Gas-phase elimination reactions of pentane-2,4-dione, methyl acetoacetate, ethyl acetoacetate, 3-phenylhydroazopentane-2,4-dione, and ethyl 3-0x0-2-phenyl-hydrazonobutyrate have been measured in the temperature ranges of 744-783, 662-695, 614-663, 604-664, and 503 -555 K, respectively, using a flow-thermolysis technique. These compounds undergo unimolecular first-order elimination reactions, for which log A = 11.9, 11.2, 11.7, 11.5, and 11.7 s-l and E, = 198.3, 167.1, 141.7, 165.6, and 141.7 kJ mol-l, respectively. The kinetic data and product analysis shows that the reactions are highly affected by the electronic nature of the substituents at the carbonyl and methylene carbon atoms of the substrates investigated. 0 1995 John Wiley & Sons, Inc.

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Pyrolysis of the Schiff bases of 1‐arylmethyleneamino‐1,2‐dihydro‐4,6‐dimethyl‐2‐oxopyridine‐3‐carbonitriles (1–5) has been studied. These compounds eliminate via a six‐membered transition state to produce substituted benzonitriles and 2‐hydroxy‐4,6‐dimethylpyridine‐3‐carbonitrile. These eliminations are unimolecular first‐order reactions. The kinetic data gave a good correlation with σ0 values of the substituents on the aryl group with ρ = 0.83 at 520 K. Utilization of the pyrolytic reaction in synthesis of various benzonitriles is considered, and mechanistic information has been obtained by comparing the kinetic data and product analysis of the Schiff bases with their open‐chain substituted benzaldehyde cyanoacetylhydrazones (6–9) analogues. © 1996 John Wiley & Sons, Inc.