Aldehydes oxidation with permanganate

Mechanism The mechanism of the aliphatic side-chain oxidation as shown in Scheme 7.34 probably involves manganese-oxygen-carbon bonding with subsequent reduction of manganese and oxidation of carbon to yield aldehyde, which is much more vulnerable to oxidation with permanganate. 

The relatively slight difference in susceptibility to oxidation of the hydroxyl and propylene side chains makes it difficult to oxidize the propylene chain without affecting to some extent the hydroxyl substituent, unless it has been protected. Dichromates have been used to accomplish the oxidation step in this process of manufacture but are open to the objection that oxidation tends to go beyond the easily oxidized aldehyde stage, with resultant formation of acids. The same is true of oxidation with permanganate. Less potent agents, such as nitrobenzene, have consequently been used for the direct oxidation of isoeugenol to vanillin. 

The PMR spectrum of baluchistanamine exhibits signals for an amine N-methyl, an amide A-methyl, three methoxyl groups, ten aromatic protons, and one aldehydic proton. On the supposition that baluchistanamine is derived biogenetically from oxyacanthine, also found in B. baluchistanica, the latter base was oxidized with permanganate in acetone to afford, in low S%) yield, a product identical with baluchistanamine. 

Any functional group that undergoes oxidation with permanganate interferes with the test (phenols, aryl amines, most aldehydes, primary and secondary alcohols, etc.). 

Scheme 6.63. A representation of the conversion of a terminal alkyne to an a-ketocarboxylic acid by oxidation with permanganate under neutral conditions (Mn04 ).The oxidation of the aldehyde (via the hydrate) requires a second equivalent of permanganate (Mn04 ) as described for the oxidation of alcohols (Chapter 8).

Oxidative cleavage of the terminal double bond of 49 by ozonolysis to the aldehyde followed by permanganate oxidation to the acid and esterification with diazomethane produced the methyl ester 50. Dieckmann cyclisation of 50, following the procedure developed in Holton s laboratory (LDA, THF, -78 °C, 0.5 h, then HOAc, THF), gave the enol ester 5J in 93% yield (90% conversion). Decarbomethoxylation of 5J. was carried out by temporarily protection of the secondary alcohol (p-TsOH, 2-methoxypropene, 100%), and heating the resulting compound 52 with PhSK in DMF, at 86 °C (3 h) to provide 53a or, after an acidic workup, the hydroxy ketone 53b. 92% yield. 

Aminobenzamidines 808 can also be combined with aldehydes to give dihydro intermediates 809, which provide 2-substituted -anilinoquinazolines 810, after oxidation with potassium permanganate in a separate step <2000T9343>. 

Hydroxymethylpyridazines are easily oxidized with selenium dioxide to the corresponding aldehydes. Oxidation of the corresponding secondary alcohols with chromic acid in aqueous sulfuric acid gives ketones, while oxidation of a hydroxymethyl group with permanganate leads to the pyridazinecarboxylic acids. Hydroxymethyl groups are converted into chloromethyl groups with thionyl chloride or phosphorus oxychloride. 

Alkyl and fused aryl substituents (as in benzimidazoles) are oxidized by permanganate to carboxyl substituents. Oxidation of methylimidazoles with selenium dioxide is only useful in the case of benzimidazoles for the synthesis of imidazole aldehydes.426 The chemiluminescence of aryl-substituted imidazoles has been studied.427... 

It is difficult to prepare aldehydes by the cleavage of carbon-carbon double bonds with pennanganate under aqueous conditions. In water, aldehydes exist at least partly as the corresponttog hydrates, RCH(0H)2, and are therefore very susceptible to further oxidation by permanganate. Consequently the products obtained are usually cartexylic acids. Aldehydes have been obtained in good yields only when the products are deactivated, as in equation (17). ... 

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