OXIDATION PRODUCTS 85 



Although it has been found possible to produce in vitro a 

 small quantity of glucuronic acid from glucose by the action 

 of hydrogen peroxide, this is not a practical method. In 

 the animal and vegetable world, however, conditions appear 

 frequently to arise in which the aldehyde group of the sugar is 

 protected from oxidation by coupling with some other group 

 as a glucoside, leaving the primary alcohol at the other end 

 of the molecule open to attack. Such coupled glucuronic 

 acids occur normally in the urine of animals, but may be 

 increased in quantity by the administration of certain sub- 

 stances. In the plant world glucuronic and galacturonic 

 acids appear similarly combined with other complexes ; the 

 former has been reported as a constituent of glycyrrhizin * 

 and scutellarin f while the latter occurs in pectins. 



These aldehyde acids are known collectively as " uronic " 

 acids ; when heated with hydrochloric acid they are con- 

 verted into furfural with evolution of carbon dioxide. f A 

 method for their estimation based upon the measurement of 

 this carbon dioxide has been devised by ToUens and Lefevre,J 

 and modified by Nanji and Norman. § 



When heated with Bial's reagent, glucuronic acid gives 

 the same colour as pentoses and methyl pentoses, the colour, 

 however, develops rather more slowly. 



When boiled with an equal volume of hydrochloric acid 

 and a small quantity of i per cent solution of naphtho- 

 resorcin in alcohol, the solution darkens, and on shaking up 

 the warm solution with benzene the latter acquires a reddish- 

 violet colour which shows an absorption band at the D line.|l 

 Solutions of pentoses, hexoses or disaccharides under the same 

 conditions yield no colour or at most a faint yellow to the 

 benzene. 



A point of some importance arises in connection with the 

 possibility of the uronic acids acting as intermediate stages 



* Tschirch and Gauchmann : " Archiv. d. Pharm.," 1908, 246, 550. 

 t Goldschmiedt and Zerner : " Monat. d. Chem.," 1910, 31, 441, 476. 

 X Tollens and Lefevre : " Ber. deut. chem. Gesells.," 1907, 40, 4519. 

 § Nanji and Norman : " J. Soc. Chem. Ind.," 1926, 45, 337 T. 

 li Neuberg and Saneyoshi : " Biochem. Zeit.," 191 1, 36, 56 ; van der 

 Haar : id., 1918, 88, 203. 



