II. CHEMISTRY 



225 



2. Physical Properties 



Pyridoxine hydrochloride, CsHuXOs-IICl, occurs as white platelets, 

 melting point 204 to 206° with decomposition. The free base, CgHnNOa , 

 melts at 1()0°. The compound is optically inactive.'- Both base and hydro- 

 chloride readily sublime without decomposition. 



The hydrochloride is freely soluble in water but sparingly in alcohol 

 and acetone.* The base is soluble in methanol and is not precipitated from 

 methanol solution bv ethyl ether.'' 



2600 



3000 



3400 



3700 



Fig. 1. Absorption spectra of vitamin Bo at: O, pH 4; •, pH 5.1; V, pH 6.75 



(Stiller et aL"). 



Rapid destruction of pyridoxine by light occurs in neutral and alkaline 

 solutions.'^ In 0.1 N HCl there is very little destruction. 



The tautomeric properties of pyridoxine are well illustrated by the 

 changes in its ultra\aolet absorption produced by varying the hydrogen 

 ion concentration.^- The single maximum at 2925 A. at pH 2 diminishes in 

 intensity at pH 4.5, and concomitantly a new maximum appears at 3275 

 A. This latter band increases in intensity when the pH is changed to 6.75, 

 and the 2925 .V. maximum disappears but a new ])and appears at 2500 \. 

 When the pH is further raised to 10.2 both Ixuids increase in intensity and 



'« M. Hochberg, D. Mehiick, L. Segel, and H. L. User, ./. Biol. Clicm. 148, 253 (1943). 



