EXAMINATION OF SUGARS 29 



cuprous oxide CugO. This reaction is quantitative and 

 can be used for the estimation of sugars (see p. 152). 



Cane sugar does not give this reaction unless it has 

 been previously inverted by boiling for a few seconds 

 with a dilute acid, whereby it is converted into equal 

 molecules of glucose and fructose — 



Cane sugar Glucose Fructose. 



The sugars on oxidation with Fehling's solution give 

 many different substances, such as tartronic, formic, and 

 oxalic acids. 



{c) Reaction with Phenylhydrazine. — Two grams of 

 glucose or fructose are dissolved in 15 c.c. water and the 

 solution added to 2 grams phenylhydrazine dissolved in 

 just sufficient dilute acetic acid. The mixture is heated 

 for half an hour on the water-bath, when the whole of 

 the sugar is precipitated in the form of its glucosazone. 

 Cane sugar does not give this reaction unless inverted, 

 and the acid used for hydrolysis neutralised. 



The formation of glucosazone from glucose takes 

 place in three stages with the intermediate formation of 

 glucose phenylhydrazone, thus — 



(i.) CH.OH CHoOH 



I I 



CHOH CHOH 



I I 



CHOH CHOH 



I = I +H2O 



CHOH CHOH 



I I 



CHOH CHOH 



I I 



CHO + HgN.NH.CeHg CHiN.NH.CgHg 



Phenylhydrazine. 



