Reaction of 4,4′-dimethyldiphenyl ether with phosphorus trichloride in the presence of anhydrous aluminum chloride

Article abstract of DOI:10.1007/s11172-005-0209-4

The reaction of 4,4′-dimethyldiphenyl ether with phosphorus trichloride in the presence of anhydrous aluminum chloride was studied. This reaction affords 2,8-dimethyl-10H-10λ⁵-phenoxaphosphine 10-oxide as virtually the only product. In air, the latter in an alkaline solution is quantitatively transformed into 10-hydroxy-2,8-dimethyl-10H- 10λ⁵-phenoxaphosphine 10-oxide.

Full text of DOI:10.1007/s11172-005-0209-4

Russian Chemical Bulletin, International Edition, Vol. 53, No. 12, pp. 2881—2883, December, 2004
2881
Reaction of 4,4´ꢀdimethyldiphenyl ether with
phosphorus trichloride in the presence of anhydrous aluminum chloride
ꢀ
I. I. Ponomarev, Yu. Yu. Rybkin, E. I. Goryunov, P. V. Petrovskii, and K. A. Lyssenko
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: rybkin@ineos.ac.ru
The reaction of 4,4´ꢀdimethyldiphenyl ether with phosphorus trichloride in the presence of
5
anhydrous aluminum chloride was studied. This reaction affords 2,8ꢀdimethylꢀ10Hꢀ10λ ꢀ
phenoxaphosphine 10ꢀoxide as virtually the only product. In air, the latter in an alkaline
5
solution is quantitatively transformed into 10ꢀhydroxyꢀ2,8ꢀdimethylꢀ10Hꢀ10λ ꢀphenoxaꢀ
phosphine 10ꢀoxide.
Key words: 4,4´ꢀdimethyldiphenyl ether, phosphorylation of aromatic compounds, phosꢀ
5
phorus trichloride, 2,8ꢀdimethylꢀ10Hꢀ10λ ꢀphenoxaphosphine 10ꢀoxide.
Polyheteroarylenes are of great interest as thermally
stable and heatꢀ and fireꢀresistant systems,1 matrices for
catalyst immobilization, and solid electrolytes for protonꢀ
conducting membranes.2 One of promising classes of
polyheteroarylenes3 includes aromatic polybenzimidazoles
based on dicarboxylic acids and tetramines.4—7 The aim
of the present study was to synthesize new types of
polybenzimidazoles containing hydroxyphosphoryl fragꢀ
ments chemically bound to the polymer chain. It should
be noted that the attachment of the P atom through P—C
bonds is optimal for providing high chemical and thermal
stability of such polymers,8 and the system can be addiꢀ
tionally stabilized if the P atom is simultaneously involved
in a fused aromatic heterocycle.
However, we found that the Friedel—Crafts reaction
followed by hydrolysis of the reaction mixture under the
conditions, which were completely identical to those
described earlier,10 afforded 2,8ꢀdimethylꢀ10Hꢀ10λ5ꢀ
phenoxaphosphine 10ꢀoxide (3) (Scheme 1) rather than
phosphinic acid 1. Compound 3 was isolated in 84% yield.
Therefore, the results of our investigation reject the asꢀ
sumption of the intermediate formation of phosphoric
acid chloride.
Scheme 1
Taking into account the data presented in the monoꢀ
graph,9 it can be concluded that 10ꢀhydroxyꢀ2,8ꢀdiꢀ
methylꢀ10Hꢀ10λ5ꢀphenoxaphosphine 10ꢀoxide (1) (after
its oxidation to the corresponding dicarboxylic acid) is
the most interesting phosphorusꢀcontaining fused heteroꢀ
cyclic system suitable for the construction of hydroxyꢀ
phosphorylꢀcontaining polybenzimidazoles. Earlier,10 it
has been demonstrated that compound 1 can be prepared
in high yield from readily available compounds, such as
PCl3, AlCl3, and 4,4´ꢀdimethyldiphenyl ether. It has been
suggested10 that intramolecular Friedel—Crafts cyclizaꢀ
tion initially affords acid chloride 2 followed by its oxidaꢀ
tion to acid chloride of pentavalent phosphorus, whose
hydrolysis gives compound 1.
