170 GLUCOSIDES 



whilst the enzyme amygdalase * contained in yeast, is only 

 able to effect a partial hydrolysis to glucose and mandelo- 

 nitrile glucoside.f 



C2oHo,NO„ + H,0 = CgHiaOe + Cj^H^NOg 



On the other hand, emulsin can hydrolyse other gluco- 

 sides, besides amygdalin, such as salicin, arbutin, etc. 



THE CONSTITUTION OF THE GLUCOSIDES. 



The constitution of the natural glucosides can be best 

 understood by a brief consideration of the simplest known 

 artificial glucosides which have been synthesized from glucose. 



The constitution of glucose is ordinarily represented by 

 the formula CH2OH CHOH CHOH CHOH CHOH CHO, 

 which shows it to be a pentahydric alcohol and an aldehyde 

 at the same time. When dissolved in water, however, it 

 behaves in a peculiar manner, exhibiting the phenomenon 

 of muta-rotation, that is to say, the optical activity of the 

 resulting solution does not attain a steady value until some 

 time after the solution has been made up. 



The change is supposed to be connected with some altera- 

 tion in its molecular configuration which may be explained by 

 assuming that the compound 



/OH 

 CHjOH CHOH CHOH CHOH CHOH CH^ 



^OH 



is temporarily formed,^ but that water is thereupon split off 

 again between one of the hydroxyl groups of the terminal 

 carbon atom and the hydroxyl attached to the fourth carbon 

 atom as follows : — 



OH 



I /OH 



CH„OH CHOH CH CHOH CHOH CH<: -» 



' \OH 



!;H CHOH CHOH CI 



CH5OH CHOH CH CHOH CHOH CHOH + H3O 



•Caldwell and Courtauld : " Proc. Roy. Soc, Lond.," B., 1907, 79, 350. 



t Fischer: " Ber. deut. chem. Geselle.," 1899, 28, 1509. 



X Compare the formation of similar compounds from other aldehydes (p. 149). 



