![Claisen rearrangement
• [3,3]-sigmatropic rearrangement
• allyl phenyl ether is converted thermally to an unsaturated carbonyl compound
followed by rearomatisation
Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur](https://image.slidesharecdn.com/ethersandepoxide-190926174338/85/Ethers-and-epoxide-25-320.jpg)
![Crown Ether
•Structure
cyclic polyethers derived from repeating
—OCH2CH2— units
•Properties
form stable complexes with metal ions
•Applications
synthetic reactions involving anions
•Naming
x = total no. of atoms in ring: [x] Crown- no. of oxygen atoms
Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur](https://image.slidesharecdn.com/ethersandepoxide-190926174338/85/Ethers-and-epoxide-39-320.jpg)
Ethers and epoxide
- 1. ETHERS AND EPOXIDE Dr. T. Geetha Assistant Professor Department of Chemistry St. Mary’s College, Thrissur
- 2. Ethers - R-O-R linkage Symmetrical ethers • R =R’ • Simple ethers • Dimethyl ether Me -O –Me • Diethyl ether Et - O -Et Unsymmetrical ethers • R ≠ R’ • Mixed ethers • Ethyl methyl ether Me -O –Et • Methyl phenyl ether Me – O-Ph
- 3. Nomenclature •Simple ethers - assigned common names • Name both alkyl groups bonded to the oxygen, arrange these names alphabetically, and add the word ether • For symmetrical ethers, name the alkyl group and add the prefix “di-” Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 4. Nomenclature - IUPAC system • One alkyl group is named as a hydrocarbon chain, the other is named as part of a substituent bonded to that chain: • Name the simpler alkyl group as an alkoxy substituent by changing the –yl ending of the alkyl group to –oxy. • Name the remaining alkyl group as an alkane, with the alkoxy group as a substituent bonded to this chain Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 5. Nomenclature - IUPAC system • CH3CH2CH2OCH3 ➢1-methoxypropane • CH3CH(OCH3)CH3 ➢2-methoxypropane • CH3CH(CH3)OCH3CH(CH3) ➢2-(2-Propoxy)propane
- 6. Polyether • More than one ether linkage • Named as Oxa derivative of alkane corresponding to total number of C & O atom present • CH3-O-CH2CH2CH2-O-CH3 ➢ 1,3-dimethoxypropane or 2,6-Dioxaheptane • CH3OCH2CH2CH3 ➢2-oxapentane Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 7. Cyclic ether • Epoxides – alkene oxides • 3 membered cyclic ether Ethylene oxide Propyleneoxide Butyleneoxide Epoxy ethane 1,2-Epoxypropane 2,3-Epoxybutane Ethene oxide 1,2 – Propene Oxide 2,3- Butene Oxide Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 8. Cyclic ether • Tetrahydrofuran • Tetrahydropyran
- 9. Cyclic ether - IUPAC Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 10. Structural isomerism • Exhibits metamerism • Functional group isomers Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 11. Preparation • Dehydrogenation of alcohol • Industrial synthesis for diethyl ether: 2 CH3CH2-OH + H2SO4 140oC CH3CH2-O-CH2CH3 + H2O • SN2 mechanism • Not generally useful for syntheses of ethers in the lab: a) Only symmetric ethers can be made this way. b) Conditions are very compound specific ( at 180o ethanol would yield ethylene instead of the ether) Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 12. Williamson ether synthesis • reaction between a metal alkoxide & alkyl halide • R-O-Na+ + R´-X → R-O-R´ + NaX • R´-X should be CH3 or 1o • SN2 mechanism Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 13. Another Example + CH3CHCH3 ONa CH2Cl (84%)CH2OCHCH3 CH3 Alkyl halide must be primary Alkoxide ion can be derived from primary, secondary, or tertiary alcohol Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 14. CH3CHCH3 OH Na (s) CH2OH HCl or SOCl2 CH2OCHCH3 CH3 CH2Cl + CH3CHCH3 ONa (84%) 1o Halides & Alkoxides Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 15. What if the alkyl halide is not primary? SN2 vs E2 CH2ONa + CH3CHCH3 Br CH2OH + H2C CHCH3 Elimination produces the major product. Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 16. Alkoxides • Alkoxides can be prepared from alcohols by a BrØnsted-Lowry acid—base reaction • For example, sodium ethoxide (NaOCH2CH3) is prepared by treating ethanol with NaH • NaH is an especially good base for forming alkoxide - by-product of the reaction, H2, is a gas that just bubbles out of the reaction mixture Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 17. oxygen is sp3 hybridized, bond angle ~ 109.5o ethers are polar; no hydrogen bonding mp/bp moderate water insoluble Ethers and epoxides exhibit dipole-dipole interactions because they have a bent structure with two polar bonds Diethyl ether = very important organic solvent, polar, water insoluble, bp = 35o. Very flammable & forms explosive peroxides R O R' : : Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur Physical properties:
