GAS-PHASE KINETICS OF ELIMINATION-REACTIONS OF PENTANE-2,4-DIONE DERIVATIVES - PART II[1] - THERMOLYSIS OF DERIVATIVES AND ANALOGS OF 3-PHENYLHYDRAZONOPENTANE-2,4-DIONE

Six analogues and derivatives (1-6) of 3-phenylhydrazonopentane-2.4-di one (7) were subjected to gas-phase thermolysis. The Arrhenius log A ( s(-1)) and Ea (kJ mol(-1)) of the analogues (1-5) are, respectively: 1 0.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(p-nitrophenylhydrazono)-propanone (2), 10.68 and 144.9 for l-cyano-1-(p-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 s(-1) and 141.3 kJ mol(-1). The rates of reaction at 600 K are compared wit h those of the title diketone (7) and of pentane-2,4-dione (8) and rat ionalized in terms of a plausible elimination pathway involving a semi concerted six-membered transition state. (C) 1998 John Wiley & Sons, I nc.