Tombari E, Salvetti G, Ferrari C, Johari G P
Istituto per i Processi Chimico-Fisici del CNR, via G. Moruzzi 1, 56124 Pisa, Italy.
J Phys Chem B. 2007 Jan 25;111(3):496-501. doi: 10.1021/jp067061p.
We report a real time study of the enthalpy release and heat capacity during the course of HCl-catalyzed hydrolysis of sucrose to fructose and glucose. Measurements were performed during both isothermal conditions and during slow heating and then cooling at a controlled rate. The reaction rate constant of the first-order kinetics follows an Arrhenius relation with activation energy of 109.2 kJ/mol of sucrose. On hydrolysis, the enthalpy decreases by 14.4 kJ/mol of sucrose at 310 K, and the heat capacity, Cp, increases by 61 J mol-1 K-1 of sucrose in the solution. The enthalpy of hydrolysis decreases with increase in the temperature and DeltaCp on hydrolysis increases. The effects are attributed to change in the configurational and vibrational partition functions as one covalent bond in sucrose breaks to form two molecules, which then individually form additional hydrogen bonds and alter the water's structure in the solution. Cp of the solution increases with temperature less rapidly before sucrose hydrolysis than after it. This may reflect an increase in the configurational contribution to Cp as the hydrogen bond population changes.
我们报告了一项关于盐酸催化蔗糖水解为果糖和葡萄糖过程中焓释放和热容的实时研究。在等温条件下以及在缓慢加热然后以可控速率冷却的过程中进行了测量。一级动力学的反应速率常数遵循阿仑尼乌斯关系，蔗糖的活化能为109.2 kJ/mol。水解时，在310 K下，每摩尔蔗糖的焓降低14.4 kJ，溶液中每摩尔蔗糖的热容Cp增加61 J mol⁻¹ K⁻¹。水解焓随温度升高而降低，水解时的ΔCp增加。这些影响归因于蔗糖中的一个共价键断裂形成两个分子时，构型和振动配分函数的变化，这两个分子随后各自形成额外的氢键并改变溶液中水的结构。蔗糖水解前溶液的Cp随温度升高的速度比水解后慢。这可能反映出随着氢键数量的变化，构型对Cp的贡献增加。
