Effect of mixtures of water and organic solvents on the acidities of 5-membered heteroaromatic carboxylic acids

✍ Scribed by Chang Kiu Lee; Eun Hee Jeoung; In-Sook Han Lee

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2000
• Tongue: English
• Weight: 472 KB
• Volume: 37
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570370126

✦ Synopsis

Abstract

p__Ka__ values of various 5‐membered heterocyclic aromatic carboxylic acids (p__Ka__^s^) were determined in solutions of 20.3, 35.2, 50.1, 65.1, and 79.9 weight percent of organic solvents in water. The p__Ka__^s^ values show good linearity when they are ploted as a function of the dielectric constants of the mixed solvents methanol, ethanol, isopropyl alcohol, and tert‐butyl alcohol. On the other hand, the p__Ka__^s^ values show a poor correlation with the dielectric constants in aqueous acetonitrile, N,N‐dimethylformamide, dimethyl sulfoxide, and dioxane. The p__Ka__ values in pure water and in pure organic solvent could be calculated by extrapolation of the plot of the p__Ka__^s^ versus percentage of organic solvent. The p__Ka__^s^ values of 4‐ and 5‐sub‐stituted 2‐thiophenecarboxylic acids were also determined, and the ρ values are calculated in the same series of the solvents.