Color Reactions of Keturonic Acids and a Color Test Differentiating α- and β-Glucosides. ∗

Abstract

Color reactions of the keturonic acids have recently become of importance to biology and medicine. In previous papers we have shown that a series of these acids can be prepared from carbohydrates by oxidation of their aqueous solutions with bromine. 1 , 2 The solutions of the keturonic acids used in the experiments reported here were prepared as follows:

1% solutions of pure carbohydrates were placed in glass-stoppered flasks together with enough bromine to provide a small excess of liquid bromine throughout the experiments. These mixtures were kept in the dark for 42 days at 25 °C. They were then aerated with washed air (and at times with carbon dioxide) to remove the excess bromine and then neutralized with potassium hydroxide to pH 7, using a spot plate. The color tests were applied to aliquots, with the results given in Table I.

In the ferric chloride test of Fenton and Jones 2 we added one drop of 10% ferric chloride solution and 3 drops of 10% potassium hydroxide solution to 5 cc. of neutral sugar solution. The purple color obtained from oxidized glycerol solution indicates that hydroxypyruvic acid is formed 3 and the similar colors from oxidized erythritol, inositol and the pentoses suggest similar products in these cases. These keturonic acids, and also those from glucosamine and ascorbic acid, give green Molisch 4 tests. The Molisch colors from oxidized α- and β-methylhexosides are distinctly different.

Oxidation products from triite and tetrite alcohols give no ketose reactions; those from pentites, the Tashiro-Tietz reaction 4 ; those from hexites and heptites give both the Selivanoff 4 and Tashiro-Tietz reactions. Only keturonic acids from aldoheptoses give positive ketose reactions. Oxidized ketoses, together with their oligo- and polysaccharides, still give positive ketose reactions. The behavior of glucosans and ascorbic acid with these reagents is note-worthy.