Thermal Stability of Amine Compounds and Dichloromethane

Abstract

Dichloromethane is employed as a common solvent in the chemical industry. Due to its low boiling point of 39.7 °C it can be used for the extraction of amine compounds. However, caution is advised while handling and storing amine compounds diluted in dichloromethane, since there were incidents with unexpected reactions between amine compounds and dichloromethane in the past (Bretherick’s Handbook of Reactive Chemical Hazards, 2007). For instance, an exothermic reaction occurred during a distillation at 30 °C of a mixture of ethylene diamine and dichloromethane, which subsequently deflagrated (Nolan, 1983). In a later study, the decomposition energy was determined as ?HR = -343 kJ/mol (4.04 kJ/g) based on the amount of dichloromethane (Heskey, 1986). Further incidents in the near past are also known among experts, including the reaction of complex molecules with amine functional groups with dichloromethane are also known among experts (Neuenfeld, 2008).Figure 1: Blown up waste drum with dichloromethane, morpholine, methanol as main components. (Neuenfeld, 2008)This shows that there is largely unknown potential risk, which requires a more detailed investigation. Therefore the reaction between different amine compounds and dichloromethane was investigated, in order to determine the thermal stability and the reactivity of the amine compounds toward dichloromethane. The thermal stability was investigated by DSC (differential scanning calorimetry). For this purpose, different amine compounds and different molar percentages of amine and dichloromethane were selected. The amine compounds in this study were divided in two categories: aliphatic amines, which also include cyclic amines, and aliphatic-aromatic amines. Two main variables were first compared, the onset of the effect and its decomposition energy.The investigations show that for aliphatic-aromatic amines, the decomposition energy decreases with the molecular weight of the compound. Cyclic amines show the highest decomposition energy, which is also related with the lowest onset temperature. The results show significant decomposition reactions in ranges of the boiling of dichloromethane. Such reactions were further investigated using different adiabatic calorimetric techniques such as VSP2 (Vent Sizing Package) and Dewar calorimetry.