Abstract:

Aldehydes can undergo a rapid reversible nucleophilic addition reaction with sodium bisulfite, which can be used to remove aldehydes from the mixture. The kinetics of these reactions mostly focused on low carbon aliphatic aldehydes and aromatic aldehydes, lacking of kinetic studies on high carbon aliphatic aldehydes, besides, the commonly analytical methods such as iodine titration and ultraviolet spectrophotometry had many limitations in application. In this paper, heptaldehyde was taken as the research object, and the reaction processes between heptaldehyde and sodium bisulfite were monitored by means of ReactIR at 283.15—298.15 K. Through the calculation and fitting of the experimental data, the rate constants and equilibrium constants of the reaction at different temperatures were obtained, and the kinetic equation of the reaction was determined, which provided a theoretical basis for the separation of heptaldehyde. The results show that as the reaction temperature increases, the reaction rate of heptaldehyde increases, while the equilibrium conversion rate decreases. The addition reaction of heptaldehyde and sodium bisulfite is an exothermic process, and the reaction heat is -60.01 kJ?mol^-1. The activation energy of the forward reaction is 34.68 kJ?mol^-1, and the pre-exponential factor of the forward reaction is 1.369×10⁷ L?mol^-1?min^-1. The activation energy of the reverse reaction is 94.69 kJ?mol^-1, and the pre-exponential factor of the reverse reaction is 2.500×10¹⁵ min^-1.

Key words: heptaldehyde, sodium bisulfite, nucleophilic addition reaction, kinetics, equilibrium

摘要：

醛能与亚硫酸氢钠发生快速的可逆亲核加成反应，该反应可用于去除混合物中的醛。目前醛类加成的动力学研究多集中于低碳醛或芳香醛，缺少高碳脂肪醛的相关数据，且常用的分析方法如碘量法和紫外分光光度法应用局限性大。以庚醛为研究对象，利用在线红外光谱仪，实时监测了283.15~298.15 K温度下庚醛与亚硫酸氢钠的加成反应过程，通过对实验数据的计算与拟合，求得不同温度的反应速率常数和平衡常数，确定了反应的动力学方程，为庚醛的分离应用提供理论基础。结果表明，随着反应温度升高，庚醛反应速率增大，而平衡转化率减小。庚醛与亚硫酸氢钠的加成反应为放热过程，反应热为-60.01 kJ?mol^-1。正反应的活化能为34.68 kJ?mol^-1，指前因子为1.369×10⁷ L?mol^-1?min^-1，逆反应的活化能为94.69 kJ?mol^-1，指前因子为2.500×10¹⁵ min^-1。

关键词: 庚醛, 亚硫酸氢钠, 亲核加成反应, 动力学, 平衡