Download - The reactions of carbohydrates
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The reaction
s ofcarbohydrate
s
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• Reactions of monosaccharide's
• Reactions of disaccharides
• Reactions of polysaccharides
• Colour reactions
NAVEENA GIRISHMSc PLANT SCIENCECENTRAL UNIVERSITY OF
KERALA
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Glucose
Bromine water
Gluconic acid
Glucose
Con.
HNO3
Glucaric acid +H2
O
OXIDATION
SPECIFIC FOR ALDOSE MILD
STRONG
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12
34
5
5 reactions
Reduction
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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.
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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 )
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• Glucose /fructose + hydrogen cyanide = glucose cyanohydrid / fructose cyanohydrin
Glucose/ fructose + hydroxyl amine =glucose amine / fructose amine +water
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Glucose/ fructose + phenyl hydrazine (condenses)
Glucose/ fructose phenylhydrazone(warmed with excess phenyl hydrazine)
Glucosazone /fructosazone
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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
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Acetylation
glucose / fructose + acetic anhydrideglucose /fructose pentaacetate + acetic acid
MethylationGlucose / fructose + penta methyl glucose (In presence of DRY HCl)
Methyl fructoside /methyl glucoside + H2O
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Glucose / fructose
Dimethyl sulphate
In presence of alkali
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pentamethyl fructose pentamethyl glucose
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Enediol RearrangementIn base, the position of the C=O can shift Aldose ketose
Chemists use acidic or neutral solutions of sugars to preserve their identity.
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Epimerization
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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
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Ester Formation
Acetic anhydride with
pyridine catalyst converts
to acetate esters.
Eg . Glucose +acetic
anhydride+phosphoric acid
Glucose 1 phosphate
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Aldoses& ketoses are converted to acetals by treatmentwith alcohol in the presence of acid
• Aldose /ketose +ammonia = glycosylamine
Aldose
ketose
Acid Base
Forms
Acetals
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Ether Formation
• Convert all -OH groups to -OR, using a Williamson synthesis, after converting sugar to acetal
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Ruff DegradationAldose chain is shortened by oxidizing the aldehyde to -COOH, then decarboxylation
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Kiliani-Fischer Synthesis• This process lengthens the aldose chain
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Sucrose
sucrose•200 degree c •Losswater
caramel •Brown amorphus mass
Sugar charcol •Strong heating
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Inversion of cane sugarhydrolysis
Sucrose invertase
glucose + fructose
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Sucrosate formation
• Sucrose +Ca hydroxide
Ba hydroxide
Sr hydroxide
Respective sucrosate formation with water
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sucrose
Con. HNO3
OXALIC ACID + WATER
SUCROSE
CON. HCl
Laevulinic acid
sucrose
Octacetyl
sucrose
Acetic
acid
oxidation
Acetylation
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Dehydration
• Sucrose
con. H2SO4
CO2C
H2O
SO2
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METHYLATION• SUCROSE + DIMETHYL SULPHATE = OCTAMETHYL
SUCROSE +SULPHURIC ACID• IN PRESENCE OF ALKALI
• FERMENTATION• SUCROSE+ H2O GLUCOSE + FRUCTOSE
ETHANOL+ CO2
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NO REACTION WITH
• Tollens reagent• Fehlings • Benedicts
• Phenyl hydrazine• Hydroxyl amine
Non reducing sugar
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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
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Hydrolysis
• On boiling with dil. Acid , starch become dextrin then ultimately yield glucose
• Starch hydrolysed by enzyme diastase , yield maltose
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Cellulose
Hydrolysed with acid to
yield glucose
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Nitration
CON H2SO4, CON HNO3, CELLULOSE
MONO NITRATE
DI NITRITE
TRI NITRITE
MANUFACTURE PLASTICS , PHOTOGRAPHIC FILM
GUN COTTON ,EXPLOSIVE
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ACETYLATION
ACETIC ANHYDRIDE , GLACIAL ACETIC ACID ,SULPHURIC ACID
DI AND TRI ACETATESSYNTHETIC FIBRES PAINTS AND VARNISHES
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Colour reactions
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Molischs test• It is indicative of carbohydrate• Furfural / hydroxy furfural formed by the
action H2SO4 • Condenses to form violet ring with alpha
naphthanol
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Barfoeds test
• Acetic acid + cupric acetate –barfoeds solution
• Monosaccharides test
• Cuprous oxide makes red ppt.
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Benedicts test• Benedicts solution – CuSO4 + sodium
carbonate + sodium citrate +H2O• Reducing sugar • Red ppt of cuprous oxide , depending on con.
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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
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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
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Seliwanoff test
• For ketoses• Reagent – HCl + resorcinol• Ketose + HCl =furfural derivative +
recorcinol= deep red colour•
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Diphenylamine test
• Reagent – H2SO4 , DIPHENYL AMINE,GLACIAL ACETIC ACID
ADD TO TEST SOLUTION BOIL
10’
2 DEOXY SUGAR
BLUE / GREEN COLOUR
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Schiff test
ALDOSE + SCHIFFS = MAGENTA COLOUR
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Anthrone method
• Furfural formation by H2SO4
• Naphthanol form blue colour show prescence of carbohydrate
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