Base catalysed acetylene-allene isomerisations

Abstract

The isomerisations of l-hexyne, 2-hexyne, 3-hexyne, 1,2-hexadiene and 2,3-hexadiene have been studied in solutions of sodium amide in liquid ammonia. Results are in accord with a stepwise acetylene-allene-acetylene path. Kinetic acidities of the protons involved in these isomerisations cannot be determined directly without the use of isotope tracer techniques but methods are discussed by which these acidities could be determined. Free energy changes of isomerisation cannot be determined in this base catalyst system. The reductions of 1-hexyne, 2-hexyne, 3-hexyne, 1,2-hexadiene and 2,3-hexadiene in sodium-ammonia solutions have been studied and a mechanism is proposed for the apparently anomalous reduction of l,2-hexadiene. The possibility of acid catalysed acetylene-allene rearrangements is discussed.