%0 Journal Article
%T Acid-Free Nitration of Benzene and Toluene in Zeolite NaZSM-5
%A Scott J. Kirkby
%J ISRN Physical Chemistry
%D 2013
%R 10.1155/2013/164868
%X 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¡ãC. 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. 1. 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. Approximately 95% of the >1.5 106 tonnes of nitrobenzene produced annually is used in the production of aniline [1]. Most of the remainder is used for precursors in rubber, pesticides, dyes, and pharmaceuticals such as Acetaminophen [1, 2]. Para-nitrotoluene is used in the synthesis of p-toluidine, which in turn is used to manufacture dyes and as accelerators for cyanoacrylate adhesives [3]. ZSM-5 is a medium pore pentasil zeolite [4, 5] with two perpendicular channel systems (see Figure 1). The first is a straight channel of elliptical cross section of 0.55 0.51£¿nm, and the second is sinusoidal with dimensions of 0.56 0.53£¿nm [6]. Its most valuable industrial process is the isomerization of xylenes to enhance the fraction of para-xylene in the product stream [7¨C9]. This is thought to result from the aluminosilicate channel wall restricting the available transition state volume and enhancing the diffusion of the para-isomer down the pores [10]. The void space of the channel system easily accommodates para-substituted benzene rings, but is too restricted to allow easy movement of ortho- and meta-substituted species. ZSM-5 would thus be ideal for the selective formation of
%U http://www.hindawi.com/journals/isrn.physical.chemistry/2013/164868/