Alcohols, primary with manganese dioxide

Tritium-labelled disenedoylretronedne (64) required for studies of the biological properties of pyrrolizidine alkaloids, has been prepared by acylation of [9- H2]retronedne by senedoyl chloride. The label was introduced into retronedne following the Corey method of oxidation of the primary allylic alcohol function of unlabelled retronedne (65) with manganese dioxide in the presence of potassium... 

Oxidation of tazettinol with manganese dioxide afforded 2-(4-hy-droxyphenyl)-4,5-methylenedioxybenzyl alcohol. Presumably the primary oxidation product (CLVI) underwent jS-elimination to give CLVII,... 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

Benzo[6]thiophene aldehydes have also been prepared by oxidation of the corresponding primary alcohol with fer -butyl chromate,518 nitric acid,518 or manganese dioxide,337,565 and by reaction of the... 

Allylic alcohols are more easily oxidised than saturated alcohols and in this case rates are greatest for the equatorial isomers [42]. Activated manganese dioxide is commonly used for selective oxidations of allylic alcohols, although it will also attack saturated alcohols slowly under special conditions [44]. Its mechanism of action is not understood, although some relevant observations have been reported [43]. 2,3-Dichloro-5,6 dicyanobenzoquinone (DDQ) is a very mild and selective oxidant for allylic alcohols [43]. Kinetic studies [46] on 3a- and 3 9 hydroxy-A -systems (8) revealed a higher rate of oxidation of the pseudo-equatorial 3 -alcohol K jK a = 6), and a large primary isotope effect Kj)IKb ca. 1/5) when the C(3) H was replaced by deuterium. These results indicate a rate-determining hydride abstraction from C(3>, with preferred removal of the pseudo-axial 3C1-H as a result of optimum a-7i overlap in the transition state (9). However, a detailed analysis of thermodynamic parameters shows that the cause of the rate difference appears mainly in the term (A5 ) rep-... 

Jones reagent (1, 142-143). Primary allylic or benzyUc alcohols are oxidized in high yield with chromic acid in acetone. Thus cinnamyl alcohol is oxidized to cinnamaldehyde in 84% yield, and benzaldehyde is obtained from benzyl alcohol in 76% yield. Manganese dioxide has usually been used in such oxidations. 

Peroxymonosulfuric acid is highly unstable, decomposes dangerously on heating, and evolves oxygen at room temperamre. It may react violently with organic matter and readily oxidizable compounds. Violent explosions have been reported with acetone, due to the formation of acetone peroxide (Toennis 1937). It may explode when mixed with many primary and secondary alcohols, manganese dioxide, cotton, many metals in finely divided form, and aromatics such as benzene, phenol, and aniline. 

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 readily available and stable compound barium manganate has been shown to be an efficient oxidizing agent for the oxidation of primary and secondary alcohols to carbonyl compounds. It has similar activity to manganese dioxide but is claimed to be better for the preparation of certain aldehydes e.g. the furan aldehyde (11) is produced in 80% yield whereas with Mn02 the yield is less than 20%. 

The oxidation of primary alcohols using chromic acid, chromic oxide-pyridine complex, manganese dioxide, etc., gives aldehydes in good yields. Allylic alcohols are readily oxidized at room temperature with active manganese dioxide. 

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