Synthesis, inhibition effects and quantum chemical studies of a novel coumarin derivative on the corrosion of mild steel in a hydrochloric acid solution

Abstract

Background: The acid corrosion inhibition process of mild steel in 1 M HCl by 4-[(2-amino-1, 3, 4-thiadiazol-5-yl)methoxy]coumarin (ATC), has been investigated using weight loss technique and scanning electron microscopy (SEM). ATC was synthesized, and its chemical structure was elucidated and confirmed using spectroscopic techniques (infrared and nuclear magnetic resonance spectroscopy).

Findings: The results indicated that inhibition efficiencies were enhanced with an increase in concentration of inhibitor and decreased with a rise in temperature. The adsorption equilibrium constant (K) and standard free energy of adsorption (ΔGads) were calculated. Quantum chemical parameters such as highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy (EHOMO and ELUMO, respectively) and dipole moment (μ) were calculated and discussed. The results showed that the corrosion inhibition efficiency increased with an increase in both the EHOMO and μ values but with a decrease in the ELUMO value.

Conclusions: Our research show that the synthesized macromolecule represents an excellent inhibitor for materials in acidic solutions. The efficiency of this macromolecule had maximum inhibition efficiency up to 96 % at 0.5 mM and diminishes with a higher temperature degree, which is revealing of chemical adsorption. An inhibitor molecule were absorbed by metal surface and follow Langmuir isotherms low and establishes an efficient macromolecule inhibitor having excellent inhibitive properties due to entity of S (sulfur) atom, N (nitrogen) atom and O (oxygen) atom.

Keywords: (thiadiazol-5-yl)methoxy)coumarin; Corrosion inhibitor; Isotherm; Weight loss.

Fig. 1

Influences of concentrations vs time for ATC on corrosion rate at 303 K

Fig. 2

Influences of concentrations vs time for ATC on corrosion efficiencies at 303 K

Fig. 3

Influences of concentrations vs temperatures for ATC on corrosion efficiencies at fixed time

Fig. 4

The SEM micrograph for MS in in acidic medium in absence of ATC

Fig. 5

The SEM micrographs, for MS in acidic medium with 0.5 mM of the corrosion inhibitor at 30 °C for 5 h as immersion time in presence of ATC

Fig. 6

Linear equation

Fig. 7

The suggested mechanism of action of the ATC as corrosion inhibitor

Fig. 8

Electronic properties of (a) 3d-structure of ATC; (b) HOMO orbital; (c) LUMO orbital; (d) total electron density; (e) Fukui (f−) function; f Fukui (f+) function

Fig. 9

The three dimensional structure of ATC