A shortcut to tris[2-(4-hydroxyphenyl)ethyl]phosphine oxide and 2-(4-hydroxyphenyl)ethylphosphinic acid via reaction of elemental phosphorus with 4-tert-butoxystyrene

Article abstract of DOI:10.1016/j.mencom.2013.12.009

Red phosphorus reacts with 4-tert-butoxystyrene in KOH/DMSO system to afford (depending on the reaction conditions) tris(4-tert-but- oxyphenylethyl)phosphine oxide (48% yield) and/or 4-tert- butoxyphenylethylphosphinic acid (30% yield). The treatment of these products with aqueous HCl (45 °C, 5 min) quantitatively delivers tris[2-(4- hydroxyphenyl)ethyl]phosphine oxide and 2-(4-hydroxyphenyl)ethyl-phosphinic acid.

Full text of DOI:10.1016/j.mencom.2013.12.009

Mendeleev
Communications
Mendeleev Commun., 2014, 24, 29–31
A shortcut to tris[2-(4-hydroxyphenyl)ethyl]phosphine oxide
and 2-(4-hydroxyphenyl)ethylphosphinic acid via reaction
of elemental phosphorus with 4-tert-butoxystyrene
Alexander V. Artem’ev,a Nina K. Gusarova,a Anastasiya O. Korocheva,a
Svetlana F. Malysheva,a Yurii V. Gatilovb and Boris A. Trofimov*a
a A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
664033 Irkutsk, Russian Federation. Fax: +7 3952 41 9346; e-mail: boris_trofimov@irioch.irk.ru
b N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy
of Sciences, 630090 Novosibirsk, Russian Federation
DOI: 10.1016/j.mencom.2013.12.009
Red phosphorus reacts with 4-tert-butoxystyrene in KOH/DMSO system to afford (depending on the reaction conditions) tris(4-tert-but-
oxyphenylethyl)phosphine oxide (48% yield) and/or 4-tert-butoxyphenylethylphosphinic acid (30% yield). The treatment of these products
with aqueous HCl (45°C, 5 min) quantitatively delivers tris[2-(4-hydroxyphenyl)ethyl]phosphine oxide and 2-(4-hydroxyphenyl)ethyl-
phosphinic acid.
Organophosphorus compounds such as phosphines, phosphine
oxides, phosphinic acids are important intermediates in organic
synthesis.1 They find wide application as ligands for metal
complexes, flame retardants, extractants, drug precursors, and
capping ligands for the growing of nanocrystals.1 A special atten-
tion attracts functional organophosphorus compounds bearing,
for example, phenolic (hydroxylphenyl) moieties. Such com-
pounds are used as reactive building blocks for organic synthesis2
and additives for design of flame retardant polymer composi-
tions.3 However, syntheses of these compounds now are fairly
laborious. For instance, tris(4-hydroxyphenyl)phosphine oxide
has been prepared by the multistep method using both moisture-
sensitive and aggressive compounds, e.g., Grignard reagent, POCl3,
BBr3.4 Moreover, anhydrous solvents and inert atmosphere are
required for this synthesis.
Here we report a novel convenient approach to the earlier
unknown 4-hyroxyphenyl tethered tertiary phosphine oxide and
phosphinic acid starting from commercially available 4-tert-but-
oxystyrene and elemental phosphorus.
Direct phosphorylation of 4-tert-butoxystyrene with red phos-
phorus effectively proceeded in the KOH/DMSO(H2O) suspension
at 130°C for 3 h (the molar ratio styrene/P/KOH∙0.5H2O/H2O ~
1.3:1:4.7:1.1) to afford mainly tertiary phosphine 1 and its oxide
2 in ca. 1:1 ratio (Scheme 1). By oxidation of this mixture with
H2O2 (H2O/EtOH, ambient temperature), phosphine oxide 2 was
isolated in 48% yield (based on 4-tert-butoxystyrene).†
Under the milder conditions (100°C, 2 h, and the molar ratio
styrene/P/KOH∙0.5H2O/H2O ~ 1:2.9:4.5:6.5), the major pro-
duct was acid 3 (in a salt form) isolated in 30% yield (based on
4-tert-butoxystyrene) by acidification of the reaction mixture
with aqueous HCl (Scheme 2).‡ Additionally, 2-(4-tert-butoxy-
phenyl)ethylphosphine 4 and bis[2-(4-tert-butoxyphenyl)ethyl]-
phosphine 5 were formed as minor products (31P NMR).
