Question

For the preparation of 1 -phenylethanol and 2 -phenylethanol by using phenylmagnesiu mild acidification on reactant respectively is (A) \(\mathrm{HCHO}\) and \(\mathrm{CH}_{3} \mathrm{CHO}\) (B) \(\backslash_{\mathrm{O}}\) and \(\mathrm{CH}_{3} \mathrm{CHO}\) (C) \(\mathrm{CH}_{3} \mathrm{CHO}\) and C1CC1 (D) \(\mathrm{CH}_{3} \mathrm{COOCH}_{3}\) and

Short answer

The correct combination of reactants for the formation of 1-phenylethanol and 2-phenylethanol is (A) \(HCHO\) and \(CH_3CHO\).

Step-by-step solution

Understand the Grignard reagent and its reaction mechanism

Phenylmagnesium bromide is a Grignard reagent, which is an organometallic compound containing a carbon-metal bond. Grignard reagents are known for their strong nucleophilic properties, allowing them to attack electrophilic carbon atoms in various carbonyl compounds, resulting in the addition of new carbon-carbon bonds.

Consider the formation of 1-phenylethanol

1-phenylethanol is an alcohol with the phenyl group (Ph) bonded to the carbon adjacent to the hydroxyl group (OH). The general structure is Ph-CH2-OH. To form this compound from a Grignard reagent, we need a carbonyl compound with one carbon addition (formaldehyde in this case, which is represented by \(HCHO\)) that can react with phenylmagnesium bromide.

Consider the formation of 2-phenylethanol

2-phenylethanol is an alcohol with the phenyl group bonded to the carbon that is next to the carbon bonded to the hydroxyl group. The general structure is Ph-CH-CH2-OH. To form this compound from a Grignard reagent, we need a carbonyl compound with two carbon additions (an aldehyde in this case, which is represented by \(CH_3CHO\), acetaldehyde) that can react with phenylmagnesium bromide.

Compare reactants with the desired products

Now that we have determined the required reactants for the formation of 1-phenylethanol and 2-phenylethanol, we can compare them to the options provided: (A) \(HCHO\) and \(CH_3CHO\) (B) \(/O\) and \(CH_3CHO\) (C) \(CH_3CHO\) and C1CC1 (D) \(CH_3COOCH_3\) and The correct combination of reactants for the formation of 1-phenylethanol and 2-phenylethanol is (A) \(HCHO\) and \(CH_3CHO\).

Key concepts

1-phenylethanol formation

1-Phenylethanol is an important organic compound with applications in various fields, including perfumes and pharmaceuticals. It is formed through the reaction of a Grignard reagent, such as phenylmagnesium bromide, with formaldehyde ( HCHO ).

In this process, the Grignard reagent serves as a strong nucleophile, attacking the electrophilic carbon atom in formaldehyde. This results in the formation of a new carbon-carbon bond, followed by mild acidification to yield the alcohol.

Here’s a simpler breakdown:

• The phenyl group ( Ph- ) in the Grignard reagent adds to the carbon of formaldehyde.
• After the nucleophilic addition, a new intermediate alkoxide ion is formed.
• A mild acid (like dilute hydrochloric acid) is used to protonate the alkoxide ion, resulting in 1-phenylethanol.

This reaction highlights the utility of Grignard reagents in building complex organic structures from simple molecules.

2-phenylethanol formation

2-Phenylethanol is another versatile alcohol, commonly used for its rose-like scent in perfumes. It is prepared using phenylmagnesium bromide and acetaldehyde ( CH_3CHO ).

The reaction mechanism is similar to that of 1-phenylethanol but involves a different carbonyl compound with two carbons.

Here's how it works:

• The phenyl group attacks the carbonyl carbon of acetaldehyde ( CH_3CHO ).
• This forms a new carbon-carbon bond and an alkoxide intermediate.
• Mild acidification converts the intermediate into 2-phenylethanol.

The choice of acetaldehyde is crucial as it adds an extra carbon to the chain, aligning with the desired structure of 2-phenylethanol.

reaction mechanism of Grignard reagents

Grignard reagents, like phenylmagnesium bromide, are renowned for their exceptional reactivity due to the presence of a carbon-metal bond. This bond gives the carbon a partial negative charge, making it a potent nucleophile.

Here's a deeper dive into the mechanism:

• Grignard reagents react with carbonyl compounds (aldehydes and ketones) by attacking the electrophilic carbon atom.
• The nucleophilic carbon forms a bond with the carbonyl carbon, creating an alkoxide intermediate.
• Subsequent treatment with a mild acid gives the final alcohol product, as the alkoxide ion is protonated.

This mechanism is a cornerstone of organic synthesis, allowing for the formation of complex molecules by adding carbon chains through straightforward reactions.