Acetals and Ketals of the Hexitols

The physical properties of acetals of allitol are listed in Table XII. 

The benzylidenation of 1,6-dibenzoyl-dulcitol gives rise to one of two products, depending upon the conditions of the reaction. The use of gaseous hydrogen chloride at room temperature for 12 hours, or of zinc chloride at 60° for 24 hours, results in the formation of a dibenzoyl-dibenzylidene-dulcitol, which melts at 119-120° and which, when treated with sodium methoxide, gives a dibenzylidene-dulcitol melting at 149-1500.1 On the other hand, when the condensation is catalyzed by zinc chloride at room temperature, the main product is an isomeric dibenzoyl-dibenzylidene-dulcitol, which melts at 147-148° and which can be saponified to a dibenzylidene-dulcitol melting at 173-174°. The unstable dibenzoyl-dibenzylidene-dulcitol (m. p. 147-148°) is converted into its stable isomer (m. p. 119-120°) by treatment with zinc chloride and benzaldehyde at 60°, Four independent lines of evidence reveal that, 

6-ditrityl-2,3,4,5-dibenzylidene-dulcitol (m. p. 233-234°), prepared by Wolfrom, Burke and Waisbrot9 from 1,6-ditrityl-dulcitol and benzaldehyde in the presence of zinc chloride at room temperature, resembled, as might be expected, the ditrityl ether (m. p. 240-242°) derived from the higher-melting (m. p. 173-174°) 2,3,4,5-dibenzylidene-dulcitol reported above. 

In 1942, Hann, Haskins and Hudson48 reported that the di-(o-nitro-benzylidene)-dulcitol described by Tanasescu and Macovski was not oxidized by lead tetraacetate and therefore could not possess the structure (1,2 5,6) arbitrarily assigned to it by the earlier workers. In view of the fact that the diacetal gave the known l,3,4,6-tetraacetyl-2,5-diben-zoyl-dulcitol when it was benzoylated in pyridine and then acetylated under acidic conditions, they regarded it as l,3 4,6-di-(o-nitrobenzyli-dene)-dulcitol, but of course this conclusion is not unequivocal. 

Three monoacetals, o-,70 wi-97 and p-nitrobenzylidene-dulcitol,97 have been described, the first being formulated, without proof, as the 3,4-derivative. The only triacetal of dulcitol of which we are aware is a tri-(o-nitrobenzylidene)-dulcitol prepared from the aldehyde and the hexitol using as the condensing agent phosphorus pentoxide,70 instead of 75% sulfuric acid which gives the diacetal already mentioned.48 6 Photochemical transformations of o-nitrobenzylidene acetals are discussed on page 148. 

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The Oxidation of Acetals and Ketals of the Hexitols with Glycol-splitting Reagents... 

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