Acetylene–allene isomerisations. Part II. Base catalysis by sodium amide in liquid ammonia

Abstract

Isomerisation of hex-1-, -2-, and -3-yne, and hexa-1,2- and -2,3-diene catalysed by sodium amide in liquid ammonia (concentrating on the first 20% or so of isomerisation of the pure compounds) is reported. The stepwise acetylene–allene isomerisation path is apparently followed. Differences in isomerisation caused by this catalyst and by potassiu t-butoxide in t-butyl alcohol are discussed. The importance of these results in view of the widely used reduction of alkynes to trans-alkenes by sodium in liquid ammonia is noted. Conjugated dienes were not formed during these isomerisations. The kinetic acidity of a proton attached to an allenic system is concluded to be greater than that of a proton conjugated to an allenic system.