Preparation of dehydro-l-(+)-ascorbic acid dimer by oxidation of ascorbic acid with arsenic acid/iodine and formation of complexes between arsenious acid and ascorbic acid

Impairment of ascorbic acid’s anti-oxidant properties in confined media: Inter and intramolecular reactions with air and vanadate at acidic pH

“…The 1 H NMR spectrum ( Fig. 1SB) for the L-ascorbic acid shows three signals and is pH dependent since ascorbic acid exists in different protonation states (pK a1 = 4.25, pK a2 = 11.79 [45][46][47][48][49][50][51][52][53]). Chemical shifts are given in Table 1 for each species in aqueous solutions at pH 2.2, 4.5 and 5.8 and their corresponding RM solutions.…”

“…Since 1 H NMR chemical shifts are sensitive to the protonation states of ascorbic acid [48,49,52,53,[61][62][63][64][65], the spectra obtained from pH 2.0 to 5.6 show that ascorbic acid is protonated in the aqueous stock solutions and inside the AOT RM (w 0 = 20). As the pH is raised (pK a1 = 4.25 [45][46][47][48][49][50][51][52][53]) the monoanionic species becomes the major species in solution and the stability of L-ascorbic acid solution decreases, since L-ascorbic acid is readily oxidized in the form of the monoanion [48]. In the presence of the transition metals, rates of oxidation also increase dramatically at low pH which suggests formation of a reactive metal-ascorbate complex [10][11][12][13]66].…”

“…If the effective ''pH" of the interface environment was raised closer to the first pK a for ascorbic acid (pK a1 = 4.25 [45][46][47][48][49][50][51][52][53]) an increased reduction rate would be expected since HAA À is a thermodynamically stronger, and kinetically faster, reducing agent than H 2 AA. Since no such increase in rate constant is observed, we conclude that the effective proton activity is not above a pH of approximately 2.5-3.0 [14] as found for aqueous solution.…”

New Coordination Modes of L‐Ascorbic Acid and Dehydro‐L‐ascorbic Acid as Dianionic Chelating Ligand for Platinum

“…The ratio between the three forms depends on the solvent and on the preparation procedure (Scheme 4). [18] Scheme 4.…”

Ascorbic Acid/Iodine and Triphenylphosphine/Iodine as Reducing Agents for the As(V)[dbnd]O Group

“…Aiming at the preparation of crystalline dehydro-L-ascorbic acid dimer, 4 AA in methanol has been oxidized by arsenic acid in the presence of a catalytic amount of iodine. 5 In this case the actual reducing agent of arsenic acid is the hydriodic acid, and the iodine produced [Eq.…”