What is the role of sulfuric acid in this synthesis (i.e., why will nitration be less effective if only nitric

Answer 1

Benzene is nitrated by refluxing with concentrated sulfuric acid and concentrated nitric acid at 50°C.

(1) 2H2SO4 + HNO3 → 2HSO41- + NO2+ + H3O+

(2) C6H6 + NO2+ → C6H5NO2 + H+

(3) H+ + H3O+ + 2HSO41- → H2O + 2H2SO4

The sulfuric acid is regenerated and hence acts as a catalyst.


Nitration of Benzene
The formation of a nitronium ion (the electrophile) from nitric acid and sulfuric acid is shown below:


Reaction of nitric acid and sulfuric acid
Selectivity is always a challenge in nitrations, Fluorenone nitration is selective and yields a tri-nitro compound [1] or tetra-nitro compound [2] by tweaking reaction conditions just slightly. Another example of trinitration can be found in the synthesis of phloroglucinol.

Other nitration reagents include nitronium tetrafluoroborate which is a true nitronium salt. This compound can be prepared from hydrogen fluoride, nitric acid and boron trifluoride [3]. Aromatic nitro compounds are important intermediates to anilines by action of a reducing agent.

Answer 2

The sulfuric acid removes the water byproduct of nitration.
Stay away from nitrations. The vapour has a nasty habit of detonating. Even in commercial explosive plants.
Vapour control is for experts.
Also some nitrated compounds are deperately poisonous. Like trinitrobenzene. It is terminally hepatotoxic. 3, I.R.A. junior/amateur teenage chemists died of progressive liver failure making that c*ap. (years ago no liver transplants then.)
(N.S.A. & D.H.L.S. please note, all the above information is in the public domain and easily accessed)(I am not giving away any secrets, synthesis instructions, nor formulae)
no specialist information there..
P.S. Wikipedia does NOT always give the whole story, reader beware. Missing details can be deadly