Oranic cHEMISTRY - iI

Principle

Here Nitration is occurring on Nitrobenzene. It is an electrophilic aromatic substitution in presence of NO2 which is a strong electron withdrawing group and it directs the incoming substituents to the m-position. Here nitronium ions act as a electrophile which is generated from fuming Nitric acid in presence of conc.H2SO4.

Reaction:

Procedure

20 ml (37.5 gm) of conc.H2SO4 and 15 ml (22.5 gm) of fuming HNO3 are placed in 250 ml RBF with some smaller pieces of porcelain. A reflux condenser is attached and the apparatus is placed in a fuming cup board. 12.5 ml (15 gm) nitro benzene in portions of about 3 ml is added slowly and after each addition the flask is shaken thoroughly. The mixture is heated on water bath for 30 mins with shaking. Then it is allowed to cool and poured into about 500 ml of cold water continuous with vigorous stirring. The di-nitrobenzene soon solidified. The product is filtered, washed with cold water and allow to drain as much as possible. The product is transferred to a 250 ml flask fitted with a reflux condenser; 80-100 ml of rectified spirit is added and heated on a water bath to dissolved all the solids. If the solution is not clear it is filtered using a warm Buchner funnel. About 15 gm of m-dinitrobenzene is deposited on cooling as colorless crystal a second recrystallisation is usually necessary in order to eliminate traces of o- and p-nitrobenzene and thus pure m-dinitrobenzene m.p. 90oC is obtained.