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Alcohol oxidation is a collection of oxidation reactions in organic chemistry that convert alcohols to aldehydes, ketones, carboxylic acids, and esters. The reaction mainly applies to primary and secondary alcohols. Secondary alcohols form ketones, while primary alcohols form aldehydes or carboxylic acids. [1] A variety of oxidants can be used.
Primary alcohols (R−CH 2 OH) can be oxidized either to aldehydes (R−CHO) or to carboxylic acids (R−CO 2 H). The oxidation of secondary alcohols (R 1 R 2 CH−OH) normally terminates at the ketone (R 1 R 2 C=O) stage. Tertiary alcohols (R 1 R 2 R 3 C−OH) are resistant to oxidation.
For oxidations to the aldehydes and ketones, two equivalents of chromic acid oxidize three equivalents of the alcohol: 2 HCrO 4 − + 3 RR'C(OH)H + 8 H + + 4 H 2 O → 2 [Cr(H 2 O) 6] 3+ + 3 RR'CO. For oxidation of primary alcohols to carboxylic acids, 4 equivalents of chromic acid oxidize 3 equivalents of the alcohol. The aldehyde is an ...
The reaction of tertiary alcohols containing an α-acetylenic group does not produce the expected aldehydes, but rather α,β-unsaturated methyl ketones via an enyne intermediate. [9] [10] This alternate reaction is called the Rupe reaction, and competes with the Meyer–Schuster rearrangement in the case of tertiary alcohols.
The inability of Fétizon's reagent to oxidize tertiary alcohols makes it extremely useful in the monooxidation of a [1,2] diol in which one of the alcohols is tertiary while avoiding cleavage of the carbon-carbon bond. [7] Fetizon's reagent oxidizes secondary alcohols selectively in the presence of tertiary alcohols
Aldehydes and ketones can be reduced respectively to primary and secondary alcohols. In deoxygenation, the alcohol group can be further reduced and removed altogether by replacement with H. Two broad strategies exist for carbonyl reduction. One method, which is favored in industry, uses hydrogen as the reductant.
This reaction can be accelerated by acidic conditions, which make the carbonyl more electrophilic, or basic conditions, which provide a more anionic and therefore more reactive nucleophile. The tetrahedral intermediate itself can be an alcohol or alkoxide , depending on the pH of the reaction.
The reaction is particularly suitable for the synthesis of aldehydes from primary alcohols. Analogously, secondary alcohols can be oxidized to form ketones. Dimethyl sulfoxide/acetic anhydride serves as oxidizing agent. Albright-Goldman-Oxidation (Aldehyd) The reaction does not proceed further to the carboxylic acid.