What is the expected outcome from the electrophilic substitution of chlorobenzene with HNO3/H2SO4 and heat?

1 Answer
anor277 · P dilip_k
Mar 11, 2016

Nitrated chlorobenzene derivatives in the 2 and 4 positions, with respect to #Cl#.

Explanation:

The conc. sulfuric/nitric acid is the classic nitrating mixture. It represents a good, old-fashioned fashioned INORGANIC, ACID BASE reaction:

#HNO_3(aq) + H_2SO_4(aq) rarr NO_2^+ + HSO_4^(-) + H_2O#

Sulfuric acid here protonates the nitric acid to give the nitronium ion and water, and bisulfate ion.

The nitronium ion, #NO_2^+#, is the electrophile that reacts with chlorobenzene (to give nitrochlorobenzene and sulfuric acid); the bisulfate ion is the base that removes #H^+# from the nitrated ring. Chlorobenzene directs to ortho and para positions with respect to the chloride (the halogen deactivates all position on the aryl ring inductively, but mesomerically directs to ortho and para postions).

So the products: 2-nitrochlorobenzene; 4-nitrochlorobenzene; 2,4-dinitrochlorobenzene. You probably could not get a third substitution to give 2,4,6-trinitro-chlorobenzene; your conditions would have to be screaming hot, and I would not be game to go near such a reaction flask.

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