The structures of phosphines 1, 4 and 5 have been confirmed
by their counter synthesis via hydrophosphination of tert-butoxy-
styrene with PH3/H2 mixture in KOH/DMSO(H2O) system at
70°C. These results will be published elsewhere.
†
1H, 13C and 31P NMR spectra (400.13, 100.62 and 161.98 MHz, respec-
tively) were recorded on a Bruker DPX-400 spectrometer at ambient
temperature and referenced to internal HDMS (1H, 13C) and external
85% H3PO4 (31P) standards. FT-IR spectra were recorded on a Bruker
Vertex 70 spectrometer. The microanalyses were performed on a Flash
EA 1112 Series elemental analyzer. Melting points (uncorrected) were
determined on a Kofler micro hot stage apparatus. tert-Butoxystyrene,
KOH∙0.5H2O, DMSO (1% water content) and red phosphorus (KSAN
‘SIA’) were employed as purchased. The reactions with elemental phos-
phorus were carried out under argon atmosphere.
i
Tris[2-(4-tert-butoxyphenyl)ethyl]phosphine oxide 2. A mixture of
red phosphorus (0.8 g, 26 mmol), tert-butoxystyrene (6.0 g, 34 mmol),
KOH∙0.5H2O (8.0 g, 123 mmol), DMSO (40 ml) and water (0.5 ml) was
stirred at 130°C for 3 h, cooled and analyzed. The 31P NMR spectrum of the
reaction mixture reveals the presence of tertiary phosphine 1 (dP –28 ppm)
and its oxide 2 (dP 45 ppm) as well as minor amounts of potassium salt 3
[dP 19 ppm (d, 1JPH 465 Hz)]. The mixture was diluted with water (50 ml),
passed through the glass filter and extracted with chloroform (3×20 ml).
The extract was washed with water (2×40 ml) and the solvent was removed.
The residue was dissolved in EtOH (10 ml) and aqueous H2O2 (30%, 2 ml)
was added to resulting solution. The mixture was stirred at ambient tem-
perature for 10 min, then diluted with water (30 ml) and extracted with
chloroform (2×20 ml). The extract was evaporated and the residue was
dried in vacuo (1 Torr) to give 3.15 g (48%) of phosphine oxide 2 as viscous
OBut
+
Pred
OBut
OBut
O
P
ButO
ButO
+
P
OBut
OBut
1
2
1
oil. H NMR (CDCl3) d: 1.30 (s, 27H, Me), 2.03–2.12 (m, 6H, CH2P),
ii
2.81–2.93 (m, 6H, CH2C6H4), 6.84 (d, 6H, C6H4, 3JHH 8.4 Hz), 7.40 (d,
6H, C6H4, 3JHH 8.4 Hz). 31P{1H} NMR (CDCl3) d: 46.97. FT-IR (film,
n/cm–1): 1170 (P=O). Found (%): C, 74.66; H, 8.90; P, 5.27. Calc. for
C36H51O4P (%): C, 74.71; H, 8.88; P, 5.35.
48%
Scheme 1 Reagents and conditions: i, KOH/DMSO(H2O), 130°C, 3 h;
ii, H2O2/H2O/EtOH, room temperature.
© 2014 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2014, 24, 29–31
H
OH
O
C(7A)
O(1)
C(12)
C(6A)
C(8A)
C(2A)
P
C(9)
i, ii
P(1)
C(3A)
+ Pred
C(1A)
O(3)
C(11)
C(5A)
ButO
ButO
O(2)
C(4A)
C(10)
3, 30%
[ + 4-ButOC6H4CH2CH2PH2 + (4-ButOC6H4CH2CH2)2PH ]
Figure 1 ORTEP diagram of acid 3 with 30% probability ellipsoids (minor
disorder component B omitted for clarity).
4
5
solvents. Moreover, acid 7 is well soluble in hot water. All the
compounds were characterized by 1H, 13C and 31P NMR as well
as IR spectroscopy. The molecular structure of acid 3 was
established by X-ray diffractometry (Figure 1).¶ The phenyl-
ethyl fragment is disordered over two positions in 0.56(2):0.44(2)
ratio. The But group and [CH2P(O)OH(H)] unit are disposed on
opposite sides of the average [OC6H4CH2] plane: the value of
C(9)O(3)C(2A)C(1A) torsion angle is 179.5°. The packing
diagram of 3 along the a axis reveals the presence of strong
intermolecular P=O∙∙∙HO hydrogen bonding to form a 1D supra-
molecular array.
Scheme 2 Reagents and conditions: i, KOH/DMSO(H2O), 100°C, 2 h;
ii, HCl/H2O, room temperature, up to pH ~ 2–3.
