5-氨基间苯二甲酸钠和5-羟基间苯二甲酸钠的热力学性质

在水溶液中合成了5-氨基间苯二甲酸钠(1)和5-羟基间苯二甲酸钠(2)固态样品,元素分析和TG-DTG确定其组成符合C8H5O4NNa2·H2O(1)和C8H4O5Na2·H2O(2).用精密自动绝热热量计测定了它们在78～400K温区的低温热容,将实验值用最小二乘法拟合,得到热容随温度变化的多项式方程,用此方程进行数值积分,得到该温区内每隔5K的舒平热容值和各种热力学函数值.用RD496-2000型微热量计测定了样品在298.15K时的标准摩尔溶解焓分别为ΔsolHmθ(1,s)=-44.552±0.164kJmol-1和θΔsolHm(2,s)=-36.055±0.154kJmol-1,计算了其水合阴离子标准摩尔生成焓分别为θΔfHm(C8H5O4N2-,aq)=-684.56±1.67kJmol-1和ΔfHmθ(C8H4O52-,aq)=-1263.43±2.13kJmol-1.用RBC-II型精密转动弹热量计测定了样品的恒容燃烧热分别为ΔcU(1,s)=-13382.14±5.28Jg-1和ΔcU(2,s)=-10339.15±4.15Jg-1,计算了它们的标准摩尔燃烧焓和标准摩尔生成焓分别为ΔcHmθ(1,s)=-3252.90±1.28kJmol-1和θΔcHm(2,s)=-2522.64±1.01kJmol-1,ΔfHmθ(1,s)=-1406.46±1.66kJmol-1,θΔfHm(2,s)=-1993.79±1.46kJmol-1.

Thermodynamics of sodium 5-aminoisophthalic acid monohydrate and sodium 5-hydroxyisophthalic acid monohydrate

The solid samples sodium 5-aminoisophthalic acid monohydrate （C8H5O4NNa2·H2O,s） and sodium 5-hydroxyisophthalic acid monohydrate （C8H4O5Na2·H2O,s） were prepared in water.The composition of the compounds were identified by element analysis and TG-DTG.Low-temperature heat capacities of sodium 5-aminoisophthalic acid monohydrate （C8H5O4NNa2·H2O,s） and sodium 5-hydroxyisophthalic acid monohydrate （C8H4O5Na2·H2O,s） were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 398 K.The experimental values of the molar heat capacities in the temperature region of 78-378 K were fitted to a polynomial equation of heat capacities （Cp,m） with the reduced temperatures （X）,X=f（T）],by a least-squares method.The smoothed molar heat capacities and thermodynamic functions of the compounds （C8H5O4NNa2·H2O,s） and （C8H4O5Na2·H2O,s） were calculated based on the fitted polynomial.The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the samples relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K.The constant volume energies of combustion of the compounds at T=298.15 K was measured by a precise rotating-bomb combustion calorimeter to be-cU（C8H5O4NNa2·H2O （s））=-13382.14±5.28 J g-1 and-cU（C8H4O5Na2·H2O （s））=-10339.15±4.15 J g-1.The standard molar enthalpies of combustion of the compounds were determined to be Δc Hmθ（C8H5O4NNa2·H2O,s）=-3252.90±1.28 kJ mol-1 and θ Δc Hm（C8H4O5Na2·H2O,s）=-2522.64±1.01 kJ mol-1.The standard molar enthalpies of formation of the compounds were calculated to be Δ f Hmθ（C8H5O4NNa2·H2O,s）=-1406.46 ± 1.66 kJ-mol-1 and Δ f Hmθ（C8H4O5Na2·H2O,s）=-1993.79±1.46 kJ-mol-1 in accordance with Hess＇law.The standard molar enthalpies of dissolution of the compounds,θ Δ sol Hm （C8H5O4NNa2·H2O,s） and Δ sol Hmθ （C8H4O5Na2·H2O,s）,have been determined as being-44.552±0.164 kJ mol-1 and-36.055±0.154 kJ mol-1 by an RD496-2000 type microcalorimeter.Finally,the standard molar enthalpies of hydrated anions of the compounds were determined as being Δ f Hmθ（C8H5O4N2-,aq）=-684.56±1.67 kJ mol-1 and θ Δ f Hm（C8H4O52-,aq）=-1263.43±2.13 kJ mol-1,from the standard molar enthalpies of dissolution and other auxiliary thermodynamic data through a thermochemical cycle.