Catalytic preparation of cyclopropane-structured fuel intermediate pyrazoline by triflic acid
The acid catalysts for the preparation of the cyclopropane-structured high energetic fuel intermediate pyrazoline by intramolecular cyclization of hydrazone were screened experimentally.Among them,triflic acid had the strongest acidity,and it was used to catalyze the synthesis of 3,5,5-trimethyl-2-pyrazoline with a conversion of 98％and a selectivity of more than 99％.The corresponding cyclopropane structure products were prepared by high-temperature denitrification of pyrazoline with a conversion of more than 95％.In addition,based on the density functional theory B3LYP/6-311G(d,p)level,the mechanism and sites of acid-catalyzed cyclization reaction of hydrazone were calculated,which indicated that acid catalysis could effectively reduce the activation energy of the reaction,and promote the cyclization reaction.The Mulliken charge distribution analysis showed that the protonation of hydrazone was the key initial step of the reaction.The above results showed that strong acid catalysts were favorable to accelerate the reaction rate of hydrazone to pyrazoline,and the steric hindrance of hydrazone was the key factor for the reaction.The substrates with smaller steric hindrance had higher conversion.This study provides a feasible method for the synthesis of pyrazoline and the preparation of cyclopropane structured fuels.
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