112 THE CARBOHYDRATES. [cH. V 



112. Prepare the osazone as directed in Ex. 109. It is identical 

 with glucosazone. 



NOTE. The reaction between fructose and an excess of phenyl-hydrazine 

 is as follows : 



CH 2 OH CH : N.NH.C 6 H 5 



c = o c : N.NH.C.HS 



I + 3 C 6 H 5 .NH.NH 2 = | 



*(CHOH) 3 *(CHOH) 8 



CH 2 OH CH 2 OH 



+ 2 H 2 O + NH 3 + C 6 H 6 NH 2 



The configuration of the three secondary alcoholic groups indicated by * is 

 identical in glucose and fructose (see formula on page 101). It follows that the 

 osazones are identical. 



113. Repeat Ex. no. It is obtained with great brilliance. 



114. To about 15 drops in a test-tube add 6 drops of a i per 

 cent, alcoholic solution of a-napthol and 5 cc. of concentrated HC1. 

 Boil. The solution becomes deep purple as soon as the mixture is 

 vigorously boiling. 



NOTES. i . This modification of the furfurol test is given only by fructose, 

 sucrose and the pentoses. Glucose, maltose, lactose, and the common poly- 

 saccharides only give an intense colour after being boiled from i to 2 minutes. 



2. Fructose, either in the free state or produced from sucrose by acid 

 hydrolysis and the pentoses, readily yield furfurol (furfuraldehyde) by the 

 action of strong HC1. With H 2 SO 4 furfurol is readily produced from all 

 carbohydrates (see Ex. no). 



3. Furfurol is HC CH 



HC\ /C.CHO 



O 



It reacts with a-napthol, thymol, bile salts (see Ex. 315) in the presence of 

 strong acids to give coloured compounds. 



4. Proteins that contain a carbohydrate group also give a reaction 

 (see Ex. 26). 



115. Seliwanoff's test for fructose. To 5 cc. of Seliwanoff's 

 reagent add a few drops of the sugar and heat the solution to boiling. 

 A red colouration and a red precipitate are formed. The precipitate 

 dissolves in alcohol, to which it imparts a striking red colour. 



NOTES. The reagent is prepared by dissolving 0-05 gram, of resorcin in 

 100 cc. of hydrochloric acid, diluted with its own volume of water. 



The test is also given by glucose after long boiling, but a precipitate is not 

 usually formed. 



