Cleavage of Glycols

Saccharose consumes 3 moles (cf. Reaction 4.113) and maltose 4 moles of periodate. The final conclusion as to sugar linkage positions and ring structure is drawn from the periodate consumption, the amount of formic acid produced (in the case of saccharose, 1 mole maltose, 2 moles) and the other carbonyl fragments which are oxidized additionally by bromine to stable carboxylic acids and then released by hydrolysis. The glycol splitting reaction should be considered an optional or complementary method to the permethylation reaction applied in structural elucidation of carbohydrates. 

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Ozonolysis of alkenes (end of Section 6.4) and cleavage of glycols (Section 14.11) afford carbonyl compounds. These reactions, once used for structure determinations, have been superseded by spectral methods. 

Oxidative Cleavage of Glycols and Related Compounds 21O-De-hydrogen-uncoupling... 

Cleavage of glycols with these reagents proceeds according to the following stoichiometry ... 

Review.1 The reactions of C6H5I(OAc)2 are mainly oxidations in which iodine(III) is reduced to iodine(I) and closely resemble those of lead tetraacetate, such as cleavage of glycols. For this reaction, phenyliodine(III) bis(trifluoroacetate) is the preferred reagent (6, 301). 

Oxidation. The salt effects rapid cleavage of glycols in high yield. It can be used also for the oxidation of secondary nitro compounds to ketones (Nef reaction).- An excess of the guanidine base is used to form the nitronatc, which is then oxidized to the ketone by the salt. Yields are —80-95%, and are higher than those obtained with iodosylbenzene, C HjIO. Oxidation of primary nitro compounds by his method gives only low to moderate yields of aldehydes. 

The anodic oxidation method is highly efficient for the oxidative cleavage of glycols (22) and related compounds. The oxidation of glycols and glycol ethers in methanol results in a clean cleavage to the corresponding carbonyl compounds (equation 44). ... 

The anodic oxidation of enol ethers in methanol yields a-methoxylated carbonyl conqKxinds, which are useful intermediates for the synthesis of carbonyl compounds utilizing the technique of oxidative cleavage of glycols (equation 4S). ... 

Periodic acid is a versatile oxidant since, depending on pH, the redox potential for the periodate-iodate couple varies from 0.7 V in aqueous basic media to 1.6 V in aqueous acidic media. Based on this observation, Villemin and Ricard devised an oxidative cleavage of glycols, in which /nc50-l,2-diphenyl-... 

Periodic acid is a versatile oxidant since, depending on pH, the redox potential for the periodate-iodate couple varies from 0.7 V in aqueous basic media to 1.6 V in aqueous acidic media.Based on this observation, Villemin and Ricard devised an oxidative cleavage of glycols, in which mcjo-l,2-diphenyl-1,2-ethanediol was oxidized by periodic acid on alumina to benzaldehyde in 82% yield in aqueous ethanol (90% ethanol) at room temperature in 26 h. The same supported oxidant converted aromatics into quinones. In the presence of transition metal complexes (Mn ), a-arylalkenes suffer oxidative cleavage to aldehydes. For example, tran.r-stilbene gives benzaldehyde at room temperature. 

Criegee, R. Oxidation with quadrivalent lead salts. II. Oxidative cleavage of glycols. Ber. 1931, 64B, 260-266. 

The mechanism of 1,2-cleavage of glycols with sodium bismuthate is generally considered to be similar to that with lead tetraacetate and periodic acid [40CB563], although there is still some controversy [50JCS(C)1907]. A cyclic bismuthate diester is postulated as a plausible intermediate, though the rates of oxidation observed are not so different between cis- and trans-, 2-cyclohexanediols. 

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