Sun Xiao-qiang
2007
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Journal
Fine chemicals
Abstract
Pyrazole formate derivatives are intermediates for preparing new insecticides.In order to simplify technological conditions and reduce production costs,ethyl 2-(ethoxymethylene)-3-oxobutanoate(Ⅰ) was synthesized from ethyl acetoacetate and ethyl orthoformate in 75 % yield.The reaction was performed by refluxing in acetic anhydride for 4 h.Then w(NH_2NH_2·H_2O)=80% hydrazine hydrate was dropped slowly to Ⅰ at 0~5 ℃ on ice-water bath to produce ethyl 3-methyl-1H-pyrazole-4-carboxylate(Ⅱ) by cyclization at r.t.for 0.5 h in 75% yield,m.p.46~47 ℃.Finally,3-methyl-1H-pyrazole-4-carboxylic acid was obtained by hydrolysis of Ⅱ in w(NaOH)=10% aqueous sodium hydroxide in 88% yiled,m.p.237~238 ℃.3,5-Dimethyl-1H-pyrazole-4-carboxylic acid was synthesized from ethyl acetoacetate and acetyl chloride with the similar method by condensation,cyclization and hydrolysis,respectively in 52%,75% and 85% yield.Structures of the intermediates and the products were confirmed by m.p.,IR,MS,~1HNMR and ~(13)CNMR.Enlargement experiments were carried out on a 50-fold scale and the yields of the target products were identical with those in small tests.The process was suitable for industrial production.