The inhibitive effect of medium‐sized polymethyleneimines on the corrosion of iron in HCl solution is particularly good, and this effective inhibition is closely related to the angle of C‐N‐C bond or to strain in the ring as has been observed previously. The inhibition mechanism of the cyclic imines is developed further in this paper. Comparative studies on inhibition effectiveness of dimethylpolymethyleneammonium chlorides, N‐phenylpolymethylene‐imines, and the cyclic imines were carried out. Synergistic effects of iodide ion on the inhibition by cyclic imines and cyclic ammonium chlorides were also studied. Corrosion rate measurements on pure iron were made in HCl solution by polarization, hydrogen evolution, and weight loss. From the results, it was concluded that good inhibition of medium‐sized polymethyleneimine is caused by donation of the unshared π‐electron pair of its nitrogen atom to the metal.
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Aramaki et al. (1969) studied this question.