Additional Methods for Oxidizing Alcohols

Additional Methods for Oxidizing Alcohols

– Many other reagents and procedures have been developed for oxidizing alcohols.

– Some are simply modifications of the procedures we have seen.

– For example, the Collins reagent is a complex of chromium trioxide and pyridine, the original version of PCC.

– The Jones reagent is a milder form of chromic acid: a solution of diluted chromic acid in acetone.

– All of the chromium reagents produce by-products and washings that contain hazardous chromium salts and must be collected as hazardous waste.

– In many cases, simple oxidants such as household bleach (sodium hypochlorite, NaOCl) can accomplish the same oxidations as chromic acid without using heavy metals, and without generating hazardous waste.

– Oxidations using sodium hypochlorite involve mildly acidic or basic conditions that may be better than chromic acid for acid sensitive compounds.

Additional Methods for Oxidizing Alcohols

– Two other strong oxidants are potassium permanganate and nitric acid.

– Both of these reagents are less expensive than the chromium reagents, and both of them give by-products that are less environmentally hazardous than spent chromium reagents.

– Both permanganate and nitric acid oxidize secondary alcohols to ketones and primary alcohols to carboxylic acids.

– Used primarily in industry, these strong oxidants can form explosive mixtures and cleave carbon–carbon bonds if the temperature and concentrations are not precisely controlled.

– The Swern oxidation uses dimethyl sulfoxide (DMSO) as the oxidizing agent to convert alcohols to ketones and aldehydes.

– DMSO and oxalyl chloride are added to the alcohol at low temperature, followed by a hindered base such as triethylamine.

– The reactive species (CH3)2 Cl, formed in the solution, is thought to act as the oxidant in the Swern oxidation.

Secondary alcohols are oxidized to ketones, and primary alcohols are oxidized only as far as the aldehyde.

– The by-products of this reaction are all volatile and are easily separated from the organic products

Additional Methods for Oxidizing Alcohols

– Like the Swern oxidation, the Dess–Martin periodinane (DMP) reagent oxidizes primary alcohols to aldehydes and secondary alcohols to ketones without using chromium or other heavy-metal compounds.

– The reaction with DMP takes place under mild conditions (room temperature, neutral pH) and gives excellent yields.

– The DMP reagent, which owes its oxidizing ability to a high-valence iodine atom, is a commercially available solid that is easily stored

Summary of Alcohol Oxidations

Additional Methods for Oxidizing Alcohols

Solved problem for Oxidizing Alcohols

Suggest the most appropriate method for each of the following laboratory syntheses:

(a) cyclopentanol → cyclopentanone


– Many reagents are available to oxidize a simple secondary alcohol to a ketone.

– Most labs would have chromium trioxide or sodium dichromate available, and the chromic acid oxidation would be simple.

– Bleach (sodium hypochlorite) might be a cheaper and less polluting alternative to the chromium reagents.

– DMP and the Swern oxidation would also work.

(b) oct-2-en-1-ol oct-2-enal


– This synthesis requires more finesse.

– The aldehyde is easily over-oxidized to a carboxylic acid, and the double bond reacts with oxidants such as Our choices are limited to PCC, DMP, or the Swern oxidation.

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