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Chlorobenzene: Properties, Reactivity & Uses

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

In this lesson we will be focussing on the organic compound known as chlorobenzene. Topics we will be exploring include its properties, how it is synthesized, reactions it undergoes, and uses of the compound.

Popular Only for a Moment

Have you ever heard the term DDT before? Dichlorodiphenyltrichloroethane (DDT) is an organic compound that was once used as an insecticide in the early 1900's. It got a lot of press for its powerful effects, and got even more for its negative environmental and human health impacts. The use of DDT in agriculture was banned in the 1970's, after its acute toxicity to humans and implications in breast cancer became concerns.

DDT is an organochlorine compound that is a derivative of another compound known as chlorobenzene. Although DDT gets a lot of bad publicity, chlorobenzene itself is actually an organochlorine compound that is quite useful in a variety of applications. In this lesson, we are going to be learning about the properties of chlorobenzene, how it's made, the reactions it undergoes, and finally, some ways it can be utilized.

Properties of Chlorobenzene

One of the most important properties of chlorobenzene is its polarity. Since chlorine is more electronegative than carbon, chlorobenzene is polar, with chlorine bearing a partial negative charge and carbon being partially positive.


Polarity of chlorobenzene
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Chlorobenzene is not soluble in water, as are most aryl halides. When chlorobenzene is mixed with water, two separate layers form with the bottom layer being chlorobenzene since it's more dense (heavier) than water.

How Chlorobenzene is Synthesized

In order to synthesize chlorobenzene, the go-to method on large scales is to take benzene and react it with molecular chlorine in the presence of an iron (III) chloride (FeCl3) catalyst. The nice thing about this reaction is benzene, chlorine, and FeCl3 are all extremely cheap, abundant starting materials and that helps in keeping the commercial cost of chlorobenzene low to consumers and researchers.


Synthesis of chlorobenzene
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Although less popular on large industrial scales, chlorobenzene can also be made from aniline in a reaction called the Sandmeyer reaction, named after its discoverer Traugott Sandmeyer. In this reaction, we first make what's called a diazonium salt from aniline by the action of sodium nitrite NaNO2.


Diazonium salt synthesis from aniline
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Once the diazonium salt is made, simply adding in some copper chloride (CuCl) will make chlorobenzene. The reaction conditions are fairly mild, making this a handy way to make our desired molecule.


Final step of the Sandmeyer reaction to give chlorobenzene
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Reactions of Chlorobenzene

Chlorobenzene is a useful compound for other organic reactions. It can undergo electrophilic aromatic substitution (EAS) reactions with different electrophiles to give di-substituted aromatic rings. Due to the electronegative nature of the chlorine, when another group of atoms is attached to chlorobenzene, the new group will always go ortho (directly adjacent to the chlorine) or para (directly across from the chlorine).

Nitration

Chlorobenzene can be nitrated (addition of an -NO2 group) if it's reacted with nitric and sulfuric acids.


Nitration of chlorobenzene
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