Anhydrides of pentitols

Until 1945 no anhydrides of xylitol or any other pentitol had been described. In that year a patent was granted to Grandel73 to make anhydrides of pentitols by heating them with a catalyst, followed by vacuum distillation. Xylitol on being heated with methionic acid followed by vacuum distillation gave monoanhydroxylitol and a dianhydro-(73) F. Grandel (to Alien Property Custodian), U. S. Pat. 2,375,915 (1945). 

Although no proof has been offered, the dianhydride of xylitol that was obtained by Grandel73 most probably has the meso 1,4 2,5-ring structure that is represented by XCII. 

The extension of the new technique of reductive desulfurization to other aryl 1-thiopentosides has resulted in the preparation of the remaining two possible 1,5-anhydropentitols, namely, 1,5-anhydro-D-arabitol and the meso 1,5-anhydroribitol. Fletcher and Hudson76 obtained 

5-anhydro-D-arabitol (XCIV) by the reductive desulfurization of either 2 -naphthyl l-thio-a-D-arabinopyranoside triacetate or phenyl 1-thio-a-D-arabinopyranoside triacetate. Later, Jeanloz, Fletcher and Hudson77 obtained the third isomeric 1,5-anhydropentitol namely, 1,5-anhydroribitol (XCY). It was obtained by condensation of tribenzoyl-/3-D-ribopyranosyl bromide with potassium 2-thionaphtholate, forming 2 -naphthyl 2,3,4-tribenzoyl-l-thio-/J-D-ribopyranoside which gave the anhydroribitol on being heated with Raney nickel in alcohol and subsequent debenzoylation. 

The anhydrides of hexahydric alcohols have already achieved marked usefulness in chemical industry and many of their derivatives show definite promise of value in industry and in medicine. 

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Although the polyhydric alcohols derived from sugars have been the subject of numerous investigations over many years, the inner ethers or anhydrides of these substances have been for the most part neglected, despite the fact that many of them were isolated and some description of their properties recorded before the advent of the twentieth century. In recent years, however, the anhydrides of polyhydric alcohols derived from sugars have received marked attention in several countries. Some indeed have achieved importance in chemical industry. Most interest has been centered on the anhydrides of pentitols and hexitols and this article will be restricted to a discussion of the chemistry of these substances. 

V. Tables of Properties of Pentitol and Hexitol Anhydrides and Their Derivatives. 225... 

An article on the anhydrides of polyhydric alcohols appeared in Volume 5 of this Series,1 and it is the purpose of the present article to bring the subject up to date. Wiggins article1 was limited to the anhydrides of the pentitols and hexitols the present article will include the anhydrides of tetritols and of alditols higher than the hexitols. However, anhydrides having the three-membered (oxirane) ring will not be considered, as they are discussed elsewhere in this Volume.13 2,5-Anhydrides of aldoses are also treated in this Volume.lb... 

However, if the reasons already given for the differences in ease of anhydridation of the pentitols are valid, 1,4-anhydro-D-arabinitol (8) should be the chief product, because, in 7, not only would there be a transannular, nonbonded interaction between the hydroxymethyl group and the 2-hydroxyl group, but the (bulky) hydroxymethyl group and the 3-hydroxyl group would be in eclipse. 

Hydrogenation of Glycals.—Hydrogenation of the glycals leads to the dihydro compounds, namely, the 1,5-anhydrides of the 2-desoxyhexitols, pentitols, etc. 

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