The Hydrolysis of Hydroxamic Acid Complexants in the Presence of Non-oxidizing Metal Ions 1: Ferric Ions

Abstract

Hydroxamic acids (XHAs) are organic compounds with affinities for cations such as Fe 3+ , Np 4+ and Pu 4+ and have been identified as useful reagents in nuclear fuel reprocessing. Acid catalysed hydrolysis of free XHAs is well known and may impact negatively on reprocessing applications. Hydrolysis of metal bound XHAs within metal ion-XHA complexes is less understood. With the aid of speciation diagrams, we have modelled UV-visible spectrophotometric kinetic studies of the acid-catalysed hydrolysis of acetohydroxamic acid (AHA) bound to the model ion Fe(III). These studies have yielded the following for the hydrolysis of AHA in the Fe(AHA) 2+ complex at 293 K: (i) the order with respect to [H + ] during the rate determining step, m = 0.97, the same as for the free ligand, indicating a similarity of mechanism; and (ii) the rate parameter, k 1 =1.02 x 10-4 dm 3 •mol-1 •s-1 , greater than that for the free ligand, k 0 = 1.84 x 10-5 dm 3 •mol-1 •s-1 for pH >-0.5, a result consistent with a Hammett analysis of the system.

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

“…Farkas et al [19] suggest that the transition of the dominant species from mono-to bis-to tris-as ligand concentration is increased can be followed by the absorption maximum moving from 510 to 470 to 420 nm for the mono-, bis-and tris-complexes, respectively. over this pH range is supported by preliminary results in our previous paper [11].…”

“…Preliminary speciation calculations [11] suggest that this may be achieved by recording the spectra in a large excess of iron (III). Thus, three solutions were If it is assumed that ΔH o and ΔS o are invariant with temperature, the Van't Hoff isochore may be written as:…”

“…Whilst there have been many studies of hydroxamic acid hydrolysis and their complexation reactions with Fe(III) ions, there have been relatively few studies of the stability of the Fe(III)-hydroxamate complexes towards hydrolysis. We have previously reported on the kinetics of the hydrolysis of hydroxamic acids both in free solution and when bound to metal ions and developed a kinetic model describing this process at ambient temperatures [11,13]. However, the applications of hydroxamic acids in biological-related fields requires an understanding of the behaviour of these systems at temperature of biological interest, for example in vivo (310K) or temperatures at which proteins start to denature ( ~ 325K) [14].…”

Reductometric Titration and Quantum Chemical Study of Oxalohydroxamic Acid for Determination of Manganese in Ores and Alloys

“…Extensive works have been carried out on their synthesis [1], complexation with metal ions [2], gravimetry [3], colorimetry [4], kinetics [5][6][7][8][9], spectrophotometry [10] and medical applications [11][12][13][14]. Benzohydroxamic acid was used as a reductometric titrant for determination of manganese, chromium [15] and cerium, uranium [16].…”

Hydroxamic Acids as a Reductometric Titrants: Determination of Cerium in Alloys

“…Extensive works have been carried out on their synthesis 1 , complexation with metal ions 2 , gravimetry 3 , colorimetry 4 , kinetics [5][6][7][8][9][10] , spectrophotometry 11 and medical applications [12][13][14][15] . Benzohydroxamic acid (BHA) was used as a reductometric titrant for determination of Mn, Cr 16 and Ce, U 17 .…”