CARBOHYDRATES 



43 



From the standpoint of physiological processes, glucuronic acid 

 is the most interesting and important oxidation product of glucose. 

 It is often found in the urine of animals, as the result of the partial 

 oxidation of glucose in the animal tissues. Normally, glucose is 

 oxidized in the body to its final oxidation products, carbon dioxide 

 and water. But when many difficultly oxidizable substances, 

 such as chloral, camphor, turpentine oil, aniline, etc., are intro- 

 duced into the body, the organism has the power of combining 

 these with glucose to form glucosides. These so-called " paired " 

 compounds are then oxidized to the corresponding glucuronic 

 acid derivatives and eliminated from the body in the urine. No 

 phenomenon similar to this occurs in plants, however, and glu- 

 curonic acid has never been found in plant tissues. 



Synthesis and Degradation of Hexoses. Monosaccharides of 

 any desired number of carbon atoms can be produced from aldoses 

 having one less carbon atoms, by way of the familiar " nitrile " 

 reaction. Aldoses, like all other aldehydes, combine directly with 

 hydrocyanic acid, forming compounds known as nitriles, which 

 contain one more carbon atom than was present in the original 

 aldehyde; the cyanogen group can easily be converted into a 

 COOH group ; and this, in turn, reduced to an aldehyde, thus pro- 

 ducing an aldose with one more carbon atom than was present 

 in the initial sugar. These changes may be illustrated by the 

 folio whig equations: 

 (1) CHO + HCN 



:ci 



(2) 



(CHOH) 3 

 (CH 2 OH 



Aldopentose 



CN 



(CHOH) 4 



H 2 OH 



Nitrile 



COOH 

 (CHOH), 



CH 2 OH 



Acid 



+ H 2 



- 



CH 2 OH 



Acid 



CHO 



= (CHOH) 4 

 CH 2 OH 



Aldohexose 



It is possible, by this process, to advance step by step from 

 formaldehyde to higher sugars, Emil Fischer and his students 



