12 



F-AMINOBENZOIC ACID 



for the differentiation of the isomeric aminobenzoic acids. Three samples 

 of the solution to be examined are treated individually with potassium 

 ferrocyanide, potassium ferricyanide, and sodium nitrosylopentacyano- 

 ferrate (II), and the three mixtures are exposed to sunlight. Table III 

 indicates the colors formed in this test. These colored complexes can be 

 extracted with butanol from the acidified aqueous solutions. 



Other reactions in which the production of color has been attributed to 

 the presence of PABA have appeared in the literature. Mayer^^ found that 

 Myohaclerium tuberculosis (human strain) when grown on a medium con- 

 taining PABA elaborates a yellow pigment. The process is enzymatic and 

 requires ions of magnesium and iron. Glucose, ascorbic acid, or sodium 

 cyanide represses formation of the pigment. Little is known concerning the 

 nature of this material, other than that it appears to be some oxidation 

 product of PABA. 



TABLE III 

 Color Test for the Differentiation of the Isomeric Aminobenzoic Acids 



Acid 



K4Fe(CN)6 



K3Fe(CN)6 



Na2Fe(CN)jN0 



Brown-yellow 

 Brown-yellow 

 Brown-red 



III. Industrial Preparation 



H. M. WUEST 



The role of p-aminobenzoic acid in human nutrition has not been estab- 

 lished, nor is a deficiency disease in higher animals known that is caused 

 by its absence in the feed. The industrial importance of the compound as 

 a vitamin is therefore very limited. PARA and its salts, howe\ei', are recom- 

 mended in rickettsial diseases, including Rocky Mountain spotted fever 

 and scrub typhus (4 to C) g. daily). ^ 



The U. S. Pharmacopeia describes PABA as a reagent (not as a pharma- 

 ceutical) and gives criteria for its purity.- Tlie industrial preparation starts 

 from p-niti'otolueiie, whicli is oxidized (e.g., with diiulc nitric acid) to 

 p-nitr()l)enzoic iwid; the reduction to th(> amino acid is done with tin or 

 iron and hydrochloric acid oi- by catalytic hydrogenation. 



88 R. L. Mayer, ./. liacteriol. 48, 337 (19 II). 

 ' i\I. E. Howard, Modern Diufz; l']ncycl()|)edia, |). (KM. Drug l*ul>lishcrs, Xcw Wtvk 



1952. 

 ^ U. S. Pharmacoi)cia, 141 h revision, p. 735, 1947. 



