Kinetic studies on allyl radicals. Part 1.—Toluene-carrier pyrolysis of 4-phenyl-but-l-ene and hexa-1,5-diene and the heat of formation of the allyl radical

Abstract

The toluene-carrier pyrolyses of 4-phenylbut-1-ene and hexa-1,5-diene between 850 and 950°K using a stirred-flow reactor system are described in which detailed product analyses have been carried out. Mechanism of product formation are discussed. For hexa-1,5-diene, recombination competes with abstraction of a hydrogen atom from toluene, and combination with a benzyl radical, for allyl radicals produced in the initial, unimolecular split, (3), C₆H₁₀→2C₃H₅(3) With assumptions about the rate constants for recombination, log k₃(sec^–1)= 13.4 – 56,000/4.574T, which gives, assuming no activation energy for the recombination, ΔH_f(C₃H₅)= 37 kcal mole^–1. The transition state for (3) is discussed briefly.