Synthetic Technology Study Of4-chloro-3-ethyl-1-methyl-pyrazole-5-carboxylic Acid

In recent years, pyrazoleamide insecticide and acaricide has become theresearch hot spot in new pesticides because of its mechanism of novel, highefficiency, broad spectrum insecticide and acaricide.4-Chloro-3-ethyl-1-methyl-pyrazole-5-caboxylic acid is the key intermediate in the synthesis ofnew type of pyrazoleamide insecticide and acaricide tolfenpyrad andtebufenpyrad. Compared with the literature, a new green synthetic route withsimple operation and mild reaction conditions was designed in this paper, andwhich is more environment friendly for industrial productionThis paper studied the synthetic method of4-chloro-3-ethyl-1-methyl-pyrazole-5-caboxylic acid from diethyl oxalate and2-butanone bycondensation, cyclization, chlorination, methylation, hydrolytic acidification. Wesynthesized the intermediates hexanoic acid,2,4-dioxo-, ethyl ester (2) fromdiethyl oxalate and2-butanone by Claisen condensation.3-Ethyl-5-pyrazole-carboxylate(3) was prepared through the Knorr cyclization of compounds2andhydrazine hydrate.With the methylation of DMC and compounds3we gained3-ethyl-1-methyl-5-pyrazolecarboxylate(4).4by electrolytic chlorination togenerate4-chloro-3-ethyl-1-methyl-5-pyrazolecarboxylate (5). Lastly we gainthe target product4-chloro-3-ethyl-1-methyl-pyrazole-5-caboxylic acidthrough hydrolytic acidification.Methylation reaction used dimethyl carbonate as methylating reagentinsteaded of the highly toxic reagent dimethyl sulphate for the first time, andmake the reaction green, got a yield of70.1%.Chlorination reaction used electrolytic chlorination insteaded ofenvironmentally unfriendly reagents sulfuryl chloride for the first time, thesynthesis process was not only greener but also higher yield to90%, and reaction conditions were optimized to identify the optimum conditions.