Synthesis and characterization of chromium (III), iron (II), copper (II) complexes of 4-amino-1-(p-sulphophenyl)-3-methyl-5-pyrazolone based acid dyes and their applications on leather

• Seven pyrazolone dyes and their Cr (III), Fe (II), Cu (II) complexes were synthesized.
• Acid dyes applied to leather exhibit elevated wash, light and rubbing fastness.
• The synthesized dyes display very high exhaustion and fixation values as well.

A new series of 4-amino-1-phenyl-5-pyrazolone based azo acid dyes (3a–g) has been synthesized from p- Sulphophenyl methyl pyrazolone (1). The synthetic methodology involved the nitrosation of p-sulphophenylmethylpyrazolone followed by reduction to 1-(p-sulphophenyl)-3-methyl-4-amino-5-pyrazolone. Diazotization of intermediate 1-(p-sulphophenyl)-3-methyl-4-amino-5-pyrazolone and coupling with 1-phenyl-5-pyrazolone derivatives (2a–g), in alkaline medium to yield different acid dyes. Multichromic metal complexes of these dyes (5a–g, 6a–g and 7a–g) with 3d transition metals Chromium, Iron and Copper were also accomplished. The structures of all newly synthesized compounds were confirmed by analytical data and spectroscopic techniques. The synthesized dyes were applied on leather to assess their light fastness, wash fastness and rubbing fastness and were shown to possess high values of 5–6, 4–5 and 4–5 respectively by maximum dyes.

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