Quantification of Ylide Formation in Phosphonium-Based Ionic Liquids Reacted with CO₂

Abstract

Phosphonium-based ionic liquids (ILs) paired with aprotic heterocyclic anions (AHAs) are found to react with CO 2 to form both a carbamate product and a carboxyl product. The carboxyl product is formed primarily at elevated temperatures through the formation of a phosphonium ylide intermediate. The formation of the carboxyl product leads to the formation of the neutral azole, which can lead to an irreversible process if the neutral azole is sufficiently volatile. To understand how the ILs would behave in a CO 2 capture process operated at elevated temperatures, it was necessary to quantify the two reaction products. CO 2 was reacted with seven different AHA ILs to determine the equilibrium amounts of carbamate and carboxyl, the equilibrium constants for both reactions, and the rate of CO 2 absorption by each reaction path. The reactions were tracked and quantified in situ by using ATR-FTIR spectroscopy, while NMR spectroscopy was used after equilibrium was reached to determine the extent of each reaction at multiple temperatures and pressures. It was found that both the basicity and molecular size of the anion play key roles in the formation of the phosphonium ylide. In the extreme case of only half of the reacted product was the desired carbamate at 60 °C. Although there is a significant amount of the carboxyl product formed, the carbamate is kinetically favored.

Ammonium-, phosphonium- and sulfonium-based 2-cyanopyrrolidine ionic liquids for carbon dioxide fixation

“…Our computational thermodynamic results are in qualitative agreement with the experimentally determined CO 2 sorption by the [P 6,6,6,14 ][2-CNpyr] RTIL. 29 In particular, the gas capacities were 0.5 mol CO 2 /mol RTIL at 333 K and 0.7 bar; 0.6 mol CO 2 / mol RTIL at 333 K and 1.5 bar; 0.7 mol CO 2 /mol RTIL at 333 K and 2.0 bar. Although the experimental capacity of the investigated RTIL is far below the theoretical limit of 2.0 mol CO 2 /mol RTIL the obtained sorption performance is outstanding.…”

“…7,10,12,[24][25][26][27] The most promising RTILs in the context of CO 2 sorption are normally composed of bulky organic cations and chemically active anions, such as aprotic heterocyclic anions (AHAs). [28][29][30] Their bulkiness and asymmetry sterically prevent RTILs from crystallizing at the ambient temperature. Higher conformation flexibility of the particles in the liquid aggregate state favors a more robust performance of the substance as a greenhouse gas scavenger.…”

“…The presently applied RTILs are represented by very different chemical structures, ranging from heterocycles to quaternary ammonium-and phosphonium-based, ternary sulfonium-based families. 5,29,[31][32][33][34] RTILs, as a rule, possess fine-tunable physical and chemical properties. [35][36][37][38][39][40] The latter makes them attractive for several applications, in which traditional solvents perform poorly.…”

Understanding of the interactions between azole-anion-based ionic liquids and 2-methyl-3-butyn-2-ol from the experimental perspective: the cage effect

“…The present work is aimed at investigating the interactions between AILs and MBY in detail from the experimental perspective using physicochemical properties, 1 H NMR spectroscopy, and dynamic light scattering, to clarify the process of the interactions between AILs and MBY, as well as the respective roles of the anion and cation of AILs. On the one hand, it will further reveal the mechanism of MBY activation, which is essential to understand the reaction mechanism in detail, 27 and on the other hand, it will accumulate reliable engineering data for process design. 27 Considering the importance of transfer properties to the chemical process and theoretical design, first, based on the concentration-dependent η of AIL + MBY mixtures measured at T = (293.15 to 333.15) K, the derivatives of η with the mole fraction of AIL ( x AIL ) and (Δ η /Δ x ) were carefully analysed to explore the interactions between AILs and MBY and the aggregation of AILs in the system, which were verified by 1 H NMR chemical shifts of P-CH 2 of [P 66614 ] + .…”

“…On the one hand, it will further reveal the mechanism of MBY activation, which is essential to understand the reaction mechanism in detail, 27 and on the other hand, it will accumulate reliable engineering data for process design. 27 Considering the importance of transfer properties to the chemical process and theoretical design, first, based on the concentration-dependent η of AIL + MBY mixtures measured at T = (293.15 to 333.15) K, the derivatives of η with the mole fraction of AIL ( x AIL ) and (Δ η /Δ x ) were carefully analysed to explore the interactions between AILs and MBY and the aggregation of AILs in the system, which were verified by 1 H NMR chemical shifts of P-CH 2 of [P 66614 ] + . Second, the interaction parameters ( g ji – g ii ) of AIL + MBY mixtures were obtained from η through the Eyring-UNIQUAC equation and were employed to investigate the difference between the bulk and the local composition ( x i – x ii ) through the LC model, which were used to reveal the microscopic interaction and evaluate the ideality of the mixtures, and the obtained results were further confirmed by the excess properties such as V E and isentropic compressibility deviations (Δ k s ).…”