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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.
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 Weinreb–Nahm ketone synthesis. The major advantage of this method over addition of organometallic reagents to more typical acyl compounds is that it avoids the common problem of over-addition. For these latter reactions, two equivalents of the incoming group add to form an alcohol rather than a ketone or aldehyde. This occurs even if the ...
The rate of the overall reaction depends on the slowest step, so the overall reaction will be first order when the reaction of the energized reactant is slower than the collision step. The half-life is independent of the starting concentration and is given by t 1 / 2 = ln ( 2 ) k {\textstyle t_{1/2}={\frac {\ln {(2)}}{k}}} .
The reaction can be done at room temperature and is quickly complete. Many other functional groups will not be affected by this reaction. The Dess–Martin oxidation may be preferable to other oxidation reactions as it is very mild, avoids the use of toxic chromium reagents, does not require large excess or co-oxidants, and for its ease of work up.
The reaction generated an alcohol 3 which was directly reacted without purification with PTSA to afford alkene 4 in 86% yield as a single isomer. Hydrogenation and a subsequent benzyl- deprotection of the alkene intermediate according to the reported procedure afforded (+)-biotin in 73% yield over two steps.
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.
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.