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The mechanism of neutral amino acid decomposition in the gas phase. The elimination kinetics of N,N ‐dimethylglycine ethyl ester, ethyl 1‐piperidineacetate, and N,N ‐dimethylglycine
Author(s) -
Ensuncho Adolfo,
Lafont M. Jennifer,
Rotinov Alexandra,
Domínguez Rosa M.,
Herize Armando,
Chuchani Gabriel,
Quijano Jairo
Publication year - 2001
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.1043
Subject(s) - chemistry , decarbonylation , decarboxylation , kinetics , reaction rate constant , medicinal chemistry , amino acid , thermal decomposition , reaction mechanism , stereochemistry , organic chemistry , catalysis , biochemistry , physics , quantum mechanics
The gas‐phase elimination kinetics of the ethyl ester of two α‐amino acid type of molecules have been determined over the temperature range of 360–430°C and pressure range of 26–86 Torr. The reactions, in a static reaction system, are homogeneous and unimolecular and obey a first‐order rate law. The rate coefficients are given by the following equations. For N,N‐dimethylglycine ethyl ester: log k 1 (s −1 ) = (13.01 ± 3.70) − (202.3 ± 0.3)kJ mol −1 (2.303 RT) −1 For ethyl 1‐piperidineacetate: log k 1 (s −1 ) = (12.91 ± 0.31) − (204.4 ± 0.1)kJ mol −1 (2.303 RT) −1 The decompositon of these esters leads to the formation of the corresponding α‐amino acid type of compound and ethylene. However, the amino acid intermediate, under the condition of the experiments, undergoes an extremely rapid decarboxylation process. Attempts to pyrolyze pure N,N‐dimethylglycine, which is the intermediate of dimethylglycine ethyl ester pyrolysis, was possible at only two temperatures, 300 and 310°C. The products are trimethylamine and CO 2 . Assuming log A = 13.0 for a five‐centered cyclic transition‐state type of mechanism in gas‐phase reactions, it gives the following expression: log k 1 (s −1 ) = (13.0) − (176.6)kJ mol −1 (2.303 RT) −1 . The mechanism of these α‐amino acids differs from the decarbonylation elimination of 2‐substituted halo, hydroxy, alkoxy, phenoxy, and acetoxy carboxylic acids in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33:465–471, 2001