Synthesis and absorption properties of five new heterocyclic disazo dyes containing pyrazole and pyrazolone and their acute toxicities on the freshwater amphipod Gammarus roeseli

Abstract In this study, five new heterocyclic disazo dyes containing pyrazole and pyrazolone were synthesised (3a‐3e). The synthesised disazo dyes were characterised by elemental analysis and Fourier Transform–infrared and proton nuclear magnetic resonance spectroscopy. The effects of two different solvents upon the absorption ability of the dyes substituted with electron‐withdrawing and electron‐donating groups were examined in detail. In addition, the acute toxicity of each synthesised azo dye was evaluated using a short‐term bioassay with Gammarus roeseli (Crustacea: Amphipoda) for 48 hours. According to the evaluations, the dyes 3a, 3b and 3d were categorised as slightly toxic, and the dyes 3c and 3e as practically non‐toxic. Considering the toxicity of the dye 3a, it was determined that the substitution of the electron‐withdrawing group in the azo dye resulted in more toxicity, while the substitution of the electron‐donating group resulted in less toxicity. It was also found that the presence of the strongly electron‐withdrawing group resulted in the azo dye becoming more toxic in comparison with the presence of the weakly electron‐withdrawing group, but that the presence of the strongly electron‐donating group resulted in the azo dye becoming less toxic in comparison with the presence of the weakly electron‐donating group. It is contended that this study is novel and of great importance in terms of synthesising new azo dyes, investigating their absorption properties and assessing their acute toxicities.