II. CHKMISTRY 11 



E. COLOR KKACTIONS 



A miinbor of color reactions haxc been (icscribt'd with reference to 

 PABA. One such reaction, wliich may be used as a ([ualitative test for the 

 acid, is to be found in MuUiken."^ The addition of one (h-op of a saturated 

 sohition of bleaching; powtler to an aciueous sohition of the acid produces a 

 red to violet coloration which changes to an opacjue orange after 5 minutes. 



The coloriuK^ric method for the determination of sulfanilamide developed 

 b_y Marshall and his colleagues^^"^' and subsequently modified by Bratton 

 and ^FarshalF has since been applied to the estimation of P.VBA.*^ The 

 basis for the method is the formation of a red to purple dye which results 

 when diazotized P.VBA is made to couple with a suitable arylamine. 



When PAB.V in glacial acetic acid solution is made to react with a 1 % 

 solution of p-dimethylaminobenzaldehyde in the same solvent, a deep- 

 yellow color is produced. Tauber and T.aufer^^ have described a quantitative 



CH, 



X— <^ ^— CHO + HoN— <^ ^— COOH 



CH, 



CHs 



— CH=N— <x >— COOH 



CH3 



assay for PABA based on this reaction. The test is not given by the ali- 

 phatic amino acids or by tyrosine, phenylalanine, glutathione, urea, panto- 

 thenic acid, niacin, niacinamide, or thiamine. Substances which were found 

 to give rise to a similar coloration (e.g., the 0- and m- aminobenzoic acids 

 and their esters, anihne and some of its derivatives) are not normally 

 present in biological materials. 



Kirch and Bergeim^^'^^ observed that diazotized thiamine will couple 

 with PAB.\ to yield a red-colored dye. 



Xakahara and his associates^" have devised a scheme based on color tests 



" E. K. Marshall, Jr., K. Emorson, Jr., and W. C. Cuttiufi, ./. Am. Med. Assoc. 108, 



953 (1937). 

 8»E. K. Marshall, Jr., I'roc. Sue. Expll. Biul. Med. 36, 122 (1937). 

 81 E. K. Marshall, Jr., J. Biol. Chem. 122, 263 (1937-1938). 

 « A. C. Bratton and E. K. Marshall, Jr., ,/. Biol. Chem. 128, 537 (1939). 

 " E. Strau.ss, F. C. Lowell, and M. Finland, ./. Clin. /nw.s/. 20, 1S9 (1941). 

 8^ H. Tauhor and S. Laufer, ./. Am. Chem. Soc. 63, 14SS (1941). 



85 E. II. Kirch and O. BerKeim. ./. Biol. Chem. 148, 445 (1943). 



86 E. R. Kirch and (). Bergeim, ./. Bi(d. Chem. 143, 575 (1942). 



8' W. Nakahara, S. Ugami, and Y. Nagata, Set. Papers Inst. Phys. Chem. Research 

 (Tokyo) 42, 45 (1945) [C.A. 42, 1531 (1948)]. 



