Acetohydroxamatoiron(III) Complexes: Thermodynamics of Formation and Temperature Dependent Speciation

Abstract

1 Acetohydroxamatoiron (III) complexes Andrieux et al. AbstractStudies of the thermodynamics of formation of the acetohydroxamatoiron(III) complexes were carried out in acidic media at temperatures ranging from 293 to 323 K. Through the isolation of the unique UV -visible spectra of all three complexes, it was possible to determine their formation constants and deduce enthalpies and entropies of formation as well as their molar absorptivities. The enthalpies of formation of the mono-, bis-and trisacetohydroxamatoiron(III) complexes were found to be -56.4, -17.09 and +19.74 kJ•mol -1 , respectively. Following the determination of the enthalpy and entropy of formation of these complexes, speciation diagrams were calculated for the complexes at temperatures ranging from 293 to 323 K.

Complexation Chemistry of Zirconium(IV), Uranium(VI), and Iron(III) with Acetohydroxamic Acid

“…In order to obtain absorbance spectra useful for the determination of stability constants in SQUAD, distinct concentration ratio ranges of Fe(III) and AHA were determined from the Hyperquad Simulation and Speciation (HySS) program (21) and previous literature (16,17). Critically assessed equilibrium data indicated that the formation of Fe(OH) 2þ only becomes significant above pH 2.17 (17,22,23). Therefore, the hydrolysis of Fe(III) was not of consideration in HySS, as the pH of all solutions was 1 and the concentration of the ferric ion was low.…”

“…Acetohydroxamic acid forms strong complexes with iron(III) which can be monitored by observing the intense color of the complex formation. Conditional stability constants of Fe(AHA) 2þ , FeðAHAÞ þ 2 , and Fe(AHA) 3 in 0.1 mol Á L À1 NO À 3 and pH 1.0 at 25 C are reported and compared with previously reported values (16,17).…”

“…Note: Conditional stability constants for Andrieux el al (17). at 25 C for 0 pH 1.00 and NO À 3 % 0.1 mol Á L À1 were calculated from their published data for comparative purposes using 9.33 (3) as the pK a for AHA at I ¼ 0.1 mol Á L À1 .COMPLEXATION OF Zr, U, AND Fe WITH AHA 1735 Downloaded by [The University of Manchester Library] at 09:42 20 December 2014…”

The effect of acetohydroxamic acid on stainless steel corrosion in nitric acid

“…To determine the origin of this colouration, the working solution was sampled after electrochemical 8 scanning, diluted and analysed using UV-vis spectrophotometry (not shown). Comparison with absorbance peak values for acetohydroxamatoiron(III) complexes reported by Andrieux et al [14], revealed the presence of the monoacetohydroxamatoiron(III) complex suggesting that electrogenerated Fe(III) is sequestered from the electrode surface in this form.…”

“…The stock solution was kept refrigerated up to a maximum of five days and colourmetrically checked daily for AHA degradation using UV-vis spectrophotometry [14].…”