二氯苯的蒸发焓和升华焓测定

DETERMINATION OF STANDARD ENTHALPIES OF VAPORIZATION AND SUBLIMATION OF THREE DICHLOROBENZENES

在进行分子内非键合相互作用的热化学研究中,我们已用燃烧量热法测定了各种取代的氯代苯在凝聚态的标准生成焓。为了排除分子间的相互作用,以得到准确的气态生成焓,需要这些化合物的标准蒸发焓或升华焓。文献中这类数据不多,且相当一部分是用测量蒸气压随温度变化按Clapeyron-Clausius方程计算的,不如直接量热法准确。对高取代的氯代苯,由于蒸气压很低,实验困难,数据更缺。为此,我们用量热法测定了三个二氯苯异构体的蒸发焓和升华焓,并结合已有的文献数据,建立了氯代苯标准蒸发焓和升华焓与其沸点的线性关系,估算了其余未知的数据。

By using an LKB 8721-3 vaporization calorimeter, enthalpies of vaporization of o-and m-dichlorobenzenes and enthalpy of sublimation of p-dichlorobenzene at 298.15K were determined as 48.53±0.12, 47.40±0.08 and 65.15±0.20 kJ mol^(-1) respectively. Data of ΔH_v° and ΔH_s° for chlorobenzenes reported here and in literature and their normal boiling points, t_b in ℃, can fit following two linear equations: ΔH_v° (kJ mol^(-1))=17.51+0.17269 t_b; ΔH_s° (kJ mol^(-1))=26.25+0.22349 t_b. From these equations other unknown values of ΔH_v° and ΔH_s° of chlorobenzenes have been estimated.