1 88 GLUCOSIDES 



Preparation. 



Salicin may be prepared by boiling the willow bark with 

 water which will extract a certain amount of tannin, colouring 

 and other matters together with the salicin. The greater part 

 of impurities may be precipitated by the addition of lead 

 acetate. The precipitate is then filtered and a stream of 

 sulphuretted hydrogen is passed through the filtrate in order 

 to remove the lead. The filtrate on evaporation yields crystals 

 of salicin which may be further purified by recrystallization 

 from alcohol. 



Another method is to treat the bark with benzene in order 

 to remove resinous substances, colouring matters, etc., and then 

 digest with alcohol (sp. gr. -85). The solution thus obtained 

 will contain the glucoside and tannin ; the latter substance 

 may be removed by precipitation with hide powder or with 

 gelatine. The filtrate will contain the salicin, which on evapora- 

 tion and cooling will be deposited in the form of crystals. 



Salicin is hydrolysed by emulsin to glucose and the alcohol 

 saligenin according to the following equation : 



C 13 H 18 7 + H 2 = C 6 H U 6 + C 6 H 4 OH CH 2 OH 



Salicin Saligenin 



By the action of sulphuric acid and potassium bichromate 

 salicin is oxidized to salicylic aldehyde C 6 H 4 OHCHO ; this 

 substance is a fragrant colourless liquid, b.p. 196, which 

 occurs in the essential oil of Spircea Ulmaria ; it is soluble in 

 water, the solution giving an intense violet coloration with ferric 

 chloride ; salicylic aldehyde stains the skin yellow. 



By employing dilute nitric acid as the oxidizing agent, 

 salicin is converted into helicin, a glucoside which on hydrolysis 

 yields glucose and salicylic aldehyde : 



c i3 H i 8 O 7 + O = C 12 H 16 O 7 + H 2 O 

 Salicin Helicin 



C 12 H 1? 7 + H 2 = C 6 H 12 6 + C 6 H 4 OHCHO 

 Helicin Salicylic aldehyde 



The investigations of Weevers tend to show that ordinarily 

 in the decomposition of salicin, saligenin is really an inter- 

 mediate substance, the ultimate products being glucose and 

 catechol. Thus salicase splits salicin into glucose and sali- 



