Benzene and its reactions 10-11

Question 1

What is an electrophile?

Answer 1

An electrophile is an atom(or group of atoms) that is attracted to an electron-rich centre, where it accepts a pair of electrons to form a new covalent bond.

Question 2

Write out the reaction for the nitration of benzene.

Answer 2

Question 3

Explain the process/conditions to produce nitrobenzene.

Answer 3

The nitrating mixture is usually prepared in a round-bottomed or pear-shaped flask. Concentrated nitric acid and concentrated sulfuric acid are first mixed together carefully while cooling the mixture in a beaker of cold water. Benzene is then added carefully to the nitrating mixture, keeping the temperature below 50*C.

Once all of the benzene has been added, a reflux condenser is fitted to the flask and the mixture is heated at 50*C in a water bath. If the reaction mixture gets hotter, then more than one nitro group may be substituted onto the benzene ring.

Nitrobenzene is a pale yellow liquid.

Question 4

What are the uses of nitrobenzene?

Answer 4

It is an important starting material in the preparation of dyes, pesticides and pharmaceuticals ( such as paracetamol ).

Question 5

Describe how methylbenzene(also called toluene) can be nitrated, and how its nitration differs from that of benzene and name the product from the reaction and outline its uses.

Answer 5

Toluene can also be nitrated with a mixture of concetrated nitric and sulfuric acids. The reaction is faster than the nitration of benzene, and can lead to the formation of 2,4,6-trinitromethylbenzene ( trinitrotoluene, TNT). This is an explosive.

Question 6

Describe the halogenation of benzene.

• describe the halogen carriers required
• what type of reaction this is

Answer 6

Although benzene doesn’t react with halogens on their own, it does react in the presence of a special type of catalyst called a halogen carrier. Examples of common halogen carriers include FeCl₃, FeBr₃,AlCl₃and AlBr₃. Iron metal can also be used because it will react with any halogen present to form the required iron(III) halide.

As with nitration, this is an electrophilic substitution reaction in which one of the hydrogen atoms on the benzene ring is replaced by a halogen atom.

Question 7

Describe the reaction of benzene with chlorine.

• what are the uses of chlorobenzene?
• what are the reaction conditions?
• Write out the reaction.

Answer 7

• Chlorine reacts with benzene at room temperature and pressure in the presence of AlCl₃, FeCl₃ or Fe (as the halogen carrier) to produce chlorobenzene.
• Chlorobenzene is used as a solvent and in the production of pesticides.

Question 8

Describe the reaction of benzene with bromine.

• Conditions required
• Uses of the products
• write out the reaction

Answer 8

Benzene reacts with bromine in the same way that it reacts with chlorine. This time, the halogen carrier catalyst needed is AlBr_3, FeBr₃ or Fe. The organic product is bromobenzene, a compound used in the preparation of pharmaceuticals.