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
Na. Al-awadi et al., 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, J PHYS ORG, 13(9), 2000, pp. 499-504
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.