- 18. Chemical reaction of ethers • Two lone pair – Lewis Base • Basic property – • • Forms etherates with Lewis acid such as BF3 R O R' : : Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 19. Chemical reaction of ethers • Basic property – • Oxonium salt with cold conc. inorganic acid R O R' : : Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 20. Chemical reaction of ethers Acid cleavage R-O-R´ + (conc) HX heat R-X + R´-OH If excess of HX is used, the alcohol formed reacts further to give alkyl halide R-O-R´ + (conc) HX heat R-X + R´-X X = Br, I Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 21. Acid cleavage Mechanism 1) O CH2CH3CH3CH2 + HX H O CH2CH3CH3CH2 + X H O CH2CH3CH3CH22) X + CH3CH2 X + HO CH2CH3 3) CH3CH2 OH + HX CH3CH2 OH2 4) CH3CH2 OH2 + X CH3CH2 X + H2O + X Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 22. Reactions of unsymmetrical ether • When alkyl group of an ether is 1o or 2o • SN2 mechanism • nucleophile I- attacks the least substituted C of oxocation CH3- O-CH2CH3 + H-I CH3- O-CH2CH3 + I- I- + CH3- O-CH2CH3 CH3I + CH3-CH2-OH If excess of HI is used , ethanol is converted to ethyl iodide .. + + Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur H H
- 23. When alkyl group of an ether is 3o slow + I- Fast SN1 reaction Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur HI+
- 24. Reaction of aryl ether • Anisole reacts with HI CH3-O-CH3 + HI CH3I +C6H5OH Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 25. Claisen rearrangement • [3,3]-sigmatropic rearrangement • allyl phenyl ether is converted thermally to an unsaturated carbonyl compound followed by rearomatisation Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 26. Claisen rearrangement • Allyl group migrates to ortho position • Inversion of allyl group during rearrangement • No cross product when reaction carried out with mixture of allyl phenyl ethers – Intramolecular mechanism Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 27. Claisen rearrangement • ortho position is preferred • If both ortho position occupied – migrate to para position Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 28. Zeisel’s method -estimation of methoxy group The precipitate of AgI is collected washed dried and weighted Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 29. Zeisel’s method No. of methoxy group in compound = (w2 x M)/(234 x w1) M= Molecular mass of sample Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 30. Epoxide - Preperation • Epoxidation of alkene • Reaction of alkenes with peracid Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 31. Epoxidation of alkene Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 32. Preparation from halohydrin • Addition of HOX to an alkene gives a Halohydrin • Treatment of a Halohydrin with base gives an epoxide • Intramolecular Willamson Ether synthesis Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 33. Industrial synthesis of ethylene oxide • Controlled oxidation (using oxygen or air) of ethylene over a silver catalyst • Exothermic • Excessive rise in temperature & over oxidation – complete combustion liberating H2O & CO2 • High temperature cause degradation of catalyst Ag/Al2O3 also acts as catalyst Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 34. Acid catalyzed ring opening SN1 Mechanism Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 35. Acid catalyzed ring opening Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 36. Base catalyzed ring opening Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 37. Comparison SN1 Mechanism SN2 Mechanism Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 38. Comparison – unsymmetrical epoxide Acid catalyzed ring opening Base catalyzed ring opening Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 39. Crown Ether •Structure cyclic polyethers derived from repeating —OCH2CH2— units •Properties form stable complexes with metal ions •Applications synthetic reactions involving anions •Naming x = total no. of atoms in ring: [x] Crown- no. of oxygen atoms Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 40. These compounds are called Crown ethers because their molecule have a crown- like shape. The bracket number represents the ring size and the terminal numbers gives the number of oxygen. The oxygen are usually separated by two carbons. Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 41. 18-Crown-6 negative charge concentrated in cavity inside the molecule Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 42. Ion Size & Crown Ether Complexes K+ Na+ Li+ 18-Crown-6 12-Crown-4 15-Crown-5 Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 43. Preparation • First Synthesis of Ether - Pedersen - 1967 Dibenzo-18-crown-6 Nobel Prize in 1987 Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 44. Preparation Triethylene glycol tosylate + Triethylene glycol Potassium tertiary Butoxide Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 45. Application • Formation of Host Guest complex – inclusion compound • Phase transfer catalyst – maintains homogeneity between aqueous and organic substrate • Reaction between aq. KMnO4 & Organic substrate in organic solvent is accelerated by adding crown ether • Chiral crown ether used for resolution of racemic mixture • Accelerates nucleophilic substitution and elimination reaction Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur
- 46. Reference • Morrison & Boyd, Organic Chemistry, VIth ed, Prentice Hall of India Pvt. Ltd., New Delhi, 1998 • Bruice – Organic Chemistry, 3rd edition, Pearson Education, New Series 2001 • B.S. Bahl & Arun Bahl, Adv. Org. Chemistry., S.Chand & Co New Delhi • Tiwari, Mehrothra, & Vishnoi, Text book of Organic Chemistry., Vikas Publishing House Pvt.Ltd, New Delhi Ethers and Epoxides – Dr. T. Geetha, St. Mary’s College, Thrissur