Cr-PILC

Another approach to designing shape-selective heterogeneous oxidation catalysts was to use redox metal oxides as the pillaring agents in the preparation of pillared clays. These redox pillared clays have been used for a number of selective oxidations. Chromium pillared montmorillonite (Cr-PILC) is an effective catalyst for the selective oxidation of alcohols with tert-butyl hydroperoxide. 7 Primary aliphatic and aromatic alcohols are oxidized to the aldehydes in very good yields. Secondary alcohols are selectively oxidized in the presence of a primary hydroxy group of a diol to give keto alcohols in excellent yields (Eqn. 21.12). 2... 

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... 

Cr-PILC also catalyzes the benzylic oxidation of acylmethylene compounds to the corresponding carbonyl compounds in good to excellent yields with tert-butyl hydroperoxide as the oxidant.45 This reaction is selective for the production of mono carbonyl compounds from substrates in which more than one benzylic methylene group is present. Tetralin (8) was oxidized to a-tetralone (9) and bibenzyl (10) to desoxybenzoin (11) in very good yields. No dicarbonyl... 

Allylic oxidation is also promoted by Cr-PILC catalysts with good yields of the a,p-unsaturated ketones being produced under mild reaction conditions. Again, tertiary C-H bonds were not oxidized under these conditions but the oxidation of a CH2 group was favored over that of a CH3 entity (Eqn. 21.19). ... 

The Cr-PILC catalyzed benzylic and allylic oxidations also provide a facile approach to the oxidative deprotection of allyl and benzyl ethers and amines. Treatment of allyl or benzyl ethers with one equivalent of tert-butyl hydroperoxide in the presence of Cr-PILC at room temperature resulted in the oxidative cleavage of the allyl- or benzyl-oxygen bond to give the alcohol but when two equivalents of tert-butyl hydroperoxide (TBHP) were used, the alcohol was oxidized further to the aldehyde or ketone (Eqn. 21.21).47 Oxidation of allyl amines resulted in the cleavage of the allyl-nitrogen bond to give the des-allyl amine.47 Benzyl amines, however, were oxidized to the benzamides (Eqn. 21.22).45... 

Chromia pillared and pillared-delaminated clays have been synthesized from different montmori I Ionites and characterized by a variety of methods. Chromia-sulfide pillared materials show a high activity and selectivity in thiophene HDS and the consecutive hydrogenation of butene. The use of different clays as starting materials for the preparation of Cr-PILC enables control of their textural properties and chromium loading and thus to tailor the activity of these catalysts. 

Therefore, these results indicate that Cr-K10 has, at least in part, a pillared structure. The results for Cr-PB indicate (Fig. 1 and Table 1) that this material has a micro-porous structure with some contribution of mesopores (shape of Nj adsorption-desorption isotherm) and a narrow pore volume distribution with a maximum at a pore radius of 2.1 nm. All Cr-PILC studied exhibit hysteresis loop of type H4 [11] which can be attributed to solids with a slit-shaped porous structure. Heat treatment results only in a small decrease of the BET surface area for both Cr-KIO and Cr-PB (Table 1). Sulfidation does not influence significantly the porous texture of both Cr-PILC as well [12]. 

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