GB641015A - Production of pyrazoles - Google Patents

Abstract

Pyrazoles are produced by reacting in an acid medium, a 1,3-dicarbonylic compound <FORM:0641015/IV (b)/1> where X is hydrogen or a hydrocarbon radical, and R is the radical of an alcohol or phenol, with a hydrazine <FORM:0641015/IV (b)/2> where Q is hydrogen or an aliphatic or aromatic radical. Pyrazole is obtained with an acetal of malonaldehyde and hydrazine or hydrazine hydrate. Other acetals specified are tetramethyl and methyl triethyl malonaldehyde acetals, di - (1,3,3 - triethoxy) - propyl ether, 1,1,3,3-tetramethoxy-butane, -1- (or 2-) phenylpropane, and -2-ethyl-butane, and 1,1,3,3-tetraethoxy heptane. The acetals may be prepared as described in Specification 642,830. Substituted hydrazines include phenyl, chlor-, brom-, iodo-, and nitro-phenyl hydrazines, 2-chlor-4-nitro- and 2-brom-4-methyl-phenyl hydrazines, tolyl, benzyl, naphthyl, and alkyl hydrazines. The reactants may be dissolved in a solvent such as methanol, ethanol or isopropanol, alone or mixed with water, made acid with, for example, hydrochloric, hydrobromic or sulphuric acid or boron trifluoride. Temperature may be from atmospheric up to reflux temperature or higher. In examples: (1) 2,4-dinitrophenyl hydrazine, methyl triethyl malonaldehyde acetal, hydrochloric acid, and 95 per cent ethanol are heated under reflux, the addition of water precipitating 2,4-dinitrophenyl pyrazole; (2) hydrazine hydrate is reacted with the same acetal in water at room temperature, pyrazole being recovered from the reaction mixture; (3) di-(1,3,3-triethoxy propyl)-ether replaces the acetal of (1) to give the same product. U.S.A. Specification 1,879,210 is referred to.