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

2-Phenoxypropanoic acid together with five of its aryl derivatives, its phe nylthio and its N-phenylamino analogues were pyrolyzed at 494-566 K. The re actions were homogeneous, polar and free from catalytic and radical pathway s, and obeyed a first-order rate equation. The limits of the Arrhenius log A (s(-1)) and E (kJ mol(-1)) values obtained fur these reactions averaged 1 1.98 +/- 1.71 and 158.1 +/- 17.4, respectively. Analysis of the pyrolysates showed the elimination products to be carbon monoxide, acetaldehyde and th e corresponding phenol, thiophenol or aniline compounds. The pyrolysis of 2 -phenoxy- and 2-(N-phenylamino)-1-propanol was also investigated over the t emperature range 638-792 K. The kinetic results and products analysis lend support to a reaction pathway involving a five-membered cyclic polar transi tion state. Copyright (C) 2000 John Wiley & Sons, Ltd.