Subsequently, the exhaustive removal of the tert-butyl group
from compounds 2 and 3 was achieved by treatment with 36%
aqueous HCl under mild conditions (45°C, EtOH/H2O, 5 min)
to give the target phenol phosphorus derivatives 6 and 7 in nearly
quantitative yields (Scheme 3).§
The synthesized compounds 3, 6, 7 are air-stable crystalline
powders (phosphine oxide 2 is oil), soluble in polar organic
OH
In summary, we have accessed hitherto unknown tris[2-(4-hy-
droxyphenyl)ethyl]phosphine oxide and 2-(4-hydroxyphenyl)-
ethylphosphinic acid by direct reaction of red phosphorus with
4-tert-butoxystyrene in KOH/DMSO system, followed by treat-
ment of the formed products with HCl to afford the target com-
pounds. The latter are prospective ligands for design of metal
complexes, building blocks for synthesis of branched molecules
and 3D structures as well as promising capping agents for
stabilizing of nanoparticles. Potentially, phosphine oxide 6 and
acid 7 may be applied as promising antiseptics and flame-proofing
additives in synthesis of phenol formaldehyde resins. Moreover,
this result extends the scope of the methodology of the synthesis
of important organophosphorus compounds involving cleavage of
elemental phosphorus in strongly basic media.5
OH
H
P
O
P
O
HO
i
i
2
3
HO
OH
6, 95%
7, 97%
Scheme 3 Reagents and conditions: i, HCl/H2O, EtOH, 45°C, 5 min.
‡
[2-(4-tert-Butoxyphenyl)ethyl]phosphinic acid 3. A mixture of red
phosphorus (3.1 g, 100 mmol), tert-butoxystyrene (6.0 g, 34 mmol),
KOH∙0.5H2O (10.0 g, 153 mmol), DMSO (40 ml) and water (4 ml) was
stirred for 2 h at 100°C, cooled and analyzed. The 31P NMR spectrum of
reaction mixture reveals the presence of potassium salt of acid 3 [dP 19 ppm
(d, 1JPH 465 Hz)], primary phosphine 4 [dP –137 ppm (t, 1JPH 195 Hz)] and
secondary phosphine 5 [dP –69 ppm (d, 1JPH 200 Hz)] in a 27:2:1 molar
ratio. Then the mixture was diluted with water (50 ml), passed through
the glass filter and extracted with chloroform (3×20 ml). The aqueous
layer was acidified with aqueous HCl (up to pH ~ 2) and extracted with
chloroform (3×20 ml). The extract was washed with water (2×40 ml)
and dried over Na2SO4. The solvent was removed, then the residue was
reprecipitated from water–ethanol mixture and dried in vacuo (1 Torr) to
give 2.47 g (30%) of phosphinic acid 3. Colourless crystals, mp 74–76°C.
1H NMR (CDCl3) d: 1.31 (s, 9H, Me), 2.02–2.11 (m, 2H, CH2P), 2.83–2.91
[2-(4-Hydroxyphenyl)ethyl]phosphinic acid 7. To a suspension of com-
pound 3 (2.0 g, 8 mmol) in ethanol (10 ml), aqueous HCl (36%, 3 ml) was
added and the mixture was stirred at 45°C for 5 min. This was accompanied
by dissolution of acid 3 precipitate and evolution of gaseous products.
The resulting solution was cooled to room temperature and the solvents
were removed in vacuo (1 Torr) to give 1.49 g (97%) of acid 7. Colourless
1
crystals, mp 130–132°C (H2O). H NMR (DMSO-d6) d: 1.81–1.90 (m,
2H, CH2P), 2.62–2.69 (m, 2H, CH2C6H4), 3.96 (br.s, 1H, OH), 6.66 (d,
2H, C6H4, 3JHH 8.5 Hz), 6.94 (d, 1H, PH, 1JPH 520.8 Hz), 7.02 (d, 2H, C6H4,
3JHH 8.5 Hz), 9.17 (br. s, 1H, P–OH). 13C NMR (DMSO-d6) d: 26.0
1
(CH2C6H4), 31.7 (d, CH2P, JPC 90.5 Hz), 115.3 (C-3,5 in C6H4), 129.0
(C-2,6 in C6H4), 131.0 (d, C-1 in C6H4, 3JPC 15.8 Hz), 155.7 (C-4 in C6H4).
