Chemical properties of aromatic nitrocompounds

The nitro group strongly deactivates the benzene ring towards electrophilic substitution. Nitro group is electron withdrawing group and thus causes electron deficiency at ortho and para positrons as is clear from the resonating structures of nitro benzene.

resonating structures of nitro benzene

Since the meta positron is relatively rich in electron density compared to ortho and para positrons electrophilic attack is more likely to occur at meta position. Thus the -NO2 group is meta directing as far as electrophilic ring substitution is concerned.

Electrophilic substitution reaction
nitration sulphonation chlorination of nitrobenzene
Influence on the reaction of other functional group
The presence of nitro group facilitates nucleophilic substitution of otherwise unreactive aromatic halides by stabilizing the intermediate carbanion.

nitro group facilitates nucleophilic substitution

Reduction of nitrobenzene
The nitro group can be removed from an aromatic ring via the following steps:

i) reduction of nitro group to amine

ii) diazotization of amine with HNO2

iii) reductive removal of the diazonium group using sodium borohydride or hypophosphorus acid/Cu+mixture.

reductive removal of the diazonium group using sodium borohydride

Uses of nitrobenzene

Approximately 95% of nitrobenzene is consumed in the production of aniline.

Specialized applications

More specialized applications include the use of nitrobenzene as a precursor to rubber chemicals,pesticides, dyes, explosives, and pharmaceuticals. Nitrobenzene is also used in shoe and floor polishes, leather dressings, paint solvents, and other materials to mask unpleasant odors. Redistilled, as oil of mirbane, nitrobenzene has been used as an inexpensive perfume forsoaps. A significant merchant market for nitrobenzene is its use in the production of the analgesicparacetamol (also known as acetaminophen) (Mannsville 1991)[2]. Nitrobenzene is also used in Kerr cells, as it has an unusually large Kerr constant.


Organic reactions

Aside from its conversion to aniline, nitrobenzene is readily converted to related derivatives such asazobenzene, nitrosobenzene, and phenylhydroxylamine. The nitro- group is deactivating, thus substitution tends to occur at the meta-position.


Safety

Nitrobenzene is highly toxic (TLV 5 mg/m3) and readily absorbed through the skin.

Although nitrobenzene is not currently known to be a carcinogen, prolonged exposure may cause serious damage to the central nervous system, impair vision, cause liver or kidney damage, anemia and lung irritation. Inhalation of fumes may induce headache, nausea, fatigue, dizziness, cyanosis, weakness in the arms and legs, and in rare cases may be fatal. The oil is readily absorbed through the skin and may increase heart rate, cause convulsions or rarely death. Ingestion may similarly cause headaches, dizziness, nausea, vomiting and gastrointestinal irritation.

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