department of chemistry iii b.sc. chemistry

JUSTICE BASHEER AHMED SAYEED COLLEGE FOR WOMEN(Autonomous) Chennai 18.

S.I.E.T.

DEPARTMENT OF CHEMISTRY

III B.Sc. Chemistry

ORGANIC CHEMISTRY-I

UNIT – III

CARBOHYDRATES CONT….

GLUCOSE PREPARATION AND REACTIONS

Mrs. G. Jeelani Begum

Assistant Professor in Chemistry

J. B. A. S. College for Women (Autonomous) Chennai

GLUCOSE

7 July 2021Mrs. G. JEELANI BEGUM

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• Glucose is a simple sugar with six carbon atoms and one aldehyde

group has a chemical formula C6H12O6.

• It is also known as dextrose. It is referred to as aldohexose as it

contains 6 carbon atoms and an aldehyde group.

• Glucose is optically active dextrorotatory isomer and hence known as Dextrose.

• Glucose is found in most sweet fruits, especially grapes

(20–30%), and honey. It is an essential constituent of

human blood. The blood normally contain 65 to 110 mg

(0.06 to 0.1%) of glucose per 100 ml. in diabetic persons

the level may be much higher.

• In the combined form glucose occurs in abundance

in cane sugar and in polysaccharides such as starch and cellulose.

PREPARATION OF GLUCOSE.

Glucose is produced commercially by the hydrolysis of

starch with dilute hydrochloric acid at high temperature

under pressure.

An aqueous suspension of starch obtained from corn is acidified withhydrochloric acid, It is then heated when the hydrolysis is complete, theliquid is neutralised with sodium carbonate the resulting solution isconcentrated under reduced pressure to get the crystals of glucose.


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From Cane Sugar


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Glucose can also be prepared by hydrolysing

the Cane sugar in presence of mineral acid like dilute

hydrochloric acid or by action of an enzyme invertase.


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Physical properties of glucose.

Glucose is a white crystalline solid, When crystallized from cold

water, it forms glucose monohydrate (C6H12O6.H2O), mp 86°C.

It is extremely soluble in water, only sparingly so in ethanol, and

insoluble in ether. It is about three-fourths as sweet as cane sugar (sucrose).

It is optically active, and the ordinary naturally occurring form is (+)-

glucose.

Melting Point: 146 °C

Density: 1.54 g/cm³

Molecular Weight/ Molar Mass: 180.16 g/mol


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Uses of glucose:

• As a sweetening agent in syrups and confectionery.

• As food for infants.

• As a reducing agent in silvering of mirrors and to convert

indigo blue to indigo white in vat dyeing.

• As a raw material for wine and alcohol manufacture.


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Chemical Properties of Glucose:

Aldehyde group

• In glucose structure

how many -OH gps

& secondary alcoholic

groups are present? Secondary alcoholic group

Primary alcoholic group


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Reactions of Hydroxyl groups:


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• Glucose reacts with acetyl chloride or acetic anhydride

it forms Penta acetyl glucose.

Reactions of Aldehyde group:


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With Hydrogen cyanide: (HCN)

Glucose reacts with HCN to form glucose cyano hydrin.

With Hydroxyl amine:

• Glucose reacts with hydroxyl amine to form glucose oxime

7 July 2021 Mrs. G. JEELANI BEGUM 11

With Phenyl Hydrazine

• Glucose reacts with phenyl hydrazine to form glucose phenyl hydrazone.

CH=O

(CHOH) 4 + H2 N NHC6H5

- H2O

CH2 OH

Glucose phenyl hydrazone


CH= NNHC6H5

(CHOH) 4

CH2 OH

With excess of Phenyl hydrazine:

• Glucose reacts with phenyl hydrazine to form glucosazone or osazone.

CH=O

1st molecule 2nd molecule

(CHOH) 4 + H2 N NHC6H5 + 2HNNH C6 H5

- H2O

CH2 OH - C6H5 NH2

- NH3

Glucose phenylhydrazone

H2 N NHC6H5

3rd molecule

- H2O


CH= NNHC6H5

CHOH

(CHOH) 3

CH2 OH

CH= NNHC6H5

C=O

(CHOH) 3

CH2 OHCH= NNHC6H5

C= NNHC6H5

(CHOH) 3

CH2 OH

Glucosazone / Osazone

With excess of Phenyl hydrazine:


With Hydrazine:

• Glucose reacts with hydrazine to form glucose hydrazone.

CHO

(CHOH) 4 +NH2NH2

- H2O

CH2 OH

Glucose hydrazone


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CH= NNH2

(CHOH) 4

CH2 OH

Oxidation:


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Oxidation with Nitric acid:Glucose reacts with strong oxidising agent forming glucaricacid or saccharicacid


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Oxidation with Bromine water:Glucose reacts with mild oxidising agent forming gluconic acid


Reduction with Concentrated HI and red phosporous at 370K:

CHO

370K

(CHOH) 4

Conc.HI &

CH2 OH red P 2- iodohexane

n- hexane


CH3CHI(CH2)3CH3

CH3(CH2) 4CH3

Reduction with Sodium amalgam:


Reduction with Tollen’s Reagent (Ammoniacal Silver nitrate solution):


With Fehling’s Solution (Alkaline Copper sulphate and Sodium potassium tartrate:

•


With Conc.HCl & With Zymase:

Glucose reacts with Concentrated Hydrochloric acid it forms Laevulinic acid.

