PTC IS THE PHASE TRANSFER CATALYSIS HERE TYPES OF PTC ARE DISCUSSED , THEORIES OF CATALYSIS AND MECHANISM OF PTC, ADVANTAGES OF PTC, APPLICATION OF PTC
2. CONTENTS
Introduction
Mechanism of PTC reaction
Theories of PTC
Types of phase transfer catalyst
Advantages of phase transfer reaction
Application of phase transfer catalysis
References
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3. Introduction
o Catalysis :-Catalysis is the process of increasing the rate of a chemical
reaction by adding a substance known as a catalyst.
o Definition :- Phase transfer catalysis (PTC) refers to reaction between two
substances located in different immiscible phases in the presence of catalyst.
o Heterogenous catalysis.
o It facillate the migration of a reactant from one phase into another phase
where reaction occurs.
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4. Following three factors plays important role in the successful use of
phase transfer catalyst reaction :-
i. Influence of solvent :-Solvent should be aprotic and immiscible with
water to avoid strong interaction with ion pairs.
ii. Influence of cation :- The large number of carbon atom around the
central N atom in the PTC.
iii. Salt effect:- Addition of sodium hydroxide and potassium carbonate
increases the extraction coefficient many times and thus increases the
rate of reaction.
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5. Theories of catalysis
1) Intermediate Compound formation theory (Homogenous catalyst reaction )
2) Adsorption theory ( Heterogenous catalyst reaction )
1) Intermediate compound formulation theory:
According to this theory one of the reactants combines with catalyst to form intermediate product,
which carries out the reaction,
E.g. A + C = AC
AC + B =AB + C
A + B + C = AB + C
where A and B are reactants, C is the catalyst and AC is the intermediate product.
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6. 2) Adsorption Theory:
In general adsorption theory applies to heterogeneous catalytic reactions. The catalyst
functions by the adsorption of the reacting molecules on its surface. The adsorption reaction
undergoes four types of steps.
( i) Adsorption of reactant molecule:
The reactant molecules A and B strike the surface of the catalyst.
The reaction molecules held up by the partial chemical bond.
ii ) Formation of intermediate complex:
The reactant molecule adjacent one another join to
form an intermediate complex ( A-B ). The intermediate complex is unstable.
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7. ( iii ) Decomposition of intermediate complex:
The intermediate complex breaks to form the products C and D.
The product molecules hold to the catalyst surface by partial chemical bond.
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( iv ) Release of product:
The product particles are released from the surface.
9. Types of phase transfer catalyst
o Quaternary ‘Onium’ salts such as ammonium, phosphonium ,
antimonium and tertiary sulphonium salts.
Some of the PTC’s normally used are:-
1) Aliquat 336 : N+CH3(C8H17)3 Cl
Methyl trioctylammonium chloride
2) Benzyl trimethylammonium chloride or bromide (TMBA)
N+(CH3)3 CH2 C6H5 X-
3) Benzyl triethylammonium chloride
N+(C2H5)3 CH2 C6H5 X-
4) Cetyl trimethylammonium chloride or bromide (CTMAB)
N+ (CH3)3 (CH2)15 CH3 X- 19-12-2019
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10. Types of phase transfer catalysed reactions
Phase transfer reactions
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Liquid-Liquid phase
transfer reaction
Solid-Liquid phase
transfer reaction
Solid-gas phase
transfer reaction
Triphase catalyst
• Insolubilized ammonium
and phosphonium salts
• Insolubilized crown
ethers and cryptands
• Insolubilized cosolvents
11. Advantages of PTC
1. Do not require vigorous conditions and the reaction are fast.
2. Do not require expensive aprotic solvents.
3. Do not require high temperature ; the reaction usually occur at low temperature.
4. There is no need for anhydrous conditions since water is used as one of the
phases.
5. With the help of PTC , the anion is available in organic solvent and so its
nucleophilicity increases.
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12. Applications of phase transfer Catalysis
1) Nitriles From Alkyl Halides :-
R-X + NaCN RCN + NaX
2) Benzoyl Cyanides from Benzoyl Chloride:-
PTC
Organic Aqueous
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O
Cl
+ Na N N
O
+ Na Cl
Bu4 N +X-
Benzoyl
cyanide
Benzoyl
chlolride
Sodium
cyanide
Nitrile
14. 4) Esterification :-Carboxylic acids can be esterified with alkyl halides in the
presence of triethylamine.
RCO2Na + RX RCO2R + Na X
5)In the field of Pharmaceuticals like Synthesis of various drugs like dicyclomine,
phenoperidine ,oxaladine ,ritaline ,etc.
6) Williamson Ether Synthesis :-
C8H17OH + C4H9Cl C8H17OC4H9 + C8H17OC8H17
PTC
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Alcohol Alkyl halide
Ether By-product
Carboxylic
acid as sod.
salt
Alkyl
halide
Ester