Abstract
A highly efficient method for the synthesis of dihydropyrazole derivatives has been established by using CaO as a solid basic catalyst. It was found that a 77.1% yield of 3,5-diphenyl-4,5-dihydropyrazole-1-carboxamide was obtained at ratio of aminourea hydrochloride/chalcone of 1.2:1 after 3 h at a reaction temperature of 65°C. The reaction efficiency was greatly enhanced, with the 3,5-diphenyl-4,5-dihydropyrazole-1-carboxamide yield reaching 91.2%, when the commercial CaO was modified by benzyl bromide in a simple way. The effects of modification and reaction conditions on the yields as well as the mechanism were studied thoroughly. From the results of FTIR and thermogravity analysis characterisation, the modifier was shown to be bonded on the surface of CaO chemically, and almost no Ca(OH)2 was formed during the modification process. The type of chalcone has a strong influence on the yield of dihydropyrazole derivative.