Kinetics and mechanism of thermal gas-phase elimination of ?-substituted carboxylic acids: role of relative basicity of ?-substituents and acidity of incipient proton

Abstract

2-Phenoxypropanoic acid together with five of its aryl derivatives, its phenylthio and its N-phenylamino analogues were pyrolyzed at 494–566 K. The reactions were homogeneous, polar and free from catalytic and radical pathways, and obeyed a first-order rate equation. The limits of the Arrhenius log A (s−1) and E (kJ mol−1) values obtained for these reactions averaged 11.98 ± 1.71 and 158.1 ± 17.4, respectively. Analysis of the pyrolysates showed the elimination products to be carbon monoxide, acetaldehyde and the corresponding phenol, thiophenol or aniline compounds. The pyrolysis of 2-phenoxy- and 2-(N-phenylamino)-1-propanol was also investigated over the temperature range 638–792 K. The kinetic results and products analysis lend support to a reaction pathway involving a five-membered cyclic polar transition state. Copyright © 2000 John Wiley & Sons, Ltd.