GB779703A - Pyrazolone compounds and a process for making them - Google Patents

Abstract

The invention comprises pyrazolones of the formula: <FORM:0779703/IV(b)/1> where R is benzyl or nuclear-substituted benzyl, R1 is hydrogen or C1-C4 alkyl and R2 and R3 are C1-C4 alkyl or aralkyl. These are prepared from the corresponding pyrazolones without the 4-substituent by treatment with nitrous acid to introduce a 4-nitroso group, reduction to 4-amino and reaction with an aliphatic or aromatic aldehyde in the presence of a reducing agent. Reduction of the nitroso group may be effected by zinc and acid, hydrogen and a Group 8 catalyst, or sodium bisulphite; the latter gives a sulphamic acid which is subsequently hydrolysed. The groups R2 and R3 may be introduced successively with two different aldehydes or simultaneously with two mols. of the same aldehyde. The reducing agent for this step may be formic acid, zinc and acid, or hydrogen and a catalyst. The two reduction steps may be carried out in one process the aldehyde being added at the beginning. Instead of the 4-nitroso group there may be used compounds containing a 4-nitro-, 4-halo, 4-alkylideneamino or 4-aralkylideneamino substituent. Examples show the preparation of products and intermediates where R is benzyl, p-methylbenzyl or o-methoxybenzyl, R1 is methyl or n-propyl and R2, R3 are dimethyl, diethyl, methylisobutyl or methyl-benzyl. In general the benzyl group may be substituted by halogen, lower alkyl or lower alkoxy. 1-Benzyl - 2 - methyl - 3 - n - propyl - 5 - pyrazolone is obtained by heating benzylhydrazine with ethyl butyrylacetate and alkylating the product with methyl iodide. 1-(o-Methoxybenzyl)-2 : 3 - dimethyl - 5 - pyrazolone is obtained similarly.