cellulose derivativesb.ppt

HHT341 Dr. Nyoman Wistara 1


Reactivity and Accessibility of Cellulose

O

OH

OH

O

CH2

OH

OH

O

OO

H2C OH

HO

Reactivity:

• Etherification:• Ionization of hydroxyl• Acidity and dissociation

tendency: HO-6 < HO-3 < HO-2

• Esterification: • Highest reactivity: HO-6

Accessibility:

• Relative ease by which hydroxyl groups can be reached by the reactants.

• Sterical reason: HO-6 is the most reactive for bulky substituent.

• Accessibility Vs. Crystallinity


Effect of crystallinity and hydrogen bonding on the acetylation of cotton fibers.

a. Original fibersb. Destruction of crystalline by ethylene amine treatment, followed by

subsequent drying.c. As (b), but without subsequent drying.


Degree of Substitution (DS)

Strongly swollen state cellulose:

• OH accessible to the reactants

• Homogeneous products obtained when DS = 3

• Less than DS-3:

1. Unreacted glucose units

2. Monosubstituted units :

• 2-derivatives

• 3-derivatives

• 6-derivatives

3. Disubstituted units :

• 2,6-derivatives

• 3,6-derivatives

• 2,3-derivatives

4. Fully substituted units:

• 2,3,6-derivative

O

OH

OH

O

CH2

OH

OH

O

OO

H2C OH

HO


Swelling and Dissolution of Cellulose:• Swelling extent: solvent and nature of cellulose sample

• Swelling type:

• intercrystalline swelling

• intracrystalline swelling

• Significant swelling in diameter and insignificant in length

of cellulose fiber

• Water retention of cellulose fibers varies depending on:

• Equilibration of hysteresis

• Chemical composition

• Swell in electrolyte solution: hydrated ions require more

space than water molecules

• Intracrystalline swelling: by concentrated solution of strong

bases or acids and some salts:

• Limited : combined at certain stoichiometric

proportion with cellulose ordered region, not

destroying interfibrillar bonding

• Unlimited: bulky swelling agents form complexes with

cellulose and break adjacent bonds.


Abbreviation Formula Properties

Schweizer’s solution (Cuoxam)

[Cu(NH3)4](OH2) Dark blue. Extensive depolymerization of cellulose in the presence of oxygen.

CED (Cuen) [Cu(en)2](OH)2a Dark blue. Depolymerization of

cellulose in the presence of oxygen.

Cadoxen [Cd(en)3](OH)2 Colorless, useful for optical measurements. Cellulose shows good stability in this solvent.

EWNN [FeT3]Na6b Greenish. Cellulose shows good

stability in this solvent.

a en is ethylenediamineb T is tartrate

Properties of Common Cellulose Solvents (Sjostrom 1993)


A. Ester of Inorganic Acids• Cellulose is esterified with certain inorganic acids:

• Nitric acid

• Sulfuric acid

• Phosphoric acid

• Acid prerequisites:

• Bring about strong swelling

• Esterifification: typical equilibrium reaction: alcohol and acid ester + water

• The most important product: cellulose nitrate

(1) Cellulose Nitrate

2H2SO4 NO2HONO2 + + H3O + 2HSO4 ……….. (1)

NO2 + HO Cell NO2 OH Cell NO2 OH Cell + H … (2)

ESTERS


DS Solvent Applications

1.9 – 2.0 Ethanol Plastics

1.9 – 2.3 Esters, ethanol, ether-alcohol Lacquers

2.0 – 2.3 Esters Films, cements

2.4 – 2.8 Acetone Explosives

Commercial Grades of Cellulose Nitrate:

(2) Cellulose Sulfate:• Prepared using a variety of reagent combinations.

• Active agents is SO3

• Suitable reagents for preparing cellulose acetate:

• Sulfuric acid/ethanol, propanol, butanol

• Fuming sulfuric acid/sulfur trioxide

• Sulfur trioxide/sulfur dioxide, dimethylformamide, carbon disulfide

• Chlorosulfonic acid/sulfur dioxide, pyridine

• Water soluble, can be used as thickening agents.


2 H2SO4 + + SO3H3O HSO4......... (1)

The Reaction Steps:

Cell OH + SO3 Cell O

H

SO3 Cell O SO3 + H ......... (2)

Cell OH + H2SO4 Cell O

H

H + HSO4 Cell O SO3 H3O .....(3)+


B. Ester of Organic Acids

(1) Cellulose Acetate:

• Replacing cellulose nitrate in many products

• Acetylation of cellulose is a heterogeneous system:

• Reagent diffusion controlling the reaction rate.

• Fiber need to be swollen

• Production via solution process:

• Pulp treatment with AcOH + catalyst (H2SO4) swell and

increase fiber reactivity

• Acetylation: addition of acetic anhydride + H2SO4 (catalyst) in

the presence of AcOH.

• After full acetylation, triacetate is dissolved.

