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BACKGROUND
Principle: Nitration is occurring on nitrobenzene. It is an electrophilic aromatic substitution reaction in presence of NO2, which is a strong electron withdrawing group and it directs the incoming substituents to the meta position. Here nitronium ions act as the electrophile which is generated from fuming nitric acid in presence of concentrated sulphuric acid.1
Aim: To prepare m-dinitrobenzene from nitrobenzene by Nitration reaction
Reaction:
Mechanism: Electrophilic aromatic substitution-
Use: Used in organic drug synthesis
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REQUIREMENTS
Chemicals: Fuming nitric acid- 15 ml
Conc. sulphuric acid- 20 ml
Nitrobenzene- 12.5 ml
Apparatus: Round bottomed flask
Reflux condenser
Funnel
Measuring cylinder
Beaker
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PROCEDURE
21 ml (37.5 g) of concentrated sulphuric acid and 15 ml (22.5 g) of fuming nitric acid are placed in a 250 ml RBF with a few smaller pieces of porcelain. A reflux condenser is attached and the apparatus is placed in a fuming cupboard. 12.5 ml (15 g) of nitrobenzene 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 min. with shaking. Then it is allowed to cool and poured into about 500 ml of cold water cautiously with vigorous stirring. The dinitrobenzene soon solidifies. The product is filtered, washed with cold water and allowed 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 dissolve all the solid. If the solution is not clear, it is filtered using a warm Buchner funnel. About 15 g of m-dinitrobenzene is deposited on cooling as colourless crystal. A second recrystallisation is, usually necessary in order to eliminate traces of o- and p-dinitrobenzene, and thus pure m-dinitrobenzene, m.p. 90° is obtained.
Calculation
Molecular formula of nitrobenzene = C6H5NO2
Molecular formula of m–dinitrobenzene = C6H4N2O4
Weight of nitrobenzene = 123 g/mole
Weight of m–dinitrobenzene = 168 g/mole
Theoretical yield
123 g of nitrobenzene gives 168 g of m–dinitrobenzene
Therefore, 15 g of nitrobenzene should give…………………. ? (X) g of m–dinitrobenzene
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CONCLUSION
The yield of synthesized m–dinitrobenzene was found to be 73.24 %.
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REFERENCES
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Vogel’s Textbook of Practical Organic Chemistry by Brian S. Furniss, Antony J. Hannaford, Peter W. G. Smith & Austin R. Tatchell; Fifth Edition; Page No. – 855.
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Practical Organic Chemistry by Frederick George Mann and Bernard Charles Saunders Published By Longman Inc., Fourth Edition; Page No. 160
