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Vol. G8ing point determination with authentic 2,4-methylenexylitol caused no depression of this value. The yield was 2.8 g. (889$). The series of reactions constitutes a definitive proof that monomethylene-gluco-gulo-heptitol is 3,5-methylene-gluco-Qulo-heptitol.Although the expected dialdehydo oxidation product from 3,5-methylene-gluco-guZo-heptitol could not be crystallized, i t was isolated in a separate experiment in the Form of its di( phenylhydrazone). The latter compoui~d crystallized from 30 parts of alcohol as small, light yellou plates which melted with decomposition a t 188-190'. SummaryProof is presented that the monobenzylidene-gluco-gulo-heptitol (m. p. 21s') which Emil Fischer discovered is the 3,5-benzylidene acetal. The condensation of gluco-gulo-heptitol with formaldehyde also gives a high yield of a monoacetal which proves to be 3,5-monomethylene-glucocub-heptitol. These 3,5-monoacetals are those to he expected from generalizations relating the configuration of polyhydric alcohols and the structure of their derived benzylidene and methylene acetals.Crystalline 2,4-benzylidene-xylitol and a number of its derivatives have been described. RETHESDA, R~ARYLAND RECEIVED MAY 9, 1946 'CONTRIBUTIOS FROM THE STERLING-\VIS1 IIROP RESEaRCH [NSTIrUTE ]

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