Vicinal diols periodic acid cleavage

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). 

Periodic acid cleavage of vicinal diols is often used for analytical purposes as an aid m structure determination By identifying the carbonyl compounds produced the con stitution of the starting diol may be deduced This technique finds its widest application with carbohydrates and will be discussed more fully in Chapter 25... 

The results of some oxidations with potassium permanganate differ depending on the pH of the reaction. For example, stearolic acid gives 9,10-diketostearic acid at pH 7-7.5 (achieved with carbon dioxide) and azelaic acid on treatment at pH 12 [864]. In some reactions, potassium permanganate is used as a catalyst for oxidation with other oxidants, such as sodium periodate. Thus alkenes are cleaved to carbonyl compounds or acids via vicinal diols obtained by hydroxylation with potassium permanganate, followed by cleavage by sodium periodate [763, 552]. 

Mechanism of Periodic Acid Cleavage of Vicinal Diols... 

A reaction characteristic of vicinal diols is their oxidative cleavage on treatment with periodic acid (HIO4) The carbon-carbon bond of the vicinal diol unit is broken and two carbonyl groups result Periodic acid is reduced to iodic acid (HIO3)... 

The oxidative cleavage of the central carbon-carbon bond in a vicinal diol 1, by reaction with lead tetraacetate or periodic acid, yields two carbonyl compounds 2 and 3 as products. 

Vicinal diols (glycols) are easily cleaved under mild conditions and in good yield with NaI04 or H5I06. Mechanistically an intermediate diester of periodic acid is formed first. The successive cleavage of this intermediate 20 leads in an one-step process to the carbonyl 21 and the iodine(V) species 23. 

The oxidative cleavage of carbon-carbon bonds in vicinal diols [756, 759] is a reaction widely used in saccharide chemistry. Besides its application in this reaction, periodic acid achieves the oxidative coupling [757] or oxidation to quinones [758] of polynuclear aromatic hydrocarbons, the oxidation of methyl groups in aromatic compounds to carbonyl groups [760], the conversion of epoxides into dicarbonyl compounds [761], and the oxidative cleavage of trimethylsilyl ethers of acyloins to carboxylic acids [755]. 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

The mechanism of the cleavage of vicinal diols can be represented by the reaction of diols with periodic acid, HIO4 or H5IO6 (equation 296). 

Potassium permanganate oxidation of lappaconine (86) yielded oxolap-paconine (88). Further oxidation of oxolappaconine with periodic acid produced secooxolappaconine (89). However, some controversy has developed about the lead tetracetate cleavage of the C-8-C-9 vicinal diol... 

Cleavage of vicinal diols to carbonyl compounds can be achieved by using periodic acid (HIO4) (Section 15.12). 

Section 17.3 reviewed the oxidation of alkenes to give dihydroxylation. Ozonolysis is a good method for the oxidative cleavage of alkenes, but vicinal diols are also subject to oxidative cleavage and the products are aldehydes or ketones. Two common reagents used for this purpose are periodic acid (HIO4) and lead tetraacetate [Pb(OAc)J. 

FIGURE 16.73 The cleavage of vicinal diols by periodic acid. 

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

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