472 NIACIN 



2615 A. (the same as for nicotinic acid), with the molecular extinctions of 

 the maxima decreasing; as the pH values increased. The molecular extinction 

 coefficients for the peak values are plotted against the pH values in Fig. 6. 

 (e) Dissociation Constants. Jellinek and Gordon^^ studied the hydrolysis 

 of nicotinamide in hydrochloric acid solutions and found that it differed 

 considerably from the hydrolysis of other amides such as benzamide in that 

 the first-order rate constants for the hydrolysis did not pass through a 

 maximum between 0.5 A^ and 8.6 A^ HCl. According to their results, two 

 reactions occur. An equilibrium is set up rapidly: H+ RCONH2 + H+ :^ 

 H+RCONHs+ followed by a slow hydrolysis: H+RCONH3+ + H3O+ -^ 

 H+RCOOH + NH4+ + H+. The hydrolysis showed a positive salt effect 

 (NaCl) . The effects of temperature and hydrochloric acid concentration on 

 the rate of hydrolysis were determined. 



The dissociation constant due to the amido group and the thermodynamic 

 dissociation constant of the nitrogen in the ring were also evaluated spec- 

 troscopically by Jellinek and Wayne.''' Their results indicated a constant 

 of 2.24 X 10"" for the nitrogen in the ring and 3.16 X IQ-^^ as the base 

 constant for the amido group, the latter agreeing well with the studies of 

 HCl hydrolysis. 



(/) Chemical Proverties. Many of the chemical properties of nicotinamide 

 have been referred to previously. Nicotinamide undergoes the Hoffman 

 degradation to 3-aminopyridine.^'' If nicotinamide is distilled with P2O5 at 

 25 mm. pressure or SOCI2 at 100°, 3-cyanopyridine is formed.^^ 



— CONHo 



' S0CI2 



-CN 



or P2O5 



Nicotinamide and esters of nicotinic acid react with acids and alkyl 

 halides to form cjuaternary salts as already depicted for nicotinic acid."- ^^"'^^ 



The carbon in the 6 position seems to be the most reactive ring carbon 

 in nicotinamide.^^ Karrer et al.^'' have demonstrated that an amide group 



" H. H. G. Jellinek and A. Gordon, J. Phys. & Colloid Cfiem. 53, 996 (1949). 



^^ A. Philips, Ann. 288, 253 (1895). 



'5 I. M. Heilbron and H. M. Bunbury, Dictionary of Organic Compounds, Vol. III. 



Oxford University Press, New York, 1946. 

 '« W. Konig, J. prakt. Chem. 69, 105 (1904); 70, 19 (1904). 

 " W. Ciusa and G. Nebbia, Gazz. chim. Hal. 79, 521 (1949). 

 '« M. F. Zienty, J. Am. Phann. Assoc. 37, 99 (1948). 

 7s W. E. Knox and W. I. Grossman, /. Am. Chem. Soc. 70, 2172 (1948). 

 80 P. Karrer, F. Kahnt, R. Epstein, W. Jaffe, and T. Ishii, Helv. Chim. Acta 21, 223 



(1938). 



