X] 



GLUCOSIDES 



167 



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 vacuo 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 re- 

 crystallized 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 : 



CisHiaOv + H2O = CgHpH • CH,OH + C^HiaOe 



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

 way the progress of the reaction can be demonstrated (see also p. 168). 



Indican. This glucoside occurs in shoots of the so-called "Indigo 

 Plants," Indigofera Anil, I. erecta, I. tinctoria, I. sumatrana: also in 

 the Woad (Isatis tinctoria), in Polygonum tinctorium and species of the 

 Orchids, Phajus and Galanthe. When boiled with acid or hydrolyzed by 

 an enzyme contained in the plant, it gives glucose and indoxyl: 



/\ 



-c-o 



.^\ 



+ H,0 



CH 

 Indican 



-C'OH 



+ CeHisOe 



CH 



Indoxyl 



The colourless indoxyl can be oxidized either artificially or by an 

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



/\ 



C'OH HO-C- 



+ 20+ II 



,. n CH 



Indoxyl 



"^ ,Ay 



/\ 



2HoO + 



-CO OC 



/S 



NH' 



'^NH^^ 



\NH 



Indoxyl Indigo 



The relationship between indoxyl and tryptophane (see p. 135) should 

 be noted. 



V 



