Mechanism of elimination of amino acid derivatives in the gas phase. Pyrolysis kinetics of ethyl picolinate, ethyl 1-methylpipecolinate and picolinic acid

The kinetics of the gas‐phase elimination of the title compounds were determined in a static reaction system over the temperature range 180.8–419.4 °C and the pressure range 15–86 Torr (1 Torr = 133.3 Pa). The reactions are homogeneous and unimolecular and obey a first‐order rate law. The observed rate coefficients are represented by the following Arrhenius equations: for ethyl picolinate, log[k1(s−1)] = (11.30 ± 0.24) −(180.9 ±­3.0) kJ mol−1 (2.303 RT)−1, for ethyl 1‐methylpipecolinate, log[k1(s−1)] = (13.36 ± 0.31) −(209.5 ± 3.9) kJ mol−1 (2.303 RT)−1 and for picolinic acid, log[k1(s−1)] = (12.05 ± 0.10) −(135.7 ± 0.9) kJ mol−1 (2.303 RT)−1. The data from this work together with those reported in the literature confirm previous considerations that amino acids or α‐nitrogen substituents of carboxylic acids undergo an extremely rapid decarboxylation process. The pyrolysis kinetics of picolinic acid, which is an intermediate of ethyl picolinate elimination, showed a dramatic fast decomposition into pyridine and CO2 gas. The decarboxylation process of α‐amino or α‐nitrogen substituents of carboxylic acids differs from the decarbonylation elimination of several known α‐substituted carboxylic acids in the gas phase. Copyright © 2002 John Wiley & Sons, Ltd.