Electrochemical and quantum chemical studies on the formation of protective films by alkynols on iron

Abstract In order to find out the effect of cathodic and anodic polarisation on the formation of inhibitor films we measured the electrochemical impedance of an iron electrode in sulphuric acid and in hydrochloric acid solutions in the presence of oct-1-yn-3-ol or 2-〈2-(1,1-dimethyl-prop-2-ynyloxy)-ethoxy〉-ethanol inhibitors. We found that the anodic polarisation helped the initial binding of the inhibitor to the iron surface. Cathodic polarisation does not influence the initial formation but, if applied at a later stage, promotes the growth of the inhibitor film. The results support the assumption that film formation on iron surfaces from alkynols takes place in a two-step process: first chemisorption, then polymerisation. The binding of alkynols to iron was studied in model electronic structure calculations which indicate that a dative bond is formed between Fe and the triple bond. The calculated vibrational frequencies of the alkynol bound to iron can be used to successfully interpret the IR spectra found in the literature.