The transition state in ester pyrolysis. Part 9. On the ‘surface-catalysed’ mechanism for the elimination

Abstract

The ‘surface-catalysed’ mechanism of ester pyrolysis, recently proposed to account for the difference between observed alkene product distributions, and those predicted on the basis of alkene thermodynamic stability, is unsoundly based. Not only can all the known product patterns be accounted for primarily in terms of steric and statistical factors, the electronic contribution to thermodynamic stability being unimportant but, in addition, the classical demonstration of the supposed importance of the thermodynamic effect is shown to be experimentally incorrect.

Moreover where it has been examined the elimination pattern is the same in reactors with both active and deactivated surfaces which further rules out surface catalysis as an explanation of these patterns. Steric acceleration is emphasized as a factor governing the elimination pattern and is demonstrated by the marked increase in reactivity (per β-hydrogen) along the series: ethyl acetate < 3-methylbutyl acetate < 3,3-dimethylbutyl acetate.