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Redox, kinetics, and complexation chemistry of the Cr VI /Cr V /Cr IV ‐ D ‐glycero‐ D ‐gulo‐heptono‐1,4‐lactone System
Author(s) -
Mangiameli María F.,
González Juan C.,
García Silvia,
Bellú Sebastián,
Santoro Mabel,
Caffaratti Evangelina,
Frascaroli María I.,
Peregrín Juan Manuel Salas,
Atria Ana M.,
Sala Luis F.
Publication year - 2010
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1745
Subject(s) - chemistry , redox , reactive intermediate , reaction intermediate , reaction mechanism , formic acid , kinetics , gluconic acid , radical , medicinal chemistry , stereochemistry , catalysis , organic chemistry , physics , quantum mechanics
When a 60‐times or higher excess of D ‐glycero‐ D ‐gulo‐heptono‐1,4‐lactone (GHL) over Cr VI is used, reaction yields D ‐gluconic acid, formic acid and Cr III as final products. The redox reaction involves formation of intermediates, Cr IV and Cr V species, reacting with GHL at comparable rates. Cr IV is a very reactive intermediate and does not accumulate during this reaction; its rate of disappearance is 2.0 × 10 4 and 4.0 × 10 3 times higher than Cr VI or Cr V reaction with GHL, respectively. Kinetic studies show that the redox reaction proceeds through a mechanism combining Cr VI → Cr IV → Cr II and Cr VI → Cr IV → Cr III pathways. This mechanism is supported by the observation of free radicals, superoxoCr III (CrO 2 2+ ) and oxo‐Cr V as intermediates species. Complete rate laws for the GHL/chromium redox reaction are described in the present work. EPR spectra show that five‐coordinate oxo‐Cr V bischelates ( g iso1 = 1.9802; g iso2 = 1.9803) are formed at pH ≤ 4 where the OH and O‐ring groups of GHL participate in the bonding to oxo‐Cr V . Penta‐coordinated oxo‐Cr V monochelates are observed as minor species ( g iso3 = 1.9866; g iso4 = 1.9879) in addition to the major penta‐coordinated oxo‐Cr V bischelates. Copyright © 2010 John Wiley & Sons, Ltd.