Jo. Morley et Dw. Roberts, MOLECULAR MODELING STUDIES ON AROMATIC SULFONATION .1. INTERMEDIATES FORMED IN THE SULFONATION OF TOLUENE, Journal of organic chemistry, 62(21), 1997, pp. 7358-7363
Molecular modeling studies suggest that the mechanism of the sulfonati
on of toluene with sulfur trioxide proceeds via the formation of a pi-
complex (4b) which rearranges to form a Wheland intermediate (5). This
structure is unable to form toluenesulfonic acid (8) directly and pre
fers to react with a further molecule of sulfur trioxide to form a pyr
osulfonate intermediate (6a) which undergoes a facile prototropic rear
rangement involving the transfer of the ring hydrogen at the sp(3) car
bon of 6a to the sulfonate oxygen atom to form the corresponding acid
(7). The formation of toluenesulfonic acid (8) appears to arise from a
n exothermic reaction of between the pyrosulfonic acid (7) and toluene
. The overall calculated thermodynamic change in moving from the react
ion of one molecule of sulfur trioxide with toluene to the sulfonic ac
id (8b) is fully consistent with an estimated experimental value of -3
3.5 kcal mol(-1) for the same reaction using simple alkylbenzenes.