Anhydro compounds phenylosazones

The anhydrolactose phenylosazone was also obtained by the deacetylation of lactose phenylosazone heptaacetate. The anhydro compound gave a pentaacetate, thus proving that an oxide ring is present. 

Although Fischer described a lactose phenylosazone anhydride in 1887, little attention was paid to substances of this type until 1935 when Diels and Meyer reported the isolation of monoanhydrides of D-glucose phenylosazone, D-galactose phenylosazone, D-xylose phenylosazone, L-arabinose phenylosazone, lactose phenylosazone, and cellobiose phenylosazone, as well as a dianhydride of maltose phenylosazone, by boiling the corresponding osazones in alcoholic solution with a little sulfuric acid. Because of the apparent identity of the D-glucose phenylosazone anhydride with the 3,6-anhydro-D-glucose phenylosazone of Fischer and Zach, Diels and Meyer formulated these compounds as 3,6-anhydrides. 

This compound was isolated by Diels and Meyer " on boiling o-glucose phenylosazone in methanol containing traces of sulfuric acid. They believed it to be identical with 3,6-anhydro- o-glucose phenylosazone, which had previously been prepared by other means." After observing differences in the physical properties of the two compounds, they suggested formula XVII, which they modified a year later " by proposing the pyrazole structure XVIII. This was found to be inadequate for several reasons, and the bicyclic formula XIX, or XX, was put forward by Percival." ... 

The formazan reaction, again, was found suitable for clarifying these points. Diels anhydro- D-glucose phenylosazone, like n-glucose phenyl-osazone, does not react in pyridine solution, while in an alkaline ethanol medium an osazone formazan is obtained which crystallizes as black nee-dles. Mild acetylation of this compound yields the black diacetate of Diels anhydro- D-glucose phenylosazone formazan. Analysis showed both acetyl groups to be oxygen-linked. 

The fact that the formazan is formed ehminates structures XVII, XVIII, and XXI, which do not meet the conditions for this reaction. This fimiishes dired evidence in place of the indirect evidence on which Hardegger and Schreier had discarded structures XVIII and XXI. The bicyclic structure XIX, and XX, proposed by Percival" can be dismissed on comparison of the ultraviolet spectra. This compound, after coupling, should contain the two chromophoric groups of the simple formazans, whereas osazone formazans contain three of them. Anhydro- D-glucose phenylosazone formazan and its diacetate display practically the same maxima (maxima at 335 and 405 ran and 340 and 405 m/x, respectively) as does the indisputably-acyclic pyruvaldehyde phenylosazone formazan (maxima at 335 and 410 m/t), and these peaks differ substantially from the values for the simple sugar for-... 

Anhydro-osazones are also obtained when osazones are refluxed with acetic acid thus, di-0-acetyl-3,6-anhydro-n-n6o-hexulose 1-iV -acetyl-phenylosazone (92) is formed, together with the dianhydro-osazone (described on p. 178), from n-aroWwo-hexulose phenylosazone (43) and boiling acetic anhydride. On deacetylation, compound (92) yields Diels anhydro-osazone (90), and (92) can be prepared from the latter by acetylation with boUing acetic anhydride. 

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