Chapter 13, Problem 49P

Interpretation Introduction

Interpretation:

The equations for the preparation of each of the given compounds from benzene or toluene and any necessary organic or inorganic reagents are to be written.

Concept Introduction:

In electrophilic aromatic substitution, all electrons donating substituents are ortho and para directing, while all the electron withdrawing substituents are meta directing.

When aromatic ring having two comparably activated positions then the substitution usually takes place at the less hindered position.

The reagent zinc amalgam and concentrated hydrochloric acid is use to convert a carbonyl group into methylene unit. This reaction is known as Clemmenson’s reduction.

In Friedel-Crafts acylation, acyl halides are used to yield aryl ketones.

In Friedel-Crafts alkylation, alkyl halides are used to yield aryl substituted alkanes.

A mixture of nitric acid and sulfuric acid produces a nitronium ion which behaves as an electrophile in electrophilic aromatic substitution reactions.

Reagent bromine in acetic acid indicates bromination reaction.

Reagent sulfur trioxide in sulfuric acid indicates sulfonation reaction.

Oxidation of benzylic carbon atom is done using the ${\text{KMnO}}_{\text{4}}\text{,}{\text{H}}_{\text{2}}\text{O}$ in hydrochloric acid to convert the methyl group into a carboxylic acid group.

Answer to Problem 49P

Solution:

a) Reaction equations for the synthesis of isopropyl benzene from benzene is shown below:

b) Reaction equations for the synthesis of $\text{p-isopropylbenzenesulfonic acid}$ from benzene are shown below:

c) Reaction equations for the synthesis of $\text{2-bromo-2-phenylpropane}$ from benzene are shown below:

d) Reaction equations for the synthesis of $\text{4-tert}\text{.butyl-2-nitrotoluene}$ from toluene are shown below:

e) Reaction equations for the synthesis of $\text{m-chloroacetophenone}$ from benzene are shown below:

f) Reaction equations for the synthesis of $\text{p-chloroacetophenone}$ from benzene are shown below:

g) Reaction equations for the synthesis of $\text{3-bromo-4-methylacetophenone}$ from toluene are shown below:

h) Reaction equations for the synthesis of $\text{2-bromo-4-ethyltoluene}$ from toluene are shown below:

i) Reaction equations for the synthesis of $\text{3-bromo-5-nitrobenzoic acid}$ from toluene are shown below:

j) Reaction equations for the synthesis of $\text{2-bromo-4-nitrobenzoic acid}$ from toluene are shown below:

k) Reaction equations for the synthesis of $\text{1-phenyloctane}$ from benzene are shown below:

l) Reaction equations for the synthesis of $\text{1-phenyl-1-octene}$ from benzene are shown below:

m) Reaction equations for the synthesis of $\text{1-phenyl-1-octyne}$ from benzene are shown below:

n) Reaction equations for the synthesis of $\text{1,4-ditertiarybutyl-1,4-cyclohexadiene}$ from benzene are shown below:

Explanation of Solution

a) The structure for isopropyl benzene is:

Benzene undergoes Friedel-Crafts alkylation with isopropyl chloride with aluminum chloride to yield isopropyl benzene as shown below:

b) The structure of $\text{p-isopropylbenzenesulfonic acid}$ is:

In the above structure, the isopropyl substituents, isopropyl and sulfonic acid are para to each other.

Benzene undergoes Friedel-Crafts alkylation with isopropyl chloride with aluminum chloride to yield isopropyl benzene. In the second step, isopropyl benzene is treated with the solution of sulfur trioxide in sulfuric acid yields $\text{p-isopropylbenzenesulfonic acid}$. Sulfonation will occur predominantly at para position since isopropyl substituent is ortho-para directing.

