reactions of carbohydrates

The reaction

s ofcarbohydrate

s

• Reactions of monosaccharide's

• Reactions of disaccharides

• Reactions of polysaccharides

• Colour reactions

NAVEENA GIRISHMSc PLANT SCIENCECENTRAL UNIVERSITY OF

KERALA

Glucose

Bromine water

Gluconic acid

Glucose

Con.

HNO3

Glucaric acid +H2

O

OXIDATION

SPECIFIC FOR ALDOSE MILD

STRONG

12

34

5

5 reactions

Reduction

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.

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 )

• Glucose /fructose + hydrogen cyanide = glucose cyanohydrid / fructose cyanohydrin

Glucose/ fructose + hydroxyl amine =glucose amine / fructose amine +water

Glucose/ fructose + phenyl hydrazine (condenses)

Glucose/ fructose phenylhydrazone(warmed with excess phenyl hydrazine)

Glucosazone /fructosazone

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

Acetylation

glucose / fructose + acetic anhydrideglucose /fructose pentaacetate + acetic acid

MethylationGlucose / fructose + penta methyl glucose (In presence of DRY HCl)

Methyl fructoside /methyl glucoside + H2O

Glucose / fructose

Dimethyl sulphate

In presence of alkali

pentamethyl fructose pentamethyl glucose

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.

Epimerization

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

Ester Formation

Acetic anhydride with

pyridine catalyst converts

to acetate esters.

Eg . Glucose +acetic

anhydride+phosphoric acid

Glucose 1 phosphate

Aldoses& ketoses are converted to acetals by treatmentwith alcohol in the presence of acid

• Aldose /ketose +ammonia = glycosylamine

Aldose

ketose

Acid Base

Forms

Acetals

Ether Formation

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

Ruff DegradationAldose chain is shortened by oxidizing the aldehyde to -COOH, then decarboxylation

Kiliani-Fischer Synthesis• This process lengthens the aldose chain

Sucrose

sucrose•200 degree c •Losswater

caramel •Brown amorphus mass

Sugar charcol •Strong heating

Inversion of cane sugarhydrolysis

Sucrose invertase

glucose + fructose

Sucrosate formation

• Sucrose +Ca hydroxide

Ba hydroxide

Sr hydroxide

Respective sucrosate formation with water

sucrose

Con. HNO3

OXALIC ACID + WATER

SUCROSE

CON. HCl

Laevulinic acid

sucrose

Octacetyl

sucrose

Acetic

acid

oxidation

Acetylation

Dehydration

• Sucrose

con. H2SO4

CO2C

H2O

SO2

METHYLATION• SUCROSE + DIMETHYL SULPHATE = OCTAMETHYL

SUCROSE +SULPHURIC ACID• IN PRESENCE OF ALKALI

• FERMENTATION• SUCROSE+ H2O GLUCOSE + FRUCTOSE

ETHANOL+ CO2

NO REACTION WITH

• Tollens reagent• Fehlings • Benedicts

• Phenyl hydrazine• Hydroxyl amine

Non reducing sugar

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

Hydrolysis

• On boiling with dil. Acid , starch become dextrin then ultimately yield glucose

• Starch hydrolysed by enzyme diastase , yield maltose

Cellulose

Hydrolysed with acid to

yield glucose

Nitration

CON H2SO4, CON HNO3, CELLULOSE

MONO NITRATE

DI NITRITE

TRI NITRITE

MANUFACTURE PLASTICS , PHOTOGRAPHIC FILM

GUN COTTON ,EXPLOSIVE

ACETYLATION

ACETIC ANHYDRIDE , GLACIAL ACETIC ACID ,SULPHURIC ACID

DI AND TRI ACETATESSYNTHETIC FIBRES PAINTS AND VARNISHES

Colour reactions

Molischs test• It is indicative of carbohydrate• Furfural / hydroxy furfural formed by the

action H2SO4 • Condenses to form violet ring with alpha

naphthanol

Barfoeds test

• Acetic acid + cupric acetate –barfoeds solution

• Monosaccharides test

• Cuprous oxide makes red ppt.

Benedicts test• Benedicts solution – CuSO4 + sodium

carbonate + sodium citrate +H2O• Reducing sugar • Red ppt of cuprous oxide , depending on con.

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

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

Seliwanoff test

• For ketoses• Reagent – HCl + resorcinol• Ketose + HCl =furfural derivative +

recorcinol= deep red colour•

Diphenylamine test

• Reagent – H2SO4 , DIPHENYL AMINE,GLACIAL ACETIC ACID

ADD TO TEST SOLUTION BOIL

10’

2 DEOXY SUGAR

BLUE / GREEN COLOUR

Schiff test

ALDOSE + SCHIFFS = MAGENTA COLOUR

Anthrone method

• Furfural formation by H2SO4

• Naphthanol form blue colour show prescence of carbohydrate

Thank u