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13.4 Chemical Properties of
Monosaccharides
Tautomerization (enol-keto tautomerization)
Reduction
[H]
Oxidation
[O]
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Example of Tautomerization
5th Reaction in glycolysis
Triosephosphate
isomerase
Dihydroxyacetone
phosphate
Glyceradehyde
3-phosphate
Mechanism:
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Example of Reduction
Hydrogenation of xylose
CHO
H
HO
H
H2, metal
catalyst
OH
H
OH
O
HO
HO
OH
CH2OH
xylose
OH
xylitol
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.
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Example of Oxidation
Oxidation of glucose
OH
OH
O
Br2, BaCO3
HO
HO
OH
glucose
OH
[O]
O
HO
HO
OH
O
gluconic acid
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
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Learning Check
1. 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?
positive
negative
(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
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Learning Check
2. 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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