Amination of Ketene: A Theoretical Study

Abstract

The reactions of NH3, (NH3)2, and (H3N·H2O) with ketene have been studied by ab initio calculations. Attack by the dimer (NH3)2 or by (H3N·H2O) through six-membered cyclic transition states is found to be favored, with a preference of 12.8 kcal/mol for initial addition of (NH3)2 to the CO bond of the ketene giving the enol amide, as compared to initial addition to the CC bond to give the more stable amide directly. These results are in contrast to previous theoretical studies for the reaction of monomeric NH3 with ketene, in which direct addition to the CC bond was reported to be favored, and for the reaction of ketene with (H2O)2, in which addition to the CO bond is calculated to be only 1.9 kcal/mol more favorable than addition to the CC bond. The barrier via 10ts for the NH3-catalyzed rearrangement of the enol amide/ NH3 complex 6 to the amide is 16.5 kcal/mol above that of 6, consistent with the experimental observation of an intermediate in ketene amination, and the barrier for reversion of 6 to the ...