Catalyzed Reaction of Isocyanates (RNCO) with Water Mark E. Wolf,y Jonathon E. Vandezande,z,{ and Henry F. Schaefer III∗,y yCenter for Computational Quantum Chemistry, University of Georgia, 140 Cedar Street, Athens, Georgia 30602, USA z1st Source Research, 617 Hutton St., Raleigh, North Carolina 27606, USA {Zymergen, 5980 Horton Street, Suite 105, Emeryville, California 94608, USA E-mail:
[email protected] Phone: +1 706 542-2067. Fax: +1 706 542-0406 Abstract The reactions between substituted isocyanates (RNCO) and other small molecules (e.g. water, alcohols, and amines) are of significant industrial importance, particularly for the development of novel polyurethanes and other useful polymers. We present very high level ab initio computations on the HNCO + H2O reaction, with results tar- geting the CCSDT(Q)/CBS//CCSD(T)/cc-pVQZ level of theory. Our results affirm that hydrolysis can occur across both the N−C and C−O bonds of HNCO via con- certed mechanisms to form carbamate or imidic acid with ∆H0K barrier heights of 38.5 −1 and 47.5 kcal mol . A total of 24 substituted RNCO + H2O reactions were studied. Geometries obtained with a composite method and refined with CCSD(T)/CBS single point energies determine that substituted RNCO species have a significant influence on these barrier heights, with an extreme case like fluorine lowering both barriers by close to 20 kcal mol−1 and most common alkyl substituents lowering both by approxi- mately 4 kcal mol−1. Natural Bond Oribtal (NBO) analysis provides evidence that the 1 predicted barrier heights are strongly associated with the occupation of the in-plane C−O* orbital of the RNCO reactant.