Molecular rearrangements in homogeneous gas‐phase elimination reactions. Pyrolysis kinetics of alkyl methanesulphonates

The rates of elimination of several alkyl methanesulphonates were determined in a seasoned, static reaction vessel over the temperature range 300–420°C and the pressure range 28–163 Torr. The reactions are homogeneous, unimolecular and follow a first-order rate law. The overall rate coefficients are given by the following equations: for isobutyl methanesulphonate, log k1 (s−1) = (12·51 ± 0·38) − (177·0 ± 2·1) kJ mol−1 (2·303RT)−1; for 2-phenyl-1-propyl methanesulphonate, log k1(s−1) = (12·62 ± 0·04) − (176·2 ± 0·5) kJ mol−1 (2·303RT)−1; for neopentyl methane-sulphonate, log k1(s−1) = (13·35 ± 0·42) − (198·2 ± 5·2) kJ mol−1 (2·303RT)−1; and for 3-chloro-2,2-dimethyl-1-propyl methanesulphonate, log k1(s−1) = (13·87 ± 0·42) − (218·2 ± 5·4) kJ mol−1 (2·303RT)−1. Rearrangements in these methanesulphonate pyrolyses may proceed via an intimate ion-pair type of mechanism. Consequently, the results appear to confirm that intramolecular migration through autosolvation is possible in gas-phase elimination reactions of certain types of organic molecules.