Alcohols, secondary, oxidation with potassium permanganate

Primary and secondary alcohols are oxidized slowly at low temperatures by benzyltriethylammonium permanganate in dichloromethane primary alcohols produce methylene esters (60-70%), resulting from reaction of the initially formed carboxylate anion with the solvent, with minor amounts of the chloromethyl esters and the carboxylic acids. Secondary alcohols are oxidized (75-95%) to ketones [34] the yields compare favourably with those obtained using potassium permanganate on a solid support. 1,5-Diols are oxidized by potassium permanganate under phase-transfer catalytic conditions to yield 8,8-disubstituted-8-valerolactones [35] (Scheme 10.1). 

Extension of the scope of the methodology to a full stereocontrol in the addition sequence A in order to obtain either, Z-anti- or l,2-ry -diol units was hampered by the inherent //-selectivity of the addition of 2-TST to a,/3-dialkoxy aldehydes. Control of the selectivity by the use of Lewis acids acting as chelating agents was also foiled by substantial decomposition of 2-TST. This limitation was overcome by conversion of the 7 //-adduct into the syn-isomer via an oxidation-reduction sequence <1989JOC702>. The secondary (Rj-alcohol 457 was oxidized to ketone 461 with potassium permanganate partly solubilized with TDA-1 (tris[2-(2-methoxyethoxy)ethyl]amine). It was proved that under these neutral nonaqueous oxidation conditions no appreciable racemization occurred via exchange... 

Several references have appeared on the use of solid-phase oxidants. Solid potassium permanganate-copper sulphate mixtures oxidize secondary alcohols to ketones in high yield, and pyridinium chromate or chromic acid on silica gel are described as convenient off-the-shelf reagents for oxidation of both primary and secondary alcohols. Anhydrous chromium trioxide-celite effects similar transformations only when ether is present as co-solvent. An excellent review, with over 400 references, on supported oxidants covers the use of silver carbonate-celite, chromium trioxide-pyridine-celite, ozone-silica, chromyl chloride-silica, chromium trioxide-graphite, manganese dioxide-carbon, and potassium permanganate-molecular sieve. 

The use of sofid supports in conjunction with permanganate reactions leads to modification of the reactivity and selectivity of the oxidant. The use of an inert support, such as bentonite (see Clays), copper sulfate pentahydrate, molecular sieves (qv) (151), or sifica, results in an oxidant that does not react with alkenes, but can be used, for example, to convert alcohols to ketones (152). A sofid supported permanganate reagent, composed of copper sulfate pentahydrate and potassium permanganate (153), has been shown to readily convert secondary alcohols into ketones under mild conditions, and in contrast to traditional permanganate reactivity, the reagent does not react with double bonds (154). 

It yields a monobromide melting at 41°, a semi-carbazone melting at 220° to 221 °, and an oxime melting at 106°. When reduced with sodium and alcohol it yields a secondary alcohol, which forms large crystals melting at 51°. On oxidation by cold 3 per cent, solution of potassium permanganate it yields geronic acid, a keto-acid of the constitution—... 

Acidified potassium permanganate solution, KMn04(aq), acts as an oxidizing agent when it comes in contact with alcohols. In this investigation, you will discover how potassium permanganate reacts with a primary, a secondary, and a tertiary alcohol. 

Exercise 15-32 Explain why oxidation of secondary alcohols with 180-labeled potassium permanganate produces an 1sO-containing ketone in acidic solution, but not in basic solution. 

The treatment of secondary alcohols with powerful oxidants such as nitric acid [466, 468], chromium trioxide [5 ( ], or potassium permanganate... 

The oxidation of a secondary alcohol to a ketone or a primary alcohol to an aldehyde using dimethyl sulfoxide (DMSO) with oxalyl chloride at low temperature is called the Swern oxidation. Oxidation of an alkene with osmium tetroxide or potassium permanganate gives a cis-l,2-diol. 

Rapid oxidation of secondary alcohols may be carried out using hydrated copper permanganate in dichloromethane. Water is an essential component in the reaction. Mixtures of potassium permanganate and copper sulphate may also be used, as may a variety of hydrated metal salts, although in these cases experimental details and yields were not reported. Bispyridinesilver permanganate has been shown to be an efficient reagent, soluble in organic solvents, for the oxidation of benzylic primary amines and alcohols to benzaldehydes. The intermediacy of nitrite esters is implicated in oxidations of alcohols with ferric nitrate on KIO bentonite. ... 

Similarly to potassium permanganate, chromic acid oxidizes primary alcohols to aldehydes and secondary alcohols to ketones. With tertiary alcohols chromic acid esters are formed (32, 33) which are yellow to red. 

Primary alcohols can be identified by oxidizing them to aldehydes with chromic acid or potassium permanganate in the presence of 2 n sulfuric acid. The aldehyde formed can be isolated by distillation and identified in the form of its dimedone derivative (see p. 230). Primary alcohols can be identified in this manner in the presence of secondary and tertiary alcohols, because dimedone condenses only with aldehydes, i.e., with products of a mild oxidation of primary alcohols. Carbonyl compounds can be isolated from an aqueous distillate by precipitating them with 2,4-dinitrophenyl-hydrazine (see p. 218). If paper chromatography cannot be used for identification (see p. 222), it is advisable to oxidize at least 500 mg of alcohol. 

---