Luminol radical anion

The luminol dianion Lum2< > does not exist in appreciable quantities in aqueous solvents hydrogen peroxide and a catalyst such as hemin are required. Thus another mechanism seems to be at work here. Perhaps a hydrogen atom is abstracted from the luminol monoanion Lum( > to yield a luminol radical anion 55 which then reacts with oxygen or a radical ion derived from hydrogen peroxide according to 3,4,109)... 

Aqueous alkaline luminol solutions can be excited to chemiluminescence by pulse radiolysis, the only additional requirement being oxygen 119h The suggested mechanism is that hydroxyl radicals attacking luminol monoanions, followed by reaction of the luminol radical anion thus formed with oxygen ... 

The reaction between hydroxyl radical and luminol results in the quantitative formation of hydroxylated products, which are known to be radical scavengers (Scheme 19) °. The reduction of luminol radical anion by these species decreases the emission intensity, unless HO is generated rapidly in high concentrations . The emission observed under these conditions may be attributed to one-electron oxidation of luminol by hydroxyl radicals, yielding luminol radical anion, or by hydroxyl-mediated generation of potent one-electron oxidants from its reaction with bases. Moreover, the addition of HO to luminol or its monoanion results in an adduct able to react very rapidly with O2, yielding, in addition to hydroxylated luminol, superoxide (Scheme 19) °. 

A similar study has been carried out by the pulse radiolytic production of luminol radical anions and oxygen radical ions simultaneously [77]. 

Since there is no effect of H2O2 concentration on the integrated chemiluminescence intensity, the conclusion was drawn that oxygen radical anion activates the luminol radical anions to chemiluminescence, forming the non-radical diazaquinone perhydrate (59) ... 

These results involving the luminol radical anion are compatible with other proposals for the luminol mechanism. Steps after the peroxide intermediate are not specifically detected, and must occur with a rate constant of 10 s ... 

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