Thermodynamics of solution of two forms of DL-α-amino-n-butyric acid in water

Abstract

Two crystalline polymorphic forms of DL-α-amino-n-butyric acid have been obtained and have been shown to be identical to the A-form and B-form previously described by Iitaka and coworkers. The two forms differ in heat of solution and in their solubility in water. We find that for the A-form at 298 K, ΔH°s= 374 cal mol–1, ΔG°s= 1772 cal mol–1 and ΔS°s=–4.7 cal K–1 mol–1 and for the B-form ΔH°s= 1653 cal mol–1, ΔG°s= 1883 cal mol–1 and ΔS°s=–0.8 cal K–1 mol–1. Although the B-form is the stable form at 298 K, it is predicted from the above measurements that the A-form should be the stable form above ∼ 326 K.