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Elimination kinetics and mechanism of primary, secondary and tertiary α‐hydroxycarboxylic acids in the gas phase
Author(s) -
Chuchani Gabriel,
Martin Ignacio,
Rotinov Alexandra,
Dominguez Rosa M.
Publication year - 1993
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.610060109
Subject(s) - chemistry , kinetics , torr , gas phase , homogeneous , primary (astronomy) , medicinal chemistry , polar , reaction rate constant , atmospheric temperature range , stereochemistry , organic chemistry , thermodynamics , physics , quantum mechanics , astronomy
The rates of elimination of primary, secondary and tertiary α‐hydroxycarboxylic acids were determined in a seasoned, static reaction vessel over the temperature range 280–390°C and the pressure range 30–201 Torr. The reactions, in the presence of a free radical inhibitor, are homogeneous, unimolecular and follow a first‐order rate law. The rate coefficients are given by the following equations: for glycolic acid, log k 1 (s −1 ) = (14·03 ± 0·24) − (209·3 ± 1·5) kJ mol −1 (2·303 RT ) −1 ; for lactic acid, log k 1 (s −1 ) = (12·24 ± 0·11) − (182·8 ± 1·3) kJ mol −1 (2·303 RT ) −1 ; and for 2‐hydroxyisobutyric acid, log k 1 (s −1 ) = (12·91 ± 0·13) − (174·7 ± 1·5) kJ mol −1 (2·303 RT ) −1 . The basicity and the ease with which the hydroxy group is removed from primary to tertiary α‐hydroxycarboxylic acids are reflected in rate enhancement. The mechanism of these eliminations appears to proceed through a semi‐polar five‐membered cyclic transition state.