240 A. L PJXGEK AND EMU, .1. BAUMAXX 



have not yet been separated, as have the two forms of glucose and other 

 sugars. 



Fructose is reduced by sodium amalgam to two alcohols, d-maunitol 

 and d-sorbitol being formed in equal quantities. 



. By oxidation with mercuric oxid, for example, fructose is converted 

 to acids having less than six carbon atoms, such as carbonic, formic, glycol- 

 lic, oxalic, tartaric and d-erythroiiic acids. When boiled with dilute mineral 

 acids, it forms levulinic acid (CJL { CO CH' 2 CH, COOH), 

 formic acid and other substances. Levulinic acid is a characteristic degra- 

 dation product of hexoses and hexosans, and is used as a means of differ- 

 entiating between hexoses and pentoses. 



Levulinic acid is a colorless oil that boils at 146 C. at 18 mm. pres- 

 sure. It crystallizes in rhombic leaflets when placed over sulphuric acid in 

 a cool place. The crystals are deliquescent, easily soluble in water, al- 

 cohol and ether, and melt at 33 C. 



Pentoses. Eight aldopentoses are theoretically possible, and of these 

 seven are known. Pentoses exhibit mutarotation, and therefore, like the 

 hexoses, indicating that they exist in an a and P and Y lactone fcrm. Two 

 of them, arabinose and xylose, are widely distributed in the vegetable 

 world as polysaccharides, called pentosans. They are very resistant to 

 the action of alkali and are hydrolyzed by dilute acids to form the -simple 

 sugars : 



(C 5 H 8 4 ) E + (H 2 0) n > (C 6 H 10 5 ) n 



Pentosan Pentose 



Pentoses are distinguished from hexoses by their behavior when boiled 

 for a long time with hydrochloric acid. Hexoses are converted to levtilinie 

 acid by this treatment, while pentoses form furf uraldehyde. Pentoses may 

 be estimated by the use of this reaction. The furfuraldehyde is distilled 

 off and then coupled with phloroglucinol and the condensation product 

 is weighed. 



