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Draw the product formed when phenylacetaldehyde \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CHO}\right)\) is treated with each reagent. Phenylacetaldehyde is partly responsible for the fragrance of the flowers of the plumeria tree, which is native to the tropical and subtropical Americas. a. \(\mathrm{NaBH}_{4}, \mathrm{CH}_{3} \mathrm{OH}\) e. \(\mathrm{Ph}_{3} \mathrm{P}=\mathrm{CHCH}_{3}\) b. \([1] \mathrm{LiAlH}_{4} ;[2] \mathrm{H}_{2} \mathrm{O}\) f. \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH} \mathrm{NH}_{2}\), mild acid c. \([1] \mathrm{CH}_{3} \mathrm{MgBr} ;[2] \mathrm{H}_{2} \mathrm{O}\) g. \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}\), mild acid d. \(\mathrm{NaCN}, \mathrm{HCl}\) h. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (excess), \(\mathrm{H}^{+}\) i. \(\mathrm{NH}\), mild acid j. \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}, \mathrm{H}^{+}\)

Step by step solution

01

Reduction with Sodium Borohydride

Phenylacetaldehyde is treated with NaBH鈧� in CH鈧僌H, a mild reducing agent. NaBH鈧� specifically reduces aldehydes to primary alcohols. Thus, the carbonyl group in phenylacetaldehyde gets reduced to an alcohol group, forming phenyl-ethanol.

02

Wittig Reaction

In reaction with Ph鈧働=CHCH鈧�, phenylacetaldehyde undergoes a Wittig reaction. The aldehyde group reacts with Ph鈧働=CHCH鈧� to form a new carbon-carbon double bond, replacing the carbonyl group with a vinyl group. This yields the alkene: styrene.

03

Reduction with Lithium Aluminium Hydride

LiAlH鈧� is a strong reducing agent that reduces aldehydes to primary alcohols. Phenylacetaldehyde, when treated with LiAlH鈧� followed by water, is reduced to phenyl-ethanol, similar to NaBH鈧� reduction.

04

Formation of Imine

Reaction with (CH鈧�)鈧侰HNH鈧� and a mild acid converts the aldehyde group of phenylacetaldehyde into an imine. The amino group reacts with the carbonyl carbon, resulting in a C=N bond, with release of water.

05

Grignard Reaction

The reaction with CH鈧僊gBr followed by water leads to nucleophilic addition of the methyl group from CH鈧僊gBr to the carbonyl carbon of phenylacetaldehyde. This forms a secondary alcohol after hydrolysis: 2-phenylpropan-2-ol.

06

Cyanohydrin Formation

NaCN, in the presence of HCl, reacts with phenylacetaldehyde to form a cyanohydrin. The cyano group (-CN) adds to the carbonyl carbon, converting the aldehyde into a cyanohydrin with a hydroxyl (-OH) and cyano group.

07

Formation of a Secondary Amine

Reaction with (CH鈧僀H鈧�)鈧侼H and a mild acid converts phenylacetaldehyde into a secondary amine. The aldehyde forms an iminium ion that reacts with the secondary amine, followed by reduction to form a more stable amine.

08

Acetal Formation

When phenylacetaldehyde is treated with excess CH鈧僀H鈧侽H and H鈦�, it undergoes acetalization. The carbonyl group reacts to form an acetal, where both oxygen atoms are ethoxy groups derived from ethanol.

09

Ammonia Reaction

Phenylacetaldehyde, when treated with NH鈧� in mild acid, undergoes a reaction similar to imine formation. However, instead of forming a stable imine, further reaction pathways such as the formation of an aminal might occur.

10

Cyclic Acetal Formation

In the presence of HOCH鈧侰H鈧侽H and H鈦�, a diol protection occurs. Phenylacetaldehyde reacts to form a five-membered cyclic acetal, where the diol forms ether linkages with the original carbonyl carbon.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Reduction Reactions

Reduction reactions involve converting an organic compound to a simpler form by adding hydrogen or removing oxygen. In the case of phenylacetaldehyde, reduction typically targets the carbonyl group. The use of reducing agents like Sodium Borohydride (NaBH鈧�) or Lithium Aluminium Hydride (LiAlH鈧�) in these reactions can help achieve this transformation.

NaBH鈧� is a milder reducing agent and is specifically employed to reduce aldehydes to primary alcohols. When phenylacetaldehyde is treated with NaBH鈧� in the presence of methanol, the aldehyde is gently converted to phenyl-ethanol.

On the other hand, LiAlH鈧� is a more potent reducer and also reduces carbonyl groups to form the corresponding alcohol. Therefore, treating phenylacetaldehyde with LiAlH鈧� followed by water similarly yields phenyl-ethanol. Both agents are effective, but their reactivity levels and handling conditions can be different.

Wittig Reaction

The Wittig reaction is an important method in organic synthesis to create alkenes. It involves the transformation of a carbonyl group into a double bond with the help of a phosphonium ylide. When phenylacetaldehyde reacts with the Wittig reagent Triphenylphosphine (Ph鈧働) teamed with a ylide such as CHCH鈧�, the carbonyl group is smoothly converted into a C=C double bond.

This transformation results in the formation of an alkene, specifically styrene in this scenario. The Wittig reaction is valuable due to its ability to control the position and stereochemistry of the newly formed double bond.

Grignard Reaction

The Grignard reaction is a cornerstone of organic synthesis for forming carbon-carbon bonds, crucial for creating complex molecules. The reaction involves the use of a Grignard reagent, typically an organomagnesium compound such as CH鈧僊gBr, which serves as a strong nucleophile.

When phenylacetaldehyde is subjected to a Grignard reaction, the methyl group in the Grignard reagent attacks the electrophilic carbonyl carbon, leading to the addition of a carbon group. After hydrolysis, it gives rise to a secondary alcohol, specifically 2-phenylpropan-2-ol. This mechanism showcases the versatility of Grignard reactions in constructing new molecular frameworks.

Imine Formation

Imines are compounds characterized by a carbon-nitrogen double bond. They are essential intermediates in organic synthesis, often formed by the reaction of an amine with a carbonyl compound. In the example of phenylacetaldehyde, when it reacts with an amine like (CH鈧�)鈧侰HNH鈧� in the presence of a mild acid, imine formation occurs.

The process involves the nucleophilic attack of the amine's nitrogen on the carbonyl carbon, followed by a dehydration step that leads to the elimination of a water molecule, establishing a carbon-nitrogen double bond. Imines can be further used in subsequent reactions, showcasing their importance as synthetic intermediates.

Acetal Formation

Acetals are formed by reacting a carbonyl compound with an alcohol under acidic conditions. They are vital for protecting carbonyl groups during chemical reactions. When phenylacetaldehyde is treated with an excess of ethanol and an acidic catalyst, it undergoes acetalization.

This process involves the transformation of the carbonyl group into a structure featuring two ether groups. Acetals are stable under neutral to basic conditions, which makes them excellent protecting groups for preserving the desired parts of a molecule while other reactions occur. The reaction emphasizes the utility of acetals in complex organic synthesis, offering a tactical advantage when performing sequential reactions.