How did Baeyer synthesize indigo?
My synthesis of indigo began with the condensation of isatin with phosphorus trichloride, producing indoxyl, which then oxidizes to indigo. I systematically explored the reduction of isatin and the behavior of oxindole derivatives. The key was recognizing that indigo is a dimer of indoxyl, and I demonstrated this by isolating intermediates. I also studied the indigoid group extensively, publishing 'Untersuchungen über die Indigogruppe.' The synthesis was a triumph of structural reasoning: I deduced the correct formula for indigo based on its reactions with reducing agents and acids. This work showed that natural products could be replicated in the laboratory, though the industrial route required modifications by Karl Heumann to use aniline and chloroacetic acid. My method proved the cyclic structure of indigo and its aromatic character.
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