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.