Rate of Formation of Carbon Dioxide By PER FINHOLT, ROLF B. PAULSSEN, INGER ALSOS, and TAKERU HIGUCHI*
It is shown that the rate of cFrbon dioxide formation in aqueous solutions of ascorbic acid under oxygen-free conditions closely arallels the loss of the acid from the system at a PH lower than 7. In strongly altaaline solutions, less than one molecule of carbon dioxide seems to be produced from each molecule of the acid. In addition to the rate data, temperature dependencies under varying pH conditions are reported.
HIS PAPER is concerned with the rate of Tevolution of carbon dioxide during breakdown of ascorbic acid in oxygen-free aqueous solutions. In a previous communication (l), the over-all loss of the acid from these systems was treated. The production of the gas itself aside from the loss of the vitamin is of serious concern in pharmaceutical formulation since it represents a hazard in tightly sealed containers.
Several authors have shown that carbon dioxide is one of the products formed by the decomposition of ascorbic acid. Taylor et al. (2) followed the evolution of the gas while heating ascorbic acid in 12% hydrochloric acid in a stream of nitrogen. Carbon dioxide evolved was absorbed in absorption tubes, which were weighed at 0.5 hour intervals. The evolution of carbon dioxide from ascorbic acid rapidly reached 28% by weight, after which it was slow for many hours more, finally attaining a total value in excess of 3001,. If only the lactonized carboxyl group supplied carbon dioxide, the evolution should have been 25.0%. The results indicate that the carboxyl group decomposes rapidly and that there is a further slow decomposition evolving more carbon dioxide.
Flores and Brunner (3) tested the stability of partially neutralized 10% ascorbic acid solutions by heating in an autoclave a t 120' for 1 hour. Carbon dioxide formed was absorbed in 20% sodium hydroxide solution in a Lunge nitrometer. The authors found the maximum amount of carbon dioxide formed and the maximum decrease in the ascorbic acid concentration at pH 4. As no buffer substances were added to the solu-