It was first isolated by Mitcherlich in 1834. It has the odour of bitter almonds and is sold as an artificial oil of bitter almonds under the name oil of Mirabane.
Methods of Preparation
1. Labaratory method
In the laboratory nitrobenzene is prepared by the action of a mixture of conc. HNO3 and conc. H2SO4 on benzene at the ordinary temperature.
50 ml of concentrated nitric acid and 50 ml of concentrated sulphuric acid acid are taken in a round bottomed flask and cooled. 50 ml of benzene is added to this mixture slowly by instalments adding 2-3 ml at a time. The temperature , during the addition of benzene is not allowed to increase above 55Oc. when the whole the benzene is added,the flask is heted on a water bath to a temperature of 60oC about an hour. The flask is then cooled and transferred to a separating funnel. Nitrobenzene forms the upper layer. Lower layer of acids is drawn off, nitrobenzene washed with water several times to remove acids. It is then allowed to stand over the fused calcium chloride and distilled using an air condenser.
Pure nitrobenzene distils at a temperatures 208-2110C
2. Commericial Method
On a large scale also, nitrobenzene is prepared by the action of a mixture of nitric acid and sulphuric acid on benzene. At the end , the spent acids are withdrawn and the nitrobenzene layer given the necessary washings.
1. Nitrobenzene is a pale yellow liquid when freshly prepared but it darkens somewhat with age.
2. It boils at 210 Oc and has a specific gravity 1.087.
3. It is insoluble in water but is soluble in alcohol and ether.
4. It has an odour like that of bitter almonds.
5. It is volatile with steam.
Nitrobenzene is a typical compound and gives all the general reactions.
A. Reactions due to NO2
1. Replacement reactions
The nitro groups are firmly attached to the nucleus . Thus it is very difficult to replace it.
2. Reduction reactions
a. In acidic medium
When reduced with a tin and hydrochloric acid,it is converted to aniline.
The conversion is believed to proceed through the following stages
O + 2H
Aniline Phenyl hydroxyl
b. In alkaline medium
Alkaline reducing agents like zinc dust and sodium hydroxide or stannous chloride and sodium hydroxide , reduce nitrobenzene successively to azoxybenzene,azobenzene and hydrazobenzene.
O + 2H
Aniline Phenyl hydroxyl
c. In neutral medium
Neutral reducing agents like zinc dust and water or aluminium-mercury couple reduce it to phenyl hydroxylamine.
B. Reactions of benzene nuclues:
Nitrobenzene undergoes the usual reactions of the benzene nucleus . The incoming group occupies the meta position with respect to the nitro group.
It is further noted that the reactions of nitrobenzene towrds the above reagents is much less as compared to that of benzene.
A. It has been extensively used for making the shoe polishes as it dissolves dyes and penetrate the leather well.
B. It is used as a scent for cheap soaps.
C. It has also been used for making the floor polishes.
D. It has also been used as an oxidising agents in organicx synthesis.