Phosphine oxide 3 was prepared as a white powder,
which does not melt up to 300 °C. Its structure was conꢀ
firmed by elemental analysis and NMR spectroscopy (1H,
1
31P, and 31P{1H}). The H NMR spectrum has a doublet
at δ 8.50 with the spinꢀspin coupling constant of 527.4 Hz.
Since the virtually identical constant is observed in the
31P NMR spectrum (see the Experimental section), this
signal can be assigned with certainty to the proton of the
P—H fragment of molecule 3. Phosphine oxide 3 is rather
stable to atmospheric oxygen both in the solid state and in
organic solvents (for example, in DMSO), but it is
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2762—2765, December, 2004.
1066ꢀ5285/04/5312ꢀ2881 © 2004 Springer Science+Business Media, Inc.

2882
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 12, December, 2004
Ponomarev et al.
C(12´)
C(13´)
C(11´)
C(10´)
very rapidly oxidized upon treatment with an aqueous
KOH solution in air to give hydroxyphosphine oxide 1
(Scheme 2).
C(14´)
C(5´)
C(6´)
C(9´)
O(1´)
Scheme 2
C(4´)
C(8´)
P(1´)
C(3´)
C(1´)
C(2´)
C(7´)
O(1)
O(3)
C(14)
P(1)
C(1)
C(9)
C(2)
C(8)
The structure of compound 1 was also confirmed by
elemental analysis and NMR spectroscopy (1H and
31P{1H}). The 1H NMR spectrum shows a broad singlet at
δ 4.75 belonging to the proton of the P—OH group inꢀ
stead of a doublet for the proton of P—H. Compound 1 is
stable in air up to 300 °C.* At temperatures higher than
350 °C, compound 1 is dehydrated in vacuo to form
pyrophosphinate 4 (Scheme 3).
C(7)
C(10)
C(11)
C(3)
C(13)
O(2)
C(6)
C(5)
C(12)
C(4)
Fig. 1. Overall view of molecule 4 in the crystal. The H atoms
are omitted.
Scheme 3
to elongation of the P(1´)—O(3) bond (1.628(2) Å)
compared to the P(1)—O(3) bond (1.602(2) Å), the
P(1)—O(1) bond being only slightly longer than the
P(1´)—O(1) bond (Table 1).
Since the P atoms in the 31P{1H} NMR spectrum of a
solution of compound 4 are indistinguishable (singlet at
δ 2.43), the phosphoryl groups are located, presumably,
in cis positions.
In air, anhydride 4 is rapidly hydrolyzed to give again
the starting compound 1. This process occurs much more
extensively in waterꢀcontaining polar organic solvents.
The structure of anhydride 4 was established by Xꢀray
diffraction analysis. Both phosphorusꢀcontaining heteroꢀ
cycles in pyrophosphinate 4 are planar, but their strucꢀ
tures are slightly different (Fig. 1).** The phosphoryl group
P(1)=O(1), unlike P(1´)—O(1´), is located above the
plane of the adjacent phosphorusꢀcontaining ring. The
shortest intramolecular O(1)...C(8) and O(1)...C(13) disꢀ
tances (3.071(2) and 3.128(2) Å, respectively) are slightly
smaller than the sum of the corresponding van der Waals
radii (3.31 Å). The O(1)—P(1)—P(1´)—O(1´) pseudoꢀ
torsion angle is 163°. The dihedral angle between the
planes of the rings is 128.4°. 1
Table 1. Selected bond lengths (d) and bond angles (ω) in the
crystal of compound 4
Bond
d/Å
Bond
d/Å
P(1)—O(1)
P(1)—O(3)
P(1)—C(1)
P(1)—C(8)
O(2)—C(6)
O(2)—C(13)
1.470(2) P(1´)—O(3)
1.602(2) P(1´)—O(1´)
1.764(3) P(1´)—C(1´)
1.760(3) P(1´)—C(8´)
1.367(4) O(2´)—C(6´)
1.372(4) O(2´)—C(13´)
1.628(2)
1.460(2)
1.753(3)
1.767(3)
1.375(4)
1.366(4)
Angle
ω/deg
Angle
ω/deg
O(1)—P(1)—C(1) 115.5(1) O(1´)—P(1´)—O(3)
107.0(1)
O(1)—P(1)—O(3) 112.5(1) O(1´)—P(1´)—C(1´) 117.2(1)
O(1)—P(1)—C(8) 117.0(1) O(3)—P(1´)—C(1´) 104.7(1)
O(3)—P(1)—C(1) 104.9(1) O(1´)—P(1´)—C(8´) 117.1(1)
O(3)—P(1)—C(8) 102.3(1) O(3)—P(1´)—C(8´) 106.6(1)
C(8)—P(1)—C(1) 102.9(1) C(1´)—P(1´)—C(8´) 103.2(1)
C(13)—O(2)—C(6) 123.5(2) C(6´)—O(2´)—C(13´) 123.7(2)
P(1)—O(3)—P(1´) 132.0(1)
The differences in the positions of the phosphoryl
groups lead to changes in the bond lengths and, primarily,
* Solutions of this compound in organic solvents are also stable.
