COMPUTATIONAL REACTION MECHANISM STUDY OF THE SCHIFF BASE FORMATION BETWEEN PARA-SUBSTITUTED ANILINE AND PYRROLE-2-CARBALDEHYDE

Musa E. Mohamed* and Kamal Khalifa Taha

ABSTRACT

Computational reaction mechanism study based on the Restricted Hartree- Fock calculations (RHF/3-21G) of the formation of Schiff base of para-methoxyaniline, para-methylaniline and anline with Pyrrole-2-carbaldehyde was conducted. The reaction mechanism was found to involve two steps, namely: (1) formation of a carbinolamine and (2) dehydration of the carbinolamine to give the final schiff base, through six-membered ring transition states. The carbinolamine is intermediate and dehydration is rate determining step of the reaction. The formation of Schiff base between the para-substituented aniline and pyrrole adehyde requires the contribution of one auxiliary water molecule as a true reactive in order to facilitate proton transfer, and allows the nucleophilic attack of the incoming amine to carbonyl group. The para-methoxy substituent has less energy barrier than the other two substituents, according to more electron withdrawing effect.

Keywords: Schiff base, Six-membered ring transition state, Restricted Hartree-Fock.