13.4 Chemical Properties of Monosaccharides

1

Tautomerization (enol-keto tautomerization)

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Reduction

Oxidation

O OH

OH

(HO)n

OH O

OH

(HO)n

OH OH

OH

(HO)n

OH OH

O

(HO)n

O OH

OH

(HO)n

[H]

O OH

OH

(HO)n

[O]O O

OH

(HO)n

OH OH

OH

(HO)n

Example of Tautomerization

2

Dihydroxyacetone phosphate

5th Reaction in glycolysis

C

C

H2C

O

O

P O-O

O-

OHHH

Mechanism:

Glyceradehyde 3-phosphate

Triosephosphateisomerase

C

C

H2C

OH

O

P O-O

O-

OH

H

C

C

H2C

O

O

P O-O

O-

OHH

H

H+

H+ C

C

H2C

O

O

P O-O

O-

OH H

H

H+

C

C

H2C

O

O

P O-O

O-

OH H

HH

H+ C

C

H2C

O

O

P O-O

O-

OH

HH

Example of Reduction

3

Hydrogenation of xylose

Xylitol , a common ingredient in chewing gum and other food products, was first discovered almost simultaneously by German and French chemists in the late 19th century. Xylitol is produced by hydrogenation (reduction) of xylose, which converts the aldopentose into a primary alcohol.

CHO

OHH

HHO

OHH

CH2OH

xylose

HO H

OH

OH

OH

O

OHO

HOOH OH

H2, metal catalyst

CH2OH

OHH

HHO

OHH

CH2OH

HO OH

OH

OH

OH

xylitol

Example of Oxidation

4

Oxidation of glucose

Gluconic acid occurs naturally in fruit, honey, and wine. As a food additive (E574[2]), it is an. It is used as acidity regulator or cleaning products. Calcium gluconate is used to treat burns from hydrofluoric acid. Quinine gluconate is a salt between gluconic acid and quinine, which is used for intramuscular injection in the treatment of malaria. Zinc gluconate injections are used to neuter male dogs. Iron gluconate injections have been proposed in the past to treat anemia

OHO

OH

HOOH OH

Br2, BaCO3O

HO

OH

HOOH O[O]

glucose gluconic acid

HO

OH

OH

OH

OH

OH

O

5

Learning Check1. Tollens' reagent (Ag(NH3)2

+) can be used to differentiate aldoses and ketoses (Tollens’ test). Which of the following description is correct based on the following reaction scheme of Tollenes’ test?

(a) This is an oxidation where sugar is reduced .(b) This is a reduction where sugar is reduced.(c) The starting sugar is a lactone.(d) The produced sugar is a lactone.(e) None of the above

OHO

OH

HOOH OH

OHO

OH

HOOH O

+ 2 Ag+ 2 Ag(s)+

positive negative

6

Learning Check2. Which of the following is the tautomer (isomer from tautomerization) of glucose?

(a) I(b) II(c) III(d) IV(e) None of the above

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OHO

OH

HOOH OH

+

glucose

O

HO

HO

HO

OH

OH

OHO

OH

HOOH O

OHHO

OH

HOOH OH

O OH

OH

HO

HOOH

I II III IV