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UBC Theses and Dissertations

The synthesis and pyrolysis of 4, 5-dimethyl-3-carbomethoxy-2-pyrazoline and 3,5-dimethyl-e-carbomethoxy-1-pyrazoline Morris, Peter

Abstract

The products arising from the liquid-phase pyrolyses of 3,5-dimethyl-3-carbomethoxy-1-pyrazoline and 4,5-dimethyl-3-carbomethoxy-2- pyrazoline have been isolated and identified. The pyrolysis of 3,5-dimethyl-3-carbomethoxy-1-pyrazoline has been found to yield a mixture of 5 isomers consisting of 15% methyl trans-2-methyl-2-pentenoate, 10% methyl cis-2-methyl-2-pentenoate, 3% methyl trans-2-methyl-3-pentenoate. 45% methyl cis-1,2-dimethylcyclopropane-1-carboxylate and 27% methyl trans-1,2-dimethylcyclopropane-1-carboxylate. The pyrolysis of 4,5-dimethyl-3-carbomethoxy-2-pyrazoline yielded a mixture of 7 isomers consisting of 25.5% methyl trans-3-methy1-2-pentenoate, 26% methyl cis-3-methyl-2-pentenoate, 3% methyl trans-3-methyl-3-pentenoate, 2% methyl cis-3-methyl-3-pentenoate, 26% methyl trans-1,2-dimethylcyclo-propane-3-carboxylate, 16% methyl cis-1,2-dimethylcyclopropane-3-trans-carboxylate and 0.8% methyl 3-ethyl-3-butenoate. Pyrolysis of both pyrazolines has also been obtained in the vapour-phase and under these conditions a higher proportion of cyclopropanecarboxylic esters was formed than that obtained in the liquid-phase pyrolysis: 3,5-dimethyl-3-carbo-methoxy-1-pyrazoline yielded a mixture containing 94.5% cyclopropane carboxylic esters and 4,5-dimethyl-3-carbomethoxy-2-pyrazoline yields a mixture containing 67% of cyclopropane carboxylic esters. The vapour-phase pyrolysis of the 1-pyrazoline occurred readily at 200° whereas the vapour-phase pyrolysis of the 2-pyrazoline was found to require a catalyst. This catalyst is believed to facilitate the transformation of the 2-pyrazoline to the readily pyrolisable 1-pyrazoline form. Studies have been made of the equilibration of the unsaturated, esters arising from the pyrolysis of the pyrazolines and have shown that the composition of the olefin portion of the pyrolysis mixture in general is not an equilibrium mixture. A mechanism for the pyrolysis is suggested. The unsaturated esters arising from the pyrolysis of 4,5-dimethyl-3-carbomethoxy-2-pyrazoline have been synthesised and identified and structural assignments have been made.

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