REARRANGEMENT OF ISOTOPICALLY LABELED DIAZONIUM SALTS

The extent of rearrangement of Ar15N+≡N to ArN+≡15N accompanying hydrolysis has been studied for Ar = p-CH3C6H4, m-CH3 C6H4, p-CH3OC6H4, and p-ClC6H4. The rate of rearrangement is 0.026 ± 0.012 times the hydrolysis rate in these cases and for the unsubstituted compound studied before, and thus parallels the hydrolysis closely, but the rate does not follow the Hammett σ or ordinary migratory aptitudes. The reaction is kinetically first order, has the same activation energy as the hydrolysis, and is not suppressed by 3 M sodium bromide. It is unaffected by the isotopic composition of dissolved nitrogen. Suppression by nucleophiles is a necessary consequence of a previously suggested mechanism through a diazirine cation; this mechanism must therefore be rejected for this thermal reaction. In only one minor feature is the original evidence wrong: there is no reason to suspect a markedly greater selectivity at low concentration of added nucleophiles. The parallel to the isoelectronic isonitrile rearrangement is very poor. © 1969, American Chemical Society. All rights reserved.