(a) How do you convert the following? (i) phenol to anisole (ii) ethanol to propan-2-ol (b) Write the mechanism of the following reaction: $$\mathrm{C_2H_5OH\xrightarrow[443\ K]{H_2SO_4}CH_2{=}CH_2+H_2O}$$ (c) Why does phenol undergo electrophilic substitution more easily than benzene?

(a)(i) Phenoxide + CH₃I (Williamson). (ii) Ethanol →Cu/573K→ ethanal →CH₃MgBr, H₂O⁺→ propan-2-ol. (b) Protonation → slow loss of H₂O to C₂H₅⁺ → β-H elimination. (c) +M of –OH enriches the ring at o/p.

CBSE Class 12 · Alcohols Phenols and EthersLong Answer

WhatsApp Email

(a) How do you convert the following?
(i) phenol to anisole
(ii) ethanol to propan-2-ol
(b) Write the mechanism of the following reaction:

C_{2} H_{5} OH H_{2} S O_{4} 443 K C H_{2} = C H_{2} + H_{2} O

Solution

(a)(i)

C_{6} H_{5} OH NaOH C_{6} H_{5} ONa C H_{3} I C_{6} H_{5} OC H_{3} + NaI

(ii)

C_{2} H_{5} OH Cu 573K C H_{3} CHO C H_{3} MgBr H_{2} O/ H^{+} C H_{3} CH (OH) C H_{3}

(b) E1 mechanism:

Protonation: C $_{2}$ H $_{5}$ OH + H $^{+}$ → C $_{2}$ H $_{5}$ \overset{+}{O}H $_{2}$ .
Slow ionisation: C $_{2}$ H $_{5}$ \overset{+}{O}H $_{2}$ → C $_{2}$ H $_{5}^{+}$ + H $_{2}$ O.
β-H loss: C $_{2}$ H $_{5}^{+}$ → CH $_{2}$ =CH $_{2}$ + H $^{+}$ .

(c) The –OH lone pair delocalises into the ring (+M), raising electron density at the o/p carbons — electrophiles attack phenol far faster than benzene (bromination needs no catalyst).

CBSE Class 12 Board · Subjective

Practise more: all CBSE board PYQs on Alcohols Phenols and Ethers →

CBSE Class 12 · Alcohols Phenols and EthersLong Answer

Solution

More board questions on Alcohols Phenols and Ethers