194 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



(14) Hydroxylamine. Glucose reacts with hydroxylamine to 

 form an oxime. The oxime loses water on heating with concentrated 

 sodium hydroxide giving the nitrile of gluconic acid. On further heat- 

 ing hydrogen cyanide is split off and a pentose is formed. 



A pentose is more easily obtained by oxidising gluconic acid with 

 hydrogen peroxide in the presence of ferrous salts. 



B. FRUCTOSE. 



Fructose gives all the reactions given by glucose, but the following 

 differences should be noted : 



(3) Reduction. Fructose on reduction with sodium amalgam 

 gives a mixture of sorbitol and mannitol. 



(4) Oxidation. Fructose on oxidation gives trihydroxybutyric 

 acid and glycollic acid 



(6) Action of Concentrated Hydrochloric Acid. On boiling a 

 solution of fructose with concentrated hydrochloric acid, the solution 

 generally becomes red or red-brown before it ultimately turns dark 

 brown. 



(7) Reduction of Metallic Oxides in Alkaline Solution. Al- 

 though fructose is a ketose, it nevertheless reduces metallic oxides in 

 alkaline solution. This is due to the terminal CO.CH 2 OH group 

 which is easily oxidisable. Though acetone does not reduce metallic 

 oxides, monohydroxyacetone CH 3 . CO . CH 2 OH does, as it contains 

 the above grouping. 



(9) Formation of Osazones. Fructose gives a phenylosazone 

 identical with phenylglucosazone, as can be seen when the crystals are 

 examined under the microscope, melting-point, analysis, etc. 



(10) Fermentation. Fructose ferments more rapidly than glucose 

 with yeast. * 



(12) Rotation. Fructose solutions are laevorotatory. Laevo- 

 rotatory fructose is known as ^-fructose on account of its stereo- 

 chemical relationship to glucose ; the asymmetry of glucose is the basis 

 of the stereochemical configuration of all carbohydrates. 



Special Test. Selivanoff s Test. On adding a few crystals of 

 resorcinol to a mixture of equal parts of concentrated hydrochloric 

 acid and water and a very small quantity of fructose solution and 

 heating, the solution becomes red in colour and deposits a brownish-red 

 precipitate, which dissolves in alcohol giving a red solution. 



<o-Hydroxymethylfurfural is formed by the action of the acid 

 upon fructose and combines with the resorcinol giving the red pig- 

 ment. 



