The benzylidene groups of the di-O,O-benzylidene derivative of D-xylose diethyl dithioacetal have been located at the 2,4:3,5 positions, and not at the 2,3:4,5 positions suggested by Zinner, Rembarz, Linke, Ulbricht. Partial hydrolysis yielded the 2,4-O-benzylidene compound, from which 3-O-β-D-xylopyranosyl-D-xylose (rhodymenabiose) was prepared.