Reaction equations for the synthesis of $\text{p-isopropylbenzenesulfonic acid}$ from benzene are shown below:

c) The structure of $\text{2-bromo-2-phenylpropane}$ is:

In the structure for the final product, the phenyl group and a bromine atom is attached to $\text{C-1}$ carbon atom of propane. To get this product, benzene should be the starting compound that must be used. In the first step, benzene undergoes Friedel-Crafts alkylation with isopropyl chloride with aluminum chloride to yield isopropyl benzene. In the second step, isopropyl benzene is treated with $\text{N-bromosuccinimide }$ in presence of benzoyl chloride giving $\text{2-bromo-2-phenylpropane}$ as the major product. Reaction equations for the synthesis of $\text{2-bromo-2-phenylpropane}$ from benzene are shown below:

d) The structure of $\text{4-tert}\text{.butyl-2-nitrotoluene}$ is:

To get this product, toluene should be the starting compound that must be used. In the first step, toluene undergoes Friedel-Crafts alkylation with tertiary butyl chloride with aluminum chloride to yield tert-butyl toluene. In the second step, the tert-butyl toluene undergoes a nitration reaction to yield the product in which the nitro substituent is attached to the ortho position of the methyl group and meta position of the tertiary butyl group. Due to steric hindrance, the product in which the nitro group is attached at the ortho position of the tertiary butyl group is less favorable.

Reaction equations for the synthesis of $\text{4-tert}\text{.butyl-2-nitrotoluene}$ from toluene are shown below:

e) The structure for $\text{m-chloroacetophenone}$ is:

To get this product, benzene should be the starting compound that must be used. In the first step, benzene undergoes Friedel-Crafts acylation with acyl chloride with aluminum chloride to yield $\text{acetophenone}$. In the second step, $\text{acetophenone}$ undergoes chlorination to form $\text{m-chloroacetophenone}$. This reaction takes place in presence of a Lewis acid such as aluminum chloride. Acyl group is meta directing and deactivator. The regioselectivity of this reaction will be controlled by the acyl group.

Reaction equations for the synthesis of $\text{m-chloroacetophenone}$ from benzene are shown below:

f) The structure of $\text{p-chloroacetophenone}$ is:

In order to get this product, benzene should be the starting compound that must be used. In the first step, benzene undergoes chlorination reaction in presence of a Lewis acid such as aluminum chloride to yield chlorobenzene. In the second step, chlorobenzene undergoes Friedel-Crafts acylation with acyl chloride with aluminum chloride to yield $\text{p-chloroacetophenone}$. Chlorine is ortho-para directing substituent. The regioselectivity of this reaction will be controlled by the chlorine substituent.

Reaction equations for the synthesis of $\text{p-chloroacetophenone}$ from benzene are shown below:

g) The structure for $\text{3-bromo-4-methylacetophenone}$ is:

On order to get this product, toluene should be the starting compound that must be used. In the first step, toluene undergoes Friedel-Crafts acylation with acyl chloride with aluminum chloride to yield $\text{4-methylacetophenone}$. In the second step, Lewis acid is present such as aluminum chloride, $\text{4-methylacetophenone}$ undergoes chlorination reaction to yield $\text{3-bromo-4-methylacetophenone}$. Methyl is ortho-para directing substituent and activator while acyl group is a meta director and deactivator. The regioselectivity of this reaction will be controlled by the methyl substituent.

Reaction equations for the synthesis of $\text{3-bromo-4-methylacetophenone}$ from toluene are shown below:

h) The structure for $\text{2-bromo-4-ethyltoluene}$ is:

To get this product, toluene should be the starting compound that must be used. In the first step, toluene undergoes Friedel-Crafts alkylation with ethyl chloride with aluminum chloride to yield $\text{4-ethyltoluene}$. In the second step, $\text{4-ethyltoluene}$ undergoes bromination reaction in presence of a Lewis acid such as Iron (III) bromide to yield $\text{2-bromo-4-ethyltoluene}$. Methyl and ethyl both are ortho-para directing substituent. The regioselectivity of this reaction will be controlled by the methyl substituent.

Reaction equations for the synthesis of $\text{2-bromo-4-ethyltoluene}$ from toluene are shown below:

i) The structure for $\text{3-bromo-5-nitrobenzoic acid}$ is:

To get this product, toluene should be the starting compound that must be used.

In the first step, toluene undergoes oxidation of benzylic carbon atom in toluene with ${\text{KMnO}}_{\text{4}}\text{,}{\text{H}}_{\text{2}}\text{O}$ followed by hydrochloric acid giving benzoic acid.

In the second step, benzoic acid undergoes a nitration reaction with a mixture of nitric acid and sulfuric acid giving $\text{3-nitrobenzoic acid}$. The regioselectivity of this reaction is controlled by the benzoic acid substituent which is meta directing.

