SALICIN 187 



capable of furnishing an aldehydic group and the same 

 reactions are likewise given by salicylic and cinnamic alde- 

 hydes, while coniferin contains no aldehyde group but yields 

 vanillin on oxidation. 



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 : 



C 16 H 22 S + H 2 = C 6 H 12 6 + C 10 H 12 3 

 Coniferin Coniferyl 



alcohol 



The latter is a crystalline substance melting at 73. 



Both coniferin and coniferyl alcohol when oxidized with 

 potassium bichromate and sulphuric acid yield vanillin, 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 artificial vanillin, but has now been replaced by the oxidation of 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 : 



CH = CHCH 2 OH CHO 



|OCH 3 



OH OH OH 



Coniferyl alcohol Vanillin Isoeugenol 



SALICIN. 



Salicin, C 13 H 18 O 7 , occurs in the bark of Salix viminalis. 

 It has a bitter taste and crystallizes in colourless prisms and 

 scales. It is sparingly soluble in cold water but is more soluble 

 in hot alcohol, especially amyl alcohol, and may be extracted 

 from aqueous solutions by means of this solvent. Microscopic- 

 ally, salicin is indicated by the fact that it gives a bright red 

 colour with strong sulphuric acid, also with Frohde's reagent * 

 it yields a violet coloration. On steeping the section in a 

 solution of emulsin, saligenin is produced which gives a blue 

 colour with ferric chloride. 



* Sodium molybdate dissolved in concentrated sulphuric acid. 



