2—氨基—2—甲基—1,3—丙二醇从280K到其熔点间的热容和相变

Heat Capacity and Phase Transition of 2-Amino-2-Methyl-1, 3-Propanediol from 280K to Its Melting Point

用绝热量热计测量了2-氨基-2-甲基-1,3-丙二醇从280K到其熔点间的热容和相变。首次发现该物质在352.89和353.72K处有一个双叉(bifurcated)型固-固相变,并准确测定其熔点为384.08K。双叉型固-固相变和固-液相变的相变焓经测定分别为(23.46±0.29)和(2.78±0.05)kJ·mol^(-1)。提出了“比例分配法”用以解析两个相变温度极其接近的一级相变的相变焓,并据此估算得组成双叉型相变的两个固-固相变的相变焓分别为(5.00±0.75)和(18.46±0.75)kJ·mol^(-1)。讨论了形成双叉型固-固相变的原因。

The heat capacity of 2-amino-2-methyl-1, 3-propanediol was measured from 280K to its melting point by means of an automated adiabatic calorimeter. A bifurcated solid-solid transition was found for the compound with the temperaturos of the maxima occurring at (352.89±0.01)K and (353.72±0.01)K. The total enthalpy of the bifurcated transition was determined to be (23.46±0.29) kJ·mol^(-1), and resolved into the enthalpies of two solid-solid transitions, solid Ⅲ→Ⅱ and solid Ⅱ→Ⅰ. The enthalpies and entropies of the transitions were determined to be (5.00±0.75) and (14.20±2.1)J·K^(-1)·mol^(-1) for the solid Ⅲ→solid Ⅱ, (18.46±0.75) and (52.2±2.1)J·K^(-1)·mol^(-1) for the solid Ⅱ→Ⅰ and (2.78±0.05) and (7.23±0.13) J·K^(-1)·mol^(-1) for the solid-liquid respectively. It may be assumod that there are O—H—O, N—H—O, O—H—N and N—H—N hydrogen bonds between the molecules of 2-amino-2-methyl-1, 3-propanediol. The difference in strength between O—H…O and N—H—N hydrogen bonds is considered to be a reasonable explanation of the bifurcated transition.