The Catalytic Reaction Mechanisms of Isocyanurate Formation Catalyzed by Potassium Catalyst Elucidated by Computational Chemistry

摘要

Isocyanurate, a robust chemical structure, is widely applied for many kinds of polyurethane and its related materials as cross-linking agent, flame-retardant, and so on, because of its quite stable property. It is well known that isocyanurate can be formed by trimerization of isocyanates by using some kinds of catalyst such as potassium carboxylates or quaternary ammonium salts. However the sequence of the catalytic reaction mechanisms of the isocyanurate formation has not been clearly investigated, probably because the mechanism has large number of reaction steps and is highly complicated. Computational chemistry method is particularly useful for the elucidation of such complicated mechanism because it can decompose the whole reaction path into elemental reactions. In this investigation, the detailed reaction mechanisms of isocyanurate formation from HDI catalyzed by potassium acetate have been elucidated by application of Density Functional Theory (DFT) using GAUSSIAN09 program. It was revealed that potassium atom plays an important function of assembling isocyanate groups one by one, and Gibbs free energy of the reaction system gradually rises step by step along the reaction path. At the final step of the sequence isocyanurate ring forms and Gibbs free energy falls sharply.