Comparative study of oxidation by chromium(V) and chromium(VI)- Part 2

S. SIGNORELLA; M. RIZZOTTO; V. DAIER; M.I. FRASCAROLI; C. PALOPOLI; D.M. MARTINO; A. BOUSSEKSOU; L. SALA

JOURNAL OF THE CHEMICAL SOCIETY, DALTON TRANSACTIONS

Año: 1996 p. 1607 - 1611

0300-9246

The kinetics and mechanism of the oxidation of 2-deoxy-u-glucose (dGlc) by CrVI which yields 2-deoxy-d-gluconic acid and CrIII as final products when a ten-fold or higher excess of sugar over CrV´ is used, have been studied. The redox reactions occur through CrVI   CrIV   CrIII and CrVI    CrV    CrII  paths. The experimental data were fitted with a multilinear regression program. The complete rate law for the chromium(v1) oxidation reaction is expressed by -d[CrV´]/dt = {c[Hf]  (d e[H+]  f[H´]´) [dGlc])[CrV´], where experimental data were fitted with a multilinear regression program. c = (5 k 1) x 10 dm3 rnolF´s-´, d = (3 k 2) x lo4 dm3 m o l - ´ ~ - ~e ,= (115 k 13) x dm6 rnol-, s-´= (5 k 1) x 10 dm3 rnolF´s-´, d = (3 k 2) x lo4 dm3 m o l - ´ ~ - ~e ,= (115 k 13) x dm6 rnol-, s-´ and,f = (402 k 17) x 10 dm9 mol-, s-l, at 50 "C. Chromium(v) is formed in a rapid step by reaction of the radical dGlc and CrV´a nd Crv reacts with dGlc faster than does CrV1.T he chromium(v) oxidation of dGlc follows the rate law -dCrv/dt = (k, + k2[T3´])[dGlc)[CrV], where k, = 2.52 x lop4 dm3 mol-´ s and radical dGlc and CrV´a nd Crv reacts with dGlc faster than does CrV1.T he chromium(v) oxidation of dGlc and k, = 54.0 dm6 mol-´ s ´, at 25 "C. The EPR spectra show that three 1 : 1 CrV : dGlc intermediate complexes = 54.0 dm6 mol-´ s ´, at 25 "C. The EPR spectra show that three 1 : 1 CrV : dGlc intermediate complexes (gl = 1.978 1, g, = 1.9752, g, = 1.9758) are formed in rapid pre-equilibria before the redox steps. c = (5 k 1) x 10 dm3 rnolF´s-´, d = (3 k 2) x lo4 dm3 m o l - ´ ~ - ~e ,= (115 k 13) x dm6 rnol-, s-´= (5 k 1) x 10 dm3 rnolF´s-´, d = (3 k 2) x lo4 dm3 m o l - ´ ~ - ~e ,= (115 k 13) x dm6 rnol-, s-´ and,f = (402 k 17) x 10 dm9 mol-, s-l, at 50 "C. Chromium(v) is formed in a rapid step by reaction of the radical dGlc and CrV´a nd Crv reacts with dGlc faster than does CrV1.T he chromium(v) oxidation of dGlc follows the rate law -dCrv/dt = (k, + k2[T3´])[dGlc)[CrV], where k, = 2.52 x lop4 dm3 mol-´ s and radical dGlc and CrV´a nd Crv reacts with dGlc faster than does CrV1.T he chromium(v) oxidation of dGlc and k, = 54.0 dm6 mol-´ s ´, at 25 "C. The EPR spectra show that three 1 : 1 CrV : dGlc intermediate complexes = 54.0 dm6 mol-´ s ´, at 25 "C. The EPR spectra show that three 1 : 1 CrV : dGlc intermediate complexes (gl = 1.978 1, g, = 1.9752, g, = 1.9758) are formed in rapid pre-equilibria before the redox steps.