Crown ethers

Crown ethers
NOMENCLATURE
GENERAL SYNTHESIS OF CROWN ETHER
AZA CROWN
CRYPTAND
APPLICATIONS
1. SYNTHETIC APPLICTION
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

2. ANALYTICAL APPLICATION
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


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

1. CROWN ETHERS 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.

7. 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.

8. 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.

9. APPLICATIONS 1. SYNTHETIC APPLICTION 2. ANALYTICAL APPLICATION

10. 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

11. 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

12. 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.

13. 2. ANALYTICAL APPLICATION 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

14. 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