Osones, characterization

Another method of preparing keto aldonic acids, those of the 2-keto type, is by oxidation of the corresponding osone. Neuberg and Kitasato obtained 18 g. of calcium 2-keto-D-gluconate from 20 g. of the osone by the action of bromine at 20 . Similarly, 2-keto-n-galactonic and 2-keto-maltobionic acids were prepared by Kitasato. The substances were characterized generally as the brucine salts because of the amorphous nature of the calcium salts. 

Compounds of this class are characterized by their instability in acidic solutions, in which hydrolysis of the enolic ether grouping is followed by an elimination, to give unsaturated, osone derivatives, namely, 3,4-dideoxy-D-j(lj/cero-hex-3-enos-2-ulose (85, R = H) and its 6-methyl ether (85, R = Me), which are unstable, undergo ring contraction, and lose the elements of water to give, ultimately, 5-(hydroxymethyl)- and 5-(raethoxy-methyl)-2-furaldehyde (86, R = H or Me). For the monomethyl ether (84, R = H), this decomposition is complicated by a side reaction probably involving the formation of 3,6-anhydro structures. 

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