186 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



CH 9 OH 



i.H 



I 



.C.OI 

 HO.C.H 



HO 



I 

 H.C.OH 



AH. 



d-sorbose. 



Constitution of the Aldoses (Glucose). 



Analysis and molecular weight determinations show that glucose has the 

 empirical formula CH 12 O<j. The 6 atoms of carbon are joined together 

 in a straight chain as is shown by its reduction with hydriodic acid into normal 

 hexyl iodide. The stability of the compound and the formation of esters 

 with 5 molecules of acid show the presence of five OH groups attached to 

 different carbon atoms. The remaining group is an aldehyde group as shown 

 by the aldehyde reactions and the formation of an acid, gluconic acid, by 

 oxidation. Further oxidation of glucose gives a dibasic acid by the oxidation 

 of the primary alcohol group. 



Glycuronic acid, another oxidation product of glucose, is formed in the 

 animal body ; in the formation of this compound the primary alcohol group 

 of glucose is oxidised whilst the aldehyde group is unchanged. Glycuronic 

 acid is formed under certain conditions, e.g. after the administration of 

 chloral hydrate. Chloral, and also other compounds, apparently combine 

 with the aldehyde group of glucose ; the alcohol group is then oxidised in 

 the body and the combination product (paired glycuronic acid) is excreted in 

 the urine. The best source of glycuronic acid is euxanthic acid, the calcium 

 and magnesium salt of which constitutes the yellow pigment, Indian 

 yellow. This is obtained from the urine of cows that have been fed on 

 mango leaves. Glycuronic acid is prepared by hydrolysis of the Indian 

 yellow, or other combination product. We have therefore 



CH 2 OH CH a OH COOH COOH 



(CHOH) 4 (CHOH) 4 (CHOH) 4 (CHOH) 4 



CHO COOH COOH CHO 



Glucose. Gluconic acid. Saccharic acid. Glycuronic acid. 



Constitution of the Ketoses (Fructose). 



The 6 carbon atoms in fructose are present in a straight chain. It can 

 be reduced to normal hexyl iodide. Five hydroxyl groups are present. On 

 oxidation fructose breaks down giving trihydroxybutyric acid and glycollic 

 acid, which shows the presence of a ketone group and in the position shown 

 in the formula. Further proof of the position of the ketone group is given 

 by the formation of a cyanohydrin which yields an acid. This acid on 

 reduction gives methylbutylacetic acid. 



Glucose and the other hexoses are represented above as hydroxy 

 aldehydes, but this constitution does not entirely explain all their 

 chemical and physical properties. 



(i) A freshly prepared solution of glucose shows a higher rotatory 

 power than a solution which has been kept for some hours (Muta- 

 rotation). Tanret has isolated from glucose solutions, under certain 



