406 THIAMINE 



B. CHEMICAL AND PHYSICAL PROPERTIES 



Thiamine hydrochloride erystalhzes into colorless, monoclinic needles, 

 which have a melting point of about 250°, a characteristic smell, and a slightly 

 bitter taste. These crystals are stable to the atmospheric oxygen. They are 

 very solul^le in water, much less so in alcohol, and insoluble in ether, and 

 other fat solvents. Thiamine chloride hydrochloride crystallizes from alco- 

 holic aqueous solutions as the hemihydrate, Ci2Hi70N4SCl-HCl-3^H20. 

 Thiamine hydrochloride in water forms a strongly acid solution pH of a 

 5% solution about 3.5; in solution with a pH less than 5 it is fairly stable 

 to heat and oxidation ; this solution shows two absorption bands in the ultra- 

 violet at 235 and 267 mju. 



At a pH of 5 or higher, it is destroyed by autoclaving, and at a pH of 7 

 or more by boiling or merely storing at room temperature. 



By treatment with sulfite it is readily split into the pyrimidine and thia- 

 zole parts. 



In a highly alkaline solution thiamine is oxidized by ferricyanide to thio- 

 chrome (cf. Section VII). 



C. CONSTITUTION 



The work of the above-mentioned investigators has shown that the thia- 

 mine molecule consists of a pyrimidine compound and a thiazole compound, 

 connected by a CH2 bridge. The structural formula of the thiamine hydro- 

 chloride is: 



H CH3 CHa-CHaOH 



C Cf=^C 



/^\ / 



N C CH2 N3 



I 2 6 II I ^^ 



CH3— C CNH2— HCl CI C? — 



\i/ I 



N H 



The elucidation of the constitution was greatly relieved by the discovery 

 of Williams et al}^ that thiamine is quantitatively split by sulfite in faintly 

 acid solutions into the pyrimidine and the thiazole halves: 



C12H18ON4SCI2 + NaoSOs = C6H9N3SO3 + CeHgNSO + 2NaCl 



D. SYNTHESIS 



The synthesis of thiamine has been performed in different ways. It is 

 possible to synthesize the pyrimidine nucleus and the thiazole nucleus sepa- 



11 R. R. Williams, E. R. Buchman, and A. E. Ruehle, J. Am. Chem. Soc. 57, 536 

 (1935). 



