42 CHEMISTRY OF PLANT LIFE 



Glucose (CeHizOe) Methyl Glucoside (C 7 H M O) 



CHO CHO 



(CHOH) 4 (CHOH) 4 



CH 2 OH CHOH 



CH 3 ' 



A general formula for glucosides is R- (CHOH) 5- CHO; and the R 

 may represent a great variety of different organic radicals (see 

 the chapters dealing with Glucosides and with Tannins). When 

 the glucosides are hydrolyzed, they yield glucose and the hydroxyl 

 compound of the radical with which it is united. All the state- 

 ments which have been made with reference to glucosides, apply 

 equally well with reference to fructosides, galactosides, manno- 

 sides, etc. 



It is possible, by various laboratory processes, to replace 

 additional hydrogen atoms in the glucose molecule with the same or 

 other organic radicals, thus producing glucosides containing two or 

 more R groups; but most of the natural glucosides contain only 

 one other characteristic group. 



Oxidations. When the hexoses are oxidized they give rise to 

 three different types of acids, depending upon the conditions of 

 the oxidation and the kind of oxidizing agent used. With glucose, 

 for example, the relationships involved may be illustrated as 

 follows: 

 CHO COOH CHO COOH 



(CHOH) 4 (CHOH) 4 (CHOH) 4 (CHOH) 4 



I I I I 



CH 2 OH CH ? OH COOH COOH 



Glucose Gluconic acid Glucuronic acid Saccharic acid 



An important property of the acids of the gluconic type is that 

 when heated with pyridine or quinoline to 130-150 they undergo 

 a molecular rearrangement whereby the acid corresponding to 

 an isomeric sugar is produced. For example, gluconic acid, under 

 these conditions, becomes mannonic acid, which can be reduced to 

 mannose. The process is reversible; mannose can be converted 

 to mannonic acid, thence to gluconic acid, thence to glucose. 

 Similarly, galactonic acid can be converted into talonic acid, and 

 this to talose, and this process is reversible. These facts afford 

 another means of conversion of one sugar into another. 



