ALDEHYDO-l-ARABINOSE TETRA-ACETATE¹

Abstract

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

Determination of Methoxyl and Ethoxyl Groups in Acetals and Easily Volatile Alcohols

“…Kinsman and Noller recommended the use of 0.1 ml. of bromine in the analysis of a sample of methoxyl or ethoxyl content equivalent to 20 ml. of 0.1 N sodium thiosulfate.…”

“…A second method of analysis, the so-called double distillation procedure, involves distillation of the alcohol (or corresponding alkyl iodide) from the substance being analyzed, into hot hydriodic acid, the remainder of the procedure being carried out as in the gravimetric procedure of Zeisel or the more rapid volumetric procedures of Viebock and co-workers (15,16). The double distillation procedure has been used for the determination of the lower alcohols in dilute aqueous solutions containing aldehydes (18), for the determination of the glycosidic methyl group in sugars (5), for the determination of acetals (6,9,20), and as one of several methods investigated to determine their reliability in the methoxyl analysis of organic liquids (3). The results obtained with the double distillation procedure have not been altogether satisfactory and the apparatus is troublesome to operate.…”