title: Crystalline 2,3:4,5-di-O-isopropylidene-DL-arabinose diethyl dithioacetal: some reactions of acetal derivatives of arabinose.
abstract: Acetonation of the diethyl dithioacetals of D- and L-arabinose gives the corresponding 2,3:4,5-diisopropylidene acetals (2a and 2b) as oils having [alpha]D +82 and -81 degrees, respectively; in admixture, the enantiomers form a well crystallized racemate, m.p. 43-45 degrees. The initial product of acetonation is the 4,5-monoisopropylidene acetal. Demercaptalation of 2a with mercury(II) chloride-cadmium carbonate gives 2,3:4,5-di-O-isopropylidene-aldehydo-D-arabinose (5) in high yield, but the literature procedure employing mercury(II) chloride-mercury(II) oxide affords a mixture of 5 and 1,2:3,4-di-O-isopropylidene-beta-D-arabinopyranose (6). A trace of acid readily and completely converts the aldehydo derivative 5 into the cyclic diacetal 6.
mesh_terms: D000080:Acetals; D001089:Arabinose / Q000031:analogs & derivatives*; D055598:Chemical Phenomena; D002621:Chemistry; D003460:Crystallization
chemical_list: D000080:Acetals; D001089:Arabinose