Organic Chemistry

Section 22.5 Redox Reactions of Monosaccharides 927

D-erythrulose

D-ribulose

D-psicose D-fructose D-sorbose D-tagatose

D-xylulose

dihydroxyacetone

TABLE 22.2 Configurations of the D-Ketoses

OH

CH 2 OH

H

OH

CH 2 OH

H

H OH

OH

CH 2 OH

H

H OH

H OH

CH 2 OH

C O

OH

CH 2 OH

H

H OH

H

CH 2 OH

C O

OH

CH 2 OH

H

HO H

HO H OH

CH 2 OH

C O

OH

CH 2 OH

H

HO H

HO H

CH 2 OH

C O

CH 2 OH

C O

OH

CH 2 OH

H

HO H

CH 2 OH

C O

CH 2 OH

C O

CH 2 OH

CH 2 OH

C O

product. D-Mannitol, the alditol formed from the reduction of D-mannose, is found in
mushrooms, olives, and onions. The reduction of D-fructose forms D-mannitol and
D-glucitol, the C-2 epimer of D-mannitol. D-Glucitol—also called sorbitol—is about
60% as sweet as sucrose. It is found in plums, pears, cherries, and berries and is used
as a sugar substitute in the manufacture of candy.

D-Glucitol is also obtained from the reduction of either D-glucose or L-gulose.

D-Xylitol—obtained from the reduction of D-xylose—is used as a sweetening agent in
cereals and in sugarless gum.

D-glucose L-gulose

drawn upside down

H 2

Pd/C

H 2

Pd/C

HO H

OH

HOH

HOH

CH 2 OH

H

HC O

O

HO H

OH

HOH

HOH

CH 2 OH

H

CH 2 OH

D-glucitol

an alditol

HO H

OH

HOH

HOH

HC

H

CH 2 OH

1. NaBH 4


2. H 3 O+
   
   
   1. NaBH 4
   
   
   2. H 3 O+
      
      
      1. NaBH 4
         HOHOHH 2. H 3 O+
      
      
      
      
   
   
   
   

HOH

CH 2 OH

CH 2 OH

CO

D-fructose

HO H

H

HOH

HOH

CH 2 OH

HO

HC O CH 2 OH

D-mannose

HO H

HOH

HOH

CH 2 OH

HO H

D-mannitol

an alditol

CH 2 OH

HO H

HOH

HOH

CH 2 OH

HOH

D-glucitol

an alditol