Synthesis and characterization of iron stearate compounds

Abstract

A derivative of a known trinuclear iron(III) stearate cluster was prepared from ferrous sulfate and sodium stearate in ethanol/water solvent with air oxidation. It was also prepared by increasing the pH of a solution of ferrous sulfate stirred with stearic acid. The formula for the trimer as prepared here is [Fe 3O(St) 6(H 2O) 3] +St −(St − = stearate, n-C 17H 35CO 2 −). The reaction of ferric citrate with stearate to form the trimer does not go to completion. The true composition of most iron stearates has not been well established previously. Two iron stearate compounds are available commercially; of these, only “ferrous stearate” appears to be a pure compound, albeit not a simple mononuclear one. The “ferric stearate” of commerce appears to be a mixture of stearic acid and a compound similar to the iron trimer prepared here. References exist to “iron distearate hydroxide” in the literature. The physical and spectroscopic properties of this compound are very similar to those of the iron trimer prepared here. Spectral data (mid- and far-IR, 300 MHz 1H and 75 MHz 13C NMR) and TGA/DSC data are reported for stearic acid, “ferrous stearate,” “ferrie stearate,” and [Fe 3O(St) 6(H 2O) 3][St].