INTERMEDIATES IN THE DECOMPOSITION OF ALIPHATIC DIAZO-COMPOUNDS. PART 19. KINETICS AND MECHANISM OF THE REACTIONS OF 9-DIAZOFLUORENE CATION RADICAL

Article abstract of DOI:10.1039/P29840001527

The decomposition of 9-diazofluorene (FlN2) brought about at a platinum anode or by chemical oxidants, Cu(BF4)2 or (p-BrC6H4)3N(^+.)SbCl6(1-), in CH3CN solution leads to formation of mixtures of bifluorenylidene and flourenone azine in high yield.The reactions have been studied kinetically by conventional means and using the transient electrochemical techniques derivative linear sweep voltammetry (l.s.v.) and derivative cyclic voltammetry (d.c.v.).Constant-current electrolysis of FlN2 shows the characteristics of a chain process.The chemical oxidants give rise to a rate law -d/dt = k above a critical oxidant level, and the value of k is the same for both oxidants, even though their oxidation potentials are substantially different.It is inferred that the process studied is the chain propagation step in which the chain carrier reacts with a molecule of FlN2.Under the conditions of l.s.v. and d.c.v. experiments, it is shown that the instantaneously formed FlN2(^+.) is consumed in a rapid process which is second order with respect to the cation radical and has a rate constant of 1.9 x 1E8 l mol^-1 s^-1; it is suggested that this process is cation radical dimerisation.Since the product of this step rapidly yields bifluorenylidene, it is argued that the slower macroscopic chain reactions do not involve dimerisation, but rather that FlN2(^+.) rapidly attacks a further FlN2 molecule to generate the chain carrier which must have a lower oxidation potential than FlN2(^+.).Possible structures for the chain carrier are considered in the light of earlier e.s.r. evidence for a radical intermediate.

Full text of DOI:10.1039/P29840001527

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