Process for the preparation of symmetrical thioindigo compounds or mixtures of symmetrical and asymmetrical thioindigo compounds as well as bis-(phenylthio)maleic acid derivatives and thionaphthenones per se

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Listed from its EPO record in Patent Yard's archive of European patents past their term. Its claims, description and drawings are in the EPO PDF and on Google Patents, and the Claude kit works from them.

Why it's free to use

• Filed July 15, 1980 and never granted as a European patent. Had it been granted, its 20-year term would have ended July 15, 2000.
• A supplementary protection certificate, which can extend a medicine or crop-protection patent, adds at most five and a half years, so even that would have ended by January 15, 2006.
• We check European rights only. A US or other national patent in its family could still be in force: check its family on Espacenet or Google Patents.