Question

Predict the products of the following reactions.

(a) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }\mathbf{N}\mathbf{+}{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{MgBr}\mathbf{,}\mathbf{}\mathbf{then}\mathbf{}{\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$

(b) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\equiv \mathbf{N}\mathbf{+}\mathbf{DIBAL}\mathbf{-}\mathbf{H}\mathbf{,}\mathbf{then}{\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$

(c) $\mathbf{Benzyl}\mathbf{chloride}\mathbf{+}\mathbf{potassium}\mathbf{cyanide}$

(d) $\mathbf{Product}\mathbf{of}\left(\mathbf{c}\right)\mathbf{+}\mathbf{cyclopentylmagnesium}\mathbf{chloride}\mathbf{,}\mathbf{then}\mathbf{acidic}\mathbf{hydrolysis}$

(e) $\mathbf{Product}\mathbf{of}\left(\mathbf{c}\right)\mathbf{+}\mathbf{DIBAL}\mathbf{-}\mathbf{H}\mathbf{,}\mathbf{then}\mathbf{hydrolysis}$

Short answer

(a)$\text{Hexan - 2 - one}$

(b) $\text{Butanal}$

(c) $\text{2 - Phenyl acetonitrile}$

(d) $\text{1 - cyclopentyl - 2 - phenylethan - 1 - one}$

(e) $\text{2 - phenyl acetaldehyde}$

Step-by-step solution

Introduction

An organolithium reagent or Grignard reagent attacks a nitrile to form magnesium salt of an imine. The final product (a ketone) is formed by the acidic hydrolysis of the imine.This mechanism is the opposite of acid-catalyzed imine formation. In another process, a nitrile can undergo reduction with DIBAL-H to form an aluminum complex, which on hydrolysis gives the aldehyde.

The starting material used for the synthesis of a ketone can be a nitrile. The compounds containing the cyano $\left(-\text{C}\equiv \text{N}\right)$ functional group.Since nitrogen is more electronegative than carbon, the $-\text{C}\equiv \text{N}$is more polarized such as the bond of the carbonyl group. Nucleophiles can be added to just by attacking the electrophilic carbon atom. Magnesium salt of an imine is formed by the attack of Grignard or organolithium reagent to nitriles which undergoes acididc hydrolysis to form the desired ketone.

Prediction of the production

(a) The given nitrile reacts with Grignard reagent to form the magnesium salt of an imine which undergoes acidic hydrolysis to form the desired ketone .

(b) The given nitrile undergoes reduction with DIBAL-H to form an aluminum complex which hydrolyses to give an aldehyde .

(c) Benzyl chloride reacts with potassium cyanide to form 2-phenyl acetonitrile.

(d) reacts with cyclopentyl magnesium chloride to form a magnesium salt of an imine which undergoes acidic hydrolysis to give a ketone$(1-\text{cyclopentyl}-2-\text{phenylethan}-1-\text{one})$

(e) undergoes reduction with DIBAL-H to form an aluminum complex which hydrolyses to give the aldehyde