The regiochemistry of the NO 3 ‐promoted gas phase nitration of toluene and phenol with NO 2

Product studies, kinetic isotope effect measurements, linear free energy relationships and calculations have been used to study the NO 3 ‐promoted nitration of toluene and phenol in presence of NO 2 . The competition between of a rate‐determining hydrogen abstraction of NO 3 to give the benzyl radical and HNO 3 and of a rate‐determining addition‐elimination pathway has been evaluated. The preference for the nitration in ortho and para position of toluene and for the ortho position of phenol is suggested to derive from the concerted loss of nitric acid from an intermediate cyclohexadiene.A kinetic analysis suggests reasons for the dependence of the ratio ortho : para ‐nitration from the initial concentration of reactants. Copyright © 2006 John Wiley & Sons, Ltd.