Impact of temperature changes and pH on aqueous solutions of TCAB, a derived propanil contaminant

Abstract

3,4,3′,4′-tetrachloroazobenzene known as TCAB is an unwanted product derivate from the degradation of propanil herbicide. In this work UV–visible and infrared spectroscopies were used to experimentally explore the impact of pH and temperature changes of TCAB in aqueous and ethanol solutions. Two isomeric forms, cis and trans, are present in solution. The density functional theory (DFT) with PCM methodology was used to analyze the stability of each isomer in solution phase by the evaluation of solvation energy and frontier orbital energies of TCBA at 25 and 40 °C. This compound has been studied from room temperature to 50 °C, revealing the weakening of trans form with an increment of cis form in ethanol and high temperature. Interestingly, under acid conditions the protonated azo compound was evidenced in solution. We found that the cis form is predominant in aqueous solution at 40 °C and 30 min. Finally, FTIR studies show that the increasing of the temperature promote irreversible structural changes via a trans to cis interconversion process. The derivative results from this study may contributed to understanding of transformation of TCAB in aqueous solution by pH and temperature changes.