- Kinetics and mechanism of the reduction of chromium(VI) and chromium(V) by D-glucitol and D-mannitol
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The oxidation of D-glucitol and D-mannitol by CrVI yields the aldonic acid (and/or the aldonolactone) and CrIII as final products when an excess of alditol over CrVI is used. The redox reaction occurs through a CrVI → CrV → CrIII path, the CrVI → CrV reduction being the slow redox step. The complete rate laws for the redox reactions are expressed by: a) - d[CrVI]/dt = {kM2H [H-]2 +kMH [H+]}[mannitol][CrVI], where kM2H = (6.7 ± 0.3) · 10-2 M-3 S-1 and kMH = (9±2) · 10-3 M-2 S-1: b) - d [CrVI] /dt = {kG2H[H+]2 + kGH [H+]}[GLUCITOL][CrVI]. where kG2H = (8.5 ± 0.2) · 10-2 M-3 S-1 and kGH = (1.8 ± 0.1) · 10-2 M-2S-1 at 330. The slow redox steps are preceded by the formation of a CrVI oxy ester with λMAX 371 nm. at pH 4.5. In acid medium, intermediate CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxo-CrV intermediates are formed, with the alditol or the aldonic acid acting as bidentate ligands. Pentacoordinate oxo-CrV species are present at any [H+], whereas hexacoordinate ones are observed only at pH V species are not observed, CrV complexes are stable enough to remain in solution for several days to months.
- Roldan, Viviana P.,Daier, Veronica A.,Goodman, Bernard,Santoro, Mabel I.,Gonzalez, Juan Carlos,Calisto, Nancy,Signorella, Sandra R.,Sala, Luis F.
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p. 3211 - 3228
(2007/10/03)
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- A new efficient access to glycono-1,4-lactones by oxidation of unprotected itols by catalytic hydrogen transfer with RhH(PPh3)4-benzalacetone system
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Treatment of unprotected pentitols and hexitols with RhH(PPh3)4-benzalacetone system leads exclusively to glycono-1,4-lactones in 60-96% yield.
- Isaac,Aizel,Stasik,Wadouachi,Beaupère
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p. 475 - 476
(2007/10/03)
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- 2-Acetamido-2-deoxyaldonolactones from sugar formazans
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A new approach towards simple aldonic acid derivatives starting from the corresponding aldoses via the 2-acetamido-2-deoxy formazans resulted in the synthesis of 2-acetamido-2-deoxy-D-galactono-1,4-lactone (8), and its 6-deoxy (11) and 6-azido-6-deoxy (14) analogues on treatment with trifluoroacetic acid.The five-membered ring structure of the lactones and that of the intermediate lactone phenylhydrazone (7) was proved by 1H and 13C NMR studies, including deuterium-induced differential isotope shift (DIS) measurements.With sodium borohydride, lactones 8 and 11 were converted into 2-acetamido-2-deoxy-D-galactitol (15) and its 6-deoxy analogue (17), respectively.
- Zsoldos-Mady, Virag,Pinter, Istvan,Neszmelyi, Andras,Messmer, Andras,Perczel, Andras
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