* Nucleophilic Attack on Aromatic Species- (XXXVII)
Nevertheless aryl halides having no activating groups are found to
undergo ready conversion to amines with sodamide, but this reaction
has been shown to proceed via an entirely different mechanism to that
already considered. It has been shown not to be a direct replacement,
but to involve elimination of hydrogen halide followed by addition
of ammonia:
-HO S ^% NH,(XXXVIII) —
The benzyne intermediate (XXXVIII) proposed seems inSerently
unlikely but the evidence in its favour is extremely strong. Thus
when chlorobenzene, in which chlorine is attached to an isotopically-
labelled carbon atom, reacts with sodamide the intervention of
a benzyne intermediate should lead to equal quantities of two
amines; in one of which the amino-group is attached directly to the
labelled carbon and.in the other in the o-position to it. This has,
indeed, been confirmed experimentally. Similarly in the reaction of
a-halogeno-naphthalenes with R 2 NH, two isomeric compounds
should be obtained' NRaNRj(iii) Replacement of halogen in an unactivated nucleusThe chlorine in chlorobenzene only undergoes replacement by
®OH under extreme conditions due to the fact that the expected
SN2 (aromatic) intermediate (XXXVII), not being stabilised like the
examples already considered, is reluctant to form: