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A rapid and regioselective strategy have developed for synthesis of multi-functional phenazine derivatives such as 3- amino-1- (2-hydroxy phenyl) -1H- benzo[a] pyrano [2,3-c] phenazine -2- carbonitrile benzo-pyrano-phenazine (BPP), 3-amino-1-(2-hydroxy-5-methoxyphenyl)-1H-benzo[a]pyrano[2,3-c]phenazine-2-carbonitrile (MBPP) and 3-amino-1-(5-bromo-2-hydroxyphenyl)-1H-benzo[a]pyrano[2,3-c]phenazine-2-carbonitrile (BBPP) using In(OTf)3 as catalyst in simple one-pot multi-component reaction. Further, the regioselectivity of the product formation was confirmed by DFT studies. In addition, the synthesized compounds were evaluated for their corrosion inhibition strength on mild steel in 1 M hydrochloric acid solution by using weight loss and electrochemical techniques in the first time. Interestingly, the inhibition efficiency was increased up to 98.64 % with an increase in the inhibitor concentration and it was decreased with increases in temperature. These results indicate that our synthesized compounds adopt the Langmuir isotherm model. Further, the polarization measurements clearly indicate that synthesized phenazine derivatives act as mixed-type inhibitors. Also, the electrochemical impedance studies (EIS) strongly revealed that these compounds inhibit corrosion by adsorption mechanism. Moreover, the efficiency of corrosion inhibitors was explained by the surface morphology of the inhibited and uninhibited specimens and was examined using scanning electron microscopy (SEM). Finally, the correlation between the inhibition performance of phenazines and their structural parameters was clearly examined by DFT calculations.

There are collective data about the scope of various corrosion inhibitors viz., polymers, plant extracts, inorganic compounds, ionic liquids, organic molecules with hetero atoms, and π-electron clouds have been reported so far on the corrosion prevention of various metals in various corrosive media. Many reviews of literature related to organic inhibitors have been accounted for their classification, application, and mechanism of their inhibition on metals. A mini-review with specific reference to quinoxaline derivatives is summarized in this manuscript.

The present paper is aimed to review the efficiency of eco-friendly, natural and cheap bio-waste materials as corrosion inhibitors on metal surfaces in different corrosive media. Various bio-waste materials are the best substitutes for the synthetic organic, inorganic and polymeric inhibitors. Most of the bio-waste material adsorbed on the metal surface in aqueous medium followed the Langmuir adsorption isotherm. The presence of organic constituents in bio-waste materials is responsible for the protection of metals in aggressive medium. The effectiveness of these bio-waste materials to inhibit metal corrosion is well studied by non-electrochemical methods like weight loss and atomic absorption spectroscopy techniques as well as electrochemical methods like polarization and impedance measurements. Surface studies were studied through SEM, EDS, XRD, AFM and XPS techniques. Computational studies using DFT and MDS were also reported.