Chromium butyl hydroperoxide

Oxidation of sec-alcohols.1 In the presence of CH3C03H, this chromium(VI) reagent can be used in catalytic amount (2 mole %) for oxidation of sec-alcohols to ketones in high yield. Under these conditions cholesterol is oxidized to A5-3-cholestanone (84% yield). Primary alcohols can be oxidized to aldehydes (—80% yield). f-Butyl hydroperoxide or anhydrous H202 cannot replace the peracetic acid as the reoxidant. 

Aluminophosphates (A1P04) were discovered in 198248 and a large amount of research has been directed towards the incorporation of various elements into the framework of these molecular sieves 49 A particular area of study is the oxidation of primary and secondary alcohols to the corresponding carbonyl compounds, which are useful synthetic intermediates. Traditionally, alcohol transformations are performed with stoichiometric chromium(VI) reagents.50 However, due to environmental problems associated with chromium-containing effluent, attention has focused on the use of chromium in conjunction with oxidizing agents such as tert-butyl hydroperoxide.51 Sheldon and co-workers... 

OXIDATION, REAGENTS Barium mangan-ate. Benzyl(triethyl)ammonium permanganate. Bispyridinesilver permanganate. Bis(trimethylsilyl)peroxide. t-Butyl hydroperoxide. t-Butyl hydroperoxide-Benzyltri-methylammonium tetrabromooxomolyb-dale. t-Butyl hydroperoxide-Bisoxobis-(2,4-pentadionato)molybdenum. t-Butyl hydroperoxide-Chromium carbonyl. t-Bu-tyl hydroperoxide-Dialkyl tartrate-Titan-ium(IV) isopropoxide. t-Butyl hydroper-... 

One drawback associated with this type of chromium species is the frequoit requirement for a large excess of reagent. Recent attempts to combat this problem have involved the use of a PCC-celite mixture in benzene solution under reflux and more successfully a r-butyl hydroperoxide-pyridinium dichromate mixture (equation 33). ... 

A number of other chromium-based reagents have been developed for allylic oxidation for example that of stnoids by t-butyl hydroperoxide in the presence of a catalytic amount (0.0S-0.S mol equiv.) of chromium trioxide in dichloromethane solution at room temperature (equation 39). Yields vary from 32 to 69%. This modification is useful in terms of cost, operational simplicity and yields. 

A chromium hexacarbonyl-r-butyl hydroperoxide system has also been developed with the remarkable chemoselective ability to e ect allylic oxidation even in the presence of some secondary alcohols (equations 40 and 41). ... 

Under similar conditions chromium(VI) oxide and PCC woe found to be less effective. Other cooxidants were also examined hydrogen peroxide gives unacceptable amounts of overoxidation of aldehydes, whilst t-butyl hydroperoxide, di-r-butyl peroxide and benzoyl peroxide all failed as cooxidants. 

Chromium(VI) oxide can be used as a catalytic oxidant for alcohols with r-butyl hydroperoxide as the cooxidant. This reagent appears to be selective for allylic and benzylic over saturated alcohols, though ( )/(Z)-isomerization has been observed during the preparation of a,3-unsaturated aldehydes. This reagent is also a good oxidant for allylic and ben lic C—bonds these may be competing pathways in more sophisticated substrates. ... 

To overcome the problems of toxicity and work-up associated with many inorganic oxidants, it would be advantageous to develop a catalytic supported oxidant. Towards this aim, chromium(III)-impregnated Nafion 511 (NAFK) has been used as a catalytic oxidant in the presence of f-butyl hydroperoxide. This reagent gives good yields of ketones (80-100%), but unfortunately oxidation of primary alcohols leads to the formation of complex mixtures. 

Vinylcyclohexene and terf-butyl hydroperoxide, in the presence of chromium acetylacetonate, yield exclusively 4-vinylcyclohexene oxide [217]. 

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... 

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