Maximally inhibited elimination of kinetics of (2‐bromoethyl)benzene and 1‐bromo‐3‐phenylpropane in the gas phase. Anchimeric assistance of the phenyl group

Abstract

AbstractThe gas‐phase elimination kinetics of (2‐bromoethyl)benzene and 1‐bromo‐3‐phenylpropane were studied in a static system and seasoned vessels over the temperature range 390–450 °C and the pressure range 32–104 Torr. The reactions, under maximum inhibition of 4‐fold pressure of the free‐radical suppressor cyclohexene and/or propene, are homogeneous, unimolecular and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius equations: for (2‐bromoethyl)benzene, log k1 (s−1) = (13·04 ± 0·10) − (210·8 ± 1·3) kJ mol−1 (2·303RT)−1, and for 1‐bromo‐3‐phenylpropane, log k1 (s−1) = (14·09 ± 0·27) − (227·7 ± 3·6) kJ mol−1 (2·303RT)−1. The phenyl group of (2‐bromoethyl)benzene appears to provide anchimeric assistance in the HBr elimination of this compound. However, neighbouring C6H5 participation at the 3‐position in 1‐bromo‐3‐phenylpropane for a C‐4 conformation is apparently absent. The mechanisms of these reactions are discussed.