Indigo dye production by enzymatic mimicking based on an iron(III)porphyrin

• Iron(III) enzymes involved on indigo synthesis were mimicked for dye production.
• Indole is oxidized by H2O2 in the presence of a Fe(III)porphyrin in ethanol.
• A simpler and more efficient methodology is obtained relatively to bio-catalysis.
• The yields of indigo and indolinoid co-products were dependent on the metalloporphyrin system.
• The results were justified by the formation of different active species.

A novel indigo synthesis is based on a simple and cost-effective model system of the enzymes involved in the natural and biocatalytic productions. The method considers the oxidation of indole by hydrogen peroxide, being catalyzed by an iron(III)porphyrin in ethanol, as solvent, and no other additives. The yields of indigo and of the other oxidized indolinoid derivatives were found to be dependent on the metalloporphyrin system used and on the control of the oxidation conditions. Significant reductions of the environmental impact relatively to the present industrial production and of the costs relatively to the biocatalytic methodologies were obtained. The enhanced indigo production in the presence of the iron(III)porphyrin-ethanol catalytic system relatively to the manganese(III)porphyrin-acetonitrile system can be rationalized by the formation of different active species in the two systems.

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