Supported liquid-phase oxidation reactions

The recent development of inorganic crystalline-supported metal catalysts for various liquid-phase oxidation reactions such as alcohol oxidation, epoxidation, Baeyer-Villiger oxidation and oxidation via C—H activation using molecular oxygen (02) or hydrogen peroxide (H202) as an oxidant are reviewed in this chapter. 

In recent years, the unexpected observation of highly active Au as a low temperature CO oxidation catalyst59,60 has initiated extensive research activity into the use of supported gold for liquid phase oxidation reactions. In general, the adsorption characteristics and catalytic properties of Au depend crucially on particle size, which can be controlled by the preparation method and the support.61-66 The crucial question involving gold catalysis, which as yet has not been fully answered, is the concept of why Au nanoparticles exhibit such radically different behaviour than bulk Au.67-70... 

Since 1980, the applications zeolites and molecular sieves in the speciality and fine chemicals increased enormously. Zeolites are being used in the various types of reactions like cyclization, amination, rearrangement, alkylation, acylations, ammoxidation, vapour and liquid phase oxidation reactions. Zeolites and molecular sieves have also been used to encapsulate catalytically active co-ordination complexes like ship-in-bottle and as a support for photocatalytic materials and chiral ligands. Redox molecular sieves have been developed as an important class of liquid and vapour phase oxidation and ammoxidation reactions. We have discussed few typical recent examples of various types of reactions. 

Supported Metal Nanoparticles in Liquid-Phase Oxidation Reactions... 

Finally, it is appropriate to close this chapter with an example from the roots of fine chemicals the dyestuff, indigo. Manufacture of indigo involves chemistry (see Fig. 2.15) which has hardly changed from the time of the first commercial synthesis more than a hundred years ago (see earlier). Mitsui Toatsu has developed a two-step process in which indole is produced by vapour-phase reaction of ethylene glycol with aniline over a supported silver catalyst (Inoue et al., 1994). Subsequent liquid-phase oxidation of the indole, with an alkyl hydroperoxide in the presence of a soluble molybdenum catalyst, affords indigo. 

Poly(ethylene glycol) supported liquid-phase syntheses by both the reaction of (polyethylene glycol (PEG))-supported imines with nitrile oxides, generated in situ from aldoximes, (300) and 1,3-dipolar cycloadditions of nitrile oxide, generated in situ on soluble polymers with a variety of imines (301, 302) have been described. The solid-phase synthesis of 1,2,4-oxadiazolines via cycloaddition of nitrile oxide generated in situ on solid support with imines has also been elaborated (303). These syntheses of 1,2,4-oxadiazolines provide a library of 1,2,4-oxadiazolines in good yields and purity. 

Sulphuric acid catalysts are not truly heterogeneous catalysts but so-called supported liquid phase (SLP) catalysts, where the oxidation of S02 takes place as a homogeneous reaction in a liquid film covering the internal surface of the support material [2], This was proposed already in 1940 by Frazer and Kirkpatrick [6], who found that the promoting action of the common alkali metals was due to their ability to form relatively low-melting pyrosulphates, which dissolve vanadium oxides, e.g. for potassium... 

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