Glycols periodic-acid cleavage

Aqueous periodic acid can be used to achieve glycol cleavage, combined with anodic oxidation of the iodate, which is formed, back to periodate [70]. Oxidation of iodate is catalysed at a lead dioxide anode [71] but at the potentials required, aldehydes are oxidised to the corresponding acids. Due to this further reaction, the redox-mediated cleavage of diols to form an aldehyde may be difficult to achieve witli a catalytic amount of periodic acid. Cleavage using a stoichiometric amount of periodic acid, followed by recovery of the iodic acid and then its electochemical oxidation, has been achieved [72]. 

P) and concomitant liberation of 1 mol of formaldehyde. This result proves that there is a v/c-glycol present, but it does not prove whether it has an sn-3 or an sn-1 configuration. Obviously, an sn-2 configuration is eliminated by the periodic acid cleavage experiments. 

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 cleavage of a glycol probably involves a cyclic periodate intermediate like that shown here. 

Perchloric acid (79% HCIO4/CH2CI2, 0°, 1 h 25°, 3 h, 87% yield) and periodic acid (aq. dioxane, 3 h, quant, yield) cleave 1,3-dioxolanes the latter drives the reaction to completion by oxidation of the ethylene glycol that forms. Yields are substantially higher from cleavage with perchloric acid (3 AHCIO4/THF, 25°, 3 h, 80% yield) than with hydrochloric acid (HCl/HOAc, 65% yield)... 

For in = 2, 3) H5IO5, ether, THF, 77-99% yield. This method also cleaves oxathioacetals, but did not affect the acid-sensitive acetonide or 1,3-diox-olane. Note that ethereal periodic acid has been used to cleave terminal acetonides with subsequent glycol cleavage. ... 

Lead tetraacetate and periodic acid complement one another in their applicability as reagents for glycol cleavage. The water sensitive lead tetraacetate is used in organic solvents, while periodic acid can be used for cleavage of water-soluble diols in aqueous medium. 

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. 

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. 

Fig. 17.23. Mechanism of the glycol cleavage with NaI04 or H5I06, respectively. A diester of iodo(VII) acid (periodic acid) is formed initially. The ester decomposes in a one-step reaction in which three valence electron pairs are shifted simultaneously.

Vic-Glycol Content. This can be determined through use of the periodate cleavage technique. This methodology has been described earlier and with glycrophosphoserine, there will be 1 mol periodic acid consumed (per mole of... 

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. 

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