My PhD dissertation - Institut Fresnel

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Table 5. Trialkylphosphine oxides R2R'P(O).
Product R = R' = Yield
27a -C(CH3)3 -C4H9 87%
27b -C(CH3)3 -CH(CH3)2 88%
27c -C4H9 -CH2C(CH3)3 86%
27d -C4H9 -C(CH3)3 75%
27e -C2H5 -C4H9 78% [37]
27f -CH3 -C4H9 84% [38]
27g -C6H11 -C4H9 93%
27h -CH(CH3)2 -CH3 86%
Other phosphine oxides needed as reference substances were prepared by means of
known procedure from the literature. Thus, di-tert-butylmethylphosphine oxide (27i) was
prepared by Michaelis-Arbuzov rearrangement of methyldi-tert-butylphosphinite
[ ] 160
[ ] 161
[ ] 162 with
iodomethane, whereas dibutylmethylphosphine oxide (27j) and tert-butyldimethylposphine
oxide (27k) where obtained by reaction of butylmagnesium bromide or methylmagnesium
bromide with methylphosphonic dichloride and tert-butylphosphonic dichloride
respectively
[ ] 163 . Finally, the quaternary phosphonium halides were obtained from mixed
trialkyl phosphines 26a, 26c, 26d, and 26f by reaction with the appropriate alkyl halide in
diethyl ether. The hygroscopic products were collected simple filtration under anhydrous
conditions to give the starting phosphonium salts 28a - 28d (see § 3.3.4) which were further
decomposed under alkaline conditions.
3.3.5 Alkaline Decomposition of Phosphonium Halides
Several solvents, concentrations and water / solvent ratios were initially tried before
optimum conditions have been found for the alkaline decomposition reaction. First of all, a
dimethylsulfoxide/water mixture was chosen for the alkaline decomposition of
dibutyldimethylphosphonium iodide (28a), di-tert-butyldimethylphosphonium iodide (28b)
[ 164 ]
and dibutyldi-tert-butylphosphonium iodide (28c) at 60 °C. The use of this polar aprotic
solvent was mainly governed by its ability to enhance the nucleophilic activity of hydroxide
ions to accelerate the reaction rate which is known to be relatively slow in the case of
tetraalkylphosphonium salts
[ , ] 165 166 . However, since the results collected in these conditions