Question

How might you prepare the following compounds from butanoic acid? (a) Butan-1-ol (b) Butanal (c) 1-Bromobutane (d) Butyl acetate (e) Pentanenitrile (f) \(N\) -Methylpentanamide

Short answer

Convert butanoic acid to intermediates, then use reduction, esterification, substitution, and dehydration to prepare desired compounds.

Step-by-step solution

Convert Butanoic Acid to Butanoyl Chloride

To begin synthesizing different compounds from butanoic acid, it's useful to first convert it to a more reactive intermediate, butanoyl chloride. This conversion can be achieved using thionyl chloride (SOCl₂). The reaction is as follows:\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{COOH} + \text{SOCl}_2 \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{COCl} + \text{SO}_2 + \text{HCl} \]

Prepare Butan-1-ol

To form butan-1-ol, undergo the process of reduction. Convert butanoic acid or butanoyl chloride using a reducing agent such as lithium aluminum hydride (LiAlH₄), followed by hydrolysis:\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{COOH} \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} \]

Synthesize Butanal

Butanal can be obtained by the partial reduction of butanoic acid. Use a milder reducing agent, such as diisobutylaluminum hydride (DIBAL-H) at low temperature:\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{COOH} \xrightarrow[\text{low } T]{\text{DIBAL-H}} \text{CH}_3\text{CH}_2\text{CH}_2\text{CHO} \]

Obtain 1-Bromobutane

To transform butanoic acid into 1-bromobutane, use phosphorus tribromide (PBr₃) via the formation of the acyl bromide intermediate and subsequent reduction of butanoyl bromide:1. Formation of butanoyl bromide: \[ \text{CH}_3\text{CH}_2\text{CH}_2\text{COOH} + \text{PBr}_3 \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{COBr} + \text{H}_3\text{PO}_3 \]2. Reduction: Use LiAlH₄ to reduce the acyl bromide to 1-bromobutane.

Synthesize Butyl Acetate

Butyl acetate can be synthesized via an esterification reaction between butanol and acetic acid. First, reduce butanoic acid to butan-1-ol, then react it with acetic acid under acidic conditions:\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} + \text{CH}_3\text{COOH} \xrightarrow{\text{H}^+} \text{CH}_3\text{COOCH}_2\text{CH}_2\text{CH}_2\text{CH}_3} + \text{H}_2\text{O} \]

Form Pentanenitrile

Prepare pentanenitrile by converting butanoic acid to the corresponding butyl amine, then use dehydration to form the nitrile. First, prepare the amine through amide formation and reduction:1. Convert butanoic acid to butyl amine (via ammonolysis and reduction):\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{COCl} \xrightarrow{\text{NH}_3} \text{CH}_3\text{CH}_2\text{CH}_2\text{CONH}_2 \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{NH}_2 \]2. Dehydrate to nitrile using a dehydrating agent like phosphorus pentoxide (P₂O₅):\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{NH}_2 \xrightarrow{\text{P}_2\text{O}_5} \text{CH}_3\text{CH}_2\text{CH}_2\text{CN} \]

Convert to N-Methylpentanamide

To achieve the synthesis of \( N \)-Methylpentanamide, first convert butanoic acid to methyl butanamide, and then form \( N \)-methylpentanamide through methylation:1. Formation of \( N \)-methylamide:\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{COCl} + \text{CH}_3\text{NH}_2 \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{CO} \text{NHCH}_3 \]2. To ensure methylation is complete, you may methylate further using excess methyl iodide (\( \text{CH}_3\text{I} \)) if necessary.

Key concepts

Butanoic Acid Derivatives

Butanoic acid, with the formula \( C_4H_8O_2 \), is an important carboxylic acid used in organic synthesis. From this compound, various derivatives can be created by modifying the functional group. Transformation of this simple acid into different functional groups allows chemists to synthesize a diverse array of organic compounds.

Initially, butanoic acid can be converted into a more reactive acid derivative like butanoyl chloride. This is often carried out using thionyl chloride (SOCl₂), in a reaction that releases sulfur dioxide (SO₂) and hydrochloric acid (HCl). This transformation is crucial because it enables further functional group modifications due to the increased reactivity of the acyl chloride. Butanoic acid derivatives are used as intermediates in the synthesis of various alcohols, esters, amides, and nitriles. This adaptability is the cornerstone of their application in organic chemistry.

Reduction Reactions

Reduction reactions play a vital role in transforming butanoic acid derivatives into desired compounds by adding electrons or hydrogen to a molecule. In organic chemistry, this often means converting carbonyl groups into alcohols or aldehydes.

Some key reduction techniques include:

• Using lithium aluminum hydride (LiAlH₄): A strong reducing agent employed to reduce carboxylic acids and their derivatives directly to primary alcohols. For example, butanoic acid is reduced to butan-1-ol through LiAlH₄.
• Diisobutylaluminum hydride (DIBAL-H): This milder reducing agent specifically targets esters or carboxylic acids, converting them to aldehydes like butanal at low temperatures.

Understanding these reduction processes is essential for precisely modifying or synthesizing organic molecules, enabling the production of numerous useful compounds.

Esterification

Esterification is a fundamental reaction where a carboxylic acid reacts with an alcohol to form an ester and water. It is a reversible and equilibrium-driven process typically catalyzed by acids such as sulfuric acid or hydrochloric acid.

To synthesize butyl acetate from butanoic acid, one first reduces the acid to butan-1-ol, an alcohol. Following this, the alcohol undergoes an esterification reaction with acetic acid in the presence of an acid catalyst.

• In this specific case, butanol (a primary alcohol) and acetic acid form butyl acetate, a common solvent and flavoring agent.
• The reaction produces water and requires careful management to drive it to completion, often using a dehydration process to remove the water formed and shift the equilibrium toward the ester formation.

Mastering esterification provides a path to creating diverse esters necessary in flavors, fragrances, and industrial solvents.

Amide Formation

Amide formation is a crucial transformation in organic synthesis, involving the reaction of a carboxylic acid derivative with an amine. This process is significant in creating amides, which are present in proteins and various polymers.

When synthesizing \( N \)-methylpentanamide from butanoic acid, it's necessary to first convert the acid into a more reactive derivative, such as an acyl chloride. Then, this compound reacts with a primary amine such as methyl amine (\( CH_3NH_2 \)) to form the amide linkage.

• For more complex structures like \( N \)-methylated amides, further methylation using reagents like methyl iodide (\( CH_3I \)) is often required.

The ability to form amides is crucial for developing pharmaceuticals, dyes, and proteins' backbone, highlighting the importance of this mechanism in synthetic chemistry.