Chapter 18: Ethers, Epoxides, Thiols and sulfides

Unsymmetrical ether

• You have 2 different groups on both sides

Symmetrical ether

• Both groups are the same

Cyclic ether

• Oxygen atom is apart of a ring containing carbon atoms

Preparations of Ethers: William Ether synthesis Requirements:

• An alcohol

• Primary alkyl halide or primary tosylate

• a strong base (NaH or NaNH2)

• Reactants: 1. NaNH2/ THF, 2. R-OTS

The Aloxymercuration- Demercuration ether synthesis

• Reactants: 1. (CF3CO2)2 Hg/ R-OH, 2. NaBH4

• Product:

Ethers with only primary and secondary alkyl groups SN2 ( Acidic ether cleavage)

• Ether are cleaved by strong acids ( HBR, HI, H2O/ H2SO4 or CF3CO2H, etc)

• Reactants: HI, HBr, etc

Ethers with only primary and secondary alkyl groups SN2 mechanism ( Acidic ether cleavage)

• Lone pairs from O attacks H on H-X (halogen), breaking the H-X bond

• Halogen through SN2 attacks the less substituted carbon attached to the O ( not the one of the ring), breaks the C-O bond

• Product: I-CH2-CH3, OH instead of O

Ethers with tertiary alkyl group, benzylic or allylic group SN1 Mechanism ( Acidic Ether Cleavage)

• Lone pair on O from the ether attacks the H on H-Br, breaking H-Br bond

• The C-O bond breaks at the tertiary carbon, an alcohol and tertiary carbocation form

• SN1 substitution: Br- attacks the carbocation ( SN1 Product)

• E1 mechanism: Hydride shift towards the carbonation

Reactions of Epoxides: Ring opening ( basic conditions)

• Base- Catalyzed epoxide ring opening is always SN2 the nucleophile attacks the less hindered carbon

Reactions of Epoxides: Ring opening mechanism ( basic conditions)

Reactions of Epoxides: Ring opening ( acidic conditions)

• If epoxides has a tertiary carbon, benzylic or allylic carbon then SN1 reaction

• Nu attacks the more substituted carbon

Reactions of Epoxides: Ring opening mechanism ( acidic conditions)

Thiols & Sulfides

• 1. NaH ( a strong base) , 2. Aryl halide

• Product: Thiol + Aryl ring ( not including the halide)

Organometallic compounds

Reactions of Grignard reagent

Preparation of organolithium/ Reactions of organolithium

Reactions of the Gilman reagent