** The P atoms in the heterocycles are characterized by a slightly
distorted tetrahedral coordination with the intramolecular
C—P—C angle decreased to 102.9(1)°.

Reaction of bis(4ꢀmethylphenyl) ether
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 12, December, 2004 2883
P, 11.95. C14H13O3P. Compound (%): C, 64.62; H, 5.03;
Apparently, this conformation of molecule 4 is stabiꢀ
lized in the crystal due partially to stacking interactions
between the aromatic rings. In the crystal structure, molꢀ
ecules 4 are linked to form centrosymmetric dimers
through the C(1´)—C(14´) interaction of the ring with
the shortest C...C distance of 3.360(2) Å. In addition to
the stacking interactions, there is also a rather strong
C—H...O contact, viz., P(1´)—O(1´)…H(14E)—C(14´)
(H...O, 2.18 Å; C—H—O, 169°), through which the
dimers are linked to each other to form layers parallel to
the crystallographic plane bc.
P, 11.90. 1H NMR (DMSOꢀd6), δ: 2.38 (s, 6 H, Me); 4.75 (br.s,
3
4
1 H, OH); 7.26 (dd, 2 H, H(4), H(6), JH,H = 8.0 Hz, JH,P
=
7.2 Hz); 7.46 (d, 2 H, H(3), H(7), 3JH,H = 8.4 Hz); 7.59 (d, 2 H,
H(1), H(9), JH,P = 13.6 Hz). 31P{1H} NMR (DMSOꢀd6),
3
δ: 3.56 s.
5
2,8ꢀDimethylꢀ10ꢀ[(2,8ꢀdimethylꢀ10ꢀoxoꢀ10Hꢀ10λ ꢀ
phenoxaphosphinꢀ10ꢀyl)oxy]ꢀ10Hꢀ10λ ꢀphenoxaphosphine
5
10ꢀoxide (4) was prepared in quantitative yield by vacuum subliꢀ
mation of compound 1 at 350 °C. M.p. > 350 °C. 31P{1H} NMR
(DMSOꢀd6), δ: 2.43 c.
Xꢀray diffraction study of phosphine oxide 4 (C28H24O5P2)
was carried out on an automated threeꢀcircle Smart CCD
diffractometer (MoꢀKα radiation, graphite monochromator,
Experimental
ω scanning technique, 2θ
= 52°). Crystals at 110 K are triꢀ
max
clinic, a = 8.391(3) Å, b = 9.758(4) Å, c = 15.684(6) Å,
α = 100.535(9)°, β = 100.663(9)°, γ = 108.580(9)°, V =
1155.2(8) Å3, dcalc = 1.444 g cm–3, M = 502.41, F(000)= 524,
µ = 2.28 cm–1, Z = 2, space group P–1. Of a total of 5900 meaꢀ
sured reflections, 4142 independent reflections (Rint = 0.0263)
were used in subsequent calculations and refinement. The strucꢀ
ture was solved by direct methods and refined by the fullꢀmatrix
leastꢀsquares method with anisotropic displacement parameters
for nonhydrogen atoms against F2hkl. The H atoms were revealed
from difference Fourier syntheses and refined using a riding
model. The final reliability factors were as follows: wR2 = 0.1392,
GOF = 1.092 using all reflections (R = 0.0600 based on
3174 reflections with I > 2σ(I )). All calculations were carried
out on IBMꢀPC/AT using the SHELXTL PLUS program
package.
