The Kinetics of Selected Chemical Reactions

PART I The Oxidation of Ascorbic Acid by Oxygen with Cupric Ion as Catalyst The initial rate of the reaction was found to be directly proportional to the concentrations of cupric ion and ascorbic acid and inversely proportional to the square of the hydrogen ion concentration. These facts have been explained by the assumption that in the initial stages the ascorbate ion is oxidized by the cupric ion to an ion with a semiquinone-like structure, which is rapidly oxidized by oxygen to dehydroascorbic acid. The cupric ion concentration is maintained constant through oxidation by oxygen of the cuprous ion formed. An observed increase in the specific reaction rate during the course of the reaction is attributed to the accumulation of hydrogen peroxide formed through oxidation of cuprous ion by oxygen. It was found that in the absence of oxygen an equilibrium involving ascorbic acid and cupric ion as well as dehydroascorbic acid, cuprous ion, and hydrogen ion, is apparently attained. However, the results of some of the numerous experiments carried out in an attempt to measure the equilibrium cast some doubt on the reliability of the equilibrium constants determined. PART II The- Photochemical Formation of Sulfuryl Chloride from Sulfur· Dioxide and Chlorine It was found that the photochemical formation of sulfuryl chloride from sulfur dioxide and chlorine proceeds at an immeasurably slow rate when the gases are dry. It was, however, found that if the vessel walls are wet with pure sulfuric acid the formation of sulfuryl chloride takes place at a slow but measurable rate. The effect of moisture on the rate, which had been observed by earlier workers, is explained in terms of the effect of the sulfuric acid produced by the reaction of water with chlorine and sulfur dioxide. Stationary states for the photochemical reaction are compared with the thermal equilibria. PART III The Thermal Isomerization of Dimethyl Maleate Catalyzed by Iodine Rates of isomerization of dimethyl maleate in cyclohexane solution and employing iodine as a catalyst were measured. Although these rates fluctuated to a considerable extent, the kinetics appear to be compatible with an iodine atom catalysis plus a catalysis or inhibition due to some as yet undetermined factor.