The oxidation of sugars by cupric acetate-acetic acid mixtures

The study was undertaken to learn precisely upon what the oxidizing powers of cupric acetate and Fehling's solution depended. The addition of acetic acid to cupric acetate diminishes its speed of oxidation so that one sugar after another ceases to be oxidized at a rapid rate as more acid is added. The amount of acid that may be necessary to check the oxidation to any given rate depends on the concentration of the acetate; the more concentrated the acetate the more acid is required. McGuigan determined the amount of acid necessary to check oxidation of the various sugars in different concentrations of the acetate within a certain time (one half minute's boiling). The results showed that the sugars arranged themselves as follows according to the amount of acid necessary to check oxidation. Levulose (most acid required), galactose, glucose, maltose, lactose.

Solutions of different concentrations of acetate and acetic acid were prepared which would just fail to oxidize levulose to a visible reduction of cuprous oxide on one half minute's boiling. Similar solutions were prepared for the different sugars. Each of these solutions for any given sugar of one per cent, concentration had the same speed of oxidation.

The cupric ions in these solutions were measured by the electromotive force developed between the solution and a plate of copper. The hydrogen ions were determined by the inversion of cane sugar. From the figures thus obtained the result appeared that in all solutions oxidizing any one sugar with the same speed the decomposition tension of the cupric oxide in the solutions was a constant.

For the different sugars the following data for decomposition tension were obtained in those solutions that just failed to oxidize to a visible extent in one half minute's boiling.