Pyrolysis of Acetone and the Heat of Formation of Acetyl Radicals

Abstract

Pyrolysis of acetone in the presence of an excess of toluene has been studied. The rate of the decomposition has been followed by the rate of formation of CO, the following sequence of reactions being assumed: CH3·CO·CH3→CH3+CO·CH3 slowCH3·CO→CH3+CO fastThe reactions seem to be first order and unimolecular, the rate constant of the first step being determined as k=2.4·1014 exp (—72 000/RT) sec—1. It is assumed that the observed activation energy may be identified with CH3·CO–CH3 bond dissociation energy and on this basis the heat of formation of acetyl radical is calculated at — 10.8 kcal/mole. The last result is compared with the findings resulting from investigation of the pyrolyses of diacetyl and of benzyl methyl ketone. The validity of the toluene carrier technique is reviewed.