II. CHEMISTRY 203 



prodiu'cd ill solution by tho action ol" the halogens; chlorine, hroniine, and 

 iodine, acid potassium permanganate,^'' ferric salts, *^ quinone, phenolindo- 

 phenol,^ 2,C)-dichloroph(Mi()lin(lophenol,'^ methylene blue,''" and perinaph- 

 thindane trione.'-' 'Vhv formation of dehydroascorbic acid is a well-de(in(>d 

 reaction and, cons(Miueii11y, a number of the above reagents have been 

 found to give excellent results in determining L-ascorbic acid in solutions 

 of the pure substance or in the absence of interfering substances (see also 

 p. 253). IMany attempts have been made to apply such methods, including 

 potentiometric'-'- and polarographic'-^ and colorimetric'-' procedures, to the 

 determination of the amount of Nitamin C in various plant and animal 

 tissues and various biological specimens, but as far as this author is aware 

 there seems to be no single method which is generally applicable.^* Inter- 

 ference from a number of natural products makes the determination of 

 L-ascorbic acid in any one type of natural product a major research in 

 itself.^"' '-^ If stabilization of the L-ascorbic acid in an extract can be en- 

 sured, it would appear that paper partition chromatography might be use- 

 ful in dealing with this problem. 



Freshly prepared samples of dehydroascorbic acid (II), unlike solutions 

 of the parent \itamin, show no selective absorption in the ultraviolet region 

 of the spectrum and, consequently, it is believed to exist in the hydrated 

 form (III) ;*2 in alcohol it appears to form an alcoholate and, indeed, when 

 the dehydro compound is properly prepared it crystallizes readily from 

 methanol with solvent of crystallization.'" Dehydroascorbic acid undergoes 

 hydrolysis in aqueous solution,^-' '-° and in the presence of air'-* and traces 

 of copper^^ it readily decomposes to give oxalic acid. In alkaline solution 

 in the presence or absence of air it undergoes profound degradation. It is 

 thus apparent that especial care must be taken in extracting natural prod- 

 ucts and preserving the extracts, in any problems which have to do with 

 isolation or analysis. Acids, and preferably those such as w-phosphoric 



121 M. S. El Ridi, 11. INIoubasher, and Z. F. Hassan, Biochcm. J. 49, 246 (1951). 



1" L. J. Harris, L. W. Mapson, and Y. L. Wang, Biochem. J. 36, 183 (1942) ; C. Spacu 



and P. Spacu, Z. anal. Chem. 128, 233 (1948). 

 1" R. Perrin and D. D. Perrin, New Zealand J. Sci. Technol. 28A, 266 (1946); K. 



Weisner and K. Schaferna, Chem. List], 38, 211 (1944) [C'.A. 44, 5948 (1950)]; D. M. 



Coulson, VV. R. Crowell, and S. L. Friess, Anal. Chem. 22, 525 (1949). 

 »" W. B. Robinson and K. Stotz, J. Biol. Chem. 160, 217 (1945); G. Mannelli, M ikro- 



chemie ver. Mikrochim. Acta 35, 29 (1950); B. Naganna and P. Ramachandra Rao, 



Current Sci. (India) 18, 2.50 (1949). 

 1" G. W. Probst and M. O. Schultze, J. Biol. Chem. 187, 453 (1950). 

 1" S. S. Jacket, E. H. Mosbach, and C. G. King, Arch. Biochem. and Biophys. 31, 442 



(1951). 

 »" B. Pecherer, J. Am. Chem. Soc. 73, 3827 (1951). 

 '" B. Rosenfeld, J. Biol. Chem. 150, 281 (1943). 



