Chapter 16 Ethers, Epoxides, and Sulfides

1. Chapter 16Ethers, Epoxides, and Sulfides

2. 16.1Nomenclature of Ethers, Epoxides, and Sulfides

3. Substitutive IUPAC Names of Ethers name as alkoxy derivatives of alkanes CH3OCH2 CH3 CH3CH2OCH2CH2CH2Cl methoxyethane 1-chloro-3-ethoxypropane CH3CH2OCH2 CH3 ethoxyethane

4. Functional Class IUPAC Names of Ethers name the groups attached to oxygen in alphabetical order as separate words; "ether" is last word CH3OCH2 CH3 CH3CH2OCH2CH2CH2Cl ethylmethyl ether 3-chloropropylethyl ether CH3CH2OCH2 CH3 diethyl ether

5. SCH3 Substitutive IUPAC Names of Sulfides name as alkylthio derivatives of alkanes CH3SCH2 CH3 methylthioethane (methylthio)cyclopentane CH3CH2SCH2 CH3 ethylthioethane

6. SCH3 Functional Class IUPAC Names of Sulfides analogous to ethers, but replace “ether” as lastword in the name by “sulfide.” CH3SCH2 CH3 ethyl methyl sulfide cyclopentyl methyl sulfide CH3CH2SCH2 CH3 diethyl sulfide

7. Oxirane(Ethylene oxide) Oxolane(tetrahydrofuran) Oxetane 1,4-Dioxane Oxane(tetrahydropyran) Names of Cyclic Ethers O O O O O O

8. Thiirane Thiolane Thietane Thiane Names of Cyclic Sulfides S S S S

9. 16.2Structure and BondinginEthers and Epoxides bent geometry at oxygen analogousto water and alcohols

10. 105° 108.5° O C(CH3)3 (CH3)3C 112° 132° Bond angles at oxygen are sensitiveto steric effects O O H H CH3 H O CH3 CH3

11. An oxygen atom affects geometry in much thesame way as a CH2 group most stable conformation of diethyl etherresembles pentane

12. An oxygen atom affects geometry in much thesame way as a CH2 group most stable conformation of tetrahydropyranresembles cyclohexane

13. 16.3Physical Properties of Ethers

14. Table 16.1 Ethers resemble alkanes more than alcohols with respect to boiling point boiling point Intermolecular hydrogenbonding possible in alcohols; not possible in alkanes or ethers. 36°C 35°C O 117°C OH

15. Table 16.1 Ethers resemble alcohols more than alkaneswith respect to solubility in water solubility in water (g/100 mL) Hydrogen bonding towater possible for ethersand alcohols; not possible for alkanes. very small 7.5 O 9 OH

16. 16.4Crown Ethers

17. Crown Ethers structure cyclic polyethers derived from repeating —OCH2CH2— units propertiesform stable complexes with metal ions applicationssynthetic reactions involving anions

18. O O O O O O 18-Crown-6 negative charge concentrated in cavity inside the molecule

19. Ci

20. Conformational Study of the Structure of Free 18-Crown-6 N. A. Al-Jallal, A. A. Al-Kahtani, and A. A. El-Azhary* J. Phys. Chem. A 2005, 109, 3694-3703

22. O O O O O O 18-Crown-6 K+ forms stable Lewis acid/Lewis base complex with K+

23. Ion-Complexing and Solubility K+F– not soluble in benzene

24. O O O O O O Ion-Complexing and Solubility K+F– benzene add 18-crown-6

25. O O O O O O O O O O O O Ion-Complexing and Solubility F– K+ benzene 18-crown-6 complex of K+ dissolves in benzene

26. O O O O O O O O O O O O + F– Ion-Complexing and Solubility K+ benzene F– carried into benzene to preserve electroneutrality

27. Application to organic synthesis Complexation of K+ by 18-crown-6 "solubilizes" potassium salts in benzene Anion of salt is in a relatively unsolvated state in benzene (sometimes referred to as a "naked anion") Unsolvated anion is very reactive Only catalytic quantities of 18-crown-6 are needed

28. Example KF CH3(CH2)6CH2Br CH3(CH2)6CH2F 18-crown-6 (92%) benzene

29. 15-Crown-5 Na+

30. 16.5Preparation of Ethers

31. H2SO4, 130°C Acid-Catalyzed Condensation of Alcohols* 2CH3CH2CH2CH2OH CH3CH2CH2CH2OCH2CH2CH2CH3 (60%) *Discussed earlier in Section 15.7

32. Addition of Alcohols to Alkenes H+ (CH3)2C=CH2 + CH3OH (CH3)3COCH3 tert-Butyl methyl ether tert-Butyl methyl ether (MTBE) was produced on ascale exceeding 15 billion pounds per year in the U.S.during the 1990s. It is an effective octane booster ingasoline, but contaminates ground water if allowed toleak from storage tanks. Further use of MTBE is unlikely.

33. 16.6The Williamson Ether Synthesis Think SN2! primary alkyl halide + alkoxide nucleophile

34. Example CH3CH2CH2CH2ONa +CH3CH2I CH3CH2CH2CH2OCH2CH3+NaI (71%)

35. Alkoxide ion can be derived from primary, secondary, or tertiary alcohol Alkyl halide must be primary CH3CHCH3 CH2Cl + ONa CH2OCHCH3 (84%) CH3 Another Example

36. CH3CHCH3 CH2OH OH HCl Na CH3CHCH3 CH2Cl + ONa CH2OCHCH3 (84%) CH3 Origin of Reactants

37. + CH3CHCH3 CH2ONa Br CHCH3 H2C + CH2OH Elimination by the E2 mechanism becomesthe major reaction pathway. What happens if the alkyl halide is not primary?

38. 16.7Reactions of Ethers:A Review and a Preview

39. Summary of reactions of ethers No reactions of ethers encountered to this point. Ethers are relatively unreactive. Their low level of reactivity is one reason why ethers are often used as solvents in chemical reactions. Ethers oxidize in air to form explosive hydroperoxides and peroxides.

40. 16.8Acid-Catalyzed Cleavage of Ethers

41. Example HBr CH3CHCH2CH3 CH3CHCH2CH3 + CH3Br heat OCH3 Br (81%)

42. CH3CHCH2CH3 CH3CHCH2CH3 O Br •• •• CH3 •• HBr Br H •• •• CH3CHCH2CH3 CH3CHCH2CH3 O •• + •• H – O •• •• CH3 •• H Br •• •• Br CH3 •• •• •• Mechanism

43. O Cleavage of Cyclic Ethers HI ICH2CH2CH2CH2I 150°C (65%)

44. ICH2CH2CH2CH2I O HI HI – •• I •• •• •• •• •• •• I •• + O •• O •• H H Mechanism •• ••

45. 16.9Preparation of Epoxides:A Review and a Preview

46. Preparation of Epoxides Epoxides are prepared by two major methods.Both begin with alkenes. reaction of alkenes with peroxy acids(Section 6.19, stereospecific epoxidation) Sharplessepoxidation of allylic alcohols (stereoselectiveepoxidation) conversion of alkenes to vicinalhalohydrins, followed by treatmentwith base (Section 16.10)

47. Sharplessepoxidation of allylic alcohols 2001 Nobel prize

48. 16.10Conversion of Vicinal Halohydrinsto Epoxides

49. H OH H Br •• – O via: •• •• H H Br •• •• •• Example H NaOH O H2O H (81%)

50. NaOH O Epoxidation via Vicinal Halohydrins Br Br2 H2O OH antiaddition inversion corresponds to overall syn addition ofoxygen to the double bond