COMPUTATIONAL BASED STUDY OF AMINO SUBSTITUENTS' POSITION ON QUINOLINE FOR INHIBITION OF ALUMINIUM CORROSION IN HYDROCHLORIC ACID SOLUTION

Abstract

Study of some aminoquinolines by quantum chemical method on inhibition of aluminium corrosion in hydrochloric acid and effect of amino group as substituent at 6,7 and 8 position on quinoline  was investigated theoretically with the aid of material studio using density functional theory (DFT). The simulations were performed by means of the DFT electronic program DMol³ using the Mulliken population analysis in the Material Studio. DMol³ permits analysis of the electronic structures and energies of molecules, solids and surfaces. The analysis of the quantum chemical parameters, the adsorption parameters form the simulation of the molecules, the Mulliken and Hirshfeld values of the fukui indices for the three molecules of the 6-AMQ (6-aminoquinoline), 7-AMQ (7-aminoquinoline) and 8-AMQ (8-aminoquinoline) indicated that all the three molecules exhibits very high potential for inhibition of aluminium corrosion in HCl environment, with 7-OAM being the best among all. The most popular parameters which play a prominent role are the eigen values of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), the HOMO-LUMO gap (ΔE), chemical hardness and softness, electro-negativity and the number of electrons transferred from inhibitor molecule to the metal surface. The fraction of electrons transferred from the molecules to metal surfce are 0.617, 0.839 and 0.224, and the total adsorption energy are -30.92, -37.74 and -36.76 for 6-AMQ, 7-AMQ and 8-AMQ respectively. All the molecules showed very good corrosion inhibition tendency, however, 7-AMQ molecule gives better aluminium corrosion inhibition potential than other two molecules as observed from the above values. The orientation of the -NH₂ substituent on the core quinoline was found to be responsible for intra-molecular hydrogen bonding which leads to weaker attraction to the aluminium surface for the 6-AMQ and 8-AMQ molecules hence lower corrosion inhibition tendency than 7-AMQ molecule despite having the same molecular mass.