Phase transfer catalysis involves using a catalyst to transfer a reactant from one immiscible liquid phase to another where the reaction takes place. Common phase transfer catalysts are quaternary ammonium and phosphonium salts. The catalyst forms an ion pair with the reactant anion, transporting it into the organic phase where it undergoes nucleophilic substitution or other reactions. Phase transfer catalysis allows reactions between ions and organic molecules that would otherwise not interact due to being in separate phases. It has many applications in organic synthesis and pharmaceutical manufacturing.

1. PHASE TRANSFER CATALYSIS
PRESENTED BY:
ROHIT PAL
( M.PHARMACY 2NDSEMESTER)

2. CONTENTS
 Introduction
 Principle of PTC reaction
 Features of PTC
 Mechanisms of phase transfer catalyst
 Theories of phase transfer catalyst
 Types of phase transfer catalyst
 Advantages of phase transfer reaction
 Choice of phase transfer reaction
 Factors influences phase transfer reaction
 Application of phase transfer catalysis
 References

3. INTRODUCTION
• Catalysis :-Catalysis is the process of increasing the rate of a chemical reaction by adding a
substance known as a catalyst.
• A phase-transfer catalyst or PTC is a catalyst that facilitates the migration of a reactant from
one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form
of heterogeneous catalysis.
• Ionic reactants are often soluble in an aqueous phase but insoluble in an organic phase in the
absence of the phase-transfer catalyst.
• The catalyst functions like a detergent for solubilizing the salts into the organic phase. Phase-
transfer catalysis refers to the acceleration of the reaction upon the addition of the phase-
transfer catalyst.

4. • By using a PTC process, one can achieve faster reactions, obtain higher conversions or yields, make
fewer by products, eliminate the need for expensive or dangerous solvents that will dissolve all the
reactants in one phase, eliminate the need for expensive raw materials and/or minimize waste
problems. Phase-transfer catalysts are especially useful in green chemistry—by allowing the use of
water, the need for organic solvents is reduced.
• Contrary to common perception, PTC is not limited to systems
with hydrophilic and hydrophobic reactants. PTC is sometimes employed in liquid/solid and
liquid/gas reactions. As the name implies, one or more of the reactants are transported into a second
phase which contains both reactants.

5. PRINCIPLE
• The principle of PTC is based on the ability of certain phase-transfer agents (the PT
catalysts) to facilitate the transport of one reagent from one phase into another (immiscible)
phase wherein the other reagent exists.
• Reaction is made possible by bringing together the reagents which are originally in
different phases
• It is also necessary that the transferred species is in an active state for effective PT
catalytic action, and that it is regenerated during the organicreaction

6. • In 1971, Starks introduced Phase Transfer Catalysis (PTC) to explain the role of
tetraalkylammonium or phosphonium salts in the reactions between two substances
located in different immiscible phases.
e.g. the displacement reaction of 1-chlorooctane with aqueous sodium cyanide is
accelerated > 1000x by the addition of hexadecyltributylphosphonium bromide as a
PTC.

8. FEATURES OF PTC
• PTC achieve steady growth as a practical methodology for organic synthesis.
• This main features of PTC are such as:
 simple experimental operations
 mild reaction conditions
 inexpensive
 environmentally benign reagents and solvents, and
 the possibility to conduct large-scale preparations

9. MECHANISMS OF PTC
• A quaternary ammonium halide dissolved in the aqueous phase (Q+X-) undergoes anion
exchange with the anion of the reactant dissolved in the aqueoussolution
• The ion-pair formed (Q+X-) can cross the liquid-liquid interface due to its lipophilic
nature and diffuses from the interface into the organic phase, this step being the phase-
transfer
• In the organic phase, the anion of the ion-pair being quite nucleophilic undergoes a
nucleophilic substitution reaction with the organic reagent forming the desired product
(RY)
• The catalyst subsequently returns to the aqueous phase and the cyclecontinues.

10. • An overview of PTC reactions is given in the scheme bellow:

11. 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 intermediateproduct.

12. 2) Adsorption Theory:
In general adsorption theory applies to heterogeneous catalytic reactions. Thecatalyst functions by the
adsorption of the reacting molecules on its surface. The adsorption reaction undergoes four types of steps.
I ) Adsorption of reactantmolecule:
The reactant molecules A and B strike the surface of thecatalyst.
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 isunstable.

