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Mechanism of elimination of amino acid derivatives in the gas phase. Pyrolysis kinetics of ethyl picolinate, ethyl 1‐methylpipecolinate and picolinic acid
Author(s) -
Lafont Jennifer,
Ensuncho Adolfo,
Domínguez Rosa M.,
Rotinov Alexandra,
Herize Armando,
Quijano Jairo,
Chuchani Gabriel
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.568
Subject(s) - chemistry , picolinic acid , decarboxylation , arrhenius equation , reaction rate constant , kinetics , medicinal chemistry , pyrolysis , thermal decomposition , decarbonylation , pyridine , activation energy , organic chemistry , catalysis , physics , quantum mechanics
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[ k 1 (s −1 )] = (11.30 ± 0.24) −(180.9 ±3.0) kJ mol −1 (2.303 RT ) −1 , for ethyl 1‐methylpipecolinate, log[ k 1 (s −1 )] = (13.36 ± 0.31) −(209.5 ± 3.9) kJ mol −1 (2.303 RT ) −1 and for picolinic acid, log[ k 1 (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 CO 2 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.