CHEMISTRY OF PURINES AND PYRIMIDINES 119 



4 and 6;^^^ this structural requirement is essentially independent of the 

 nature of the substituent at position 2. 



When uric acid is heated for 30 hours with acetic anhydride and pyiidine, 

 8-methylxanthine is formed by a ring closure of the intermediate 4 , 5-diace- 

 tylaminouracil.^^" This result was confirmed by Biltz and Schmidt.^'*' Carbon 

 dioxide and acetic acid result from the ring closure. Bredereck, et al.^*'^ 

 have recently studied this reaction in detail. Uric acid is converted, upon 

 reaction with formic acid at 220-230°, into xanthine and carbon dioxide.^^'^ 



h. Actian of Reducing Agents; Polarographic Behavior 



Uracil is reduced to 4,5-dihydrouracil at 75° under 2 atmospheres of 

 hydrogen in the presence of a platinum catalyst.^^' Under identical condi- 

 tions, cytosine is converted to the same product, ^vith the liberation of 

 ammonia.^^^ The resulting dihydrouracil is much less stable to hot acid (as 

 well as alkah at room temperature^^^) and is thereby converted to /3-ala- 

 nine.^*^ These reactions have been exploited in a degradation procedure^^^ 

 in which each carbon atom of isotopically labeled uracil can be directly 

 analyzed for its isotope content. 



Whereas adenine and hypoxanthine are unaffected, aqueous solutions 

 of purine hydrochloride and 2-hydroxypurine each absorb one mole of 

 hydrogen at one atmosphere at room temperature under the influence of a 

 palladium-charcoal catalyst.^^^ The resulting dihydropurine derivatives are 

 quite unstable in the presence of dilute mineral acid giving rise to substances 

 containing a diazotizable amino group. 



Agents such as sodium amalgam, sodium and ethanol, etc., reduce a 

 number of pyrimidines and effect a rupture of the ring system (cf. Johnson'* 

 for details). Electrolytic reduction (lead cathode, 7-9°) of 4-methyluracil 

 in 50% sulfuric acid gives 2-hydroxy-4-methyltetrahydropyrimidine and 

 1 ,3-diaminobutane.^''^ Purone (4,5-dihydro-6-deoxyuric acid) and tetra- 

 hydrouric acid result from a similar reduction of uric acid.^^* 



Adenine, adenosine, and adenylic acid in 0.1 A'' perchloric acid are re- 



339 B. Lythgoe, A. R. Todd, and A. Topham, /. Chern. Soc. 1944, 315. 



3" H. Bredereck, I. Hennig, and W. Pfleiderer, Cheni. Ber. 86, 321, 333 (1953) : these in- 

 vestigators attribute the original work to C. F. Boehringer and sons, German Pats. 

 121,224 and 126,797 (1901). 



3" H. Biltz and W. Schmidt, Ann. 431, 70 (1923). 



3« H. Biltz and A. Beck, /. -prakt. Chem. [2] 118, 166 (1928). 



3" E. B. Brown and T. B. Johnson, J. Am. Chem. Soc. 45, 2702 (1923). 



3" E. B. Brown and T. B. Johnson, /. Am. Chem. Soc. 46, 702 (1924). 



3^^V. Lagerkvist, Acta Chem. Scand. 7, 114 (1953). 



3" A. Bendich, P. J. Russell, Jr., and J. J. Fox, /. Am. Chem. Soc. 76, in press (1954). 



'" J. Tafel and A. Weinschenk, Ber. 33, 3378 (1900). 



3« J. Tafel, Ber. 34, 258, 1181 (1901). 