• Fibrous acetylation: need suitable liquid (e.g. benzene)

• Other catalyst: perchloric acid, zinc chloride


Commercial Grade of Cellulose Acetate:

DS Solvents Applications

1.8 – 1.8 Water – propanol – chloroform Composite fabrics

2.2 – 2.3 Acetone Lacquers, plastics

2.3 – 2.4 Acetone Acetate rayon

2.5 – 2.6 Acetone X – ray and safety films

2.8 – 2.9 Methylene chloride – ethanol Insulating foils

2.9 – 3.0 Methylene chloride Fabrics

Typical Specifications for Acetylation Grade Pulp:

A – Cellulose (%) > 95.6

Pentosan (%) < 2.1

Intrinsic viscosity (dm3/kg) 550 - 750

Ether extractable (%) < 0.15

Ash (%) < 0.08

Iron (mg/kg) < 10


Mechanism of acid-catalyzed acetylation:

CH3 C O

O

C CH3

O+H

CH3 C O C CH3

OH O

CH3 C O C CH3

OH O

+ Cell OHCH3 C O C CH3

OH O

HO Cell

CH3 C O Cell

O

- CH3COOH

-H


ETHERS

• Prepared by treating alkali cellulose with alkyl, aryl halides (or sulfates), and

unsaturated compound activated by electron-attracting groups.

• Most soluble in water

• Have similar properties and specific characteristic complete each other

• Water soluble at low DS

• With hydrophobic substituents and high DS soluble in organic solvent

Cellulose ether Reagent Solvent DS

Methylcellulose Methyl chloride, dimethyl sulfate

Water 1.5 – 2.4

Ethylcellulose Ethyl chloride Organic solvents 2.3 – 2.6

Carboxymethylcellulose Sodium chloroacetate Water 0.5 – 1.2

Hydoxymethylcellulose Ethylene oxide Water 1.3 – 3.0

Cyanoethylcellulose Acrylonitrile Organic solvents 2.0

Types of Commercial Cellulose Ethers :


(1) Alkyl Ethers :

• Alkylation by using alkyl chloride• Used as additives: agricultural products, food products, ceramics,

pharmaceutical, cements, textiles, paper products, and plywood.• Mechanism bimolecular nucleophilic substitution (SN2):

By products: ethanol or methanol :

RCl + HO ROH + Cl

Cell OH + + H2OCell OHO

Cell O + R Cl Cell OR + Cl

(R = CH3 or C2H5 )

Ethanol or methanol then react with alkyl chloride to form diethyl or dimethyl ether :

ROH + HO RO + H2O

RO + R Cl ROR + Cl


(2) Hydroxyalkyl Ethers :

• Obtained from cellulose reaction with alkene oxides or their corresponding chlorohydrins.

• Reaction mechanism: base-catalyzed SN2 type substitution.

• Commercial productions : hydroxyethyl – and hydroxypropylcellulose reagents: ethylene oxide and propylene oxide.

• Formation:

+ H2C CH2

OCell O Cell O CH2CH2O

Ethylene can also reacts with hydroxide ions to form ethylene glycol:

H2C CH2

O+HO CH2OH CH2O

Ethylene can further polymerize to polyethylene oxide terminal primary hydroxyl group of the substituent reacts with additional epoxide ethylene pendant chains:

Cell O CH2CH2OH + n H2C CH2

O

Cell (O CH2CH2)n+1OHHO

• Polymerization DS of hydroxyalkyl cellulose lower than MS• MS/DS relative length of side chains a half react w/ cellulose and a half for side chains• Used for: thickener of latex paint, emulsion polymerization of PVA, paper sizing etc.


(3) Carboxymethylcellulose (CMC) :• Most widely used water-soluble cellulose derivative.• Prepared from : cellulose and sodium chloroacetate.• DS : 0.4 – 1.4; solubility increases with increasing DS.• DS: 0.6 – 0.8 good water solubility; 0.05 – 0.25 soluble in alkali only.• Used for: detergents, food, ice cream, paper coating, emulsion paints, drilling

fluids, ceramics, pharmaceuticals, and cosmetics.• Reaction mechanism:

Cell O + CH2COO

Cl

+ ClCell O CH2COO

(4) Cyanoethylcellulose :• Cellulose react with – unsaturated compounds containing strongly electron-

attracting groups substituted ethyl ethers .• Cyanoethylation acrylonitrile as reagent in strongly basic catalyst (NaOH).• Used for: insulation paper• Reaction mechanism:

Cell O + CH2 CH C N

Cell O CH2 CH C N Cell O CH2 CH C N

Cell OCH2CH2CN

+H2O

+ HO


CELLULOSE XANTHATE :• Cellulose xanthate (dithiocarbonate) Treatment of alkali cellulose with carbon disulfide• Viscose rayon and cellophane proceed via the xanthate extremely important cellulose

derivative• Xanthation reaction:

Cell O + CS

SCell O C

S

S

Alkali cellulose :18% NaOH15 – 30 oC

Pressing Shredded and Ripening to

DP: 200 – 400

Xanthation :25 – 30 oC

3 hoursDS: 0.5

DissolvingIn aqueous NaOH

Viscose(orange-colored) FilteredSpinning

(into acid bath)Rayon fibers

The process:

The rayon fiber:

Cell O C

S

S HCell OH + CS2

cellulose derivativesb.ppt

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