The Oxidation of Sugars . I . the Electrolytic Oxidation of Aldose Sugars in the Presence of a Bromide and Calcium Carbonate

A new method has been devised for the preparation of calcium salts of the sugar acids in which the sugar is electrolytically oxidized in the presence ofcalcium carbonate and a bromide. The sugar is oxidized in manner analogous to the well-known bromine oxidation, but since only a small quantity of bromide is used as a catalyst, the new method has the decided advantage that the reaction product does not contain any objectionable substances derived from the oxidant. On account of this, the separation of the product is greatly simplified, as shown by the fact that calcium gluconate, galactonate, mannonate, rhamnonate, and arabonate are easily crystallized on evaporation of the solutions resulting from the oxidation of the respective sugars. The preparation of the calcium salts of xylonic, lactobionic, and maltobionic acids is also given. The raw materials, with the exception of the bromide, which is used only in small quantities as a catalyst, are relatively cheap. This fact, in conjunction with the high current efficiency and high yield, should make the method of considerable commercial value for the preparation of calcium gluconate and related products.