Ionic Liquids based Acid-base Indicators for Aqueous to the Non-Aqueous Medium: An Overview

Visualizing acid-base equilibria and determining acid-base equilibrium constants (pK(a)) in aqueous to the non-aqueous medium is essential for understanding the various chemical and biochemical processes. This mini review highlights the possibility of fine-tuning the traditional acid-base indicator dye's physicochemical properties into ionic liquids (ILs)-integrated ones to enhance their solubility and practical applications in a wide range of solvents. These include the high sensitivity towards acid and bases by virtue of its colour and spectral properties changes. ILs-based indicators could be used to determine the pK(a) values in aqueous to the non-aqueous medium from polar to non-polar ones by overlapping indicator method. This review provides an essential idea of the emerging challenges and openings that may motivate the scientific communities to move towards IL-integrated acid-base indicators and find their dissociation constants (pK(Ind)) in any solvents depending on their solubility. The calculated pK(Ind) values could be used to determine the pK(a) values of different acids and bases in any solvents. It would also be beneficial to find a general trend of acidity and basicity from solvents to solvents using such types of indicators without alternating the main moiety. It will benefit the scientific communities to understand the pK(a) scales in different solvents.