Structure—Corrosion Inhibition Studies of Polyfunctional Metal Chelating Compounds Available to Purchase

Homologous series of polyfunctional metal chelates were synthesized. The compounds contained a sulfide group (-S-), a carboxylic group (-COOH), and varying numbers and arrangements of carbon atoms. The structure of the derivatives was varied and the effects on the corrosion inhibiting properties of compounds caused by changes in solubility, number of complexing groups and structural arrangement were examined. The corrosion inhibition provided by each compound to pure iron wire in 1 N HCl was measured. The corrosion inhibitory properties are reported. The ¹  H nuclear magnetic resonance and the¹³  C nuclear magnetic resonance (NMR) of the thioglycolic acid derivatives were measured. Pulsed NMR and Fourier transform techniques were used to measure ¹³  C NMR. The chemical shift (δ in ppm from TMS) for both the α carbon and the protons on that carbon were found to correlate with the corrosion inhibition of iron in 1N HCl by a theoretically derived relationship proposed by Donahue and Nobe. Predicted inhibition was very close to experimental results for alkyl derivatives, but phenyl-substituted derivatives appeared to inhibit by a different process. Corrosion inhibition may be predicted for alkyl thioglycolic acid derivatives by a single NMR measurement.