The mechanism of the gas-phase pyrolysis of esters. Part 6. Pyrolysis of 1-arylethyl benzoates and t-butyl phenylacetates

Abstract

Rate coefficients for pyrolysis of 1-arylethyl benzoates have been measured between 617.9 and 668.4 K and the log k_rcl values give an excellent correlation with σ⁺ values with ρ–0.72 at 600 K; this confirms that the polarity of the transition state for benzoate pyrolysis is greater than for acetates and less than for carbonates. Rate co-efficients for pyrolysis of t-butyl phenylacetates, measured between 543.3 and 600.8 K give log k_rel values which correlate with σ° values with ρ 0.39 at 600 K, confirming that the polarity of the transition state for phenylacetate pyrolysis is less than that for benzoates and N-phenylcarbamates. The phenylacetate data correlate better with σⁿ values confirming that these are more accurate resonance-free substituent constants than are σ° values.