5959-82-0Relevant articles and documents
Effect of Ionic Strength on the Kinetics of the Oxidation of Ascorbic Acid by Hexacyanoferrate(III): Comparison between Specific Interaction Theories and the Mean Spherical Approximation
Vilarino,Alonso,Armesto,Rodriguez,De Sastre Vicente
, p. 558 - 559 (2007/10/03)
The influence of ionic strength on the rate constant of the oxidation reaction of ascorbic acid by hexacyanoferrate(III) in acidic medium is investigated. The dependence of the rate constant on ionic strength is discussed according to different specific i
Ascorbic Acid Oxidation at Polypyrrole-coated Electrodes
Lyons, Michael E. G.,Breen, William,Cassidy, John
, p. 115 - 123 (2007/10/02)
The electrooxidation of ascorbic acid is examined at polypyrrole electrodes doped with chloride and dodecylbenzene sulphonate ion.Both the kinetics of oxidation and the reproducibility of the electrochemical response are found to be enhanced at the polymer-modified electrode compared to that at an unmodified metal electrode.Kinetic data for ascorbate oxidation at the polymer-modified electrodes is evaluated and rationalised in terms of specific mechanistic sequences.The use of polypyrrole-based electrodes as active components in an amperometric chemical sensor for ascorbate is evaluated.
Kinetics and Mechanism of Oxidation of L-Ascorbic Acid by Chloropentamminecobaltate(III) in Acidic Media
Martinez, P.,Rodriguez, A. F.,Zuluaga, J.
, p. 311 - 317 (2007/10/02)
The kinetics and mechanism of oxidation of L-ascorbic acid by chloropentamminecobaltate(III) ions have been studied by a spectroscopic method as a function of pH, ascorbic acid concentration, ionic strength and temperature in acidic aqueous solutions.The pH dependence of the process can be ascribed, in the acidity range investigated (pH = 0.8-2), to the direct oxidation of the ascorbic acid molecule, for which k = 7.3 * 10-5 M-1 s-1 at 25 deg C, ΔH(excit.) = 102 KJ*mol-1 and ΔS(excit.) = 19 JK-1mol-1.The results are discussed in reference to the data for this reaction in weakly acidic and basic media and for the oxidation by other oxidants.
SYNTHESIS AND REACTIONS OF SOME HYDRAZONES OF DEHYDRO-L-ASCORBIC ACID
Kilany, Yeldez El,Hamid, Hamida Abdel,Ashry El, Sayed H. El
, p. 77 - 84 (2007/10/02)
L-threo-2,3-Hexodiulosono-1,4-lactone 2-(3-chlorophenylhydrazone) and 4-(2-acetoxyethylidene)-4-hydroxy-2,3-dioxobutano-1,4-lactone 2-(3-chlorophenylhydrazone) were prepared.The two geometric isomers of the corresponding bis(hydrazone) underwent an intramolecular rearrangement to 1-(3-chlorophenyl)-3-(L-threo-glycerol-1-yl)-4,5-pyrazoledione 4-(3-chlorophenylhydrazone), which gave a tri-O-acetyl derivative upon acetylation and the anticipated formyl derivative upon periodate oxidation.Oxidation of the bis(hydrazone) with cupric chloride afforded the bicyclic compound 3,6-anhydro-3-C-(3-chlorophenylazo)-L-xylo-2-hexulosono-1,4-lactone 2-(3-chlorophenylhydrazone), whose acetylation afforded the mono-O-acetyl derivative.
COUPLING BETWEEN BINDING-INDUCED CONFORMATIONAL PHENOMENA AND STEREOSPECIFIC EFFECTS IN ASYMMETRIC REACTIONS
Barteri, Mario,Pispisa, Basilio
, p. 2073 - 2084 (2007/10/02)
The oxidation by H2O2 of L-(+)-ascorbate anion in the presence of 2,2',2",2"'-tetrapyridineiron(III) complex ions anchored to poly(L-glutamate) (FeL) or poly(D-glutamate) (FeD) has been studied at pH 7.0 and varying complex-to-polymer-residue ratio /.The reaction follows two parallel routes; one corresponds to an electron-transfer process within a substrate-catalyst adduct and the other refers to an uncatalysed pathway to the dehydroascorbic acid.Unusual phenomena are observed in the catalysis in the sense that only the conformational dissymmetry of the active sites, arising from the binding-induced coil-to-α-helix transition of polypeptide matrices by Fe(III) complex counter-ions, is able to impart stereospecific effects in the reaction.Evidence is produced to show that stereoselectivity is driven by activation entropy.The effect probably arises from the formation of a rather rigid precursor complex, with the optically active substrate molecules bound to the chiral residues of the ordered polymer surrounding the active sites.The stereochemistry of such an intermediate allows the reaction to proceed only by a remote electron-transfer pathway, through the quaterpyridine ligand of the metal chelate.Evidence suggests that the asymmetric (1+)-polyelectrolyte systems also behave as environmental controllers of the uncatalysed oxidation of the L-(+)-ascorbate anion.This effect is briefly discussed in terms of the role played by macroions in ionic reactions in solution.
