Bromobenzene to chlorobenzene through Phenyl Magnesium Bromide

Prepare chlorobenzene by starting with bromobenzene. You can use any other reagent and try to do this organic conversion question below four steps. During this conversion, you will prepare phenyl magnesium bromide as a grignard reagent.

Bromobenzene and chlorobenzene compounds

Bromine and chlorine atoms are substituted to benzene and they are alkyl halide compounds. Bromobenzene and chlorobenzene have similar reactions and physical properties. In this question, we are going to replace the bromine atom by chlorine atom. But this has to be done in several steps.

Preparation of chlorobenzene

When benzene is treated with Cl₂ in the presence of anhydrous AlCl₃, chlorobenzene is given as the product.

So, we have to prepare benzene from bromobenzene.

Bromobenzene to benzene

Most easy way to convert bromobenzene to benzene is the preparation of grignard reagent from bromobenzene and hydrolysis of it. It is one of the benzene preparing methods when we have an halogen substituted benzene.

Preparation of phenyl magnesium bromide

Bromobenzene reacts with Mg, dry ether to prepare phenyl magnesium bromide.

Phenyl magnesium bromide hydrolysis

Add water to phenyl magnesium bromide, it gives benzene as the main product and MgBr(OH). Benzene is separated and send to the next step.

Benzene, Cl₂ in the presence of anhydrous AlCl₃

A chlorine atom is substituted instead of hydrogen atom in the benzene. This reaction mechanism is a electrophilic substitution reaction. Also this reaction is named as halogenation of benzene.

Preparation of chlorobenzene from bromobenzene - full conversion

Safety precautions of using bromobenzene and chlorobenzene

Read MSDS (material safety data sheets) to know the toxicity and health issued can be occurred due to use of chemicals in this organc conversion.

Chlorobenzene

Flammable liquid and vapor. Harmful if inhaled. Toxic to aquatic life.

Injuries

• liver damage
• Breathing vapors may cause drowsiness and dizziness
• Causes eye, skin, and respiratory tract irritation.

Learn more about MSDS about chlorobenzene

Bromobenzene

Flammable liquid and vapor.

May be absorbed through intact skin. Marine pollutant.

• May cause eye and respiratory tract irritation
• Causes skin irritation.
• May cause liver damage.

Learn more about MSDS about bromobenzen

Reactions of chlorobenzene to bromobenzene

Chlorobenzene to bromobenzene

As bromobenzene to chlorobenzene, do the grignard preparation and hydrolysis. Only change is, benzene should be treated with Br₂ in the presence of AlBr₃.

Chlorobenzene to benzene

As mentioned earlier, bromobenzene and chlorobenzene have similar reaction with magnesium in ether medium.

1. First, chlorobenzene reacts with magnesium in ether medium. It gives phenyl magnesium chloride which has grignard reagent characteristics.
2. Then add water to phenyl magnesium bromide to hydrolyze the grignard reagent. Benzene is given as the organic product.

With dilute aqueous NaOH

Halogen atom cannot be replaced by -OH group in bromobenzene and chlorobenzene as aliphatic alkyl halides.