Rhamnose phenylosazone

The product gave 5-methyl-L-rhamnose phenylosazone and formed a furanoside, but not a pyranoside, with methanolic hydrogen chloride. 

Pentoses and hexoaes could be distinguished readily with phenylhydra-zine. The compound hitherto called isodulcitol was identified as a sugar by means of phenylhydrazine, and was designated as rhamnose from that time on. Glucose and fructose (which H. Kiliani had discerned to be an aldohexose and a ketohexose, respectively) and mannose were found to give one and the same phenylosazone the three sugars, therefore, have the same configuration at carbon atoms 3, 4, and 5. 

D-Glucopyranosyl-ij rhamnose (sciUabiose). Phenylosazone, m.p. 165° C. obtained from a glycoside isolated from Scilla maritima L. Complete hydrolysis gives D-glucose and L-rhamnose (128). 

The rate of formation of osazones and their solubility, which differ substantially from case to case, can also serve as characteristic features useful in the identification of sugars. For example, osazones of glucose and fructose precipitate shortly after the heating of the solution, while saccharose requires 20 — 30 min of heating. Osazones of lactose and maltose precipitate only after cooling. In addition, phenylosazones of D-glucose, D-fructose, and D-mannose (which are identical) are insoluble in cold acetone, in contrast to phenylosazones of xylose, arabinose, rhamnose, and fructose. 

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