SolutionsEther Cleavage
1. Products
Give the products of the reaction with hot concentrated HBr of:
- tert-Butyl methyl ether
- Diethyl ether (excess HBr)
- tert-Butyl bromide and methanol: the cleavage goes through the tertiary carbocation (SN1).
- Ethyl bromide: ethyl bromide and ethanol are formed first by SN2, and ethanol is in turn converted into ethyl bromide.
2. Protecting groups
Why is the OH of 2-bromoethanol protected before it reacts with sodium acetylide?
Because the OH is acidic enough to protonate the acetylide (pKa of acetylene ≈ 25 versus ≈ 16 for the alcohol) and would destroy the nucleophile. The tert-butyl ether is inert towards acetylide and is removed afterwards with acid.