SYNTHESIS AND STUDY OF AZOCYCLOPROPANES AND EXAMINATION OF THE MECHANISM OF AZOALKANE DECOMPOSITION
GERTH, DALE BERNARD
Doctor of Philosophy
Three cyclopropyl substituted azoalkanes were synthesized: azocyclopropane, tert-butylazocyclopropane, and 1,1-dimethylallylazocyclopropane. Azocyclopropane was made by reducing azoxycyclopropane with Si(,2)Cl(,6) or LiAlH(,4). Both cis and trans isomers were extraordinarily stable azoalkanes. Heating the cis isomer (> 200(DEGREES)C) causes isomerization to the trans isomer and thermolysis of the trans isomer gives mostly diazavinylcyclopropane rearrangement. The activation enthalpy for this rearrangement suggests three electron stabilization of (alpha)-azoalkyl radicals. tert-Butylazocyclopropane was synthesized using a novel reaction sequence involving Me(,3)Al. Trans-tert-butylazocyclopropane underwent a diazavinylcyclopropane rearrangement when heated (217(DEGREES)C) to give the 2-pyrazoline in 84% yield. Heating the cis isomer results in 49% isomerization to the trans isomer and 51% nitrogen (radical products). The key step in the synthesis of 1,1-dimethylallylazocyclopropane involves a sigmatropic rearrangement of the 1,1-diazene resulting from the HgO oxidation of 1-(3,3-dimethylallyl)-1-cyclopropyl hydrazine. Irradiation of 1,1-dimethylallylazocyclopropane gave the "tail" recombination product ("turnaround product") of the cyclopropyldiazenyl and 1,1-dimethylallyl radicals. Turnaround product was also detected from the thermolysis of trans-1,1-dimethylallylazocyclopropane. The nitrogen quantum yield of 1,1-dimethylallylazocyclopropane was measured in two solvents of widely varying viscosity (pentane and hexadecane) and these quantum yields were used to estimate the fraction of the heminate radical pairs that underwent internal return or formed turnaround product. A series of progressively more symmetrical 1,1-dimethylallyl substituted azoalkanes was prepared. After irradiation (366 nm), turnaround product was detected (NMR, HPLC) from several of these compounds indicating that decomposition was occurring via a diazenyl radical. The decomposition rate constants for several diazenyl radicals were calculated using free energy differences of the appropriate symmetrical and unsymmetrical azoalkanes. Several schemes were proposed to rationalize the turnaround product results. The most favorable of these schemes indicates that internal return is an important rate influencing process in the decomposition of mechanism of azoalkanes.