564 D. L. MCDONALD, H. O. L. FISCHER VOL. 12 (I953) 



ponding pentose. The procedure involved acetylation of the hexose mercaptal, followed 

 by oxidation by means of monoperphthalic acid in ether, to produce an acetylated 

 disulfone. Treatment of this disulfone with hydrazine hydrate in methanol, followed 

 by splitting the anticipated hydrazone with benzaldehyde, gave a solution from which 

 the crystalline pentose could be isolated in good yield by deionization and concentra- 

 tion in vacuo. 



The present paper reports on an improvement of this degradation scheme, in which 

 the operations are simpler and much shorter, and the yield of pentose is equally as good 

 as that previously obtained. One change was in the use of perpropionic acid rather than 

 monoperphthalic acid. In the case of the latter oxidant, the phthalic acid formed is 

 difficult to remove unless the oxidation product is soluble in chloroform, in which case, 

 use can be made of the sparing solubility of phthalic acid in this solvent. The previously 

 used acetylated sulfones were soluble in chloroform and thus their purification involved 

 no difficulty. In the present communication, the unacetylated mercaptals were oxidized, 

 and consequently another oxidant had to be chosen and perpropionic acid proved highly 

 satisfactory. Perpropionic acid was used rather than peracetic acid, for there is much 

 less danger attending the distillation of the former reagent. 



When a hexose diethyl mercaptal such as that from D-mannose (I) was dissolved 



in hot dioxane, and the solution cooled, but not sufficiently to cause crystallization of the 

 mercaptal, the addition of perpropionic acid resulted in a rapid oxidation. Within a 

 few minutes, the resulting disulfone (II) crystallized in yields of about 90 per cent. The 

 exact nature of the oxidation product has not been worked out as yet, but two compo- 

 nents were usually present in the crystalline mixture, as evidenced by paper chromatog- 

 raphy. This complexity did not affect the subsequent steps, however. The air-dried 

 product was slurried in water, and a drop of aqueous ammonia was added. The mixture 

 undergoes a rapid change, with dissolution of the sugar derivative and concomitant 

 precipitation of bis (cthanesulfonyl) methane (III), which can be removed by chloro- 

 form extraction. Concentration of the aqueous layer in vacuo gives crystalline D-arabinose 

 (IV) in yields of 80-83%, having a rotation of — 102 to — 103°. The accepted specific 

 rotation of D-arabinose et equilibrium in water is — 104.5°. 



Thus, the free, unacetylated sugar disulfone has to be treated at room temperature 

 only with very dilute aqueous ammonia to cause complete splitting into bis-(ethane- 

 sulfonyl)-methane and the next lower sugar. In the case of the acetylated disulfones, 

 hydrazine or hydroxylamine was required for the degradation, and thus our experiences 

 are comparable to those of Wohland Wollenberg in that in each case the 2/;jacetylated 

 compounds were found to degrade much more readily than the acetylated ones. It is 



References p. 206. 



