Agric. Biol. Chem., 47 (3), 607-608, 1983 607

Note yield. However, in spite of the removal of NMin vacuo, the prepared microcrystalline DAAwas not perfectly free from the solvent and was weakly pink in color. The DAA-methanol adduct according to our method,1* Pure Dehydro-L-ascorbic Acid was applied to prepare colorless microcrystalline DAA.As the final solvent for crystallization, we studied some Prepared by O2-Oxidation miscible solvents with lower boiling points than that of NM, such as ethanx>l, acetone and methyl ethyl ketone of L-Ascorbic Acid with (MEK). Taking into account the yield of the final product, MEKwas found to be the most suitable solvent for Active Charcoal as Catalyst crystallization. Mitsuaki Ohmori,* Hiroshi Higashioka Procedures for method. As previously reported, after 5 g of AAwas dissolved in 150ml of absolute methanol, 7.5 g and Masanosuke Takagi of Norit "Extra" activated charcoal was suspended in the solution. Oxygenwas bubbled at 0.21iter/min through a sintered glass for 1 hr at room temperature. The activated Laboratory of Food Chemistry, charcoal was removedfrom the reaction mixture after the College of Agriculture, completion of oxidation. Evaporation of the methanol under reduced pressure gave a viscous DAA-methanol University of Osaka Prefecture, adduct. To the viscous syrup, 30ml of MEKwas added Sakai 591, Japan and the mixture was refluxed at a little above the boiling *Osaka City Institute of Public point of MEK(79.6aC). The mixture became turbidly Health and Environmental Sciences, white and white microcrystals began to attach to the wall of the flask during reflux for about 30 min. After the Tennoji-ku, Osaka 543, Japan suspension was cooled to room temperature, the product Received July 14, 1982 was separated from the solution by filtration and washed with MEKand acetone. The filtrate was dried in vacuo, and 30ml of MEKwas again added to the residue. After the sameoperation was repeated several times, colorless Wehave previously reported a facile preparation of a microcrystals were collected, and dried at 40°C in vacuo. highly pure dehydro-L-ascorbic acid (DAA)-methanol so- This colorless microcrystalline DAAhad a mp (decom- position) of 230~232°C. With regard to the mp of lution1* by O2-oxidation of L-ascorbic acid (AA), using microcrystalline DAA,values from 220 to 225°C have Norit "Extra" activated charcoal as the catalyst. Our been reported by Kenyon and Munro,3) Pecherer,4) method is comparable with Dietz's method,2) in which AA Muller-Mulot5) (in the cases of the benzoquinone and the was oxidized by air, using palladium-carbon as the cat- mercury methods) and by Pohloudek-Fabini and Fiirtig,6) while 10 degree higher values have also been reported by alyst. Our procedure is more practical than Dietz's in Muller-Mulot5) (in the case of the chloranil method) and several aspects: the use of O2 from a pressurized cylinder instead of air shortens the time required for oxidation to about one-fifth and the resulting DAA-methanol solution contains no significant impurities. In addition, the acti- vated charcoal catalyst is much less expensive than palladium-carbon. This time we applied the above DAA-methanol solution to obtain pure DAA crystals. Dietz's method,2) using nitromethane (NM)to prepare crystalline DAAfrom a methanol solution, gave the desired product in a good

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1 1 1 1 « 1 1 1 1 1 I I ' å I å I I I 3600 2800 2000 1800 1600 1400 1200 1000 800 600 ( cm-1 ) Fig. 1. Infrared Spectrum of Dehydro-L-ascorbic Acid (in Nujol). 608 M. Ohmori, H. Higashioka and M. Takagi by Dietz2) (in the case of the NMmethod). The latter two REFERENCES values agreed with ours for DAA.The yield of colorless DAAwas ca. 64%. IR spectrum of the crystalline DAA M. Ohmori and M. Takagi, Agric. Biol. Chem., 42, agreed with that obtained by Kurata et al.7) (given in Fig. 173 (1978). 1). H. Dietz, Liebigs Ann. Chem., 738, 206 (1970). The purity was also checked by the polarographic o- J. Kenyon and N. Munro, /. Chem. Soc, 158 (1948). phenylenediamine (OPD) method8>9) to be 99.0% dimeric B. Pecherer, J. Am. Chem. Soc, 73, 3827 (1951). DAA.2>5'10~12) It is considered that the activated charcoal W. Miiller-Mulot, Hoppe-Seyler's Z. Physiol. Chem., used in a relatively large quantity as the catalyst was 351, 52 (1970). effective both as an oxidizing catalyst and as an adsorbent R. Pohloudek-Fabini und W. Fiirtig, Arch. Pharmaz. of impurities in the methanol suspension. Gas- Ber. Dtsch. Pharmaz. Ges., 292/64, 350 (1959). chromatographic analysis revealed that this DAAprep- T. Kurata, H. Wakabayashi and Y. Sakurai, Agric. aration included about 1% MEK,as was the case for NM Biol. Chem., 31, 101 (1967). in the DAAprepared according to Dietz's method.2) No S. Ono, M. Takagi and T. Wasa, Bull. Chem. Soc. other impurities apart from MEKcould be detected. Jpn., 34, 52 (1961). In order to obtain a purer DAAspecimen, we followed M. Ohmori, H. Akehashi, S. Shigeoka, S. Kitaoka Muller-Mulot's method5) for the recrystallization of DAA. and M. Takagi, Bunseki Kagaku, 26, 56 (1977). Although their original technique of pre-purification by H. Albers, E. Miiller und H. Dietz, Hoppe-Seyler's Z. meansof column chromatography was omitted, DAA Physiol. Chem., 334, 243 (1963). could easily be recrystallized from the solution of the W. Miiller-Mulot, Hoppe-Seyler's Z. Physiol. Chem., above prepared DAAin a mixture of dimethylacetamide 351, 56 (1970). and methylene chloride, whenthe requisite amountsof J. Hvosleff, Ada Cryst., B28, 916 (1972). formic acid and oxalic acid were added. The purity of the recrystallized DAAwas about 99.6%.