Acid-Free Nitration of Benzene and Toluene in Zeolite NaZSM-5

Scott J Kirkby

doi:10.1155/2013/164868

Abstract

The syntheses of nitrobenzene and p-nitrotoluene directly from benzene, toluene, and NO2 within the pore network of the initially acid-free zeolite NaZSM-5 are reported for the first time. The active species , formed by the interaction of NO2 with the Na+ cations present on the internal surface, results in the acid-free electrophilic substitution of the aromatic ring. There are two distinct reservoirs for the reagents: one associated with close proximity to the cation sites and the other associated with the siliceous areas of the pore network. Up to 34% of the hydrocarbon and 70% of the available NO2 are reacted at 50°C. Only the cation associated sites are reactive at low temperature, and there appears to be little mobility between the sites under the reaction conditions. There is no evidence of a second nitration occurring. This represents a novel route to the single nitration of benzene and toluene and for toluene, the generation of the para isomer exclusively. The pore network of the NaZSM-5 restricts the available reaction volume and transition state geometry allowing only the para-substituted product.

Highlights

As part of an investigation into employing heterogeneous catalysis to selectively produce small industrial intermediates, nitrobenzene and para-nitrotoluene were synthesized directly from benzene and toluene and NO2 in the initially acid-free zeolite, NaZSM-5.Approximately 95% of the >1.5 × 106 tonnes of nitrobenzene produced annually is used in the production of aniline [1]
It has been shown that the electrostatic fields of the Na+ cations in NaZSM-5 are capable of enhancing the electrophilic character of small molecules adsorbed into the channel system at room temperature
This would allow the use of NaZSM-5 as a heterogeneous nitration catalyst without conversion of the zeolite to an acid form and high-temperature activation of the acid sites

Summary

Introduction

As part of an investigation into employing heterogeneous catalysis to selectively produce small industrial intermediates, nitrobenzene and para-nitrotoluene were synthesized directly from benzene and toluene and NO2 in the initially acid-free zeolite, NaZSM-5. It has been shown that the electrostatic fields of the Na+ cations in NaZSM-5 are capable of enhancing the electrophilic character of small molecules adsorbed into the channel system at room temperature [18]. This would allow the use of NaZSM-5 as a heterogeneous nitration catalyst without conversion of the zeolite to an acid form and high-temperature activation of the acid sites

Experimental

Results and Discussion

Conclusions