THEORETICAL STUDY OF THE REACTION MECHANISM OF SUBSTITUTED ISOCYANATES AND ALCOHOLS

Abstract

Reactions of substituted alcohols (R-OH, where R = CH 3 , (CH 3 ) 2 CH, SiH 3 CH 2 , NH 2 CH 2 , or FCH 2 ) and isocyanates (X-NCO where X = CH 3 , CH 2 F, C 6 H 5 , SiH 3 or SiH 3 CH 2 ) were studied using B3LYP/6-31G* calculations. Activation energies of the four-membered cyclic transition complexes (TS) were calculated. In case of substituted methanols and methyl isocyanate the activation energy and Gibbs free energy was found to increase in the following order: CH 3 < (CH 3 ) 2 CH < SiH 3 CH 2 < NH 2 CH 2 < FCH 2 . Substituting the isocyanates changed the order with respect to the activation energy and Gibbs free energy: FCH 2 < SiH 3 CH 2 < C 6 H 5 < CH 3 < SiH 3 . Solvent effect was also studied for the reaction of CH 3 NCO with CH 3 OH as an example using the SCRF (CPCM) method and chlorobenzene as solvent. The activation energy was found to be very similar in an environment of a low permittivity solvent (DG(sol)=38.00 kcal/mol) and in the gas phase (DG(g)=37.77 kcal/mol). Vibrational frequencies and forces in transition state were calculated. Enthalpies (DH) and Gibbs-free energies (DG) were determined at 298.16 K and 1 atm.