The major product of the following reaction is: PhCO-CH2CH2-CN (a keto-nitrile) treated with (i) CH3MgBr (excess), then (ii) H3O^…

Question

The major product of the following reaction is: PhCO-CH2CH2-CN (a keto-nitrile) treated with (i) CH3MgBr (excess), then (ii) H3O^+.

1. A. A benzylic tertiary alcohol still bearing the intact -CN group
2. B. Ph-C(CH3)(OH)-CH2CH2-CO-CH3 (tertiary alcohol at the benzylic C and a methyl ketone from the nitrile) (Correct answer)
3. C. A diol with two -CH3 additions on the nitrile carbon
4. D. The starting keto-nitrile with the ketone unreacted

Correct Answer

Option B — Ph-C(CH3)(OH)-CH2CH2-CO-CH3 (tertiary alcohol at the benzylic C and a methyl ketone from the nitrile)

Detailed Solution & Explanation

The correct answer is Option 2.

Key Points

• Excess CH$_3$MgBr attacks both functional groups. At the ketone (PhC=O) it adds CH$_3$ to give, after workup, a tertiary benzylic alcohol Ph-C(CH$_3$)(OH)-.
• At the nitrile (-CN) the Grignard adds once to give a magnesium ketimine salt, which on acidic hydrolysis (H$_3$O$^+$) yields a methyl ketone (-CO-CH$_3$).
• The major product is therefore Ph-C(CH$_3$)(OH)-CH$_2$CH$_2$-CO-CH$_3$.