V-PILC

Such regioselectivities are unique and suggest that redox pillared clays may have broad scope and utility as selective, heterogeneous catalysts for liquid phase oxidations. Indeed, V-PILC also catalyzes the oxidation of benzyl alcohol (to a mixture of benzoic acid and benzylbenzoate) whilst a-methyl benzylalcohol is left completely untouched.71 Similarly, p-substituted benzyl alcohols are oxidized whilst o-substituted benzyl alcohols are inert.71... 

In all previous cases, V was incorporated in a monomeric form. There are also methods to introduce oligomeric V into inorganic structures. Choudary et al. (48) advocated the use of a montmorillonite, pillared with V oligomers (V-PILC). V-PILC catalyzes the epoxidation of allylic alcohols with i-BuOOH. Oligomeric V is also used to pillar anionic clays such as layered double hydroxides (LDHs) with decavanadate anions (VioOjg) (49). 

In contrast to the lack of selectivity observed in the TS-1 catalyzed oxidation of 3-penten-2-ol (1) (Eqn. 21.5), the oxidation of 1 with tert-butyl hydroperoxide (TBHP) over Cr-PILC gave the unsaturated ketone, 3, in 82% yield (Eqn. 21.13)42 while the oxidation of 1 over a vanadium pillared montmorillonite (V-PILC) gave the epoxy alcohol, 2, in 94% yield.43 V-PILC, however, does promote the oxidation of primary benzyl alcohols to the acids with tert-butyl hydroperoxide. This reaction exhibits shape selectivity in that para-substituted benzyl alcohols are oxidized while the ortho- and meta- substituted species are essentially inert (Eqn. 21.14).44... 

There is considerable current interest in the design of new catalysts by interchelating clay minerals of the smectite type with redox metal ions, leading to the formation of oxidation catalysts with interesting (shape-selective) properties [38]. For example, vanadium-pillared montmorillonite (V-PILC) proved to be an... 

In 1992, a montmorillonite catalyst was used by Choudary et al in another catalytic system for selective oxidation in a liquid phase reaction [119]. A vanadium pillared clay (V-PILC), which was prepared by refluxing VOCI3 in benzene with H-montmorillonite, was used as the catalyst. The solid was filtered, and the resulting clay was found to have 14% of its weight of intercalated vanadium. x-Ray analysis showed an increase in dimensions of montmorillonite... 

Various compounds containing V2O5 and other supported phases such as alumina or silica have been compared with (V-PILC), but only poor performance has been found. 

Polymer-supported tetrabromooxomolybdate(V) was claimed to be a heterogeneous catalyst for alcohol oxidations with TBHP . However, it seems likely that molybdenum is leached from the surface and the observed catalysis may be, at least partially, homogeneous in nature. The same applies to Cr(III) and Ce(IV) catalysts supported on a perfluorinated sulfonic acid resin (Nafion K) which catalyze the oxidation of alcohols with TBHP . Similarly, vanadium-pillared montmorillonite clay (V-PILC) ° and a zeolite-encapsulated vanadium picolinate complex were shown to catalyze... 

V-PILC = vanadium-pillared montmorillonite catalyst rhoudary. B.M. Valli, V.L.K. Prasad, A.D. J. Chem. Soc., Ghent. Commun., 1990, 721. 

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