Redox, Kinetics and Complexation Chemistry of the CrVI/CrV/CrIV -D-glycero-D-guloheptono-1,4-lactone System

MARÍA F. MANGIAMELI; JUAN C. GONZÁLEZ; SILVIA GARCÍA; SEBASTIÁN BELLÚ; MABEL SANTORO; EVANGELINA CAFFARATTI; MARÍA I. FRASCAROLI; JUAN MANUEL SALAS PEREGRÍN; ANA M. ATRIA; LUIS F. SALA,

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

JOHN WILEY & SONS LTD

Año: 2010 vol. 23 p. 960 - 971

0894-3230

When a 60-times or higher excess of D-glycero-D-gulo-heptono-1,4-lactone (GHL) over CrVI is used, reaction yields D-gluconic acid, formic acid and CrIII as final products. The redox reaction involves formation of intermediates, CrIV and CrV species, reacting with GHL at comparable rates. CrIV is a very reactive intermediate and does not accumulate during this reaction; its rate of disappearance is 2.0T104 and 4.0T103 times higher than CrVI or CrV reaction with GHL, respectively. Kinetic studies show that the redox reaction proceeds through a mechanism combining CrVI!- CrIV!CrII and CrVI!CrIV!CrIII pathways. This mechanism is supported by the observation of free radicals, superoxoCrIII (CrO2R2 ) and oxo-CrV 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-CrV bischelates (giso1¼1.9802; giso2¼1.9803) are formed at pH £ 4 where the OH and O-ring groups of GHL participate in the bonding to oxo-CrV. Penta-coordinated oxo-CrV monochelates are observed as minor species (giso3¼1.9866; giso4¼1.9879) in addition to the major penta-coordinated oxo-CrV bischelates