RIBOFLAVINE 



42. Merck & Co., U.S.P. 2355220. 

 42a. Merck & Co., B.P. 621401. 



43. Commercial Solvents Corporation, U.S.P. 2374503. 



44. Commercial Solvents Corporation, U.S.P. 2367644 ; 2367646 ; 



B.P. 621468, 621552. 



45. R. J. Hickey, Arch. Biochem., 1946, 11, 259 ; Commercial Solvents 



Corporation, U.S.P. 2387023 ; B.P. 621469. 



6. PROPERTIES OF RIBOFLAVINE 



Riboflavine is a bright yellow powder, m.p. 292° C, and its solu- 

 bility in water is 12 mg. per 100 ml. at 27-5° C, and 19 mg. per 100 

 ml. at 40° C. The aqueous solution has a strong yellowish-green 

 fluorescence, which is discharged by acids or alkalis ; the fluorescence 

 is maximal at pK 3 to 9. The solution is laevo-rotatory,^ [aj^" 

 being — 114° in a o-i N sodium hydroxide solution (concentration 

 o*i25). In neutral or acid solution, however, the rotation is very 

 much smaller. In presence of borax the rotation is strongly dextro- 

 rotatory, [a]|°° being + 340° at pK 12. Riboflavine is soluble in 

 aqueous alkali solutions. 



In view of the low solubility in water, which complicates the 

 problem of administering riboflavine, numerous methods have been 

 suggested for preparing solutions containing a relatively high concen- 

 tration of the vitamin. Thus the addition of urea or urethan,^ 

 sodium desoxycholate or N-methylacetamide,^ acetamidine salts,* 

 boric acid,^ /-tyrosine amide,^" tryptophane^ or propylene glycol with 

 or without the addition of a monohydroxymonoalkoxybenzaldehyde ^* 

 has been claimed to increase the solubility of riboflavine in water. 

 Hoffmann-La Roche ^ claimed the use of 2 : 4-dihydroxybenzoic acid 

 or its monoalkyl ethers and of gentisic acid for this purpose, whilst the 

 Winthrop Chemical Co.'' claimed the use of borax which, with alkali, 

 was said to give the complex, 



Ci7Hi906N4Na-Na2B407 . loHp. 

 Eli Lilly & Co.^ used benzoic, aminobenzoic or hydrobenzoic acid and 

 their salts, whilst M. R. Zentner ® heated riboflavine with gallic acid 

 in presence of a dilute mineral acid. Other methods of obtaining more 

 concentrated solutions of riboflavine included the formation of the 

 phthalic or succinic esters ^^ and the citric, malic or tartaric esters ; ^^" 

 and the formation of mono- and di-methylolriboflavine by reaction 

 with formaldehyde. 10^ Riboflavine is soluble in nicotinamide solu- 

 tions, the solubility increasing at pH 5 from about o-i % to about 

 2 '5 % when the nicotinamide concentration was increased from 5 to 

 50 %.^^ Both the pyridine ring and the amide group of nicotinamide 

 are involved. 



154 



