Consider the following sequence of reactions [figure] The major product P is:
- [figure]
- [figure]
- [figure]
- [figure]
Answer
(3) [figure]
Solution
Step 1: a 3° alcohol has no α-H, so over Cu at 573 K it is not dehydrogenated but dehydrated to an alkene:
[figure]
Step 2: H+ protonates 2-methylpropene to the stable 3° (tert-butyl) carbocation:
[figure]
Step 3: an oxygen of –COOH of benzoic acid attacks the carbocation; loss of H+ gives the ester:
[figure]
⇒ P = tert-butyl benzoate
Ring alkylation does not occur: –COOH strongly deactivates the ring towards Friedel–Crafts reactions.
Answer: (3)