Factors in the formation of isomerically and optically pure alkyl halides. Part VII. Rearrangements occurring during the thermal decomposition of alkyl chloroformates

Abstract

The thermal decomposition of saturated alkyl chloroformates in the liquid phase results in the formation of rearranged alkyl halides by what is considered to be an ion-pair mechanism. In the presence of pyridinium chloride (0·05 mol.) the decomposition is accelerated and appears to proceed largely by a chain of S_N2 displacements; in certain systems (Prⁿ, Buⁿ, Buⁱ, n-pentyl, 3-methylbutyl) the formation of rearranged products and olefins is thus completely eliminated. Isomerically pure 1-chloro-2,2-dimethylpropane is obtained by the decomposition of the 2,2-dimethylpropyl chloroformate–pyridine complex. Olefinic products from chloroformate pyrolyses may be accounted for in part by a carbonium-ion mechanism although the formation of alk-1-enes as the principal olefins from s-alkyl chloroformates is probably due to the operation of an intramolecular cis-elimination.