Show how you would use Grignard syntheses to prepare the following alcohol from the indicated starting material and any other necessary reagents.
(e) benzyl alcohol (Ph–CH₂–OH) from bromobenzene (Ph–Br)

검증된 단계별 안내

Step 1: Begin by preparing the Grignard reagent from the starting material, bromobenzene (Ph-Br). React bromobenzene with magnesium (Mg) in an anhydrous ether solvent (e.g., diethyl ether) to form phenylmagnesium bromide (Ph-MgBr). This reaction is represented as: Ph-Br + Mg → Ph-MgBr.

Step 2: To introduce the -CH2OH group, react the Grignard reagent (Ph-MgBr) with formaldehyde (HCHO). Formaldehyde is the simplest aldehyde and will add a single carbon to the benzene ring. The reaction proceeds via nucleophilic addition, where the carbon in Ph-MgBr attacks the carbonyl carbon of formaldehyde.

Step 3: After the nucleophilic addition, the intermediate formed is a magnesium alkoxide. This intermediate has the structure Ph-CH2-O-MgBr.

Step 4: Perform an acidic workup by adding a dilute acid (e.g., HCl or H2SO4) to the reaction mixture. This step protonates the alkoxide group (-O-MgBr) to form the desired alcohol, benzyl alcohol (Ph-CH2-OH).

Step 5: Verify the product structure and ensure that the reaction conditions are anhydrous during the Grignard reagent preparation, as Grignard reagents are highly reactive with water and will decompose if exposed to moisture.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Grignard Reagents

Grignard reagents are organomagnesium compounds, typically represented as R-MgX, where R is an organic group and X is a halogen. They are highly reactive and can act as nucleophiles, allowing them to react with electrophiles to form new carbon-carbon bonds. In the context of synthesizing alcohols, Grignard reagents can react with carbonyl compounds to yield alcohols after hydrolysis.

Nucleophilic Substitution

Nucleophilic substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophile, resulting in the replacement of a leaving group. In the case of Grignard synthesis, the nucleophilic Grignard reagent attacks the electrophilic carbon in a carbon halide, leading to the formation of a new carbon-carbon bond. This mechanism is crucial for constructing complex organic molecules.

Hydrolysis of Grignard Reagents

Hydrolysis of Grignard reagents is the process where the Grignard reagent reacts with water or an alcohol to form the corresponding alcohol and magnesium hydroxide halide. This step is essential after the nucleophilic attack, as it converts the intermediate alkoxide formed during the reaction into a stable alcohol. Understanding this step is vital for completing the synthesis of the desired alcohol product.

Show how you would use Grignard syntheses to prepare the following alcohol from the indicated starting material and any other necessary reagents.(e) benzyl alcohol (Ph–CH2–OH) from bromobenzene (Ph–Br)