Hexitols, periodate oxidation

The hexitols may be determined quantitatively by periodate oxidation. Either the amount of oxidant consumed or the amount of acid or formaldehyde liberated may be determined. This method will not... 

Oxepane (seven-membered) rings (1,6-anhydrohexitols)52 have been prepared from the 3,4-isopropylidene acetals of D-mannitol, D-glucitol, and L-iditol, by way of alkaline hydrolysis of the corresponding 1,2 5,6-dianhydrides. The ring structures of the products were established through periodate oxidation and lead tetraacetate oxidation the requisite amount of formic acid was produced, and 3 equivalents of lead tetraacetate were consumed. No inversions at any of the asymmetric centers were involved in the reactions conducted, so the oxepanes had retained the configurations of the starting hexitols. 

The stereochemistry at C-5 of each of the hexitols (6) and (7) was determined in the following way. Periodate oxidation of these hexitols afiForded dialdehydes (8) and (9), which, on subsequent reduction with sodium borohydride, afforded the enantiomeric trihydroxy ethers (10) and (11). The configuration at C-3 of the ether (10) was then correlated with that of C-4 of the known l,4-anhydro-5-deoxy-D-arabino-hexitol (12), as follows. Periodate oxidation of (12), followed by reduction of the resulting dialdehyde with sodium borohydride, yielded a trihydroxy ether that was identical with (10). If it is assumed that no inversion of configuration at C-3 or C-4 of 3,4-di-O-acetyl-D-xylal occurs during the oxo reaction, then compounds (6) and (7) are l,3-anhydro-4-deoxy-L-JC /lo-hexitol and l,5-anhydro-4-deoxy-D-arobino-hexitol, respectively. 

Purely chemical processes, such as the oxidation of D-mannitol by chlorine, normally result in a mixture of D-mannose and D-fructose, but the ratio can be appreciably shifted in favor of either of these products. Indeed, prolonged treatment (3-5 days) at low temperatures gives D-mannose in good yield, whereas several short periods (1 day) afford D-fructose exclusively. After nine chlorinations of 1 day, at 4 to 20°, 53% of the hexitol is oxidized and 49% thereof is converted into D-fructose. A theoretical yield is afforded by the photochemical oxidation of D-mannitol. When a small quantity of D-fructose is added to a much greater amount of zinc oxide and exposed to the effects of air and sunlight, D-mannose and D-fructose are formed in amounts almost proportional to the amount of sunlight. It may be concluded that an effort has been made to find a cheap source for preparation of D-fructose and to lower the production costs by use of easier isolation and purification procedures. Of the various methods presented, the isomerization reaction is certainly the most promising. 

As a corollary to this work, oxidation with periodate constitutes the basis of analytical procedures for the determination of 6-deoxyhexoses ( methylpentoses ),88 calcium gluconate89 and gluconic acid,90 hexitols,91 94... 

In connection with preliminary structural work on the hexitols, an unexpected result arose during attempted identification, by conversion into a (p-nitrophenyl)hydrazone, of the dialdehydes (8) or (9), formed by periodic acid oxidation of tbe anhydrodeoxyhexitols (6) and (7), or (21) and (22). The dialdehydes (8) were cleaved to form glyoxal and a 2-deoxytetrose [isolated as the (p-nitrophenyl)hydra-zone ]. 

L-Ascorbic acid, an enediol, has been oxidized by sodium hypoiodite and by potassium permanganate to L-threonic acid (9). Such oxidation of double bonds does not occur in the enols alone, for D-arabinal is oxidized by H2O2 and OSO4 in er butanol to D-erythronic acid in addition to D-arabinose (10). Periodic acid and lead tetraacetate are useful for the cleavage of hexitols and glycosides to glyceraldehyde and glycolaldehyde (see Chapter... 

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