Esterified carboxylic pyrazolone dyes and their in situ CuII/H2O2 catalytic oxidation

Abstract In this paper, we report the studies on in situ CuII/H2O2 catalytic oxidation for esterified carboxylic pyrazolone dyes. Our results reveal that two ortho phenolic hydroxyl pyrazolone based heterocyclic dyes can be prepared successfully by treating corresponding esterified carboxylic pyrazolone dyes with Cu(CH3COO)2·H2O/H2O2 or CuCl2·2H2O/H2O2 in the presence of DMF via the Fenton-type reaction. In addition, when Cu(CH3COO)2·H2O and CuCl2·2H2O were used under the similar reaction condition, respectively, copper(II) complexes with distinguishable nuclearities and coordination modes have been obtained. Furthermore, all the compounds have been spectrally compared, where hydrazone to deprotonated and then to hydrazone configurations have been proved before and after forming the copper(II) intermediates and subsequent demetallization. The acquisition of three intermediate copper(II) complexes of esterified carboxylic pyrazolone dyes herein via the Fenton-type reaction is suggested to provide further understanding on the study of such kind of reaction. As far as we know, this is the first study on esterified carboxylic pyrazolone dyes and also the first attempt on the extension of Fenton-type reactions for CuII/H2O2/pyrazolone system.