152 



GLUCOSIDES AND 



[CH. 



boiling alcohol. Filter and distil off the alcohol from the extract in vacuo. Extract 

 the residue with 100-200 c.c. of hot water and filter. Warm the filtrate and precipitate 

 with lead acetate solution until no more precipitate is formed. This removes flavones, 

 tannins, etc. but the arbutin is not precipitated. Filter and pass sulphuretted hydrogen 

 into the filtrate to remove any excess of lead acetate. Filter and concentrate the 

 filtrate in vacua to a syrup. Then extract twice with small quantities of ethyl acetate. 

 Concentrate the ethyl acetate on a water-bath and cool. A mass of crystals of arbutin 

 will separate out. This should be filtered off on a small filter, and recrystallized from 

 ethyl acetate. Take up a little of the purified glucoside in water and add a drop or 

 two of ferric chloride solution. A blue coloration will be given. 



Salicin. This substance occurs in the bark of various species of 

 Willow (Salix) and Poplar (Populus): also in the flower-buds of the 

 Meadow-Sweet (Spiraea Ulmaria). On hydrolysis with acids, or on 

 treatment with emulsin, salicin is decomposed into saligenin or salicylic 

 alcohol and glucose: 



C 13 H 18 7 + H 2 - C 6 H 4 OH CH..OH + C 6 H 12 O 6 



Saligenin gives a violet colour with ferric chloride solution and in this 

 way the progress of the reaction can be demonstrated (see also p. 148). 



Indican (see also p. 115). This glucoside occurs in shoots of the 

 so-called "Indigo Plants," Indigofera Anil, I. erecta, I. tinctoria, I. suma- 

 trana: also in the Woad (I satis tinctoria), in Polygonum tinctorium and 

 species of the Orchids, Phajus and Calanthe. When boiled with acid or 

 hydrolyzed by an enzyme contained in the plant, it gives glucose and 

 indoxyl : 



0-C 6 H n 5 



+ C 6 H 12 O e 



The colourless indoxyl can be oxidized either artificially or by an 

 oxidase contained in the plant to a blue product, indigotin or indigo. 



OH 



Indoxyl 



Indigo 



