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NITRATION THEORIES 57

Taking this into account, Tronov [14,15,16] and Nametkin and Zabrodina

[16a] advanced another idea, similar to Michael’s initial hypothesis. Thus on the

basis of Giersbach and Kessler’s [16b] experiments Tronov inferred that one of

the two HNO 3 molecules reacting with one molecule of benzene acts as a catalyst.

On the basis of Boedtker’s experiments [17], who found that benzene was nitrated

by ethyl nitrate in the presence of aluminium chloride, Tronov suggested the follow-

ing mechanism for this process:

(11)

By analogy with this, Tronov gives the following plan for the general mechanism

of nitration:

(12)

According to Schaarschmidt [18] the mechanism of nitration with a mixture

of nitric and sulphuric acids consists in the formation of nitric anhydride which

becomes attached to the aromatic compound. The addition compound is unstable

and decomposes, giving a nitro compound and nitric acid. The mechanism of

nitration suggested by Schaarschmidt is:

2HNO 3 + H 2 SO 4 <-> N 2 O 5 + H 2 SO 4 .H 2 O (13)

Unstable nitration product

Hetherington and Masson [19] suggested that nitrobenzene can form complexes

with H 2 SO 4 and HNO 3 and that the cation, C 6 H 5 NO 2 H+, of these complexes

reacts with HNO 3 to form dinitrobenzene:

H 2 SO 4 + C 6 H 5 NO 2 <-> C 6 H 5 NO 2 H+ + HSO 4 - (14)

HNO 3 + C 6 H 5 NO 2 <-> C 6 H 5 NO 2 H+ + NO 3 - (14a)

C 6 H 5 NO 2 H+ + H 2 O <-> C 6 H 5 NO 2 + H 3 O+ (15)

C 6 H 5 NO 2 H+ + HNO 3 <-> C 6 (NO 2 ) 2 + H 3 O+ (15a)