The Elimination Kinetics of Methoxyalkyl Chlorides in the Gas Phase. Evidence for Neighboring Group Participation

Article abstract of DOI:10.1021/j100275a015

The rates of elimination of 3-methoxy-1-chloropropane and 4-methoxy-1-chlorobutane have been determined in a seasoned, static reaction vessel over the temperature range of 410-490 deg C and the pressure range of 56-181 torr.The reactions are homogeneous and unimolecular, follow a first-order rate low, and are invariant to the presence of a twofold or greater excess of the radical chain inhibitor toluene.The overall rate coefficients are given by the following Arrhenius equations: for 3-methoxy-1-chloropropane, logk1(s^-1)=(12.92+/-0.48)-(226.0+/-6.8) kJ mol^-1(2.303RT)^-1; for 4-methoxy-1-chlorobutane, logk1(s^-1)=(12. 9+/-0.26)-(218.1+/-3.5) kJ mol^-1(2.303RT)^-1.The CH3O group in 4-methoxy-1-chlorobutane has been found to assist anchimerically the elimination reaction, where dehydrochlorination and tetrahydrofuran formation arise from an intimate ion pair type of mechanism.The partial rates for these parallel eliminations have been determined and reported.Participation of the CH3O in 3-methoxy-1-chloropropane is barely detected.The present results give further evidence of intimate ion pair mechanism through neighboring group perticipation in the gas-phase elimination of certain types of organic molecules.