FT-IR Study of the Acid Free Nitration of Benzene and Toluene Using NaZSM-5

The reaction of benzene/toluene and NO2 adsorbed into an initially acid free NaZSM-5 pellet has been studied by in situ FT-IR spectroscopy. The resulting products are consistent with an electrophilic substitution reaction with a partially charged NO2δ+ assocd. with the charge balancing Na+ cations. Under the reaction conditions, only benzene or toluene mols. adsorbed in proximity to cations in the zeolite react. In addn., for toluene, the substitution product is exclusively 4-nitrotoluene. This is in marked contrast to traditional industrial methods for the nitration of arom. rings using NO2. These involve strong acids to generate NO2+, which is the active entity in an electrophilic substitution of the ring. The enhanced selectivity of using NaZSM-5 results from the reaction occurring on the internal void space of the zeolite. This limits the reaction vol. to favor formation of the 1,4-substituted arom. ring and is an example of shape selective catalysis