Green pigments, formation

Mansuy, D., L. Devocelle, 1. Artaud, and J.P. Battioni (1985). Alkene oxidations by iodosylben-zene catalyzed by iron-porphyrins Fate of the catalyst and formation of N-alkyl-porphyrin green pigments from monosubstituted alkenes as in cytochrome P-450. Nouv. J. Chim. 9, 711-716. 

Early studies have postulated oxyrene or cationic carbene intermediates in the formation of either green pigments or the acetic acid metabolites . In subsequent investigations, however, these intermediates were ruled out, based on structural and mechanistic consideration Ortiz de Montellano and coworkers observed that while there was a strong isotope effect in the formation of the acetic acid metabolite, there was no deuterium effect in the formation of the heme-acetylene adduct. The mechanism thus postulated by these authors for the formation of the green pigment as well as the acetic acid metabolites is compatible with the evidence available to date and is shown in Scheme 12. This mechanism... 

Aldehydes - The destruction of cytochrome P-A50 by aromatic aldehydes is accompanied by equimolar loss of microsomal heme. > Aliphatic aldehydes also destroy cytochrome P-450 but, unlike the aromatic analogues, only appear to be active in vitro.Enzyme destruction by these monoaldehydes is distinguished from that mediated by phthalaldehyde by a requirement for NADPH. The incubation of octanal with hepatic microsomes from rats pretreated with radiolabeled levulinic acid to tag the heme groups causes the formation of a radiolabeled "green" pigment, but the electronic spectrum of the pigment lacks the features that characterize N-alkylprotoporphyrin IX derivatives. ... 

Resorcinol is one of the components of most oxidation dyes and, as such, is probably the most commonly used oxidation dye coupler. Brody and Bums [21] have shown that p-phenylenediamine, in the absence of hair and phenols, is oxidized to Bandrowski s base. However, when resorcinol is present, polyindophenols (XX) are formed, and the formation of Bandrowski s base is effectively prevented [21]. These brown polymeric polyindophenol pigments have been identified by elemental analysis, acetyl values, and hydrolysis to p-phenylenediamine. Low-molecular-weight di-and trinuclear species were not detected by Brody and Burns, but Shah et al. [22] have isolated a green pigment from hair dyed with mixtures of p-phenylenediamine and resorcinol. This pigment was identified as the trinuclear indophenol (XXI). 

The following scheme describes the formation of the trinudear green pigment and polyindophenols from (I) and resorcinol and is consistent with the general mechanism described earlier. This scheme suggests that the dii-minium ion (IX) is the actual active species, and its formation has already been described. In step 2, this electrophilic species attacks a resorcinol anion, para to the phenolic group, forming (XXVII), which is oxidized to indophenol in step 3. 

In step 4, p-phenylenediamine adds to the indophenol in a 1,4 manner [25, 33], producing the trinuclear species (XXVIII), which is then oxidized to the trinuclear green pigment (XXI). Several routes exist for formation of polymeric indophenols, and all are analogous to steps 4 and 5. Repetition of these steps will result in the formation of higher polymers. Because most oxidation dyes contain both p-phenylenediamine and resorcinol, the formation of these tri- and polynuclear pigments is important in the oxidative dyeing of human hair. 

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