Effect of anion α-functionalization on the water affinity of thermo-responsive phosphonium acetate-derived ionic liquids

Sidharth Sanadhya; Gregory M. Durling; Rohit Bhagwat; Jake M. Marek; Brandon L. Ashfeld; Saeed Moghaddam

Journal of Ionic Liquids (Dec 2024)

Effect of anion α-functionalization on the water affinity of thermo-responsive phosphonium acetate-derived ionic liquids

Sidharth Sanadhya,
Gregory M. Durling,
Rohit Bhagwat,
Jake M. Marek,
Brandon L. Ashfeld,
Saeed Moghaddam

Affiliations

Sidharth Sanadhya: Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 32611, United States
Gregory M. Durling: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, United States
Rohit Bhagwat: Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 32611, United States
Jake M. Marek: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, United States
Brandon L. Ashfeld: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, United States
Saeed Moghaddam: Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 32611, United States; Corresponding author.

Journal volume & issue: Vol. 4, no. 2
p. 100107

Abstract

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This study presents a facile method for assessing the effect of anion functional group substitution on the water affinity of phosphonium-acetate ionic liquids. By combining the same cation with three different α-substituted carboxylate anions, the effect of anion functional group substitution on the IL miscibility with water and hygroscopicity was experimentally evaluated and rationalized using COSMO-RS sigma profile analysis. Lower critical solution temperature (LCST) phase separation experiments and water vapor partial pressure measurements revealed that there is a stark α-substitution dependency on the affinity of water for acetate [AcO], pivalate [PivO], and trifluoroacetate [TFA] derived tributyl(octyl)phosphonium [P4448] ILs. It was found that the IL water affinities varied as: [P4448][AcO] > [P4448][PivO] > [P4448][TFA]. With the lowest water partial pressure and no LCST driven phase separation, [P4448][AcO] exhibited a high affinity for water. On the other hand, [P4448][PivO] and [P4448][TFA] exhibited LCST-driven phase separation and room temperature immiscibility, respectively, with higher water partial pressures, as a result of relatively weak water affinities. COSMO-RS sigma profile analysis revealed that the aliphatic carboxylate anions should incorporate apolar interactions commensurate with or greater than the polar hydrogen bond acceptor interactions for phase immiscibility of the corresponding IL with water. It was found that the relative magnitudes of apolar and polar interactions, assessed using the anion sigma profile peak intensity ratio (Ir), are directly correlated with the IL water affinity, and inversely correlated with the solution water activity coefficient. Therefore, it was concluded that Ir forms a quantitative link between the structural changes at the molecular level and the bulk water affinity exhibited by the ionic liquid as a whole.

Published in Journal of Ionic Liquids

ISSN: 2772-4220 (Online)
Publisher: Elsevier
Country of publisher: Netherlands
LCC subjects: Science: Chemistry
Website: https://www.journals.elsevier.com/journal-of-ionic-liquids

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