Oxidation and ammoxidation of aromatics

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 H2O2 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. 1. Introduction 2. Direct Hydroxylation of Aromatic Compounds 3. Acetoxylation of Methyl-Substituted Aromatic Compounds 4. Synthesis of Aldehydes by Side-Chain Oxidation 5. Ammoxidation of Aromatic Side-Chains 6. Conclusions.