II. CIIKMISTUY 183 



l>C(-'ame iutcnsilied durinj; \\'orld War II l)ecausc the import of citrus fruits 

 into Europe and Asia was stopped and also because there was an inadequate 

 supply of synthetic ascorbic acid to provide the dietary reciuirement. Still 

 more recently unripe walnuts (ascorbic acid content O.G to l.0%)-'^' ^^ and 

 the West Indian cherry (Malpighia punidfolia) have been found to contain 

 relatively larse amounts of ascorbic acid (1.0 to 1.4%).-^ It appears that 

 the West Indian cherry is the richest fruit source of ascorbic acid so far 

 discovered .2^ 



It is of interest to compare the difficulties encountered by Zilva, Szent- 

 Gyorgyi, and King in their early attempts to concentrate and crystallize 

 ascorbic acid before its labile chemical nature was known, with the ease 

 with which it can be isolated in the pure crystalline form from natural 

 sources now that the chemistry of the substance is known and the appro- 

 priate precautions are taken to prevent decomposition (e.g., see procedure 

 given in ref. 25). 



C. CHEMICAL NATURE AND CONSTITUTION OF l-ASCORBIC 



ACID 



Vitamin C or hexuronic acid is a white crystalline compound (formula 

 CeHsOe) with a melting point of 192° and a specific rotation in water of 

 Wd + 23°. It reacts as a monobasic acid and liberates carbon dioxide from 

 carbonates and bicarbonates to form well-defined salts with the general 

 formula CsHyOeM. Vitamin C is a very powerful reducing substance, being 

 much more strongly reducing than the normal sugars as indicated by its 

 ability to reduce Fehling's solution and Tollens' ammoniacal silver nitrate 

 at room temperature.^- Its reducing action on silver and gold salts to give 

 the metals is so efTective that the reaction has been recommended as an 

 analytical method for the determination of gold-^ and silver^^ and also for 

 determining vitamin C concentrations in certain natural products.^" It dis- 

 plays many of the color reactions shown by carbohydrates, probably be- 

 cause upon treatment with rather strong acids it gives furfuraldehyde.'" 

 The formation of the latter and the fact that upon reduction ascorbic acid 

 gives L-idonic acid'' show that the six carbon atoms in the vitamin molecule 

 form a straight chain. Ascorbic acid shows the remarkable property of 

 reacting immediately in the cold with two equivalent proportions of the 



" A. A. Klose, J. B. Stark, G. G. Purvis, J. Peat, and H. L. Fevold, Tnd. Eng. Chem. 



42, 387 (1950). 

 26 C. F. Asenjo and A. R. Froire de Guzmdn, Science 103, 219 (1946). 

 " C. F. Asenjo and C. G. Moscoso, Food Research 15, 103 (1950). 

 " E. C. Stathis and H. C. Gatos, Ind. Eng. Chem. Anal. Ed. 18. 801 (1946). 

 29 E. C. Stathis, Anal. Chem. 20, 271 (1948). 



'" C. Griebel and M. Rohkohl, Z. Lebensm. Untersuch. u. Forsch. 88, 2 (1948). 

 3> F. Micheel and K. Kraft, Hoppe-Seyler's Z. physiol. Chem. 218, 280 (1933). 



