Kinetics of the gas-phase elimination of alpha-bromophenylacetic acid under maximum inhibition

The gas phase elimination kinetics of the title compound was studied over t he temperature range of 260.1-315.0 degrees C and pressure range of 20-10 T orr. This elimination, in seasoned static reaction system and in the presen ce of at least fourfold of the free radical inhibitor toluene, is homogeneo us, unimolecular and follows a first-order rate law. The reaction yielded m ainly benzaldehyde, CO, and HBr, and small amounts of benzylbromide and CO2 . The observed rate coefficients are expressed by the following Arrhenius e quations: For benzaldehyde formation: log k(1) (s(-1)) = (12.23 +/- 0.26) - (164.9 +/- 2.7) kJ mol(-1) (2.303 RT) (-1) For benzylbromide formation: log k(1) (s(-1)) = (13.82 +/- 0.50) - (192.8 +/- 5.5) kJ mol(-1) (2.303 RT) (-1) The mechanisms are believed to proceed through a semi-polar five-membered c yclic transition state for the benzaldehyde formation, while a four-centere d cyclic transition state for benzylbromide formation. (C) 1999 John Wiley & Sons, Inc.