Question

Synthesis of 1-phenyl-1-propanol with Grignard reagent. Write out full mechanism.

Answer 1

The synthesis of 1-phenyl-1-propanol with a Grignard reagent involves the nucleophilic addition of phenylmagnesium bromide to propionaldehyde, followed by hydrolysis to yield the secondary alcohol. The key steps are preparation of the Grignard reagent, its addition to the aldehyde, and subsequent protonation.

Step-by-step explanation:

Synthesis of 1-Phenyl-1-Propanol Using Grignard Reagent

The synthesis of 1-phenyl-1-propanol using a Grignard reagent involves the reaction of phenylmagnesium bromide (PhMgBr) with propionaldehyde (CH3CH2CHO). The Grignard reagent is prepared by the reaction of bromobenzene with magnesium in the presence of dry ether. During the synthesis, the carbon-magnesium bond of the Grignard reagent acts as a nucleophile and attacks the electrophilic carbon of the aldehyde leading to the formation of a secondary alcohol after hydrolysis.

1. Preparation of the Grignard reagent: Bromobenzene reacts with metallic magnesium in dry ether to form phenylmagnesium bromide.
2. Addition of aldehyde: Phenylmagnesium bromide is then added to propionaldehyde, leading to the formation of an addition intermediate.
3. Protonation: The addition intermediate is treated with water or dilute acid after Grignard addition, which results in protonation and forms the secondary alcohol, 1-phenyl-1-propanol.

The mechanism of the reaction involves the transfer of phenyl group to the carbonyl carbon, followed by hydrolysis. This synthesis highlights the utility of Grignard reagents in forming carbon-carbon bonds, allowing for the construction of complex organic molecules.