My PhD dissertation - Institut Fresnel

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To illustrate the experimental method for the quantification of the phosphine oxides
resulting from alkaline decomposition of phosphonium halides, a detailed protocole is given
for tributylneopentylphosphonium iodide degradation:
Tributylneopentylphosphonium iodide (0.40 g, 1.0 mmol) was suspended in butanol (5.0 mL) and
a 6.0 M aqueous potassium hydroxide solution (1.0 mL) was added. Triisopropylphosphine oxide
(0.13 g, 0.76 mmol) was immediately added as internal standard. The reaction mixture was then
heated at 110 °C in a thermostated bath until no trace of starting phosphonium remained. The gases
formed during the decomposition were bubbled into a solution of bromine (0.2 mL, 0.5 g, 3 mmol) in
chloroform (5.0 mL). After the gas evolution ceased, the bromine solution was treated with a sodium
sulfite solution, phases were decantated. The organic layer was dried with sodium sulfate and the
presence of brominated adduct was immediately checked by gas chromatography (30 m, DB-1,
70 °C). Cyclohexane (20 mL) was added to the reaction slurry and the solvents were removed under
reduced pressure. The residue was dissolved in diethyl ether (15 mL), dried with sodium sulfate and
evaporated to dryness. 31 P NMR experiment was directly run on the crude mixture without any further
purification (See Figure 15). Yield: 98% according to triisopropylphosphine oxide (internal standard).
This experiment was repeated three times in the same conditions to afford an average phosphine oxide
ratio by comparison with the spectra of each individual original phosphine oxide. The average
tributylphosphine oxide/dibutylneopentylphosphine oxide was calculated of 17:83.
Figure 15. Alkaline decomposition of tributylneopentylphosphonium iodide with potassium hydroxide in a
butanol/water (8:2) mixture at 110 °C