{"id":631,"date":"2018-04-04T12:35:39","date_gmt":"2018-04-04T12:35:39","guid":{"rendered":"http:\/\/chemdictionary.org\/?p=631"},"modified":"2018-04-04T12:37:05","modified_gmt":"2018-04-04T12:37:05","slug":"nitration-of-benzene","status":"publish","type":"post","link":"https:\/\/chemdictionary.org\/nitration-of-benzene\/","title":{"rendered":"Nitration of Benzene"},"content":{"rendered":"

Introduction to nitration of benzene<\/h2>\n

Nitration of benzene is an example of elctrophilic aromatic substitution reaction. Here nitronium ion (NO2<\/sub>+<\/sup>) acts as an electrophile and reacts with benzene to form nitrobenzene. As for example Benzene reacts with concentrated nitric acid in presence of concentrated sulphuric acid as a catalyst, and form nitrobenzene.<\/p>\n

\"\"<\/p>\n

\u00a0Nitration of benzene<\/h2>\n

When benzene is treated with concentrated nitric acid and concentrated sulphuric acid at below 55o<\/sup> C temperature, nitrobenzene is formed. If we increase the temperature there is a greater chance of entering more than one nitro group in the benzene ring.<\/p>\n

\"\"<\/p>\n

The elctrophilic substitution reaction mechanism for nitration of benzene<\/h2>\n

The formation of the electrophile<\/h3>\n

Substitution of hydrogen of a benzene ring with a nitro group can only be done using nitronium ion or nitryl cation (NO2<\/sub>+<\/sup>) as an electrophile. This ion is formed by the reaction between the concentrated nitric acid and concentrated sulphuric acid.<\/p>\n

The equation<\/h4>\n

HNO3<\/sub>\u00a0+ 2H2<\/sub>SO4<\/sub>\u00a0\u2192 NO2<\/sub>+<\/sup>\u00a0+ 2HSO4<\/sub>–<\/sup>\u00a0+ H3<\/sub>O+<\/sup><\/p>\n

Here the hydronium ion (H3<\/sub>O+<\/sup>) is not involved in any further steps of the reaction whereas the hydrogensulphate ion (HSO4<\/sub>–<\/sup>) is.<\/p>\n

Electrophilic substitution<\/h3>\n

The elctrophilic substitution of benzene is occur in few steps, which are as follows:<\/p>\n

\"\"<\/p>\n

Step 1:<\/em> Addition of nitronium ion\u00a0or nitryl cation (NO2<\/sub>+<\/sup>)<\/h4>\n

When nitronium ion (NO2<\/sub>+<\/sup>) approaches towards the benzene ring 2a<\/strong>, the electropositive nitronium ion attracts by the electron rich benzene ring. Two electrons of one of the double bond inside the benzene ring breaks down to form a bond between the nitronium ion (NO2<\/sub>+<\/sup>) and the benzene ring 2b<\/strong>. Thus the delocalisation of double bond partly broken and positive charge from the\u00a0nitronium ion (NO2<\/sub>+<\/sup>) stays inside the ring. This positive charge is then delocalised all through the benzene ring just like it shows in above scheme. The hydrogen attached to the same carbon where the nitro group is attached is also shown in figure which will be removed in next step.<\/p>\n

Step 2:<\/em>\u00a0Removal of hydrogen ion\u00a0(H+<\/sup>)<\/h4>\n

The hydrogensulphate ion (HSO4<\/sub>–<\/sup>) which was formed during the formation of electrophile- nitronium ion, removes the hydrogen attached with the nitro group containing carbon. This hydrogen (H+<\/sup>) leaves the electron to the benzene ring. Thus the positive charge of the ring neutralized and delocalisation reestablished. By taking hydrogen ion,\u00a0hydrogensulphate ion (HSO4<\/sub>–<\/sup>) becomes sulphuric acid as it was before (catalyst).<\/p>\n

HSO4<\/sub>–\u00a0<\/sup>+\u00a0H+\u00a0<\/sup>\u2192 H2<\/sub>SO4<\/sub><\/p>\n

Further nitration of nitrobenzene<\/h2>\n

Nitrobenzene is very reactive and it can produce dinitrobenzene in presence of same reagent. The directing effect of nitrobenzene is 93% meta, 6% ortho and 1% para. The formation of ortho, meta and para-dinitrobenzene is as follows:<\/p>\n

\"\"<\/p>\n

Safety issues<\/h2>\n

Nitrobenzene is very toxic and it can readily absorb through the skin. So precaution must need to be taken during and after the reaction. Nitrobenzene may cause:<\/p>\n