Kinetics of elimination of several heterocyclic carbamates in the gas phase

The kinetics of the gas-phase elimination of several heterocyclic carbamates were determined in a static system over the temperature range 190.0-409.7 degreesC and the pressure range 26.5-125 Torr (1 Torr = 133.3 Pa). The reactions in seasoned vessels, with the free radical inhibitor cyclohexene and/or toluene always present, are homogeneous and unimolecular and obey a first-order rate law. The observed rate coefficients are represented by the following Arrhenius equations: for tert-butyl-1-pyrrolidine carboxylate, log k(1) (s(-1)) = (11.36 +/- 0.31) -(145.4 +/- 3.1) kJmol(-1) (2.303RT(-1); for 1-(tert-butoxycarbonyl)-2-pyrrolidinone, log k(1) (s(-1))= (11.54 +/- 0.29) - (140.8 +/- 2.8) kJmol(-1) (2.303RT)(-1); for tert-butyl-1-pyrrole carboxylate, log k(1) (s(-1))=(12.12 +/- 0.05) - (145.2 +/- 1.0)kJ ml(-1) (2.303RT)(-1); and for 1-ethylpiperazine carboxylate, log k(1) (s(-1))=(12.05 +/- 0.19) - (188.2 +/- 4.6)kJmol(-1) (2.303RT)(-1). The saturated heterocyclic carbamates show a decrease in rates of elimination due to electronic factors. Heterocyclic carbarnates with a nitrogen atom able to delocalize its electrons with pi-bonds present in the ring were found to enhance the rates due to resonance interactions. Copyright (C) 2002 John Wiley Sons, Ltd.