Chromium dioxide, oxidation alcohols

Scheme 2.3 Oxidation of primary and secondary alcohols with chromium dioxide.

Aromatic carboxylic acids can be prepared by oxidation of the corresponding benzyl alcohols and benzaldehydes. An aromatic methyl group is also sufficiently activated by the aromatic ring for it to be oxidized to the acid under vigorous conditions, such as heating with chromium(VI) oxide. Other conventional methods include the hydrolysis of aromatic nitriles and the carboxylation of aromatic Grignard reagents with carbon dioxide. 

Oxidation of alcohols. Chromium dioxide is a mild oxidant for various alcohols. It... 

Cruser and Miller have described a method for the preparation of potassium hexacyanochromate(III) whereby chromium(VI) oxide is dissolved in hydrochloric acid, reduced with alcohol, evaporated to dryness, taken up with water, and poured into a hot solution of potassium cyanide. The resulting solution is digested several hours, filtered, and allowed to evaporate in air. The following method is a modification of that given by Christensen. It differs from that of Cruser and Miller in that a dichromate is reduced with sulfur dioxide and that chromium(III) acetate instead of chromium(III) chloride is poured into potassium cyanide solution. In following the directions outlined here, special care should be exercised to obtain pure chromium(III) acetate and to avoid decomposition of the relatively unstable potassium hexacyanocbromate(III). 

Nitrobenzaldehyde has been prepared from />-nitrotoluene by treatment with isoamyl nitrite in the presence of sodium methylate,1 by oxidation with chromyl chloride,2 cerium dioxide,3 or chromium trioxide in the presence of acetic anhydride.4 It can also be prepared by the oxidation of -nitrobenzyl chloride,5 7>-nitrobenzyl alcohol,6 or the esters of -nitrocinnamic acid.7... 

The chromium oxapropadienylidene complex affords dimethyl malonate when oxidized in methanol (77), and the diester is assumed to be produced by addition of the alcohol to the first-formed tricarbon dioxide ... 

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