Question

QUESTIONS FOR m-Dinitrobenzene lab (Nitration of the aromatic molecules)

3) give the name and formula of the principal organic impurity removed during the recrystallization of the dinitrobenzene. How can you account for the presence of this impurity?

Answer 1

Recrystallization of the dinitrobenzene

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. ... 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.

removal of Impurities present in the preparation of m-dinitrobenzene

you have to use the purest available benzene in the preparation of m-dinitrobenzene since in this way the formation of derivatives of thiophene and toluene is avoided. The undesirable reaction products that must be removed are mononitrobenzene, o- and p-dinitrobenzene, polynitrocompounds, the dinitroazoxycompounds and nitrophenols . The amino compounds, if present, are eliminated when excess nitric acid is removed by the washing.

The crude m-dinitrobenzene was purified by phase transfer catalysis to transfer the p-dinitrobenzene and odinitrobenzene into nitrodiphenyl ether. The effects of oxyalkylation reagent, catalyst and reaction conditions on the purification of crude m-dinitrobenzene were investigated. The results showed that tetrabutyl ammonium bromide exhibited better activity with methanol as oxyalkylation reagent. The purity of m-dinitrobenzene reached above 99.5% under the conditions of the mass fraction of crude m-dinitrobenzene, methanol, NaOH and tetrabutyl ammonium bromide 1:0.5:0.09:0.05, reaction temperature 78°C and reaction time 40 min.