Oxidation and Ammoxidation of Aromatics

Abstract

An overview of the state of the art in the direct oxygen or nitrogen insertion to aromatic rings and side-chains by hydroxylation, acetoxylation, partial oxidation and ammoxidation is presented. The influence of a variety of catalysts and oxidants on the yields of hydroxylated products of aromatic species is discussed in more detail. The survey is also focussed on the usage of H 2 O 2 as an effective oxidising agent for hydroxylation reactions. Acetoxylation of methyl-substituted aromatic compounds to their corresponding esters in a single step is indeed an interesting area from an industrial point of view. Hence, the topics covering benzylic acetoxylation, although they are under a developmental stage for commercial exploitation, are also reviewed. The present contribution also covers the main directions of selective oxidation/ammoxidation of aromatic compounds to useful products, surveys recent developments and provides an updated discussion of the state of the art in the field of oxidation and ammoxidation of aromatics. Additionally, a comparative study of the vapour phase oxidation and ammoxidation of different alkyl aromatics to their corresponding aldehydes and nitriles using various heterogeneous catalysts is presented.Besides, the achievements and limitations of the catalysts/processes are emphasised. Furthermore, the present article includes a discussion of common features and differences in mechanistic steps of oxidation and ammoxidation reactions investigated by in situ FITR spectroscopy. The influence of acid-base properties of catalyst surfaces in connection with electronic effects of the substituents on the performance of the catalysts is also described.

Enzymatic hydroxylation of aromatic compounds

“…Catalytic cycle of tyrosinase yielding catechol and o-benzoquinones from monophenolic substrates (modified according to Fenoll et al [152,212]. (1) deoxy-tyrosinase, (2) oxy-tyrosinase, (3) hydroxylation complex of met-tyrosinase, (4) nucleophilic attack complex of the phenolic substrate and met-tyrosinase, (5) mettyrosinase, (6) diaxial binding complex of met-tyrosinase.…”

“…From the point of view of an organic chemist, the direct and selective introduction of the hydroxyl group into aromatic rings is one of the most challenging fields in modern synthesis. Though progress has been reported in using hydrogen peroxide and metal catalysts (e.g., vanadium, palladium, TiO 2 ) for the oxidation of benzene, toluene, and xylene, the number of direct hydroxylations, as well as their selectivity is still limited [1,2]. Similarly, this is also valid for direct chemical oxidations in supercritical carbon dioxide, where it is possible to oxygenate cyclic alkanes and alkenes, but not aromatic compounds [3].…”

Oxidation of Benzene Catalyzed by 2,2′-Bipyridine and 1,10-Phenantroline Cu(II) Complexes

“…More than 90% of the phenol consumed is produced via the so called cumene process [12] which is a three step process and coproduces acetone in 1:1 molar ratio with respect to phenol. However, due to the inherent environmental and energetic issues related to this process, many efforts are in progress for the development of new route for phenol production via a one step process through direct oxidation of benzene [13].…”

Synthesis, structural properties, and catalytic behavior of Cu-BTC and mixed-linker Cu-BTC-PyDC in the oxidation of benzene derivatives

“…Since this transformation is a quite demanding reaction, only very small turnover frequencies in the range of 0.15-1.04 h À1 have been reported in that work. For an overview on the activities in the field of oxidation of aromatics, the reader is referred to the review by Lücke et al [38].…”