Reactivity of H3PO towards ketones
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 5, May, 2016
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Avance III 400 (161.9 MHz) high resolution spectrometers,
respectively. ESI mass spectra were obtained on a AmazonX
mass spectrometer (Bruker Daltonik GmbH, Bremen, Germany).
Positive ions were detected in the range m/z from 70 to 1000.
Capillary voltage was –4500 V. Nitrogen was used as a drying gas
at a temperature of 250 °C and at a rate of 8 L min–1. The
samples were injected using an Agilent 1260 chromatograph
(USA). The data were processed using the DataAnalysis 4.0 proꢀ
gram (Bruker Daltonik GmbH).
and tris(αꢀhydroxyethyl)phosphine oxide in 60—70 and
40—45% yields, respectively.
As it follows from the experimental data, in all the
cases phosphine oxide H3PO acts as an agent reacting
with ketones 1—3, since its reactivity considerably exꢀ
ceeds the reactivity of phosphine PH3,6 which is also conꢀ
firmed by the target process taking place under relatively
mild conditions at a high rate and with high selectivity.
Moreover, on model reactions we experimentally conꢀ
firmed that phosphine PH3 does not react with ketones
1—4 under the conditions used.
In conclusion, the reaction of phosphine oxide H3PO
with acetone, ethyl methyl ketone, and methyl nꢀpropyl
ketone, in contrast to phosphine PH3, proceeds under mild
conditions without use of strongly acidic medium, inꢀ
creased temperature and pressure. This indicates considꢀ
erably more high reactivity of phosphine oxide H3PO as
compared to phosphine PH3 in the reactions of the formaꢀ
tion of organophosphorus compounds, that opens wide
prospects and new synthetic possibilities for selective prepꢀ
aration of organophosphorus compounds, including deꢀ
rivatives of tricoordinated phosphorus obtained by chemiꢀ
cal reduction of phosphine oxides19 and regarded as imꢀ
portant and widely used reagents for modern catalytic
chemistry and organophosphorus industry.
Electrochemical generation of phosphine oxide H3PO in the
presence of ketones 1—4 (general procedure). A solution for the
electrolysis was prepared by emulsification of white phosphorus
(100 mg, 0.81 mmol) in a mixture of water/ketone (1 : 2 v/v,
30 mL) at 70 °C. A 2 N aqueous solution of HCl (0.5 mL) was
added to the obtained finely dispersed emulsion (an opaque soluꢀ
tion) and a direct voltage was applied with the current strength
of 150 mA (i = 46.9 A m–2). Every 2 h after beginning of the
electrolysis, an aqueous solution of HCl (0.5 mL) was added to
the reaction mixture. A total volume of added hydrochloric acid
was 2.0 mL. The electrolysis time was 8 h. A resulting mixture
was extracted with dichloromethane and concentrated. The prodꢀ
1
ucts were analyzed by 31P and H NMR spectroscopy and mass
spectrometry with electrospray ionization. The conditions of
electrochemical processes and relative content of phosphorusꢀ
containing products in the reaction mixture were evaluated based
on the integral intensities of signals in the 31P NMR spectra (see
Table 1). Spectral characteristics of obtained organophosphorus
compounds are given below. 1H NMR spectra for compounds 5
and 7—10 are not reported because of the low stability of these
derivatives, which decompose by the reaction of ketone elimiꢀ
nation as described earlier22 for αꢀhydroxyisopropyldipheꢀ
nylphosphine oxide.
1ꢀHydroxyisopropylphosphine oxide (5). 31P NMR (H2O), δ:
27.0 (t.hept, J = 484.4 Hz, J = 18.2 Hz).
Bis(1ꢀhydroxyisopropyl)phosphine oxide (6). 1H NMR
(MeCNꢀd3), δ: 1.472 (d, 6 H, 2 CH3, J = 12.4 Hz); 1.479 (d, 6 H,
2 CH3, J = 13.9 Hz); 6.17 (d, 1 H, P—H, J = 440.9 Hz). 31P NMR
(H2O/acetone), δ: 55.4 (dm, J = 450.0 Hz, J = 13.9 Hz). MS
(ESI), m/z (Irel (%)): 189.0 [M + Na]+ (21).
Experimental
All the experiments were carried out under dry nitrogen using
a standard Schlenk line. Solvents were purified by distillation
immediately before use. White phosphorus used in the reactions
was purified by a solution of potassium dichromate and concenꢀ
trated sulfuric acid with subsequent recrystallization from the
solution in DMF. The thus obtained phosphorus was rolled into
balls in the molten state (50 °C) with stirring on a magnetic
stirrer with subsequent cooling. Immediately before use, the white
phosphorus was sequentially washed with ethanol, acetone, and
diethyl ether. It is important to take precautions: the white phosꢀ
phorus P4 and phosphine PH3 are very toxic, flammable, and
dangerous compounds, which require special handling condiꢀ
tions in completely inert media in a well ventilated room.
Dichloromethane was purified by distillation immediately
before use and stored in the dark in stoppered Schlenk flasks
under nitrogen. Commercial acetone (99%, Aldrich), butanone
(99%, Aldrich), pentanꢀ2ꢀone (98%, Aldrich), tertꢀbutyl methyl
ketone (98%, Aldrich), and hydrochloric acid (37%, Sigma—
Aldrich) were used without additional purification.
1ꢀHydroxyꢀ1ꢀmethylpropylphosphine oxide (7). 31P NMR
(H2O), δ: 26.3 (t.sext, J = 480.3 Hz, J = 15.0 Hz).
Bis(1ꢀhydroxyꢀ1ꢀmethylpropyl)phosphine oxide (8). 31P NMR
(H2O), δ: 55.8 (dm, J = 443.9 Hz); 54.3 (dm, J = 450.8 Hz). MS
(ESI), m/z (Irel (%)): 217.0 [M + Na]+ (28), 411.2 [2 M + Na]+
(100).
1ꢀHydroxyꢀ1ꢀmethylbutylphosphine oxide (9). 31P NMR
(H2O), δ: 27.3 (t.sext, J = 483.3 Hz, J = 13.2 Hz).
Bis(1ꢀhydroxyꢀ1ꢀmethylbutyl)phosphine oxide (10). 31P NMR
(H2O), δ: 53.2 (br.m).
Hypophosphorous acid H3PO2. 31P NMR, δ: 6.51 (t, J =
= 517.3 Hz).
Preparative electrolysis was carried out in a hermetically
sealed undivided electrolyzer20,21 equipped with an electrochemꢀ
ically soluble Al anode in galvanostatic regime (I = 150 mA)
using a B5ꢀ71/1U source of direct current.8 The cathode (Pb)
working surface was 32 cm2. The working electrode (cathode)
potential was detected by a Shch50ꢀ1 DC voltmeter relative to
the reference electrode Ag/AgNO3, 0.01 M solution in MeCN
(E°(Fc/Fc+) = +0.20 V). In the course of electrolysis, the workꢀ
ing electrode potential did not exceed –2.5 V.
Phosphorous acid H3PO3. 31P NMR, δ: 3.12 (d, J =
= 669.1 Hz).
This work was financially supported by the Russian
Science Foundation (Project No. 14ꢀ13ꢀ01122).
References
1H and 31P NMR spectra were recorded at room temperaꢀ
ture (25 °C) on Bruker MSLꢀ500 (500.1 MHz) and Bruker
1. Technology Vision 2020. The US Chemical Industry, Ameriꢀ
can Chem. Soc., Washington, 1996, 75 pp.