Chapter 16, Problem 16P

Write chemical equations, showing all necessary reagents, for the preparation of $1$-butanol

by each of the following methods:

Hydroboration–oxidation of an alkene

Use of a Grignard reagent

Use of a Grignard reagent in a way different from part (b)

Reduction of a carboxylic acid

Hydrogenation of an aldehyde

Reduction with sodium borohydride

Interpretation Introduction

Interpretation:

The chemical equations showing all necessary reagents for the preparation of $1-\text{butanol}$ by each of the given methods are to be written.

Concept introduction:

Hydroboration-oxidation of an alkene results in overall addition of water molecule across the double bond with a regioselectivity opposite to that of Markovnikov’s rule.

In the overall reaction, a hydrogen atom gets attached to the double bonded carbon atom having fewer hydrogens and the hydroxyl group gets attached to the carbon atom having greater number of hydrogens.

When a Grignard reagent reacts with formaldehyde primary alcohols are produced.

Grignard reagents are nucleophilic and react with oxiranes producing alcohols.

Aldehydes are reduced to the corresponding primary alcohols by using ${\text{LiAlH}}_4$, ${\text{NaBH}}_4$ in the presence of a catalyst.

By a suitable reducing agent like lithium aluminum hydride, carboxylic acids are reduced to the corresponding primary alcohols.

Answer to Problem 16P

Solution:

Explanation of Solution

a) Hydroboration-oxidation of an alkene to form $1-\text{butanol}$.

The structure of $1-\text{butanol}$ is shown as follows:

The hydroxyl group is attached to the C1 carbon atom. This alcohol is produced by hydroboration-oxidaton of an alkene. So in the alkene, the C1 carbon atom must be double bonded to the the C2 carbon atom. Thus, the alkene must be $1-butene$.

The regioselectivity of hydroboration-oxidation is such that the hydrogen atom will get attached to the C2 carbon atom while the hydroxyl group will get attached to the C1 carbon atom producing $1-\text{butanol}$.

The reaction is shown below:

b) Grignard reagent is used to prepare $1-\text{butanol}$.

The structure of $1-\text{butanol}$ is as follows:

Grignard reagents are nucleophilic and react with carbonyl groups forming a new carbon-carbon bond. An aqueous acid is used to convert the intermediate alkoxy ion to the corresponding alcohol.

In $1-\text{butanol}$, the hydroxyl group is attached to the C1 carbon atom. It is a primary alcohol. Thus, $1-butanol$ can be prepared by the reaction of propyl magnesium bromide with formaldehyde.

The reaction is shown below:

c) Different Grignard reagent is used to prepare $1-butanol$.

The structure of $1-butanol$ is as follows:

It is a primary alcohol. The hydroxyl group is attached to the C1 carbon atom.

Grignard reagents reacts with ethylene oxide to produce primary alcohol containing two more carbon atoms than the alkyl halide.

Thus, ethyl magnesium bromide, upon reaction with ethylene oxide, will produce $1-\text{butanol}$.

The reaction is shown below:

d) The reduction of carboxylic acid to produce $1-\text{butanol}$.

$1-\text{butanol}$ is a primary alcohol. Its structure is as follows:

Carboxylic acids, upon reduction, produce the correspionding primary alcohols.

Thus, reduction of butanoic acid with Lithium aluminum hydride will produce $1-\text{butanol}$.

The reaction is shown below:

e) Hydrogenation of an aldehyde to form $1-\text{butanol}$.

$1-\text{butanol}$ is a primary alcohol. Its structure is as follows:

Reduction of aldehydes with a suitable reducing agent produces the corresponding primary alcohols.

Thus, reduction of butanal in the presence of Lithium aluminum hydride will produce $1-\text{butanol}$.

The reaction is shown below:

f) Reduction of an aldehyde to form $1-\text{butanol}$.

$1-\text{butanol}$ is a primary alcohol. Its structure is as follows:

Sodium borohydride is used for the reduction of aldehydes and ketones to primary and secondary alcohols respectively.

Thus, reduction of butanal with sodium borohydride will produce $1-\text{butanol}$.

The reaction is shown below: