Meso-allitol

Another method of synthesis was also used. This involved the action of chloroacetaldehyde on the Grignard reagent derived from acetylene in order to obtain the meso divinylacetylene dichlorohydrin, CH2CI—CHOH—C=C—CHOH—CH C1, from which one passed to the corresponding hexynetetrol, CH2OH—CHOH—C=C—CHOH— CHjOH. This, in turn, was reduced to the hexenetetrol, CHjOH— CHOH—CH=CH—CHOH—CH2OH, by means of Bourguel s catalyst,8 a dispersion of colloidal palladium on starch. When the hexenetetrol was hydroxylated by the use of silver chlorate and osmic acid, two hexitols, dulcitol and allitol, were obtained. 

Hence, the precursors of allitol are the meso form of divinylglycol in the first of the above syntheses, and the meso form of the hexynetetrol and hexenetetrol in the second method erf synthesis. 

An amount of 16 g. of the glycol (m. p. 18°) dissolved in 250 ml. of water was oxidized with 18 g. of silver chlorate and 0.3 g. of osmic acid. The reaction mixture yielded 3 g. of allitol and no D,L-mannitol. We may therefore assign the meso configuration to the divinylglycol melting at 18°, since on hydroxylation it yielded allitol, but not D,L-mannitol. 

He also predicted from this geometric theory that the reduction of these sixteen aldohexoses would lead to only ten hexitols, of which two would be meso structures [7 = 13 (allitol) and 8 = 14 (dulcitol)], and the... 

Pure allitol (meso configuration m. p. 150-151°) was described for the first time by Lespieau and Wiemann, who synthesized it by the hydroxylation of one of the stereoisomeric forms of divinylglycol. Its structure was established rigorously by Steiger and Reichstein when they demonstrated its identity with the product obtained by the reduction of D-allose. 

The stereochemistry of the alditols formed by reduction of the aldehyde group is instructive. In the pentose series, xylitol and ribitol are meso forms, whereas D-arabinitol and D-lyxitol are identical. In the hexose series, allitol and galactitol are meso forms, and D-altritol and D-talitol are identical, as are D-glucitol and L-gulitol. 

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