A SEMIEMPIRICAL INVESTIGATION OF THE MECHANISMS FOR THE ALKYLATION OFARYLAMINES

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