Rhamnose monohydrate

The racemic mixt occurs free in poison sumac and is combined in the form of glycosides of many plants. It can be prepd by boiling xanto-rhamnin with dil sulfuric acid, filtering off the solids formed and saturating the filtrate with Ba carbonate so as to form a syrup from which the 1-rhamnose crystallizes. The prod is purified by extraction with ethanol and recrystn (Ref 2). The a-form is obtd from the racemic mixt by crystn from a hot ethanol soln. The (5-form is prepd by heating a-rhamnose monohydrate on a steam bath and then crystg it from an anhyd acet and ethanol mixt (Refs 4 5)... 

M. L. Wolfrom and A. Thompson, 6-Deoxy-ct-L-mannose (ct-L-Rhamnose) monohydrate, Methods Carbohydr. Chem., 1 (1962) 202-204. 

Form, prepd by heating a-rhamnose monohydrate on a steam bath crystallized from anhydr acetone + alcohol. Needles, mp 122-126 (rapid heating). +31.5 (1 min. p — 10). After a short time the rotation adjusts to the same final value as a-rhamnose. The 0-form is hygroscopic and changes into crystals of the a-modification upon exposure to moist air. 

Monohydrate, needles from methanol, mp 268 270 [< ] -100 (0,07 g in 10 ml glacial acetic acid) (< ) -87 (0.05 g in pyridine). Practically insol in water and the usual organic solvents. Sol in nitrobenzene, phenol, aniline, pyridine, coned adds and alkalies. The water of crystn cannot be removed at KXT in vacuo Over P,0. (Merz) may be removed at 138 in high vacuum (Zempldn). Hydrolysis gives 5,7-dihydroxy -4 -methoxyflavone, D-glucose, and L-rhamnose. 

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