A facile synthesis of 6,6′- and 5,5′-dihalogenoindigos

• Published in: Dyes and pigments Vol. 62; no. 2; pp. 101 - 105
• Main Authors: Tanoue, Yasuhiro, Sakata, Kazunori, Hashimoto, Mamoru, Hamada, Moritsugu, Kai, Norihisa, Nagai, Takeshi
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.08.2004; Elsevier
• Subjects: 3-Acetoxy-6-fluoroindole; 3-Iodo-halogenoindole; 6,6′-Dibromoindigo; Applied sciences; Chemical industry and chemicals; Dihalogenoindigo; Dyes, pigments; Exact sciences and technology; Industrial chemicals; Royal purple; Tyrian purple; Dihalogenoindigo; 6,6′-Dibromoindigo; 3-Iodo-halogenoindole; Tyrian purple; 3-Acetoxy-6-fluoroindole; Royal purple; 6,6'-Dibromoindigo; Indigoid dye; Natural dye; Purple; Chemical synthesis; Organic halogen compounds
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/S0143-7208(03)00150-5

Our convenient synthetic method for Tyrian purple was applied to syntheses of 6,6′- and 5,5′- dihalogenoindigos. The dihalogenoindigos were easily obtained by three steps of reactions from the commercially available haloindoles. Iodination of the haloindoles, followed by acetoxylation with silver acetate in acetic acid, afforded 5- or 6-halo-3-acetoxyindoles, whose alkaline hydrolysis accompanying air oxidation gave the corresponding dihalogenoindigos. The first 1H NMR spectrum of 6,6′-difluoroindigo was taken in dimethyl sulfoxide.