Chapter 10: Q15P (page 517)

Show how you would synthesize each tertiary alcohol by adding an appropriate Grignard reagent to a ketone.
(a)3-phenylhexane-3-ol (3ways)
(b) Ph₃ COH
(c) 1-ethylcyclopentanol
(d) 2-cyclopentylpentan-2-ol

Short Answer

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Step by step solution

Addition of Grignard reagent to ketone

When the Grignard reagent is added to ketone in an ether solvent, and after protonation, it forms tertiary alcohol. Two alkyl groups that are already bonded to ketone and the third alkyl group come from Grignard reagent, resulting in tertiary alcohol.

Synthesis of 3-phenylhexane-3-ol

(a) There are three ways by which 3-phenylhexane-3-ol is formed when Grignard reagent is added to the ketone.

The product formed by (i), (ii), and (iii) is shown by highlighting the bonds in black.

Synthesis of Ph3 COH

(b) When Grignard reagent (Ph-MgBr) is added to ketone (Ph₂ CO ), it attacks the carbonyl carbon of ketone, and after protonation, it results in tertiary alcohol.

Synthesis of 1-ethylcyclopentanol

(c) When Grignard reagent (CH₃ CH₂ -Mgl) is added to ketone (C₅ H₈ O ), it attacks the carbonyl carbon of ketone, and after protonation, it results in tertiary alcohol.

Synthesis of 2-cyclopentylpentan-2-ol

(d) There are three methods of synthesizing 2-cyclopentylpentan-2-ol, by changing the Grignard reagents and ketone, followed by H ₃O⁺workup. The products formed by (i), (ii), and (iii) is shown as,