SEVERAL MECHANISMS IN THE ELIMINATION KINETICS OF OMEGA-CHLOROCARBOXYLIC ACIDS IN THE GAS-PHASE

The kinetics of the gas-phase pyrolysis of omega-chlorocarboxylic acid s were examined in a seasoned static reaction vessel and in the presen ce of at least twice the amount of the free radical inhibitor cyclohex ene or toluene. In conformity with the available experimental data on rate determination, these reactions proved to be unimolecular and obey ed a first-order rate law, The presence of the primary chlorine leavin g group in Cl(CH2)(n)COOH (n = 1-4) showed a change in mechanism from intramolecular displacement of the Cl leaving group by the acidic hydr ogen of the COOH to anchimeric assistance of the carbonyl COOH to the C-Cl bond polarization in the transition state, This mechanistic consi deration is nearly the same for the series of 2-, 3-, and 4-chlorobuty ric acids. The chlorine atom at the 2-position of acetic, propionic an d butyric acids is dehydrochlorinated through a prevailing reaction pa th involving a polar five-membered cyclic transition state.