Model compounds of humic acid and oxovanadium cations. Potentiometric titration and EPR spectroscopy studies

Citation
Alr. Merce et al., Model compounds of humic acid and oxovanadium cations. Potentiometric titration and EPR spectroscopy studies, J BRAZ CHEM, 10(6), 1999, pp. 463-468
Citations number
19
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
JOURNAL OF THE BRAZILIAN CHEMICAL SOCIETY
ISSN journal
0103-5053 → ACNP
Volume
10
Issue
6
Year of publication
1999
Pages
463 - 468
Database
ISI
SICI code
0103-5053(199911/12)10:6<463:MCOHAA>2.0.ZU;2-1
Abstract
The stability constants and the isotropic EPR parameters Ao (hyperfine spli tting constant) and go (g value) were obtained by potentiometric titrations and EPR spectroscopy, respectively, of 85%v/v aqueous solutions of model c ompounds of humic acids - salicylic acid (SALA) - and both nitrohumic acids , a laboratory artifact - nitrosalicylic acids, 3-nitrosalicylic acid (3-NS A), 5-nitrosalicylic acid (5-NSA) and 3,5-dinitrosalicylic acid (3,5-DNSA) and oxovanadium cations. It was possible to record EPR spectra of those model compounds and the ion VO2+(V(IV)), and the stability constants were obtained from a solution of V O3+ (V(V)), the values for the logarithms of the stability constants rangin g from 12.77 +/- 0.04 to 7.06 +/- 0.05 for the species ML, and from 9.90 +/ - 0.04 to 4.06 +/- 0.05 for the species ML2 according to the decrease in th e acidity of the carboxylic and the hydroxyl groups in the aromatic ring of the model compounds studied as the -NO2 substituents were added. Species d istribution diagrams were also obtained fur the equilibria studied. The EPR parameters showed that as the logarithm of the overall stability co nstants increase, g(o) values also increase, while A(o) values show a tende ncy to decrease.