Crown ethers ppt

crown Ethers

1. CROWN ETHER SUBMITTED BY SHRINIDHI B R 1 ST M PHARM DEPT OF PHARMACEUTICAL CHEMISTRY JSS COLLEGE OF PHARMACY MYSURU

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. 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 .

5. 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

6. 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.

7. 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

8. 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

9. 1. SYNTHETIC APPLICTION 2.ANALYTICAL APPLICATION APPLICATIONS

10. 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 SYNTHETIC APPLICATIONS

11. 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 ESTERIFICATION

12. 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. AROMATIC SUBSTITUTION REACTION

13. 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

14. 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

15. 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