Products of the condensation reaction between morpholine or cyclohexylamine and benzaldehydes have been used extensively as volatile inhibitors of atmospheric corrosion, as well as components of lubricant compositions, biocides and preservatives in automotive cooling liquids and fuels. In this study, we examined the relationship between the electronic structure and inhibition performance of the compounds in an atmospheric corrosion test. The condensation products have significantly lower vapor pressure than parent amines, resulting in longer residence times of inhibitor species at a metal surface. Their hydrolysis in the surface humidity film produces amine species that raise pH and adsorb on iron, as well as benzaldehyde species that serve as hydrophobicizing and biocide agents. However, caution should be exercised in the choice of parent benzaldehydes, because the inhibition performance may decrease with introduction of substituents into the aromatic ring. Taking into account the toxicity data for benzaldehydes, a good compromise can be achieved using methyl and ethyl substituted derivatives.
Keywords: atmospheric corrosion, inhibitors, iron, morpholine, cyclohexylamine, benzaldehyde, electronic structure