II. CHEMISTRY 205 



obtained ilircctly from L-ascorbic acid,'*'- l)ut the reaction is slow and is 

 accompanied l\v some decomposition since oxidation precedes osazone for- 

 mation. The reaction between dehydroascorbic acid and 2,4-dinitrophenyl- 

 hydrazine which gives a prodnct corresponding to LXI\' in good yield 

 forms the basis of one of the better analytical methods for determining the 

 ascorbic acid content of plant and animal prodiicts.^^' '^^' '^^' '^'* Similar 

 derivatives have been obtained with o-phenylencdiamine'*^ and p-sulfamyl- 

 phenylhydrazine.'"^ It has also been shown that, in its reactions with the 

 varions phenylhydrazines'- and o-phenylcnediamine, L-ascorl)ic acid is par- 

 alleled by the beha\ior of D-araboascorbic acid.^^' ^^ 



2. AcYL .\ND Aryl Derivatives 



L-Ascorbic acid does not lend itself easily to acetylation, althongh it is 

 claimed that the 5 , 6-diacetate can be obtained \¥ithout too much diffi- 

 culty.''' An oily tetraacetate has been prepared by vigorous acetylation.'"' 

 Of more interest from a structural point of \'icw is the obser\'ation that 

 treatment of 5 , 6-monoacetone L-ascorbic acid with ketene, until it gives 

 no color reaction with phenolindophenol, yields the 3-acetyl-5 , G-mono- 

 acetone deri\'ative, thus showing the more active nature of the OH at Cs,'^® 

 while a suspension of L-ascorbic acid in acetone treated with ketene affords 

 2,3-diacetyl-5,6-monoacctone L-ascorbic acid.''" Various 2,3-diphenacyl 

 ethers and their corresponding 5,6-diacetates have been prepared in an 

 attempt to determine the activity of ascorbic acid when its dienol system 

 is blocked.''^ 



3. Ethers 



The methyl ethers were of primary importance because it was the study 

 of the 2,3,5, 6-tetramethyl ether of ascorbic acid which finally led to the 

 proof of the structure of L-ascorbic acid. These methyl ethers have also 

 revealed in a striking manner the unique chemical nature of the \'itamin 

 molecule. 



The hydroxyl group at C3 of the ascorbic acid molecule (I) is so much 

 more acidic than that at C2 that it can be preferentially titrated with 

 diazomethane to give 3-methyl-L-ascorbic acid (LXMII), a crystalline 

 substance that gives a blue color with ferric chloride.''"'' ''^' ''^ Simultane- 



1" J. II. Roe and C. A. Kuethcr, ./. Hiol. Chem. 147, 399 (1943); J. H. Roe and M. J. 



Ostcrling, ibid. 152, 511 (1944); O. \. Be.s.soy, O. II. Lowry, and M. J. Brock, ibid. 



168, 1!I7 (1947). 

 »'5 H. Willstaedt, Svensk. Kent. Tidf^kr. 55, 214 (1943). 

 >'« C. S. Vestling and M. C. Rebstock, J. Hiol. Chem. 152, 585 (1944). 

 "^ Y. Sumiki, S. Yamanaka, K. Oka, and A. Takeishi, ,/. Ac/r. Chem. Soc. Japan 



20, 89 (1944). 

 "» C. S. Vestling, and M. C. Rebstock, J. Hiul. Chem. 161, 285 (1945). 