In the third step, $\text{3-nitrobenzoic acid}$ undergoes bromination reaction in presence of a Lewis acid such as Iron (III) bromide to yield $\text{3-bromo-5-nitrobenzoic acid}$. The regioselectivity of this reaction is controlled by both, benzoic acid substituent and nitro substituent, which are meta directing.

Reaction equations for the synthesis of $\text{3-bromo-5-nitrobenzoic acid}$ from toluene are shown below:

j) The structure for $\text{2-bromo-4-nitrobenzoic acid}$ is:

To get the desired product, toluene should be the starting compound that must be used.

In the first step, toluene with nitric acid and sulfuric acid undergoes a nitration reaction giving $\text{3-nitrotoluene}$.

In the second step, benzoic acid undergoes bromination reaction in presence of a Lewis acid such as Iron (III) bromide to yield $\text{2-bromo-4-nitrotoluene}$. The regioselectivity of this reaction is controlled by the nitro substituent which is meta directing.

In the third step, $\text{3-nitrobenzoic acid}$ undergoes oxidation of benzylic carbon atom in toluene with ${\text{KMnO}}_{\text{4}}\text{,}{\text{H}}_{\text{2}}\text{O}$ followed by hydrochloric acid giving $\text{2-bromo-4-nitrobenzoic acid}$. The regioselectivity of this reaction is controlled by both, nitro substituent as it is a strong deactivator and meta directing.

Reaction equations for the synthesis of $\text{2-bromo-4-nitrobenzoic acid}$ from toluene are shown below:

k) The structure for $\text{1-phenyloctane}$ is:

To get this product, benzene should be the starting compound that must be used.

In the first step, benzene undergoes Friedel-Crafts acylation with octanyl chloride with aluminum chloride.

In the second step, the carbonyl group is reduced in the presence of $\text{Zn(Hg)}$ in hydrochloric acid giving $\text{1-phenyloctane}$

Reaction equations for the synthesis of $\text{1-phenyloctane}$ from benzene are shown below:

l) The structure of $\text{1-phenyl-1-octene}$ is:

In order to get this product, benzene should be the starting compound that must be used.

In the first step, benzene undergoes Friedel-Crafts acylation with octenyl chloride with aluminum chloride.

In the second step, the carbonyl group is reduced to the hydroxyl group in the presence of ${\text{NaBH}}_{\text{4}}\text{in}\text{ethanol}$.

In the third step, the resulting alcohol is heated with sulfuric acid at high temperatures to yield $\text{1-phenyl-1-octene}$.

Reaction equations for the synthesis of $\text{1-phenyl-1-octene}$ from benzene are shown below:

m) The structure of $\text{1-phenyl-1-octyne}$ is:

To get this product, benzene should be the starting compound that must be used.

In the first step, benzene undergoes Friedel-Crafts acylation with octanyl chloride with aluminum chloride.

In the second step, the carbonyl group is reduced to the hydroxyl group in the presence of ${\text{NaBH}}_{\text{4}}\text{in}\text{ethanol}$.

In the third step, the resulting alcohol is heated with sulfuric acid at high temperatures to yield $\text{1-phenyl-1-octene}$.

In the fourth step, $\text{1-phenyl-1-octene}$ is treated with bromine in presence of Iron (III) bromide. Double dehydrogenation of the product obtained in the previous step using sodium amide in liquid ammonia will give $\text{1-phenyl-1-octyne}$.

Reaction equations for the synthesis of $\text{1-phenyl-1-octyne}$ from benzene are shown below:

n) The structure of $\text{1,4-ditertiarybutyl-1,4-cyclohexadiene}$

To get the required product, benzene should be the starting compound that must be used.

In the first step, benzene undergoes Friedel-Crafts acylation with tertiary butyl chloride with aluminum chloride giving tert-butyl toluene.

In the second step again, the tert-butyl toluene undergoes Friedel-Crafts acylation with tertiary butyl chloride with aluminum chloride giving $\text{1,4-ditertiarybutyltoluene}$.

In the third step, $\text{1,4-ditertiarybutyltoluene}$ is treated with sodium in liquid ammonia, ethanol to yield $\text{1,4-ditertiarybutyl-1,4-cyclohexadiene}$

Reaction equations for the synthesis of $\text{1,4-ditertiarybutyl-1,4-cyclohexadiene}$ from benzene are shown below: