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. • 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.
O
O O
O O
O
1 ,4 ,7 ,1 0 ,1 3 ,1 6 -H E X A O X C Y C L O -O C T A D E C A N E
NOMENCLATURE
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 these are called thia
crown ethers, and if N is the heteroatom, these are
called aza crown ethers.
NH NH
NH HN
AZA CROW N ETHERS
S S
S
TIACROWNETHERS
5. O
O O
O O
O
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
O
O O
O O
O
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. • 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)
GENERAL SYNTESIS OF CROWN ETHER
7. • A second possibility is the neucleophilic 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. O
C l
O
0 -
C l
p ath a
in tram o lecu lar
p ath b
in term o lecu lar
O *
n
9. • Macrocycles containing nitrogen are called as aza crown
ethers.
• In aza crown preparation in spite of high yield no
templet effect is used.
• Tosylate and mesylate as leaving group gives the best yields.
• Incase of hallide ions y poor yields is obtained.
AZA CROWN
10. • 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.
ex:
CRYPTAND
13. • 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
Br
C
O
CH2Br
KCrown
CH3CN
Br
C
O
CH2
COOR BrRCO2
ESTERIFICATION
14. • 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.
C l
C l
C l
C l
O C H 3
K + O _ C H 3
d i c y c l o h e x a n e ( 1 8 ) c r o w n - 6
O C H 3
1 , 2 - d i c h l o r o b e n z e n e
2 - c h l o r o a n i s o l e
m e t a m e t h o x y
c h l o r o b e n z e n e
( n o t i s o l a t e d )
AROMATIC SUBSTITUTION REACTION
15. • 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
ANALYTICAL APPLICATION
16. • It is used in photocynation
• Resolution of racemic mixture
• Benzoin condensation
• Hetrocyclisation
• Synthesis of furanones
• Acetylation of secondary amines in presence
of primary amine
OTHER APPLICATION
17. REFERENCES
• Text book of organic synthesis special techniques-v k
ahluwalia,renu aggarwal
• Analytical Applications of Crown Ethers
G. S. VASILIKIOTIS, I. N. PAPADOYANNIS,’ AND TH. A.
KOUIMTZIS
Laboratory of Analytical Chemistry, University of Thessaloniki,
• Synthesis of Thiacrown and Azacrown Ethers Based on the
Spiroacetal Framework By,Marica Nikac University of Western
Sydney
• Wikipedia
