196 THE CARBOHYDRATES. 



long time can be obtained immediately by boiling or on the addition of very 

 little ammonia. 



Like the ordinary aldehydes and ketones, the sugars may be made to 

 take up hydrocyanic acid. Cyanhydrins are thus formed. These addi- 

 tion products are of special interest in that they make possible the arti- 

 ficial preparation of sugars rich in carbon from sugars poor in carbon. 



As an example, if we start from dextrose we obtain glucocyanhydrin 

 on the addition of hydrocyanic acid: 



CH 2 .(OH).[CH(OH)] 4 .COH + HCN = CH 2 (OH).[CH(OH)] 4 .CH(OH).CN. 



On the saponification of glucocyanhydrin the corresponding oxyacid is 

 formed : 



H 2 (OH).[CH(OH)] 4 .CH(OH).CN + 2H 2 



= CH 2 (OH).[CH(OH)] 4 .CH(OH).COOH + NH 3 . 



By the action of nascent hydrogen on the lactone of this acid we obtain 

 glucoheptose, CyH^Oy and according to this principle the construction 

 of sugars up to nine carbon atoms has been accomplished. 



The monosaccharides give the corresponding oximes with hydroxyl- 

 amine; thus glucose yields glucosoxime, CH 2 (OH).[CH(OH)] 4 .CH:N.OH. 

 These compounds are of importance on account of the fact, as found by 

 WoHL, 1 that they are the starting-point in the formation of one class 

 of sugars from another class, namely, the preparation of sugars poor in 

 carbon from those rich in carbon. For example pentoses from hexoses 

 (see WOHL). 



According to RUFF, by the action of hydrogen peroxide and the cata- 

 lytic action of ferric salts upon the carbohydrate monocarboxylic acids 

 the carbon chain can be shortened by the splitting off of the elements 

 of formic acid, and with the formation of the next lower aldose. NEU- 

 BERG 2 has accomplished the same result by electrolysis, and by this 

 method has split glucose step by step into formaldehyde. 



By the action of alkalies, even in small amounts, as also of carbonates 

 and lead hydroxide, a reciprocal transformation of the sugars, such as 

 d-dextrose, d-levulose, and d-mannose, may take place (LOBBY DE BRUYX 

 and ALBERDA VAN EKENSTEIN S ), and from each of these three varieties 

 of sugar the two others are produced so that after a certain time the 

 solution contains all three sugars. 



The transformation of the different varieties of sugar into each other 



1 Ber. d. d. chem. Gesellsch., 26, p. 730. 



2 Ruff, Ber. d. d. chem. Gesellsch., 31 and 32; Neuberg, Biochem. Zeitschr., 7. 



3 Ber. d. d. chem. Gesellsch., 28, 3078; Bull. soc. chim. de Paris (3), 15; Chem. 

 CentralbL, 1896, 2, and 1897, 2. 



