Periodic Acid Vicinal Diols

INSTRUCTOR PREPARATION. This reagent solution is prepared by dissolving 250 mg of periodic acid (HsIOe) in 50 mL of deionized water. 

Vicinal diols (1,2 diols) are differentiated from the simple alcohols by the characteristic reaction below. Metaperiodic add (HIO4) selectively oxidizes 1,2-diols to give carbonyl compounds  

The test is based on the instantaneous formation of a white predpitate of silver iodate (AglOs) following addition of silver nitrate  

Place 2 mL of the periodic add reagent solution in a small test tube. 

Add 2 drops of concentrated nitric add and mix the solution thoroughly. Add 2 drops of a liquid unknown (—2-5 mg of a solid) and mix again. Now add 2-3 drops of 5% aqueous silver nitrate solution. An instantaneous white precipitate constitutes a positive test. 

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Sodium periodate (sodium metaperiodate), NaI04 (mp 300 °C dec), which is commercially available, is applied mainly in aqueous or aqueous-alcoholic solutions. Like the free periodic acid, sodium periodate cleaves vicinal diols to carbonyl compounds [762], This reaction is especially useful in connection with potassium permanganate [763, 764] or osmium tetroxide [765], Such mixed oxidants oxidize alkenes to carbonyl compounds or carboxylic acids, evidently by way of vicinal diols as intermediates. Sulfides are transformed by sodium periodate into sulfoxides [322, 323, 766, 767, 768, 769, 770, 771, 772], and selenides are converted into selenoxides [773]. Sodium periodate is also a reoxidant of lower valency ruthenium in oxidations with ruthenium tetroxide [567, 774],... 

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)... 

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... 

Section 15 12 Periodic acid cleaves vicinal diols two aldehydes two ketones or an aldehyde and a ketone are formed... 

Periodic acid oxidation (Section 15 12) finds extensive use as an analytical method m carbohydrate chemistry Structural information is obtained by measuring the number of equivalents of periodic acid that react with a given compound and by identifying the reaction products A vicinal diol consumes one equivalent of penodate and is cleaved to two carbonyl compounds... 

Vicinal diol and a hydroxy carbonyl functions in carbohydrates are cleaved by periodic acid Used analytically as a tool for structure determination... 

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. 

Mechanisms involving glycol bond fission have been proposed for the oxidation of vicinal diols, and hydride transfer for other diols in the oxidation of diols by bromine in acid solution.The kinetics of oxidation of some five-ring heterocyclic aldehydes by acidic bromate have been studied. The reaction of phenothiazin-5-ium 3-amino-7-dimethylamino-2-methyl chloride (toluidine blue) with acidic bromate has been studied. Kinetic studies revealed an initial induction period before the rapid consumption of substrate and this is accounted for by a mechanism in which bromide ion is converted into the active bromate and hyperbromous acid during induction and the substrate is converted into the demethylated sulfoxide. 

SAMPLE SOLUTION (a) The a-hydroxy aldehyde unit at the end of the sugar chain is cleaved, as well as all the vicinal diol functions. Four moles of periodic acid are required per mole of D-arabinose. Four moles of formic acid and one mole of formaldehyde are produced. 

The difference between the two ethers is that 1-0-benzylglycerol contains a vicinal diol function, but 2-0-benzylglycerol does not. Periodic acid will react with 1-0-benzylglycerol but not with 2-0-benzylglycerol. 

The ratio of carbon to hydrogen in the molecular formula is ChH2h+2 (C8H1802), and so the compound has no double bonds or rings. The compound cannot be a vicinal diol, because it does not react with periodic acid. 

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. 

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). 

Sodium bismuthate, NaBiOs, cleaves vicinal diols to dicarbonyl compounds [482, 483] but offers no advantage over the more common oxidants of vicinal diols, such as lead tetraacetate and periodic acid. 

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]. 

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]. 

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). 

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