THE CARBOHYDRATES AND THEIR METABOLISM 241 



COH 

 HOCH 

 HOCH 

 HOCH 



CH 2 OH 

 1-Ribose 



CQH 

 HCOH 

 HOCH 



! -./ 



HOCH 



CH 2 OH 



1-Arabinose 



TABLE VI ALDOPENTOSES 

 COH 



COH 

 HCOH 

 HCOH 

 HCOH 



CH 2 OH 

 d-Ribose 



COH 

 HOCH 

 HCOH 

 HCOH 



CH 2 OH 



d-Arabinose 



HCOH 

 HOCH 

 HCOH 



CH 2 OH 



1-Xylose 



COH 

 HCOH 

 HCOH 

 HOCH 



CH 2 OH 



1-Lyxose 



COH 

 HOCH 



HCOH 

 HOCH 



CH 2 OH 



d-Xylose 



COH 

 HOCH 

 HOCH 

 HCOH 



I 4 



CH 2 OH 



d-Lyxose 



The same reaction is used for the qualitative detection of pentoses. 

 Color reactions are obtained by heating pentose with hydrochloric acid 

 in the presence of phloroglucinol or orcinol. 



Xylose. 1-Xylose (wood sugar) is. formed from the xylans called 

 wood gums, found in vegetable cell walls, and next to cellulose the most 

 important carbohydrate found in plants. It forms monoclinic prisms 

 or needles; has a sweet taste, is readily soluble in water and hot alcohol, 

 but not in ether. It melts at 185 according to some, as high as 154, 

 according to others. Its specific rotation is -f 85.7. The equilibrated 

 mixture has a specific rotation of + 18.5. 



It gives the usual aldose reactions. It is best identified by oxidizing 

 to 1-xylonic acid and converting the latter to the characteristic double 

 cadmium bromid salt. 



(C 5 H 9 O c ) 2 .Cd.CdBr 2 .2H 2 O 



l-Arabinose. This pentose was first isolated by Scheibler (1873). The 

 gums of cherry, plum, gum arabic, etc., are composed chiefly of arabans, 

 and from them 1-arabinose is obtained on hydrolysis with acids. 



It crystallizes in needles, melting at 160 C. It is readily soluble in 

 water, difficultly soluble in 05 per cent alcohol and almost insoluble in 