The 1H and 31P NMR spectra were recorded on a Bruker
AMXꢀ400 instrument (400.13 and 161.98 MHz, respectively) in
DMSOꢀd6. The chemical shifts δ were calculated with respect to
the residual signals for the protons of the deuterated solvent as
the internal standard (1H) and 85% H3PO4 as the external stanꢀ
dard (31P).. The melting points were measured on a Boetius hotꢀ
stage apparatus and are uncorrected. The course of the reactions
and the purity of the reaction products were monitored by TLC
on Silufol UVꢀ254 plates using a PhCH3—MeOH mixture as
the eluent. Phosphorus trichloride (ReaKhim) was purified by
distillation, and aluminum chloride (ReaKhim) was subꢀ
limed under vacuum at 300 °C. 4,4´ꢀDimethyldiphenyl ether
(Donetsk Plant of Chemical Reagents) was characterized by
m.p. 49—52 °C .
5
2,8ꢀDimethylꢀ10Hꢀ10λ ꢀphenoxaphosphine 10ꢀoxide (3). Anꢀ
hydrous freshly sublimed AlCl3 (8.5 g, 0.064 mol), 4,4´ꢀdiꢀ
methyldiphenyl ether (9.9 g, 0.05 mol), and freshly distilled
PCl3 (27.4 g, 0.2 mol) were placed in a roundꢀbottom flask
equipped with a reflux condenser and a calcium chloride tube.
The reaction mixture was heated at 80 °C for 22 h. The oily
product was poured onto ice. After 3—4 h, the precipitate that
formed was separated, washed with distilled water to neutral
pH, and dried in a vacuum desiccator at 100 °C for 4 h to
prepare compound 3 in a yield of 10.2 g (84%), m.p. > 300 °C.
Found (%): C, 68.54; H, 5.64; P, 12.54. C14H13O2P. Comꢀ
pound (%): C, 68.85; H, 5.36; P, 12.68. 1H NMR (DMSOꢀd6),
δ: 2.40 (s, 6 H, Me); 7.33 (dd, 2 H, H(4), H(6), 3JH,H = 8.6 Hz,
References
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3
4JH,P = 6.2 Hz); 7.57 (dd, 2 H, H(3), H(7), JH,H = 8.8 Hz,
3
4JH,H = 1.6 Hz); 7.75 (dd, 2 H, H(1), H(9), JH,P = 14.0 Hz,
4JH,H = 1.6 Hz); 8.50 (d, 1 H, PH, 1JH,P = 527.4 Hz). 31P NMR
(DMSOꢀd6), δ: –16.24* (dtt, 1JH,P = 527.7 Hz, 3JP,H = 14.0 Hz,
4JH,P = 6.1 Hz).
5
10ꢀHydroxyꢀ2,8ꢀdimethylꢀ10Hꢀ10λ ꢀphenoxaphosphine
10ꢀoxide (1). Phosphine oxide 3 (10.0 g, 0.04 mol) was dissolved
in a minimum volume of a 10% aqueous KOH solution. The
solution was filtered, and the filtrate was acidified with concenꢀ
trated HCl to pH 2. The precipitate that formed was separated,
washed with distilled water to pH 7, and dried in a vacuum
desiccator at 100 °C for 6 h to prepare compound 1 in a yield of
9.80 g (92%), m.p. > 300 °C. Found (%): C, 64.67; H, 5.04;
* The 31P NMR spectrum measured with proton noise deꢀ
coupling shows a singlet instead of this multiplet.
Received December 2, 2003;
in revised form September 6, 2004