In continuation of the studies being made in this Laboratory on the openchain forms of the sugar acetates, we wish to report in this paper the synthesis of the crystalline free aldehyde form of Z-arabinose tetra-acetate. Although the ring formulas for the monosaccharides meet the requirements imposed by experimental data in most cases, there are nevertheless many reactions which are best explained by the assumption of an open-chain form in equilibrium with the ring or lactal structures. This is particularly true of the reactivity of the sugars in alkaline media. The changes that Z-arabinose undergoes in alkaline solutions have been studied by Nef2 and by Evans and Conaway.3 These changes are best explained on the basis of enolic equilibria, which then require an intermediate open-chain formula, as follows This paper presents evidence that the free aldehyde form of Z-arabinose is capable of stable existence in the form of its crystalline acetate, CH2OAC-(CHOAc)3-CHO.The methods used were similar to those reported in the case of glucose4 and of galactose.5 Arabinose ethyl mercaptal was acetylated and the thioethoxy groups replaced by an oxygen atom through reaction with mercuric chloride6 and water under controlled conditions. The modifications introduced to obtain the arabinose compound consisted in the use of less water in the reaction and a slightly different method of isolation.The free aldehyde form of Z-arabinose acetate or aldehydo5-Z-arabinose tetra-acetate crystallizes in prismatic needles and has widely differing constants from the two known lactal acetates of this sugar. Chavanne7 first obtained crystals of the -form of arabinose tetra-acetate, but in too
1. 2,4-Dinitrochlorobenzene, a reagent previously proposed by the authors, has now been studied more extensively and found to be valuable for both mono-and di-mercaptans.2. Melting point and analyses are presented for eighteen 2,4-dinitrophenyl alkyl and aryl thio-ethers. In addition, data are presented for nine of the corresponding sulfones.Chapel Hill, N. C.
scientific equipment destroyed by an earthquake in Skopje, Yugoslavia, negotiations between UNESCO and the government of Yugoslavia have cleared the way for immediate shipment of gifts in kind to the University of Skopje. Scientists around the world are reminded that there is still great need for equipment for teaching and research. Lists of items required by the various departments will be provided at once, along with instructions for shipping. Please write to UNESCO
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