Faujasite catalysis of aromatic nitrations with dinitrogen pentoxide. The effect of aluminium content on catalytic activity and regioselectivity. Thenitration of pyrazole

The reaction of 1-chloro-2-nitrobenzene with dinitrogen pentoxide in dichlo romethane catalysed by H-faujasite zeolites F-712, F-720, F-780 and F-901, giving 1-chloro-2,4-dinitro- and 1-chloro-2,6-dinitrobenzene in approximate ly 30:1 ratio, is a kinetically first-order process. First-order rate const ants are independent of the concentration of N2O5 and proportional to the m ass of catalyst used. Specific rate constants, obtained by dividing the fir st-order rate constant by the mass of faujasite, are constant for a given f aujasite. Amongst the faujasites, they increase in approximate proportion t o the aluminium content. A mechanism is proposed in which the protons in th e faujasite, near aluminium in the faujasite framework, are replaced by nit ronium ions derived from N2O5 in a fast pre-equilibrium process. This produ ces active sites for transfer of nitronium ion from faujasite to aromatic i n the rate-determining step. The similar reactions of 2-nitrotoluene, too f ast for kinetic study, reveal that the ratio of 2,4- to 2,6-dinitrotoluene in the product increases with the aluminium content of the faujasite. Nitration of nitrobenzene is also catalysed by faujasite. Relative reactivi ties of nitrobenzene, 1-chloro-2-nitro- and 1-chloro-4-nitrobenzene are com pared to those found in mixed-acid nitration. Pyrazole can be nitrated readily with N2O5 over faujasites, yielding 1,4-di nitropyrazole in 80% yield under mild conditions.