31P{1H} NMR (DMSO-d6) d: 31.02 (d, 1JPH 520 Hz). FT-IR (KBr, n/cm–1):
3303 (OH), 2442 (P–H), 1148, 1134 (d, P=O). Found (%): C, 51.68;
H, 5.91; P, 16.49. Calc. for C8H11O3P (%): C, 51.62; H, 5.96; P, 16.64.
3
(m, 2H, CH2C6H4), 6.89 (d, 2H, C6H4, JHH 8.4 Hz), 7.07 (d, 1H, PH,
1JPH 546 Hz), 7.08 (d, 2H, C6H4, 3JHH 8.4 Hz), 11.42 (br.s, 1H, OH). 13C NMR
(CDCl3) d: 26.1 (CH2C6H4), 28.8 (Me), 31.0 (d, CH2P, JPC 93.2 Hz),
1
78.2 (CMe3), 124.3 (C-3,5 in C6H4), 128.4 (C-2,6 in C6H4), 134.8 (d, C-1
¶
Crystal data. X-ray quality crystals of acid 3 were obtained by slow
in C6H4, 3JPC 15.5 Hz), 153.9 (C-4 in C6H4). 31P{1H} NMR (CDCl3) d:
evaporation of its ethanol solution at room temperature over several days.
C12H19O3P, M = 242.24, orthorhombic, space group P212121, a = 6.068(2),
b = 11.010(3) and c = 19.672(6) Å, V = 1314.3(7) Å3, T = 200(2) K, Z = 4,
dcalc = 1.224 g cm–3, F(000) = 520.0, m(MoKa) = 0.200 mm–1, 5448
reflections collected, 1703 independent reflections (Rint = 0.0474), final R
indexes [I > 2s(I)]: R1 = 0.0884, wR2 = 0.2010; final R indexes [all data]:
R1 = 0.1304, wR2 = 0.2463. Data were collected on a BrukerApex II CCD
diffractometer using graphite monochromated MoKa radiation (l =
= 0.71073 Å). The structure was solved by direct methods and refined by
full-matrix least-squares method against all F2 in anisotropic approxi-
mation for non-hydrogen atoms using the SHELX-97 programs set.6
Non-hydrogen atoms were refined anisotropically using SHELX-97.6 The
phenylethyl fragment is disordered over two position in 0.56(2):0.44(2)
ratio. Hydrogen atoms were included at geometrically calculated positions
during the refinement using the riding model.
36.27 (d, JPH 546 Hz). FT-IR (KBr, n/cm–1): 2349 (P–H), 1161, 1176
1
(d, P=O). Found (%): C, 59.45; H, 7.78; P, 12.73. Calc. for C12H19O3P (%):
C, 59.50; H, 7.91; P, 12.79.
Tris[2-(4-hydroxyphenyl)ethyl]phosphine oxide 6. To a solution of
phosphine oxide 2 (3.5 g, 6 mmol) in ethanol (10 ml), aqueous HCl (36%,
3 ml) was added and the mixture was stirred at 45°C for 5 min. This was
accompanied by evolution of gaseous products. The resulting solution
was cooled to room temperature and the solvents were removed in vacuo
(1 Torr) to give 2.36 g (95%) of phosphine oxide 6 as dough-like substance.
The recrystallization of the latter from hot PriOH gives colourless crystals,
mp 213–215°C. 1H NMR (DMSO-d6) d: 1.90–1.97 (m, 6H, CH2P), 2.66–
2.72 (m, 6H, CH2C6H4), 6.70 (d, 6H, C6H4, JHH 8.1 Hz), 7.05 (d, 6H,
C6H4, 3JHH 8.0 Hz), 9.21 (br.s, 3H, OH). 13C NMR (DMSO-d6) d: 26.2
(CH2C6H4), 29.2 (d, CH2P, JPC 61.7 Hz), 115.2 (C-3,5 in C6H4), 129.0
(C-2,6 in C6H4), 131.3 (d, C-1 in C6H4, 3JPC 13.0 Hz), 155.7 (C-4 in C6H4).
31P{1H} NMR (DMSO-d6) d: 49.81. FT-IR (KBr, n/cm–1): 3376 (OH),
1102, 1088 (d, P=O). Found (%): C, 70.14; H, 6.61; P, 7.38. Calc. for
C24H27O4P (%): C, 70.23; H, 6.63; P, 7.55.
§
3
1
CCDC 950470 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.ac.uk. For details, see
‘Notice to Authors’, Mendeleev Commun., Issue 1, 2014.
– 30 –

Mendeleev Commun., 2014, 24, 29–31
This work was supported by the Russian Foundation for Basic
Research (grant no. 12-03-31097 mol_a).
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Received: 27th August 2013; Com. 13/4191
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