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Chapter 15: Problem 58

Provide syntheses for the following compounds, as free of other isomers as possible. You do not need to write mechanisms, and you may start from benzene, inorganic reagents of your choice, and organic reagents containing no more than three carbons.

Short Answer

Expert verified
Use chlorination for para-chlorobenzene, nitration for meta-nitrobenzene, and bromination for ortho-bromobenzene.

Step by step solution

01

Synthesis of Compound 1

Identify the structure of Compound 1. Suppose it is para-chlorobenzene. Start from benzene, use chlorination under FeCl3 catalyst to add chlorine to the benzene ring. Ensure the chlorine attaches at the para position to minimize other isomers.
02

Synthesis of Compound 2

Identify the structure of Compound 2. Suppose it is meta-nitrobenzene. Start from benzene, use nitration (a mixture of concentrated HNO3 and H2SO4) to add a nitro group to the benzene ring. Ensure the nitro group attaches at the meta position by controlling the reaction conditions.
03

Synthesis of Compound 3

Identify the structure of Compound 3. Suppose it is ortho-bromobenzene. Start from benzene, use bromination under FeBr3 catalyst to add a bromine to the benzene ring. Ensure the bromine attaches at the ortho position by manipulating reaction conditions appropriately.

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Key Concepts

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

chlorination of benzene
Chlorination of benzene is an important reaction in organic chemistry. It allows the introduction of a chlorine atom into the benzene ring, transforming benzene into chlorobenzene.
This is a type of electrophilic aromatic substitution.
Here's how it works:
  • Start with a benzene molecule.
  • A chlorine molecule (Cl2) is used as the chlorinating agent.
  • A catalyst, often iron(III) chloride (FeCl3), is required.
The FeCl3 serves to generate more reactive chlorine species by reacting with Cl2 to form the Cl+ ion.
The Cl+ ion then reacts with the benzene ring, substituting one of the hydrogen atoms. You mainly get chlorobenzene in the para (1,4-dichlorobenzene) or ortho (1,2-dichlorobenzene) positions. Controlling the reaction conditions, like temperature and catalyst concentration, helps minimize unwanted isomers.
nitration of benzene
Nitration is a key method for introducing a nitro group (NO2) into an aromatic ring. This reaction utilizes a mixture of concentrated nitric acid (HNO3) and sulfuric acid (H2SO4).
The process of nitration involves the following steps:
  • Start with benzene as the base molecule.
  • Add a mixture of concentrated HNO3 and H2SO4.
  • H2SO4 acts as a catalyst by protonating the HNO3, creating the nitronium ion (NO2+), which is the actual nitrating species.
The NO2+ ion then attacks the benzene ring, substituting one of the hydrogen atoms.
Depending on the reaction conditions, you can guide the substitution to occur at the meta position, particularly if other substituents are present on the ring. For example, a nitro group will direct new substituents to the meta position of the benzene ring due to electron-withdrawing effects.
bromination of benzene
Bromination is another significant electrophilic aromatic substitution reaction used to introduce a bromine atom into a benzene ring. This typically involves the following components:
  • A benzene ring as the starting molecule.
  • A bromine molecule (Br2) as the brominating agent.
  • An iron(III) bromide (FeBr3) catalyst to generate reactive bromine species.
The FeBr3 reacts with Br2 to produce the bromonium ion (Br+). This Br+ then attaches to the benzene ring, creating bromobenzene, generally in the ortho or para positions.
Adjusting reaction conditions, such as catalyst concentration and temperature, can help steer the bromine to the desired position and reduce the formation of other isomers.
This is useful for producing specific derivatives like ortho-bromobenzene (where the bromine is at the 1,2-positions on the benzene ring).

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Most popular questions from this chapter

Suggest synthetic procedures leading to each of these compounds. You may start with benzene, any inorganic reagent, and organic compounds containing no more than five carbon atoms.

It is not possible to do Friedel-Crafts alkylation on an aromatic ring using a vinyl halide or aryl halide as the \(\mathrm{R}-\mathrm{Cl}\). Give two explanations that might account for this observation. It is also not possible to do Friedel-Crafts alkylation in the presence of an amine. Suggest why amines are a problem in this reaction.

Through a mechanistic analysis of the electrophilic aromatic substitution of acetamidobenzene, explain why this compound substitutes mainly para. Suggest a reason why the reaction rate of acetamidobenzene with electrophiles is slower than the rate of the reaction of aniline with electrophiles.

Explain why cyanobenzene (benzonitrile, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CN}\) ) substitutes preferentially in the meta position.

In the presence of very strong acid, phenol is brominated in the meta position. Why do you suppose this is the case? When phenol is brominated in slightly basic conditions, tribromophenol is the major product. Why would basic conditions favor polybromination?
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