Carboxylic acids with manganese dioxide

The oxidation of aromatic aldehydes to carboxylic acids with manganese dioxide is somewhat surprising because manganese dioxide is used to oxidize toluenes to benzaldehydes. The transformation of benzaldehyde into benzoic acid is achieved in 75% yield by refluxing with manganese dioxide in petroleum ether for 24 h [S75]. 

Aldehyde 244 reacts with manganese dioxide and sodium cyanide in ethanol to give ethyl ester 245 (Scheme 19), while oxidation of alcohol 12 with sodium peroxodisulfate in the presence of a catalytic amount of ruthenium chloride furnishes the carboxylic acid 246 (Scheme 19) <1998CPB287>. 

The modified cephalosporin ceftobiprole (31-8), yet another compound that contains a double bond at the ring carbon, though in this case with a rather complex extended side chain, has shown activity in the clinic against some strains of multidrug resistant bacteria. The synthesis starts with the weU-precedented acylation of the cephalosporin (31-2), available in several steps from the commercially available 7-acetoxy cephalosporanic acid, with the activated thiadiazole carboxylic acid (31-1). The hydroxyl group in the product (31-3) is then oxidized with manganese dioxide to afford the corresponding aldehyde (31-4). This product is then condensed with the fcw-pyrrolidyl phosphonium salt (31-5), itself protected with the... 

Miscellaneous derivatives are hydrolyzed back to the starting carbonyl compounds. Hienylhydtazones of ketones are converted into the parent ketones tqion treatment with manganese dioxide.Tosylhydra-zones react with molybdenyl chloride or tungsten tetrafluoride to give both aldehydes and ketones. Sodium peroxide converts aldoximes into carboxylic acids. 

A nice example of a selective oxidation with manganese dioxide has been reported in the pyridoxine series in ethanolic KOH pyridoxine (X-71) yields 3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carboxylic acid (X-72). The same reagent in dilute sulfuric acid yields the hemiacetal X-73. 

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... 

The isomeric 1-suhstituted imidazole-5-carboxylates are made by cyclization of 3-amino-2-alkylaminopropanoic acids with triethyl orthoformate followed by active manganese dioxide oxidation of the imidazoline product (see Section 3.1.1), or from IV-substituted glycine esters, which are formylated, converted into the enolates and then condensed with potassium thiocyanate... 

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