Tailored α-hydroxyphosphonate derivatives: Green synthesis, spectroscopic characterization, DFT analysis, and high-efficiency corrosion protection for copper in acidic media

This study presents a comprehensive investigation into the synthesis, characterization, and corrosion inhibition performance of four novel alpha-hydroxyphosphonate compounds-diethyl alpha-hydroxy phenyl phosphonate (DHPP), diethyl alpha-hydroxy 4-chlorophenyl phosphonate (DHCP), diethyl alpha-hydroxy 4-methoxyphenyl phosphonate (DHMP), and E-diethyl alpha-hydroxy phenylallylic phosphonate (DHPAP). Synthesized using an environmentally friendly solvent-free method, the structures of these compounds were confirmed via Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Their efficacy as corrosion inhibitors for copper in a 1 M HCl environment was systematically evaluated using Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP). Among the inhibitors, DHMP exhibited the highest performance, achieving inhibition efficiencies of 93.46 % (EIS) and 83.25 % (PDP), followed by DHPP, DHCP, and DHPAP (efficiency order: DHMP > DHPP > DHCP > DHPAP). Surface characterization through Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) revealed the formation of protective barrier layers, effectively reducing surface roughness and minimizing copper dissolution. To elucidate the molecular basis of inhibition, Density Functional Theory (DFT) calculations provided insights into electronic properties, including HOMOLUMO energy gaps, Mulliken charges, and Molecular Electrostatic Potential (MEP) distributions. Further analyses using Non-Covalent Interaction (NCI) and Quantum Theory of Atoms in Molecules (QTAIM) emphasized the critical role of van der Waals forces and hydrogen bonding in stabilizing inhibitor-copper interactions. COSMORS studies confirmed favorable solvation behavior and charge distribution, reinforcing the experimentally observed adsorption mechanisms. This work underscores the multifunctionality of alpha-hydroxyphosphonates as effective corrosion inhibitors for industrial applications, while also paving the way for their optimization and broader utilization in corrosion science. The findings highlight the potential of these compounds to significantly advance the development of eco-friendly and efficient corrosion protection strategies.