ウレタン化の反応機構に関する計算化学的および反応速度論的研究

摘要

イソシアネート基と水酸基は，1モルずつが反応して1モルのウレタン結合を形成し(反応式1)，多官能イソシァネート化合物と多官能アルコールが反応すれば，高分子量化してポリウレタンとなる。それぞれが2官能であれば，原則として直鎖状ポリウレタンが形成される。一方，その反応機構が実際にはどのようになっているかという検討，すなわち全体の反応を素反応に分解した上で，それぞれの素反応についての構造やエネルギーの変化に関する検討は，これまで十分になされているとは言えない。%Reaction mechanisms of urethane formation reaction from isocyanate group and hydroxy group have been analyzed in detail by means of computational chemistry and kinetic experiment using ~1H-NMR. A six-membered pseudo-ring transition state (TS) structure constructed from 1 mol of isocyanate and 2 mol of hydroxy group was found to be the most rational, because the activation Gibbs energy via the TS agrees with that obtained through the kinetic experiment. The computational method shows that urethane group has the ability, like hydroxy group, to make the six-membered pseudo-ring TS and that the reaction rate should be accelerated by constructing the TS structure. However the acceleration ability of urethane group was found to be inferior to that of hydroxyl group. The results of the kinetic experiment showed that no acceleration of reaction by the generated urethane group was observed. This result supports that obtained via computational chemistry. In addition, it was found by the kinetic experiment that DMSO accelerates the reaction but that acetone has the opposite effect.