Study on addition reaction kinetics of heptaldehyde and sodium bisulfite

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. © 2021, Chemical Industry Press Co., Ltd. All right reserved.