Crown ethers are cyclic compounds composed of ether groups, primarily oligomers of ethylene oxide, with named structures like (18)-crown-6 for their specific sizes and oxygen atom counts. They can be synthesized using a template effect with metal ions and find applications in synthetic chemistry, such as esterification and aromatic substitution, as well as in various analytical methods. Additionally, variants like aza and thia crown ethers contain different heteroatoms and have their own specific applications.

1. PRESENTED BY :
KESHAV KUMAR SINGH
Reg. No.:- Y19266023
Deptt. of Chemistry
DHSGU Sagar (M.P.)

2.  Crown ethers are cyclic chemical compounds that consist of a
ring containing several ether groups.
 The most common crown ethers are oligomers of ethylene
oxide. Important members of this series are the tetramer (n = 4),
the pentamer (n = 5) and the hexamer (n = 6).
 The term "crown" refers to the resemblance between the
structure of a crown ether bound to a cation and a crown sitting on
a person's head.

3. NOMENCLATURE
 The crown ethers are designated as per IUPAC
nomenclature and also by short names (Pedersens crown
nomenclature).
 It is also represented by notations.
 Short name = (18)-crown-6.
1,4,7,10,13,16-HEXAOXACYCLOOCTADECANE

4.  The first number designates the ring size and the second
number designates the number of oxygen atoms in the ring.
 In places of oxygen other heteroatoms like sulphur and
nitrogen may be also present.
 If S is the heteroatom, these are called thia crown ethers and
if N is the heteroatom, these are called aza crown ethers.
AZA CROWN ETHERS
THIA CROWN ETHERS

5. 2 , 5 , 8 , 1 5 , 1 8 , 2 1 - h e x a o x t r i c y c l o h e x a c o s a - 1 ( 2 2 ) , 9 , 1 1 , 1 3 , 2 3 , 2 4 - h e x a e n e
2 , 5 , 8 , 1 5 , 1 8 , 2 1 - h e x a o x t r i c y c l o h e x a c o s a n e

6. GENERAL SYNTHESIS OF CROWN ETHER
 The macro cycles can be prepared by “template effect”
using metal ion as the organising agent.
 The principle of the template effect is Cyclic materials
may be formed from compound that is nucleophilic at the
one end, and electrophilic at the other end by reacting with
itself (path A).
 A second possibility is the nucleophilic or negative end of
one molecule may find the electrophilic or positive end of
another molecule (path B).
 In the later case, non cyclic products (oligomers or
polymers) will form.

8. AZA CROWN
 Macrocycles containing nitrogen are called as aza crown
ethers.
 In aza crown preparation in spite of high yield no template
effect is used.
 Tosylate and mesylate as leaving group gives the best
yields.
 Incase of halide ions poor yields is obtained.

9. CRYPTAND
 A molecular entity comprising a cyclic or polycyclic
assembly of binding sites that contains three or more binding
sites held together by covalent bonds.
 The adduct thus formed is called a "cryptate".
 The term is usually restricted to bicyclic or oligocyclic
molecular entities.

10. APPLICATIONS
1. SYNTHETIC APPLICTION
2. ANALYTICAL APPLICATION

11. 1. SYNTHETIC APPLICATIONS
 Esterification
 Saponification
 Anhydride formation
 Potassium permanganate oxidation
 Aromatic substitution reactions
 Elimination reactions
 Displacement reaction
 Generation of carbenes
 Superoxide anion
 Alkylations – 1. o-alkylations
2. c-alkylations
3. n-alkylations

12. ESTERIFICATION
 Crown ethers have been used for esterification.
 P-bromophenacyl esters have been prepared by the reaction
of p-bromophenacyl bromide with potassium salt of a
carboxylic acid using 18-crown-6 as the solubilizing agent,
which yields 92% phenacyl esters of fatty acids are obtained.
• R=H,CH3

13. AROMATIC SUBSTITUTION
REACTION
 1,2-dichlorobenzene undergoes substitution with methoxide
to give only 2-methoxychlorobenzene (2-chloroanisole).
 Here meta isomer is not obtained because it undergoes
nucleophilic aromatic substitution.

14. 2. ANALYTICALAPPLICATION
 Determination of gold in geological samples
 Super critical fluid extraction of trace metal from
solid and liquid materials
 Application of ionic liquids in analytical
chemistry
 Oxidation and determination of aldehydes
 Crown ethers are used in the laboratory as phase
transfer catalyst

15. OTHER APPLICATION
 It is used in photocynation
 Resolution of racemic mixture
 Benzoin condensation
 Hetrocyclisation
 Synthesis of furanones
 Acetylation of secondary amines in
presence of primary amine