Adsorption behavior and corrosion inhibitive characteristics of newly synthesized cyano-benzylidene xanthenes on copper/sodium hydroxide interface: Electrochemical, X-ray photoelectron spectroscopy and theoretical studies.

Elegant process for synthesis of 3-(7H-dibenzo[c,h]xanthen-7-yl)benzaldehyde (3), as new starting material to create a set of novel xanthene analogues, 2-(3-(7H-dibenzo[c,h]xanthen-7-yl)benzylidene)malononitrile (4), 3-(3-(7H-dibenzo[c,h]xanthen-7-yl)phenyl)-2-cyanoacrylic acid (5), and Ethyl-3-(3-(7H-dibenzo[c,h]xanthen-7-yl)phenyl)-2-cyanoacrylate (6), was achieved starting with available materials under mild conditions. Various concentrations (ca. 0.1-1.0 mM) of the synthesized cyano-benzylidene xanthene derivatives, namely compounds 3-6, were tested as inhibitors to control copper corrosion in alkaline solutions employing polarization and electrochemical impedance spectroscopy (EIS) measurements. Results revealed that the four studied xanthenes derivatives served as efficient (mixed-type) inhibitors. The inhibition efficiency increased with increase in inhibitor concentration.The inhibition performance of studied compounds varied according to their chemical structures. The best inhibitor, compound (5), achieved a maximum inhibition efficiency of 98.7% (calculated from corrosion current densities) and ~ 95% (estimated from charge-transfer resistance values) at a concentration of 1.0 mM. The morphology of the corroded and inhibited copper surfaces was studied by scanning electron microscopy (SEM). The adsorption of the inhibitor molecules was confirmed by high-resolution X-ray photoelectron spectroscopy (XPS) profiles. XPS data were used to compare the inhibition efficiencies exhibited by studied compounds. The oxidation rate of the Cu surface was found to be frivolous, referring to high inhibition efficiency, only in the presence of inhibitor (5), and Cu0 share is 87% of all copper components. The shares of Cu0 were significantly reduced to 43%, 26% and 20% for inhibitors (3), (4) and (6), respectively. These findings go parallel with the results obtained from electrochemical measurements. The quantum-chemical calculations of the investigated molecules were performed to support electrochemical findings, and their correlations with the inhibition efficiency of the synthesized compounds were discussed.