AbstractWhereas pyruvic acid smoothly decarboxylates in the vapour phase to give acetaldehyde, methyl pyruvate is much more stable. Between 440 and 480°, carbon monoxide is eliminated leading to methyl acetate.In an excess of toluene,allylpyruvate reacts much faster than the methyl ester, giving large proportions of CO2, CO and CH4; 4‐phenyl‐1‐butene and bibenzyl are also important products. Decomposition thus resembles that of allyl acetate11. However, the pyruvate reacts some thousand times more rapidly, the activation energy being 12 kcal · mole−1lower. This suggests the first step of allyl pyruvate breakdown to be amultiple fissioninto acetyl, CO2and allyl. Analogously, benzyl pyruvate decomposes much faster than the corresponding acetate.In an Appendix, kinetic data on allyl and benzyl esters are discussed on the basis of ‐ known or derived ‐ heats of formation; it would appear that consistency is not always