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Process for the preparation of triphenylmethane dyes

  • US 5,198,558 A
  • Filed: 12/18/1990
  • Issued: 03/30/1993
  • Est. Priority Date: 12/18/1990
  • Status: Expired due to Term
First Claim
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1. A process for the preparation of triphenylmethane dyes of the formula:

  • ##STR4## wherein R1 and R2 each denote hydrogen, C1 -C4 alkyl, benzyl or sulfobenzyl,R3 and R4 each denote hydrogen, C1 -C4 alkyl or sulfonic acidR5 denotes a phenyl, sulfophenyl, dialkylaminophenyl, C1 -C4 alkylphenyl, C1 -C4 alkyl-dialkylaminophenyl, halogenophenyl, naphthyl, sulfonaphthyl, disulfonaphthyl, or alkyldisulfonaphthylcomprisingI. oxidation of the leuco compound of the corresponding triphenylmethane dye with manganese dioxide in the presence of aqueous phosphoric acid at a temperature of about 20°

    C. to about 100°

    C.,II. adding a base selected from the group consisting of ammonia, amines, aminoalcohols, metal hydroxides of Groups IA, IIA, IIIA and mixtures thereof in an amount sufficient to neutralize the aqueous solution,III. filtration from the precipitate andIV. isolation of said triphenylmethane dye.

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