Cleavage by periodic acid

D Arabinose showing points of cleavage by periodic acid each cleavage requires one equivalent of FIIO4... 

Periodic Acid Cleavage of Carbohydrates Another method used to determine the size of carbohydrate rings is cleavage by periodic acid. Recall that periodic acid cleaves vicinal diols to give two carbonyl compounds, either ketones or aldehydes, depending on the substitution of the reactant (Section 11-1 IB). 

In saccharides, cleavage by periodic acid or sodium periodate occurs between any carbons possessing/ree hydroxy lie groups. Thus glucosazone treated with periodic acid in aqueous ethanol at room temperature is degraded to the l,2-bis(phenylhydrazone) of mesoxalaldehyde (propanone-dial) in 85% yield [759]. 

Like other compounds that contain two or more - OH or - O groups on adjacent carbon atoms, carbohydrates undergo oxidative cleavage by periodic acid, HIO4 (Sec. 16.12). This reaction, introduced in 1928 by L. Malaprade (at the University of Nancy, France), is one of the most useful tools in modern research on carbohydrate structure. 

Periodic acid also cleaves carbon-carbon bonds of a-hydroxyketones and a-hydroxyaldehydes by a similar mechanism. Following are abbreviated structural formulas for these functional groups and the products of their oxidative cleavage by periodic acid. As a way to help you understand how each set of products is formed, each carbonyl in a starting material is shown as a hydrated intermediate that is then oxidized. In this way, each oxidation can be viewed as being analogous to the oxidation of a glycol. 

FIGURE 16.74 The vicinal diol cleavage by periodic acid involves a cychc intermediate that breaks down to give a pair of carbonyl compounds. 

The cleavage of 1,2-diols 1 by periodic acid is associated with the name of the French chemist Malaprade. The reaction mechanism is related to that outlined above, and is likely to involve a five-membered ring periodate ester intermediate 7 ... 

The treatment of an alkene by 5yn-hydroxylation, followed by periodic acid (HIO4) cleavage, is an alternative to the ozonolysis, followed by reductive work-up. 5yn-diols are oxidized to aldehydes and ketones by periodic acid (HIO4). This oxidation reaction divides the reactant into two pieces, thus it is called an oxidative cleavage. 

The only difference in the synthetic sequence relative to the preparation of 12 consists of a variation in cleavage of the double bond. Employed here was a dihydroxylation followed by periodic acid treatment26 (see Chapter 5) rather than the o/onol> sis used with the C-7 through C-9 fragment L NMO, eat. OsOj. acetone, Rf. 

However, regiopure azido 1,2-diol 19 is converted to the corresponding azido carboxylic acid 22 by oxidative glycol cleavage with periodic acid in the presence of catalytic amounts of ruthenium trichloride. Interestingly, the use of sodium periodate instead of periodic acid resulted in a 10-15 % epimerization of the C-5 stereocenter. 

Most of the compounds that had been reported (before March, 1942) to show cleavage oxidation by periodic acid are recorded in the table the substances are listed alphabetically in the following groups of related compounds (1) carbocyclic compounds (2) carbohydrates (3) a-diketones and a-ketols (4) hydroxyamino compounds (5) polyhydroxy and hydroxyketo acids (6) polyhydroxy alcohols (7) steroids (8) miscellaneous compounds. French journals after May, 1940, and the majority of other foreign publications after June, 1941, were unavailable for the survey. 

Diols (glycols), such as those formed by dihydroxylation of alkenes, are cleaved by periodic acid (HI04). The products are the same ketones and aldehydes that would be formed by ozonolysis-reduction of the alkene. Dihydroxylation followed by periodic acid cleavage serves as a useful alternative to ozonolysis, and the periodate cleavage by itself is useful for determining the structures of sugars (Chapter 23). 

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. 

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