Monoliths in Heterogeneous Catalysis

Nitration of aromatics is a key process in the catalytic manufacturing of semiproducts for the synthesis of drugs, pesticides, and dyes. However, the large-scale synthesis, involving the concentrated mineral acids used as catalysts, makes nitration one of the most environmentally harmful processes, producing huge amounts of organic wastes, exhausted acids, and the products of their neutralization. A search for environmentally safer catalysts and nitrating agents appears to be an actuality. Numerous data concerning the aromatics nitration in homogeneous media have been summarized in a set of books and reviews [l-41. Recent papers are of considerable interest, since they reflect the attempts to perform nitration on heterogeneous catalysts, for example, zeolites [5–8]. The data on aromatic nitration on the surface of solid acids [9, 111 and in the gas phase [12–14] allowed us to clarify the role of intermediate Tand a-complexes, estimate the substrate and position selectivity, and elucidate the main approaches of nitration mechanism in various media. In this review the data concerning nitration on solid catalysts are summarized. We hope this information will make it possible to estimate the perspectives of heterogeneous catalyst application on a large scale.