Manganese dioxide primary alcohols

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-... 

A useful addition to the roster of oxidants converting primary alcohols into aldehydes is manganese dioxide, which can be prepared by several methods [805, 806, 807, 808, 809, 810]. It is used as a suspension in petroleum ether [8< 5, 808], ether [806, 808, 811], hexane [806, 811], benzene [808, 813], chloroform [808, 811, 813], and carbon tetrachloride [808, 813]. The oxidations are carried out at room temperature and are especially suitable for allylic and benzylic alcohols, which are oxidized more readily than the saturated alcohols [808, 810], Yields vary widely depending on the substrate, on the ratio of the substrate to oxidant (which in turn depends on the particle size of the oxide [810]), on the solvent, and on the reaction time 811] (equation 214). 

Manganese dioxide, an oxidant of primary alcohols to aldehydes, can also yield acids under proper conditions (equation 231) [1141],... 

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... 

Miscellaneous Reactions. So-called Oxidation-Wittig conditions , where a primary alcohol is oxidised using manganese dioxide in the presence of a stabilised ylide, have been applied for the first time to unactivated alcohols, producing a, 3-unsaturated esters in high yields (Scheme 18). Fluorenyl-... 

Activated manganese dioxide (MnO2) reliably oxidizes acetylenic, allylic, and benzylic alcohols to aldehydes and ketones. Saturated primary and secondary alcohols are also oxidized, albeit more slowly. The two main concerns are the activity of the manganese dioxide and the slow filtration of salts after the reaction. Activated MnOi is available commercially or may be prepared. 

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,... 

In broad terms it is only in special cases that the oxidation of hydrocarbons to primary or secondary alcohols is of practical importance. One such case is oxidation of toluene and its derivatives to the corresponding benzyl alcohols, by e.g., manganese dioxide, lead dioxide, lead tetraacetate, or Caro s acid. It is advantageous to use lead tetraacetate in glacial acetic acid solution since then the alcohol formed is protected by esterification against further oxidation. 

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. 

Oxidation of primary allylic alcohols. In the synthesis of several isomeric phytoenes (C40-conjugated trienes), Weedon et al. used Fetizon s reagent for oxidation of primary allylic alcohols to allylic aldehydes. Yields of >85% were reported. Use of manganese dioxide led to much lower yields (40-50%). 2,3-Dichloro-5,6-dicyano-l,4-benzoquinone also gave high yields, but mixtures of stereoisomers were obtained. 

Manganese dioxide is capable of oxidizing alcohols to ketones or aldehydes. The reaction proceeds via a radical intermediate (see below), producing MnO (which is Mn +) as the byproduct. Manganese dioxide is an important reagent in organic synthesis since it oxidizes primary and secondary alcohols to the aldehyde or ketone, respectively, in neutral media.This reaction was discovered by Ballet al when they precipitated manganese dioxide and used it to convert vitamin A (94) to retinal (95) in 80% yield. 49... 

Manganese dioxide oxidizes allylic and benzylic alcohols faster than primary saturated alcohols, but primary and secondary allylic alcohols react at about the same rate. This use of manganese dioxide is particularly important.i Oxidation of benzylic alcohols is also facile and a secondary benzylic alcohol is oxidized faster than a primary saturated alcohol. The secondary benzylic alcohol group in 102 was oxidized to give aryl ketone 103 (94% yield) in preference to reaction at the primary aliphatic hydroxyl. 

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. 

---