204 



ASCORBIC ACID 



acid'-^ and oxalic acid^^" which complex copper ions, are therefore recom- 

 mended for the extraction which should be done as expeditiously as possible 

 at room temperature to reduce losses by oxidation to a minimum. Solutions 

 of L-ascorbic acid are stabilized to some extent by sodium chloride, ^^^ bo- 

 rates,^^^ and various inorganic and organic compounds of sulfur. ^^^ 



Since dehydroascorbic acid (II) is the lactone of a 2,3-diketoaldonic 

 acid (LXIII), with which it is in equilibrium in aqueous solution, it is not 



HO 



CO- 



M 



HO— C 

 HO-(f 



I 

 HO— C— H 

 I 

 CH2OH 



III 



CO— I 



I 



CO 



I 



CO 



I 



H— CO- 

 I 

 HO— C— H 

 I 

 CH.OH 



II 



COOH 

 I 

 CO 



I 



CO 



I 



H— C— OH 

 I 

 HO— C— H 

 I 

 CH2OH 



LXIII 



CO -I 



I 

 R— NHN=C 



I 

 R— NHN=C 



H— CO— J 

 I 

 HO— C— H 

 I 

 CHjOH 



LXIV 



COOH 

 I 

 R— NHN=-C 

 I 

 R— NHN=C 

 I 

 H— C— OH 

 I 

 HO— C— H 

 I 

 CH2OH 



LXV 



R— N— C— OH 



II 



C— N=NR 

 I 



N=C 

 I 

 H— C— OH 

 I 

 HO— C-H 

 I 

 CH.OH 



LXVI 



R=C6Hi— , />-Br-CcH4— , ?j-NOo-CcH,— and 2,4-(NO,),-CcH3— 



surprising to find that it readily combines with phenylhydrazine and its 

 derivatives. Osazones corresponding to both the open and closed chain 

 forms of dehydroascorbic acid can readily be obtained. The osazone (LXV) 

 of the diketo acid is easily converted into the osazone (LXIV) of the diketo 

 lactone simply by recrystallization. A third compound obtained during the 

 preparation of these osazones is the pyrazolone (LXVI) which can be ob- 

 tained from (LXV) ])y treatment with alkali.''^ These compounds can be 



129 p. Gyorgy, la Vitamin Methods, p. 260. Academic Press, New York, 1950; 



Methods of Vitamin Assay, 2nded., p. 71. Interscience Publishers, New York, 1951. 

 '=*" J. D. Ponting, Ind. Eng. Chem., Anal. Ed. 15, 389 (1943); F. Wokes, Analyst 72, 



63 (1947); F. E. Hailin and I. M. Stephens, Australian J. Exptl. Biol. Med. Sci. 



25, 17 (1947); L. P. Guild, E. F. Lockhart, and R. S. Harris, Science 107, 226 (1948). 

 '3' T. Mar.x, Landwirtsch Forsch. 2, 229 (1951). 

 132 W. E. Militzer, J. Biol. Chem. 158, 247 (1945). 

 "3 R. Stadelmann, Schweiz. Apoih. Zty. 85, 865 (1947). 



