Dithioacetals solubility

Emil Fischer s initial studies [1] focused on dithioacetal formation from a variety of simple aldopentoses, aldohexoses, and aldoheptoses. The products were obtained by simply treating the sugar with an excess of ethanethiol in concentrated hydrochloric acid at low temperature ( 0°C). Many of these dithioacetals have low water solubility, crystallize spontaneously from the reaction mixtures, and can be isolated by simple filtration and washing with odd water. Fischer s key paper [1] also outlined most of the major reaction modes of the diethyl dithioacetal derivatives, later developed in detail, and thus paved the way for subsequent studies into this important class of sugar derivative. 

Water-soluble and low-melting dithioacetals (for example, derivatives of D-xylose) were virtually inaccessible to Fischer, as his technique of isolation relied on spontaneous separation of a crystalline product after dilution of the reaction mixture with water. Alternative isolative methods that were subsequently developed to deal with such problems of solubility include the use of lead carbonate,16 barium carbonate,17 or an anion-exchange resin18 to remove the acid catalyst, with subsequent removal of all or part of the diluent by evaporation, and the use of chloroform19 or ether20 to remove the excess of thiol from the water layer and induce crystallization of the product. 

D-fiflwco-Hexodialdose and n-manno-hexodialdose have been reported to give crystalline bis (diethyl dithioacetal) derivatives, by the addition of ethanethiol to the dialdose dissolved in cold concentrated hydrochloric acid. The difficultly soluble dithioacetal readily precipitated after a short time. Similarly, the crystalline bis (ethylene dithioacetal) of xylo-pento-dialdose was prepared. A liquid bis(diethyl acetal) of erj/tliro-tetrodialdose and of the isopropylidene acetal of n-i/ireo-tetrodialdose " have also been reported. 

Acid-catalyzed acetonation of L-sorbose gave a mixture of di-O-iso-propylidene and mono-O-isopropylidene derivatives, easily separated by the solubility of the former in benzene. Isopropylidenation of 2-acetamido-2-deoxy-D-xylose diethyl dithioacetal gave the 4-j5- -iso-propylidene derivative accompanied by some 3-0- 1-methoxy-1-methyl-ethyl ) -derivative (/i) when copper(Il) sulphate was used as catalyst with either propanone - 2,2-dimethoxypropane or propanone - 2-meth-oxypropene. The 3,4--0-isopropylidene derivative was obtained when sulphuric acid was used as catalyst in propanone - 2,2-dimethoxypropane. The former was considered the kinetic, and the latter the thermodynamic product. 3,4-0-Isopropylidene-L-fucopyranose... 

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