Structural characterization of a pyrazolone-based heterocyclic dye and its acid-base adduct

• An ion-pair compound 2 of a pyrazolone/benzothiazole based dye 1 is described.
• Their crystal structures, UV–vis spectra, solvatochromism and acid-base discoloration are compared.
• It is the first structural report on S-containing heterocycle based pyrazolone dyes.

The first structural report of an S-containing heterocycle based pyrazolone dye, 3-methyl-4-((6′-methylbenzo[d]thiazol-2′-yl)hydrazono)-1-phenyl-5-pyrazolone (1), is presented. The compound exhibits the hydrazone-tautomeric form. Treatment of 1 with a mixture of ammonia and acetone results in the formation of an acid-base adduct, 2, consisting of the deprotonated dye as anion and in-situ formed 2,2,6,6-tetramethylpiperidone as the cation. This acid-base adduct was investigated by crystal structure determination. Comparison of the related bonds in both compounds, 1 and 2, confirmed the formation of the anion.

A pyrazolone/benzothiazole based heterocyclic dye (1) and its novel ion-pair compound (2) have been structurally characterized, and the latter has an in situ formed 2,2,6,6-tetramethyl-4-oxopiperi dinium cation from the mixture of acetone and aqueous ammonia.Figure optionsDownload as PowerPoint slide