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Physicochemical Studies on the Decomposition of <i>p</i>-Aminosalicylic Acid and its Salts. II

1961; Pharmaceutical Society of Japan; Volume: 81; Issue: 4 Linguagem: Inglês

10.1248/yakushi1947.81.4_597

1347-5231

Nobuo Tanaka, Masayuki Nakagaki,

Analytical Chemistry and Chromatography

Following the previous report on the reaction velocity constant k to changes in pH in aqueous solution with constant ionic strength, in the decarboxylation reaction of p-aminosalicylic acid, experiments were carried out on variation in the concentration of sodium p-aminosalicylate and the minimum rate of decomposition was obtained in 0.5M concentration, as shown in Fig. 1. Various amounts of acetic acid-sodium acetate buffer were tested at a constant pH, as indicated in Table III, and the value of b=1.098 of equation (1) was obtained. The effect of the concentration of p-aminosalicylate was tested and the values of kobs. listed in Table I were obtained. From kobs. of 0.3M solutions at various temperatures, functions of temperature and H3O+ concentration were calculated and the values were interpolated in equation (2), from which equation (2′) was obtained. From this equation, kcalc. was calculated. The values of Eobs≠., ΔH≠, ΔS≠, and ΔR≠ at various temperatures were calculated from Eyring's absolute reaction rate theory and the values became the lowest at 0.5M concentration, as indicated in Table II.