TGA-MS study of the decomposition of phosphorus-containing ionic liquids trihexyl(tetradecyl)phosphonium decanoate and trihexyltetradecylphosphonium bis[(trifluoromethyl)sulfonyl] amide

Abstract

The phosphorus-containing ionic liquids (IL) decompose where ion pairs fall apart. Trihexyl(tetradecyl)phosphonium decanoate, sold as Cyphos IL 103, and Trihexyltetradecylphosphonium bis[(trifluoromethyl)sulfonyl] amide, sold as Cyphos IL 109, decompose in 200–475 °C range in air and the fragments containing organophosphorus are found here among other major fragments of hydrocarbon arms. Black residues are found after heating in air to 740 °C in TG in 5.0 and 0.6 mass/% for Cyphos IL 103 and 109, respectively. They were presumably containing P₂O₅ after oxidation. Not all the phosphorus can be counted for at 740 °C and falls short of calculated values of 10.9 and 9.3 mass/%, if residues contain nothing else but P₂O₅. Among the fragments the authors found in MS the organophosphorus fragments from decomposition of the cationic C₃₂ H₆₈ P + including P with 3–4 hydrocarbon attached as well as the major fragments of linear hydrocarbon arms. Water evolves early at lower temperature and continues to 740 °C. CO₂ comes from oxidation of carbon at high temperatures. The SO, SO₂, CF₃, CF₂CF₂ evolve in sulfur and fluorine containing anion in Cyphos IL 109. H₃PO₄ is detected, which is most likely from the reaction product of P₂O₅ and water. No P₂O₅ was found. Ash content examined by inductively coupled plasma spectroscopy (ICP) found that the phosphorus P in the ashes after burning in air to 700 °C and found 3200 ppm (or 0.62 mass/%) and 30 ppm (0.003 mass/%) in Cyphos IL 103 and 109, respectively.