BIOCHEMISTRY - CARBOHYDRATES

1. The reactions of
carbohydrates

2. • Reactions of monosaccharide's
• Reactions of disaccharides
• Reactions of polysaccharides
• Colour reactions
NAVEENA GIRISH
MSc PLANT SCIENCE
CENTRAL UNIVERSITY OF
KERALA

3. Glucose
Bromine
water
Gluconic
acid
Glucose
Con.
HNO3
Glucaric
acid
+H2O
OXIDATION
SPECIFIC FOR ALDOSE MILD
STRONG

6. 1
2
3
4
5
5 reactions
Reduction

7. Reduction of Monosaccharide
C=O of aldoses or ketoses can be reduced to C-OH
by NaBH4 or
Name the sugar alcohol by adding –itol to the root
name of the sugar; commonly known as an alditol.
Reduction of D-glucose produces D-glucitol,
commonly called D-sorbitol.
Reduction of D-fructose produces a mixture of D-
glucitol and D-mannitol.

8. Examples
• Glucose + sodium amalgam = sorbitol
• Fructose + sodium amalgam = sorbitol and
mannitol
• Glucose/fructose + HI/ Red phosphorus = n –
hexane
(prolonger heating with con. Hydroic acid and red
phosphorus )

9. • Glucose /fructose + hydrogen cyanide =
glucose cyanohydrid / fructose cyanohydrin
Glucose/ fructose + hydroxyl amine =
glucose amine / fructose amine +water

10. Glucose/ fructose + phenyl hydrazine
(condenses)
Glucose/ fructose phenylhydrazone
(warmed with excess phenyl hydrazine)
Glucosazone /fructosazone

12. Reducing action
Oxidation by TollensReagent
• Sugars that reduce Tollensreagent are called Reducing
sugars
• Tollens reagent – ammoniacal silvar nitrate solution
• Silvar mirror test
• Metallic silver formation
• Glucose gives gluconic acid + metallic silver
• Fructose gives glycollic acid +trihydroxy butyric
acid+glycollic acid + metallic silver

14. Acetylation
glucose / fructose + acetic anhydride
glucose /fructose pentaacetate + acetic acid
Methylation
Glucose / fructose + penta methyl glucose
(In presence of DRY HCl)
Methyl fructoside /methyl glucoside + H2O

15. Glucose /
fructose
Dimethyl
sulphate
In presence of
alkali

16. pentamethyl
fructose pentamethyl
glucose

17. Enediol Rearrangement
In base, the position of the C=O can shift
Aldose ketose
Chemists use acidic or neutral solutions of sugars
to preserve their identity.

18. Epimerization

19. Proton alpha to carbonyl group (in aldehyde or
ketone) is reversibly removed; form an enolate-C2
no longer chiral.
•Reprotonation can occur on either side of
• the enolate to give configuration
products

20. Ester Formation
Acetic anhydride with pyridine
catalyst converts
to acetate
esters.
Eg . Glucose +acetic
anhydride+phosphoric acid Glucose 1
phosphate

22. Aldoses& ketoses are converted to acetals by treatment
with alcohol in the presence of acid
• Aldose /ketose +ammonia
= glycosylamine
Aldose
ketose
Acid
Base
Forms
Acetals

23. Ether Formation
• Convert all -OH groups to -OR, using a
Williamson synthesis, after converting sugar
to acetal

24. Ruff Degradation
Aldose chain is shortened by oxidizing the aldehyde to -COOH,
then decarboxylation

25. Kiliani-Fischer Synthesis
• This process lengthens the aldose chain

26. Sucrose
sucrose
• 200 degree c
• Losswater
caramel
• Brown amorphus mass
Sugar charcol
• Strong heating

27. Inversion of cane sugar
hydrolysis
Sucrose
invertase
glucose + fructose

28. Sucrosate formation
• Sucrose +
Ca hydroxide
Ba hydroxide
Sr hydroxide
Respective sucrosate formation with water

29. sucrose
Con.
HNO3
OXALIC
ACID +
WATER
SUCROSE CON. HCl
Laevulinic
acid
sucrose
Octacetyl
sucrose
Acetic
acid
oxidation
Acetylation

30. Dehydration
• Sucrose
con. H2SO4
CO2C
H2O
SO2

31. METHYLATION
• SUCROSE + DIMETHYL SULPHATE = OCTAMETHYL
SUCROSE +SULPHURIC ACID
• IN PRESENCE OF ALKALI
• FERMENTATION
• SUCROSE+ H2O GLUCOSE + FRUCTOSE
ETHANOL+ CO2

32. NO REACTION WITH
• Tollens reagent
• Fehlings
• Benedicts
• Phenyl hydrazine
• Hydroxyl amine
Non reducing sugar

33. Starch
• Action of heat
• 200- 250
• Cleavage of polymer
• Dextrin (a polysccharide of lower molecular
weight )
Iodine test shows a deep blue colour with
starch

34. Hydrolysis
• On boiling with dil. Acid , starch become
dextrin then ultimately yield glucose
• Starch hydrolysed by enzyme diastase , yield
maltose

35. Cellulose
Hydrolysed
with acid to
yield glucose

36. Nitration
MONO NITRATE
DI NITRITE
TRI NITRITE
MANUFACTURE PLASTICS ,
PHOTOGRAPHIC FILM
GUN COTTON ,EXPLOSIVE

37. ACETYLATION
ACETIC ANHYDRIDE , GLACIAL ACETIC ACID ,SULPHURIC
ACID
DI AND TRI ACETATES
SYNTHETIC FIBRES PAINTS AND
VARNISHES

38. Colour reactions

39. Molischs test
• It is indicative of carbohydrate
• Furfural / hydroxy furfural formed by the
action H2SO4
• Condenses to form violet ring with alpha
naphthanol

40. Barfoeds test
• Acetic acid + cupric acetate –barfoeds solution
• Monosaccharides test
• Cuprous oxide makes red ppt.

41. Benedicts test
• Benedicts solution – CuSO4 + sodium
carbonate + sodium citrate +H2O
• Reducing sugar
• Red ppt of cuprous oxide , depending on con.

42. Fehling's Test
• Fehling's solution –( CuSO4 +CON.
H2SO4+H20)+ SODIUM POTASSIUM
TARTARATE + NaOH )
• For reducing testing
• Red ppt of cuprous oxide
• Glucose gives gluconic acid +cuprous oxide
• Fructose gives trihydroxy butyric acid+
glycollic acid +cuprous oxide

43. Bials test
• Bials reagent – ferric chloride hexahydrate
+con. HCl + orcinol
• Distinguish b/w pentose and hexose
• Furfural formation
• Furfural + orcinol + ferric iron = coloured
product
• Pentose – green
• Hexose - muddy brown

44. Seliwanoff test
• For ketoses
• Reagent – HCl + resorcinol
• Ketose + HCl =furfural derivative +
recorcinol= deep red colour
•

45. Diphenylamine test
• Reagent – H2SO4 , DIPHENYL AMINE,GLACIAL
ACETIC ACID
ADD TO TEST
SOLUTION BOIL
10’
2
DEOXY
SUGAR
BLUE / GREEN
COLOUR

46. Schiff test
ALDOSE +
SCHIFFS =
MAGENTA
COLOUR

47. Anthrone method
• Furfural formation by H2SO4
• Naphthanol form blue colour show prescence
of carbohydrate

48. Thank u