Investigation of a Self-Neutralizing, Thermally Robust Ionic Liquid As an Acid Catalyst Solvent System

The chemical industry often employs solvents and catalysts that are harmful to the environment, public health, and contribute to climate change. In industrial chemical processes, solvents are often necessary to enhance chemical reaction rates and as a means of temperature control. Many of these processes involve catalysts, often acids, that serve to increase the rate of the reaction, but create the issue of waste disposal. At present, the separations techniques involved are expensive and energy extensive. Self-neutralizing, acidic ionic liquids (ILs) can serve as an alternative solvent system that allows for non-volatile and re-usable materials to be used in high temperature processes. In this work, an alkylation reaction of t-butanol and phenol in non-hydroxylated tetraphenylphosphonium [TPP⁺] paired with bistriflimide [Tf₂N^-] as the solvent is performed. The primary focus here is to study the kinetics and equilibrium data to probe the solvation environment. This is preliminary work leading to the reaction of t-butanol and anisole in a similar IL involving [TPP⁺]’s hydroxylated analogue, [TPHP⁺], to determine the hydroxylated IL’s ability to be a sufficient catalyst through a phenolic hydroxyl on the IL cation. A series of temperature dependent reactions are completed for both reactions, and these product mixtures are analyzed via gas chromatography to further understand the kinetics of each. This data will provide an understanding of the solute-solvent interactions taking place since there is little predictability of molecular-level interactions and changes in thermal properties when modifying ILs. This information would then serve as a model in designing task specific ILs for novel solvent systems and more energy efficient processes. In this investigation, [TPP][Tf₂N] was shown to successfully solvate the reaction producing the two major products, 2-t-butylphenol and 4-t-butylphenol. There are no indications of decomposition at 220, but data acquisition of the temperature dependent reaction series approaching higher temperatures will be more informative of any possible degradation. At present, [TPP][Tf₂N] is a promising alternative to employ as a novel solvent, catalyst system and provides a foundation for better understanding the effects of modifications to per-arylated cations. These solvent, catalyst systems alleviate the chemical industry’s attribution to climate change and environmental damage.