The Preparation of Dehydro-L-ascorbic Acid and its Methanol Complex. Some Reactions of Dehydro-L-ascorbic Acid¹

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

“…NH 3 4:1, R f 0.61 [27]) and confirmed by IR [28] (sharp peak at 802 cm À1 ). Melting points were obtained using an Electrothermal Model IA9100 apparatus in capillaries, the heating starting from 25°C [16]. IR spectra were taken on a Perking Elmer Model 16PC FT-IR spectrometer and NMR spectra were run on a Bruker DPX Avance spectrometer: 400 MHz for 1 H and 100 MHz for 13 C. The 1 H NMR chemical shifts are reported in ppm downfield from 3-(trimethylsilyl)propanesulfonic acid sodium salt (Aldrich) and referenced to residual H-O-D resonance: 4.77 ppm.…”

“…When ascorbic acid is oxidized in aqueous solution, compound 4 is formed [14] which has been isolated in 79% purity [13]. When the oxidation is done in methanol [15][16][17][18], then two isomers of the 2-methyl hemi-ketal 5 are formed [19] which can be isolated as a solid [16]. However, oxidation in non-protic solvents, e.g., N,N-dimethylformamide (DMF) [20], produces the two anomers of the dimerized dehydroascorbic acid, 6 [21].…”

“…However, oxidation in non-protic solvents, e.g., N,N-dimethylformamide (DMF) [20], produces the two anomers of the dimerized dehydroascorbic acid, 6 [21]. The oxidants used are: iodine in wet methanol [15], chlorine in dry methanol [16], p-benzoquinone, chloranil or mercuric(II) acetate in DMF or dimethyl sulfoxide (DMSO) or N,N-dimethylacetamide [20], and air or dioxygen in the presence of palladium on carbon [17] or activated charcoal [18] suspended in methanol.…”

“…Its preparation from an aqueous solution of 4 is nearly impossible [15,16], whereas it can be prepared from the syrupy 5 by thermal elimination of methanol either by ''baking'' at 100°C in vacuum, with yields 23% [15] or $40% [16] or by refluxing in methyl ethyl ketone (64%) [18] or heating in nitromethane (90%) [17]. In the latter case, the product did not show the correct molecular weight [17], it had a pinkish color and was not free of solvent [18].…”

The methanol method for the quantification of ascorbic acid and dehydroascorbic acid in biological samples

“…1), thereby yielding various methyl ketals with an absorption maximum at 346 nm [12,13]. In 1994, Moeslinger et al [14] used this reaction to introduce a highly specific spectrophotometric method for the determination of dehydroascorbic acid in either human plasma or cultured cells.…”