13. ( 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.
( IV ) Release of product:
The product particles are released from the surface.

14. TYPES OF PHASE TRANSFER CATALYST
Quaternary ‘Onium’ salts such as ammonium, phosphonium, antimonium and tertiary sulphonium
salts. Some of the PTC’s normally used are:-
Aliquat 336 : N+CH3(C8H17)3 Cl
Methyl trioctylammonium chloride
Benzyl trimethylammonium chloride or bromide (TMBA)
N+(CH3)3 CH2 C6H5 X-
Benzyl triethylammonium chloride
N+(C2H5)3 CH2 C6H5 X-
Cetyl trimethylammonium chloride or bromide (CTMAB)
N+ (CH3)3 (CH2)15 CH3 X-

15. TYPES OF PHASE TRANSFER CATALYSED REACTIONS
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
1
5

16. 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.

17. PHASE TRANSFER CATALYSTS
Crown Ether
Linear Crown Ether

18. High-molecular-weight PEG (e.g. PEG 8000, PEG 2000 )

19. Typical phase-transfer catalysts
ammonium salts 1-4 and phosphonium salts 5,6
N
R
R
Me
Cl
P Br
6
n Bu
n Bu
n Bu
nBu
PBr
5
n Bu
n Bu
n Bu
nBu
X
Et
Et
Cl
Me
Me
OH
X =
(TBAB)
(TBAF)
(TBAH)
a Br b F
c OH
d HSO4
e BH3CN
f ClCrO3
1
N
R
2
N
Et
3
(TEBA)
N
Me
4
(Triton B)a R = n-C8H17
(Aliquat 336)
b R = n-C8-C10
(Adogen)

20. CHOICE OF PHASE TRANSFER CATALYST
• To use depend on factors such as reaction type, solvent, temperature, base strength and
ease of catalyst recovery and removal.
• Polyethelene glycols (PEGs): the cheapest and are stable in basic media and at elevated
temperatures.
• Crown ethers and cryptands: the most expensive.
Crown ethers and cryptands, besides their high costs, are also toxic, and are to be avoided
whenever possible.
Crown ethers Cryptand

21. FACTORS
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.

22. PTC: REACTION CATEGORY
Reactions to which PTC is applicable can be divided into
two major categories:
1. Reactions of anions that are available as salts
e.g. sodium cyanide, sodium azide, sodium acetate,
etc.
2. Reactions of anions that should be generated in situ
e.g. alkoxides, phenolates, and carbanions.

23.  In the former case the salts are used as aqueous solutions or in the form
of powdered solids, whereas the organic phase contain organic reactants
neat (when liquid) or in appropriate solvents.
 Since the phases are mutually immiscible the reaction does not proceed
unless the catalyst, usually a tetraalkylammonium salt, Q+X–, is present.

24. PTC-EXAMPLES
 PTC for anions reactant are often quaternary ammonium or phosphonium
salts
Eg. benzyltrimethylammonium chloride and hexadecyl
tributylphosphonium bromide.
 PTC for cations are often crown ethers

25. PTC-NUCLEOPHILIC SUBSTITUTION
 The catalyst transfers continuously reacting anions into the organic phase in the
form of lipophilic ion-pairs produced according to the ion-exchange equilibrium.
 They react further, for example, with alkyl halides affording nucleophilic
substitution.
Cat. regenerated

26. APPLICATIONS OF PHASE TRANSFER CATALYSIS
1) Nitriles From Alkyl Halides:-
2) Benzoyl Cyanides from Benzoyl Chloride:-
PTCR-X + NaCN
Organic Aqueous
O
Cl
+ Na N N
O
+ Na Cl
Bu4 N
+X-
Benzoyl
cyanide
Benzoyl
chlolride
Sodium
cyanide
RCN +
NaX
Nitrile

27. 3)ARYL ETHERS/THIOETHERS :-
4) Benzoin Condensation :-
ArOH +
RX
ArO
R
NaO
HPhenol Aryl ether
Benzaldehyde

28. 4) ESTERIFICATION :-Carboxylic acids can be esterified with alkyl halides inthe
Presence of triethylamine.
RCO2Na + RX
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
Alcohol Alkyl halide
Ether By-product
Carboxylic
acid as sod.
salt
Alkyl
halide
RCO2R + Na X
Ester

30. THANK YOU……..!!!!!