Question

What is the rate determining step in the nitration of benzene?

Answer 1

As far as I know, the rate determining step of the nitration of benzene is the addition of the aryl ring to the nitronium ion........

Explanation:

Aryl rings are generally nitrated by a so-called nitrating mixture, which is usually a mixture of conc. sulfuric, and conc. nitric acids. The 2 inorganic reagents deliver the nitronium ion, conceived to be `"NO"_2^+`:

`"i. " "H"_2"SO"_4+"HNO"_3 rarr "H"_2"NO"_3^(+) +"HSO"_4^-` `"; FAST"`

`"ii. " "H"_2"NO"_3^(+) rarr "NO"_2^(+) +"H"_2"O"` `"; FAST"`

`"iii " "NO"_2^(+) +"C"_6"H"_6 rarr "C"_6"H"_6"NO"_2^(+)` `"; SLOW"`

`"iv " "C"_6"H"_6"NO"_2^(+) +"HSO"_4^(-) rarr "C"_6"H"_5"NO"_2+"H"_2"SO"_4` `"; FAST"`

We would predict that `"(iii)"` as written would be the rate determining step, as it involves the decoupling of the aromatic carbocycle as the nitronium ion adds. Anyway, you should really consult your text, in order to get the important details.