Molecular Simulation of Potential Energies, Steric Changesand Substituent Effects in Urethane Formation Reactionsfrom Isocyanates

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  • SOMEKAWA Kenichi
    Graduate School of Science and Engineering, Kagoshima University 1-21-40 Korimoto, Kagoshima 890-0065, Japan
  • MITSUSHIO Masaru
    Graduate School of Science and Engineering, Kagoshima University 1-21-40 Korimoto, Kagoshima 890-0065, Japan
  • UEDA Takehiko
    Graduate School of Science and Engineering, Kagoshima University 1-21-40 Korimoto, Kagoshima 890-0065, Japan

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  • イソシアナートのウレタン化反応過程におけるエネルギー，立体変化および置換基効果の分子シミュレーション

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<p>Urethane resins show peculiar coatings, adhesives and cushions. The urethane formations from isocyanates with alcohols etc. are accompanied by carbamic acids, the esters, and their decomposed compounds for material performances. The steric and energy changes in the basic reaction processes of isocyanates、and the catalytic reaction by triethylamine were speculated by MOPAC-PM6 simulation, and the simulations compared with them by other methods. Thus, K. C. Frischs' analysis that the reactivities between substituted phenylisocyanates and an alcohol are related to Hammett substituent constants,σ (R = 0.97), was correlated with Mulliken's electronegativity, (IP + EA)/2 by PM6 method (R = 0.97). The reactions were speculated to proceed via hydrogen-bondings and six-membered ring 1:2 complexes of isocyanate with alcohol (water or amine) and by the activation energy of Ea = 4∼13 kcal mol−1. The higher reactivity is pointed out by the calculated smaller Ea value. The calculations including PM6-D3H4 were also effective for the reactivity of X-NCO. The 4 molecules' catalytic reaction of PhNCO with 2MeOH by Et3N was speculated to be accelerated from Ea = 7.23 kcal mol−1 to Ea = 3.92 kcal mol−1. The transition state structure showed the easy proton transfer by Et3N. Hydrolyses of carbamic acid and the methyl carbamate ester were compared for urethane properties, and the decomposition of the acid to diphenylurea via aniline etc. and the stability of the ester were speculated by the calculated Ea and transition state structures.</p>

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