A question came up in our worksheet to predict the reaction product of nitrous acid and concentrated nitric acid with benzene.

I quickly recognized it to be similar to the nitration reaction. Following this ChemGuide page, which gives the reaction of nitration as:

$$\ce{HNO3 + 2H2SO4 -> NO2+ + 2HSO4- + H3O+}$$

I wrote this reaction:

$$\ce{HNO2 + 2HNO3 -> NO+ + 2NO3- + H3O+}\label{a}\tag{1}$$

and thought that this electrophilic $\ce{NO+}$ would then perform EAS on the benzene to give nitrosobenzene (aka nitrosation reaction).

However, the answer given in my worksheet is nitrobenzene instead. I am unsure if the following reaction (for the generation of the electrophile $\ce{NO2+}$):

$$\ce{HNO3 + 2HNO2 -> NO2+ + NO2- + H3O+}\label{b}\tag{2}$$

is even valid. To me, reaction $\ref{a}$ seems more favorable because it involves the formation of the more stable $\ce{NO3-}$. Then why is reaction $\ref{b}$ favored instead? Why is nitrobenzene the product of this reaction, and not nitrosobenzene?


1 Answer 1


You were absolutely correct when you said that nitrosation takes place.

What actually happens is that after nitrosation occurs, concentrated $\ce{HNO3}$ oxidises the nitroso group to form nitrobenzene.

A Guidebook To Mechanism In Organic Chemistry; Chapter 6, section 6.2;Peter Sykes


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