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Elimination kinetics and mechanisms for several 2‐alkoxyacetic acids in the gas phase
Author(s) -
Chuchani Gabriel,
Rotinov Alexandra,
Dominguez Rosa M.
Publication year - 1996
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/(sici)1099-1395(199612)9:12<787::aid-poc850>3.0.co;2-x
Subject(s) - chemistry , allyl bromide , kinetics , decomposition , cyclohexene , medicinal chemistry , bromide , alkoxy group , torr , alkyl , atmospheric temperature range , organic chemistry , thermodynamics , catalysis , physics , quantum mechanics
The kinetics of the gas‐phase elimination of three 2‐alkoxyacetic acids were investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor cyclohexene. The working temperature and pressure range were 350·4–410·8°C and 57–261·5 torr, respectively. The reactions proved to be homogeneous and unimolecular and to follow a first‐order rate law. The temperature dependence of the rate coefficients is given by the following equations: for 2‐methoxyacetic acid, log k 1 (s −1 ) = (12·10 ± 0·22)−(193·3 ± 2·8) kJ mol −1 (2·303 RT ) −1 ; for 2‐ethoxyacetic acid, log k 1 (s −1 ) = (12·76 ± 0·29)−(199·6 ± 3·7) kJ mol −1 (2·303 RT ) −1 ; and for 2‐isopropoxyacetic acid, log k 1 (s −1 ) = (12·40 ± 0·32)−(193·7 ± 3·9) kJ mol −1 (2·303 RT ) −1 . The alkyl group R in ROCH 2 COOH does not seem to exert a significant effect on the rates. It is postulated that the predominant mechanism for the decomposition of the alkoxy acids involves a five‐membered cyclic transition state, where the elimination of the RO substituents is assisted by the acidic proton of the COOH group. © 1996 John Wiley & Sons, Ltd.