Glucose undergoes fermentation into ethylalcohol in the presence of the enzyme, zymase.

C6H12O6

zymase7 July 2021 Mrs. G. JEELANI BEGUM 25

CHO

(CHOH) 4 + Conc.HCl

CH2 OH

CH3COCH2CH2COOH

Laevulinic acid

C2H5OH + CO2

Reaction with Methanol and dry HCl gas


Elucidation of glucose.

The structure of glucose may be elucidated using the following points:

• Open Chain formula

• Configuration

• Cyclic structure

• Haworth representation.


Open Chain formula

1. Molecular Formula: The elemental analysis and molecular weight determination have

established that glucose has the molecular formula C6H12O6.

2. Presence of 5 OH group:

Glucose reacts with acetyl chloride or with acetic anhydride to form

pentaacetyl derivative. This shows the presence of five hydroxyl

groups in glucose. Since glucose is a stable compound, no two OH groups are

attached to the same carbon. In other words, the five OH group are on

different carbons.


3. Presence of carbonyl ( C=O) group:

Glucose reacts with hydroxylamine to form an oxime and with phenyl hydrazine it form phenylhydrazone. These reaction suggests the presence of a carbonyl group in glucose.

4. Presence of aldehyde(-CHO) group: On mild oxidation with bromine water, glucose is converted to

gluconicacid with the same number of carbon atoms. This show that the carbonyl group in glucose is an aldehyde not a ketogroup. That -CHO group has been oxidised to -COOH.

Further the presence of aldehyde group is confirmed by reduction with sodium-amalgam forming hexahydric alcohol, Sorbitol. Here -CHO


5. Presence of 6-carbon arranged in straight chain:

The complete reduction of glucose with concentrated hydrogen iodide

and red phosphorus at 370K it gives 2-iodohexane and on prolonged

heating gives n-hexane. This proves that glucose molecule is made of

six-carbon chain arranged in straight chain. (C-C-C-C-C-C)

6. Construction of open-chain formula.

Knowing that glucose has a straight 6-carbon chain

with a terminal CHO, the five OH groups, Baeyer

proposed the open-chain structure for glucose and it

can be written as :


7. Configuration of D-Glucose

The configuration of D-glucose was proved by Emil Fischer and it isstated below:

Construction of four possible D-pentoses:

• Taking the configuration of

D-glyceraldehyde as the standard, two

possible D-aldotetroses (A and B) is

obtained by adding a CHOH just

below CHO, placing OH to the right

and then to the left.


https://2.bp.blogspot.com/-v4Fcj2qFSTg/XNaZSHJAzEI/AAAAAAAAArQ/zBPaUBKyot4WolDo5xaaUVMICd0dVb06QCLcBGAs/s1600/glucose+4.png

https://2.bp.blogspot.com/-v4Fcj2qFSTg/XNaZSHJAzEI/AAAAAAAAArQ/zBPaUBKyot4WolDo5xaaUVMICd0dVb06QCLcBGAs/s1600/glucose+4.png

• Similarly, each of the two D-tetroses (A and B) gives two D-aldopentoses. Thus four possible D-aldopentoses are shownbelow:


https://4.bp.blogspot.com/-vSz5mLnarro/XNZ5EDyCWcI/AAAAAAAAApw/-LSEX20y78cHb_zIZmM8hgHXUDHr6BolwCLcBGAs/s1600/glucose+5.png

https://4.bp.blogspot.com/-vSz5mLnarro/XNZ5EDyCWcI/AAAAAAAAApw/-LSEX20y78cHb_zIZmM8hgHXUDHr6BolwCLcBGAs/s1600/glucose+5.png

D-Arabinose has configuration II or IV.

• Oxidation of D-arabinose with nitric acid oxidizes theterminal CHO and CH2OH groups forming two opticallyactive (asymmetric) dicarboxylic acids. The forms II and IVcan form two optically active (asymmetric) dicarboxylicacids, whereas I and III can give mesoacids only that has aplane of symmetry. Therefore, D-arabinose is either II or IV.

Configuration II confirmed for D-arabinose.

• D-arabinose by Killiani -Fischer synthesis yields twoepimeric aldohexoses, D-glucose and D-mannose. These onoxidation with nitric acid form two optically active(asymmetric) dicarboxylic acids. This is possible only if D-arabinose has the configuration II and not IV.


• If D arabinose has configuration IV, of the two dicarboxylicacids derived from it, one gives meso form and the other one is asymmetric (optically active). Hence D-arabinose has configuration II.

Ruff degradation of D-glucose and D-mannose produces D- arabinose in each case.

• In ruff degradation, the CHOH below CHOH is destroyed. Therefore, the configuration of the two aldohexoses, D-glucose and D-mannose, can be derived by adding a new CHOH below CHO in form II of D-arabinose.


7 July 2021 Presenter Name 36

It may be noted that in Haworth formula, all the OH groups on the right in Fischer formula are directed below the plane of the ring, while those on the left go above the plane. The terminal CH2OH projects above the plane of the ring.


department of chemistry iii b.sc. chemistry

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