to 4-chloro-5-amino-2-phenyl-3(2H)-pyridazinone in high yield in the reaction medium, thereby regenerating the catalyst. A type of catalysts are such compounds which form an intermediate compound which is soluble or dispersible in the reaction medium. In one aspect of the invention, the catalyst is such an organic compound that the intermediate compound has a melting point below the reaction temperature.
One type of catalysts is constituted by phenolic compounds which make the intermediate compound water-soluble. Examples of such phenolic compounds are 3-hydroxy-2-pyridone and 3-hydroxypyridine and phenol derivatives containing a water-solubility-imparting substituent group such as a sulphonic acid group or a carboxylic acid group, e.g. 4-hydroxyphenyl acetic acid, 4-hydroxy-benzoic acid, 1-phenol-4-sulphonic acid and 1-naphthol-5-sulphonic acid. These catalysts clearly illustrate the invention which, however, in no way shall be limited to the use of only the above-mentioned catalysts, all other catalysts complying with the above criteria being equally suitable.
The ratio between the starting material 4,5-dichloro-2-phenyl-3(2H)-pyridazone and the catalyst is from 50:1 to 2:1, calculated on molar basis.
The reaction involves the use of 1 mole of ammonia per mole of 4,5-dichloro-2-phenyl-3(2H)-pyridazinone and 1 mole of an alkaline agent neutralizing the HCl formed; hence, it is suitable to employ at least 2 mole of ammonia per mole of 4,5-

REFERENCES:
patent: 4297493 (1981-10-01), Richarz et al.
Szabo, Chem. Abs. 86, 72686b (1976).

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