Effect of morpholine, and 4-methylmorpholine on urethane formation: a computational study

Abstract

Abstract. A theoretical study of urethane formation through the reaction of phenyl isocyanate and butan1ol was carried out, without and in the presence of morpholine, and 4methylmorpholine catalysts. The reaction with and without catalysts was studied at BHandHLYP/631G(d) and G3MP2BHandHLYP levels of theories. The reaction mechanism in the presence of catalysts difers signifcantly from the catalystfree case and includes seven steps. The catalystfree system was investigated along with the catalytic process, the geometries were optimized, and the corresponding thermodynamic properties were calculated. Calculated reactant complexes were compared with crystal structures of morpholine, and 4methylmorpholine complexed with diols found in the literature. The structures were strikingly similar and thus, the validity of the proposed and studied general organocatalytic reaction mechanism was partially verifed. Meanwhile, an irregularity in the energy profle occurred due to the zwitterionic nature of an intermediate. To handle the irregularity, a correction was implemented which handles the appearance of a zwitterionic structure and the corresponding energetic properties. The results showed that morpholine is less efective catalyst compared to 4methylmorpholine, which can be associated with the diference in their PA (1523.95 and 963.07 kJ/mol, respectively). The current results prove the important role of amine catalysts in urethane synthesis which can be applied in polyurethane catalyst design and development.