. DISACCHARIDES 119 



CELLOBIOSE. Ci,.H,.Pii. 



This is a disaccharide obtained from cellulose by the 

 action of glacial acetic acid and acetic anhydride in the presence 

 of concentrated sulphuric acid. The resulting acetyl deriva- 

 tive, on treatment with alcoholic potash, yields cellobiose. It 

 reduces Fehling's solution and gives an osazone melting at 

 198°. On hydrolysis, it yields two molecules of glucose and 

 is thus isomeric with maltose, but unlike this sugar it is not 

 hydrolysed by maltase but is attacked by emulsin. From 

 these facts Haworth and Peat * conclude that cellobiose and 

 maltose are structurally identical, differing only in the stereo- 

 chemical configuration of their glucose residues. Thus cello- 

 biose is represented by the same formula, as maltose (see p. 117) 

 only is a j8-glucosido-4-glucose, whereas maltose is the cor- 

 responding a-compound. 



Iso-cellobiose. 



An isomeric sugar, isocellobiose, was obtained in the form 

 of its acetyl derivative together with cellobiose acetate on 

 acetolysis of cellulose ; on hydrolysis of the acetyl derivative 

 with baryta, iso-cellobiose f was set free. 



GENTIOBIOSE. Ci.Ha.On. 



This disaccharide % is obtained by the partial hydrolysis of 

 the trisaccharide gentianose (see p. 125) ; by the action of 

 emulsin it is converted into two molecules of glucose, from 

 which it follows that gentiobiose is a j3-glucoside. It has 

 been synthesized by the action of emulsin on glucose, § a 

 method || which provides a more convenient source for its 

 preparation, and also by the action of concentrated hydro- 

 chloric acid on glucose. *[| Gentiobiose is the biose of 



* Haworth and Peat : " J. Chem. Soc," 1926, 3094. 



t Ost and Prosiegel : " Zeit. angew. Chem.," 1920, 33, 100. Ost : id., 

 19-26, 39, 1 1 17. 



X Zemplen : " Bar. deut. chem. Gesells.," 1915, 48, 233. 



§ Herissey, Bourquelot, and Coivre : " J. Pharm. Chim.," 1913- 7> 44i- 



II Georg and Pictet : " Helv. chem. Ace," 1926, 9, 444. Berhn : " J. 

 Amer. Chem. Soc," 1926, 48, 1107. 



M For this method of preparation, see Harding : " Sugar," 1922, 240. 



