246 GLUCOSIDES 



enzyme myrosin into glucose, potassium hydrogen sulphate, 

 and allyl isothiocyanate — 



CioHieOsNKS^ + H^O = C,U,,0^ + KHSO, + CH^ : CHCH^NCS 



Sinigrin crystallizes from alcohol in needles and from 

 water in prisms, m.p, 126-127° C. 



CONIFERIN. 



This glucoside occurs in various coniferous trees, especially 

 in young parenchyma, and also in asparagus. With concen- 

 trated sulphuric acid coniferin gives a violet coloration, while 

 hydrochloric acid and phenol give a blue coloration ; it also 

 gives a bright coloration with phloroglucinol and hydro- 

 chloric acid (see p. 219). 



Coniferin crystallizes in needle-shaped crystals, m.p. 185°, 

 and is soluble in warm water and warm alcohol. On hydrolysis 

 by mineral acids or by emulsin it gives glucose and coniferyl 

 alcohol — 



CieH^Ps + HjO = CeHi,Oe + CioH^.O:, 

 Coniferin Coniferyl 



alcohol 



The latter is a crystalline substance melting at y2,°. 



Both coniferin and coniferyl alcohol when oxidized with 

 potassium bichromate and sulphuric acid yield vanilhn, the 

 aromatic constituent of the fruits of Vanilla planifolia. 



The reaction was formerly employed for the preparation of 

 artificial vanillin, but has now been replaced by the oxidation of 

 isoeugenol, which is obtained by the action of dilute alkalis 

 upon eugenol, a substance contained in oil of cloves. 



The relationship between these three substances is as 

 follows : — 



SALICIN. 

 Salicin, CiaHjgO,, occurs in the bark of Salix viminalis. 

 It has a bitter taste and crystallizes in colourless prisms and 



