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The phosphonium cation, with the generic formula [PR3R′]+ and with a judicious selection of the appropriate anion, forms many phosphonium salts that are liquid at room temperature and many have melting points below 100 °C.

Phosphonium-based Ionic Liquids offer the following advantages:
  • Phosphonium salts are thermally more stable than the corresponding ammonium salts and imidazolium salts, important for processes which operate at temperatures higher than 100 °C (e.g., removal of reaction products by distillation). Furthermore, prevention of contaminations by decomposition products is a prerequisite for multiple recycle use of solvents.
  • Phosphonium cations lack acidic protons. Thus, they are stable under basic conditions, which can be problematic for several imidazolium-based Ionic Liquids (carbene formation).
  • Phosphonium salts are, in general, less dense than water; a benefit in product work-up steps.

Sigma-Aldrich offers, in collaboration with Cytec Industries, Inc., a new class of Ionic Liquids based on phosphonium cations.

Product #



Molecular Formula

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86929 Tetrabutylphosphonium methanesulfonate ≥98.0% (NT) C17H39O3PS
86934 Tetrabutylphosphonium tetrafluoroborate for electrochemical analysis, ≥99.0% C16H36BF4P
86933 Tetrabutylphosphonium p-toluenesulfonate ≥95% (NT) C23H43O3PS
50971 Trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)amide ≥95.0% C34H68F6NO4PS2
28612 Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate ≥95.0% C48H102O2P2
96662 Trihexyltetradecylphosphonium bromide ≥95% C32H68BrP
89744 Trihexyltetradecylphosphonium chloride ≥95.0% (NMR) C32H68ClP
50826 Trihexyltetradecylphosphonium decanoate ≥95.0% (NMR) C42H87O2P
56776 Trihexyltetradecylphosphonium dicyanamide ≥95% C34H68N3P
53166 3-(Triphenylphosphonio)propane-1-sulfonate ≥99.0% (HPLC) C21H21O3PS
07349 3-(Triphenylphosphonio)propane-1-sulfonic acid tosylate ≥98.0% C28H29O6PS2