Crown ether and cryptand

BASIC DISCUSSION ABOUT THE CROWN ETHER AND CRYPTAND. INCLUDING THEIR BACKGROUND,STRUCTURE,NOMENCLATURE,CAVITY SIZE, SELECTIVITY, SYNTHESIS AND APPLICATIONS.

1. SERAMPORE COLLEGE DEPARTMENT OF CHEMISTRY STUDENT SEMINAR - 2018

2. CROWN ETHER AND CRYPTAND REPRESENTED BY- SUMAN MONDAL. SEKHAR DAS. ARPAN DAS.

3. INTRODUCTION In 1967,Charles Pederson, who was a chemist working at DuPont, discovered a simple method of synthesizing a crown ether when he was trying to prepare a complexing agent for divalent cations . He was surprised to isolate a by-product that strongly complexed  potassium  cations . Citing earlier work on the dissolution of potassium in 16-crown-4, he realized that the cyclic  polyethers represented a new class of complexing agents that were capable of binding alkali metal  cations . He proceeded to report systematic studies of the synthesis and binding properties of crown ethers in a seminal series of papers. The fields of organic synthesis, phase transfer catalysts, and other emerging disciplines benefited from the discovery of crown ethers.

4. The Nobel Prize for Chemistry in 1987 was given to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen for their efforts in discovering and determining uses of cryptands and crown ethers.

5. They are exceptionally versatile in selectively bindig a range of metal ions and a varirety organic neutral and ionic species. Crown ethers are currently being studied and used in a variety of applications beyond their traditional place in chemistry. So, why we are interested about this types of molecules?

6. CHARACTERISTICS crown ethers The mono cyclic polyether i.e. Cyclic polymers of ethylene glycol (OCH 2 CH 2 ) n are called the crown ethers. It’s inner side is hydrophilic And outer part is hydrophobic in nature. HYDROPHOBIC HYDROPHILIC

7. NOMINCLATURE :- Crown ethers are named as M-crown-N where M-represents the total no of atoms in cycle and N- represents total no of Oxygen atoms. THIACROWNS :- A special types of crown ether where the sulfur atoms takes the position of oxygen's. In thiacrowns the coordinating sites are the S-sites.

8. VARIATION OF CAVITY SIZE OF CROWN ETHERS:- The cavity size of the crown ether increases with increasing number of Oxygen atoms in the rings.

9. CROWN ETHER RELATED MACROCYCLES AND SUPRAMOLECULAR SYSTEM AND MOLECULAR RECOGNITION PODANDS- Open chain e.g - polyglymes , CH 3 (OCH 2 CH 2 ) X OCH 3 CROANDS- Monomacrocyclic e.g.- ccrown ethers CRYPTANDS – Multicyclic giving rise to spherical shape.

10. SYNTHESIS OF CROWN ETHER AND THIA CROWN CROWN ETHERS- 18-Crown-6 can be obtained by reacting 3 ethylene glycol(HOCH 2 CH 2 OH)with its corresponding dichloride in presence of aquous KOH. Actually, initially the K + - complex of 18-crown-6 is obtained and then from this complex, the free ligand may be isolated. If an organic base like NEt 3 is used instead of KOH, the crown ether is not produced.

11. How pedersen obtain dibenjo-18-crown-6 :-   Pedersen’s strategy entailed linking two  catecholate groups through one hydroxyl on each molecule. This linking defines a polydentate ligand that could partially envelop the cation and, by ionization of the phenolic hydroxyls, neutralize the bound dication . He was surprised to isolate a  by-product that strongly complexed with   cations .

12. THIA CROWNS- 14-Thiacrown-4 can be obtained this way

13. CRYPTANDS Cryptands are bicyclic or tricyclic . The multicyclic cryptands can provide the cage structure to accommodate the metal ion and other guest species. In the cage structure, they can provide the bridgehead N-atoms and other O-atoms as the donor sites.

14. SYNTHEIS OF CRYPTANDS The cryptands can be synthesized and it is illustrated for the synthesis of crypt- [2,2,2 ]. The template synthesis of the cryptands in presence of suitable alkali metal ions like K + is now being widely practised .

15. CRYPTATE EFFECT – A SPACIAL TYPE OF MACROCYCLIC EFFECT - In cryptate complexs , the metal ions are placed at the centers of the ligands. The cryptate complexes are stable than the macro monocyclic crown ether complexes. CAVITY SIZE OF THE CRYPTANDS:- The cavity diameter of cryptand increases with increasing no of Oxygen donor sites. It is evident that for Li + , Na + ,K + , the most stable cryptands are crypt-[2,1,1], crypt-[2,2,1] and crypt-[2,2,2]

16. SOME SPECIFIED CROWN COMPLEX FOR SOME SPECICIFIC IONS

17. APPLICATION OF CROWN ETHERS AND CRYPTANDS SOLUBILIZATION OF THE ALKALI METAL :The alkali metal dissolve in liquid NH 3 ,but not in the ether. But in presence of cryptand and crown ether ,the alkali metal dissolve in ether .

18. PHASE TRANSFER CATALYST:- When KF is solubilized in the organic solvents in presence of 18-crown-6 or cryptand like C222, K + ion is stabilized as [K(macrocycle)] + and the unsolvated F - ion acts as a powerful nucleophile . Similarly KMnO 4 solubilized in benzene in presence of crown-6 or suitable cryptand produces a purple solution called purple benzene.

19. SOLUBILIZATIN OF THE SALTS IN THE NONPOLAR SOLVENTS:- The macrocycles can solubilize the salts in the organic solvents through encapsulation of the metal ions in their cavities.The exterior part of the complex remains hydrophobic . K + Crown-6 [K(crown-6)] + + [e(crown-6)] - Et 2 O

20. FORMATION OF THE ALKALIDES AND ELECTRIDES: - Stabilization of the alkali metal ion(M + ) through the complexation can be given the alkalides and the electrides . Electrides :- [K(Crown-6)] + e ; [Cs(Crown-6)] + e ; etc Alkalides :- [Na(Crown-6)] + Na - ; [Na(C-222))] + Na - [K(Crown-6)] + Na - Aurides :- [Na( macrocycle )] + Au -

21. APPLICATION IN MEDICAL FIELD

22. OTHER APPLICATIONS:- They can be used for developing the ion selective electrodes. They can be used for separation of the chemically similar metal ions.( e.g.- Lanthanides, alkali metal ions etc ) based on size factor.

23. SPACIAL THANKS TO OUR RESPECTED FACULTIES:- Dr. SUDIPTA CHATTERJEE Dr. DEBDEEP CHAKBARTY Dr. RUDRAKSHA NATH BHATTACHARYA Dr. SUBHASHREE GHOSH Dr. SISIR DEBNATH Dr. KUNAL ROY Dr. PRANAB DATTA GUPTA

24. RESOURCES:- 1. FUNDAMENTAL CONCEPTS OF INORGANIC CHEMISTRY BY – A.K.DAS VOL-4 2. GENERAL AND INORGANIC CHEMISTRY BY - R. SARKAR VOL-2 3. ORGANIC CHEMISTRY BY-ANUPA SAHA & PATHAK 4. https://en.wikipedia.org/wiki/Crown_ether 5 . https:// en.wikipedia.org/wiki/Cryptand 6. https:// www.researchgate.net And many other sources.