Inhibitory protection of metals in acid solutions by cinnamaldehyde. A review

• Ya.G. Avdeev

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: Literature data on the protection of metals in acidic solutions by cinnamaldehyde (CA), by compounds with a similar chemical structure, by products of CA chemical transformations, and by various extracts and oils obtained from plant sources containing CA are summarized and analyzed. The physicochemical properties of CA, methods for its production, results of experimental studies on metal protection in acidic media using this aldehyde, and some aspects of its inhibition mechanism are considered. The practical interest in using this compound as a raw material for the production of metal corrosion inhibitors is explained by the possibility of obtaining large quantities of CA from natural plant sources. The application of CA in individual form for metal protection in acidic solutions is not promising. In contrast, the use of CA transformation products (azomethines, thiosemicarbazones, secondary amines) or its incorporation in mixed inhibitors makes it possible to achieve interesting results in metal protection under acidic conditions. Certain cinnamaldehyde derivatives belonging to the azomethine class are capable of significantly inhibiting steel corrosion in acidic solutions at temperatures up to 100°C. It is noted that under certain conditions, in the process of inhibiting steel corrosion in acid solutions, CA may exhibit an adsorption-polymerization mechanism of protective action. According to this mechanism, the inhibitor is first adsorbed on the metal surface and subsequently forms a polymeric organic layer from the adsorbed molecules, which provides the most efficient corrosion protection. From the practical point of view, it is important that this inhibition mechanism is also possible for some azomethines obtained on the basis of CA. It is this mechanism that determines the efficient protection of steel by these compounds in HCl solutions at temperatures up to 100°C. The bibliography includes 126 references.

Keywords: metals, acid corrosion, corrosion inhibitors, cinnamaldehyde, aldehydes, unsaturated aldehydes, azomethines, Schiff bases, cinnamon oil, cinnamon extract

Int. J. Corros. Scale Inhib., 2026, 15, no. 1, 58-84
doi: 10.17675/2305-6894-2026-15-1-3

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