A SEMIEMPIRICAL INVESTIGATION OF THE MECHANISMS FOR THE ALKYLATION OF ARYLAMINES

The alkylation of arylamines is an important reaction in many large scale industrial processes. Three possible mechanisms are evaluated at the semiempirical level using the alkylation of aniline with ethylene as a model system. A molecular orbital analysis is performed for each mechanism to determine the appropriate type of wavefunction required to describe the transition state. Successive levels of refinement in search algorithms are used to locate the transition state on a potential surface with up to 60 degrees of freedom. A reasonable mechanism for the AlCl3-catalyzed Friedel-Crafts alkylation is shown to be analogous to a Diels-Alder [4 + 2] concerted cycloaddition after initial beta-elimination of HCI. The Bronsted acid-catalyzed reaction shown is likely to occur via a mechanism similar to the Ene reaction, rather than initial protonation of the olefin followed by electrophilic addition to a nearby aromatic ring. (C) 1995 John Wiley & Sons, Inc.