11. ('1I1:.M1STRY 7 



and 3 ,5-diiodo-4-aminobenzoic acid, whereas iodine and the potassium salt 

 of PABA react to produce p-iodoaniUne.''-' " 



Diazotization of PABA has been used in the estimation of the vitamin 

 (see section on determination). Saunders"** recommends use of the "in- 

 verted" method for the diazotization of monoamino sulfonic or carboxylic 

 acids which otherwise are not completoly transformed to the diazonium 

 compound because of their low solubility. The "inverted" method consists 

 in adding the nitrite to the alkaline solution of the amino acid and then 

 running this mixture steadily into the chilled mineral acid. Diazotization 

 takes place instantly, and the insoluble material which forms is the diazo 

 compound. 



The formation of such PABA salts as the hydroxylamine salt,"*^ the tri- 

 ethyl lead salt,*^ and the chlorostannate''^ has been described. The acid 

 chloride can be prepared in the usual manner using thionyl chloride.'** 

 Esterification can be carried out in the conventional manner, using an- 

 hj^drous alcohols and dry hydrogen chloride.^^ In practice, the preparation 

 of PABA esters is usually accomplished by reduction of the pre\aously 

 esterified nitro compound."*^"^^ 



Esters of PABA have long been known to possess valuable properties 

 as local anesthetics.®" Although it is beyond the scope of this review to 

 discuss in great detail this aspect of the properties of PABA, it seems 

 desirable to summarize some of the more important considerations in this 



« H. L. Wheeler and L. M. Liddle, Am. Chem. J. 42, 441 (1909). 



" H. L. Wheeler and L. M. Liddle, Am. Chem. J. 42, 498 (1909). 



^^ K. H. Saunders, The Aromatic Diazo-Compounds and Their Technical Applica- 

 tions, p. 9, Edward Arnold and Co., London, 1936. 



'' R. E. Oesper and M. P. Ballard, /. Am. Chem. Soc. 47, 2424 (1925). 



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" J. G. F. Druce, Chem. News 119, 72 (1919). 



« L. McMaster and F. F. Ahmann, J. Am. Chem. Soc. 50, 145 (1928). 



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50 S. D. Goldberg, W. F. Ringk, and P. E. Spoerri, /. Am. Chem. Soc. 61, 3562 (1939) 



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"D. Curtis, U.S. Pat. 2,395,538 (Feb. 26, 1946). 



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«« A. Einhorn, Ann. 371, 125 (1909). 



