Maximally Inhibited Pyrolysis Kinetcs of Bromo Esters in the Gas Phase. The Ion Pair Mechanism

Article abstract of DOI:10.1021/j100291a041

The kinetics of the pyrolyses of two bromo esters have been investigated in a static system over the temperature range 379-419 deg C and pressure range 51-110 Torr.The reactions in seasoned vessels, and under maximum inhibition with the radical chain suppressor propene, are homogeneous, unimolecular, and follow a first-order rate law.The Arrhenius equations for these elimination processes were found to be as follows: for methyl 4-bromobutyrate, log k₁ (s^-1) = (13.38 +/- 0.59) - (216.7 +/- 7.6)kJ mol^-1 (2.303RT)^-1; for methyl 5-bromovalerate, log k₁ (s^-1) = (13.83 +/- 0.17) - (228.9 +/- 2.3) kJ mol^-1 (2.303RT)^-1.The anchimeric assistante of the carbomethoxy substituent is determinant in the elimination process, where dehydrobromination product and lactone formation result from an intimate ion pair type of mechanism.The partial rates toward each of the primary products have been determined, reported, and discussed.The present work provides further support of the intimate ion pair mechanism in the gas-phase pyrolysis of special types of organic halides.