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Chapter 15: Problem 32

How could you convert butanoic acid into the following compounds? More than one step may be required. (a) Butan-1-ol (b) 1 -Bromobutane (c) Pentanoic acid (d) But-1-ene

Short Answer

Expert verified
Butanoic acid is converted to butan-1-ol by reduction, to 1-bromobutane by substitution after reduction, to pentanoic acid by Grignard reaction, and to but-1-ene by dehydration.

Step by step solution

01

Convert Butanoic Acid to Butan-1-ol

To convert butanoic acid ( ext{C}_3 ext{H}_7 ext{COOH}) to butan-1-ol ( ext{C}_4 ext{H}_9 ext{OH}), we perform a reduction reaction. Use a strong reducing agent such as lithium aluminum hydride ( ext{LiAlH}_4). The reaction proceeds as:\[ \text{C}_3\text{H}_7\text{COOH} + \text{LiAlH}_4 \rightarrow \text{C}_4\text{H}_9\text{OH} \]This reduces the carboxylic acid group to a primary alcohol.
02

Convert Butanoic Acid to 1-Bromobutane

To convert butanoic acid to 1-bromobutane ( ext{C}_4 ext{H}_9 ext{Br}), first convert the acid to butan-1-ol using ext{LiAlH}_4 as outlined in Step 1. Then, perform a substitution reaction using hydrobromic acid ( ext{HBr}) to replace the hydroxyl group with a bromine atom:\[ \text{C}_4\text{H}_9\text{OH} + \text{HBr} \rightarrow \text{C}_4\text{H}_9\text{Br} + \text{H}_2\text{O} \]This process involves the treatment of the alcohol with concentrated ext{HBr}.
03

Convert Butanoic Acid to Pentanoic Acid

To synthesize pentanoic acid ( ext{C}_4 ext{H}_9 ext{COOH}) from butanoic acid, first increase the carbon chain length by performing a homologation. Start by converting butanoic acid to an acyl chloride using thionyl chloride ( ext{SOCl}_2):\[ \text{C}_3\text{H}_7\text{COOH} + \text{SOCl}_2 \rightarrow \text{C}_3\text{H}_7\text{COCl} + \text{SO}_2 + \text{HCl} \]Next, perform a Grignard reaction where the acyl chloride reacts with methyl magnesium bromide ( ext{CH}_3 ext{MgBr}) to extend the chain:\[ \text{C}_3\text{H}_7\text{COCl} + \text{CH}_3 ext{MgBr} \rightarrow \text{C}_4\text{H}_9 ext{COOH} \]This creates a new carbon-carbon bond, extending the chain and forming pentanoic acid after hydrolysis.
04

Convert Butanoic Acid to But-1-ene

To convert butanoic acid to but-1-ene ( ext{C}_4 ext{H}_8}), first convert the acid to butan-1-ol as in Step 1. Next, dehydrate the alcohol using acid catalysis, such as with concentrated sulfuric acid ( ext{H}_2 ext{SO}_4):\[ \text{C}_4\text{H}_9 ext{OH} + \text{H}_2 ext{SO}_4 \rightarrow \text{C}_4 ext{H}_8 + \text{H}_2 ext{O} \]The dehydration results in the formation of alkenes, and under controlled conditions, but-1-ene is obtained as the major product.

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Key Concepts

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

Reduction Reaction
A reduction reaction involves the addition of hydrogen to a compound or the removal of oxygen. In the context of converting butanoic acid to butan-1-ol, this process involves reducing a carboxylic acid (butanoic acid) to an alcohol (butan-1-ol). For this transformation, a strong reducing agent such as lithium aluminum hydride (\(\text{LiAlH}_4\)) is used.
  • Using \(\text{LiAlH}_4\) allows for selective reduction, turning the carboxylic group into a hydroxyl group.
  • The general reaction is \[\text{C}_3\text{H}_7\text{COOH} + \text{LiAlH}_4 \rightarrow \text{C}_4\text{H}_9\text{OH}\]
  • This results in the conversion of butanoic acid into the primary alcohol, butan-1-ol.
This step is important in organic synthesis as alcohols serve as versatile intermediates for further reactions.
Substitution Reaction
A substitution reaction involves replacing one group in a molecule with another. In the conversion of butan-1-ol to 1-bromobutane, a substitution reaction takes place, where the hydroxyl group (-OH) is substituted by a bromine atom due to the presence of hydrobromic acid (\(\text{HBr}\)).
  • This can be represented as: \[\text{C}_4\text{H}_9\text{OH} + \text{HBr} \rightarrow \text{C}_4\text{H}_9\text{Br} + \text{H}_2\text{O}\]
  • In practice, butan-1-ol is treated with concentrated \(\text{HBr}\), which facilitates the replacement of the -OH group with a bromine atom on the carbon chain, yielding 1-bromobutane.
  • Understanding substitution reactions is crucial for synthesizing halogenated compounds, which are often intermediates in the formation of more complex molecules.
Grignard Reaction
The Grignard reaction is a powerful tool in organic chemistry for forming carbon-carbon bonds. It involves the reaction of an organomagnesium compound, known as a Grignard reagent, with an electrophilic carbon atom.
  • In the conversion of butanoic acid to pentanoic acid, an initial reaction with thionyl chloride (\(\text{SOCl}_2\)) forms an acyl chloride.
  • This acyl chloride then reacts with methyl magnesium bromide (\(\text{CH}_3\text{MgBr}\)), a Grignard reagent, resulting in a new carbon chain.
  • The reaction sequence is:\[ \text{C}_3\text{H}_7\text{COCl} + \text{CH}_3\text{MgBr} \rightarrow \text{C}_4\text{H}_9\text{COOH} \]
  • This forms pentanoic acid after hydrolysis, which involves breaking the compound with water.
Grignard reactions are essential for elaborate organic syntheses and allow the formation of various constitutive molecules by chain elongation.
Dehydration Reaction
Dehydration reactions involve the removal of a water molecule from a compound. This type of reaction can convert alcohols into alkenes by eliminating the hydroxyl group and an adjacent hydrogen atom from the carbon skeleton.
  • In the conversion process from butan-1-ol to but-1-ene, dehydration occurs through acid catalysis, often using concentrated sulfuric acid (\(\text{H}_2\text{SO}_4\)).
  • The dehydration reaction can be represented as:\[ \text{C}_4\text{H}_9\text{OH} + \text{H}_2\text{SO}_4 \rightarrow \text{C}_4\text{H}_8 + \text{H}_2\text{O} \]
  • Controlling the reaction conditions helps to selectively produce but-1-ene as the primary product.
This type of reaction is key in the manufacturing of alkenes, which are crucial starting materials for various polymerization processes and other organic synthesis applications.

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