Solubilities of diphenylphosphinic acid in selected solvents

Article abstract of DOI:10.1021/je800049b

Diphenylphosphinic acid (DPPA) was synthesized and characterized by infrared spectroscopy (IR), nuclear magnetic resonance (¹H NMR), mass spectroscopy (MS), and elemental analysis. The melting point and the enthalpy of fusion of DPPA were measured by a differential scanning calorimeter (DSC), and the thermal stability of DPPA was measured by thermogravimetric analysis (TGA). The solubility data of DPPA in nine solvents were measured and correlated with an empirical equation. The estimated uncertainty of all the solubility values based on error analysis and repeated observations was within 2.0 %.

Full text of DOI:10.1021/je800049b

1192
J. Chem. Eng. Data 2008, 53, 1192–1195
Solubilities of Diphenylphosphinic Acid in Selected Solvents
Gai-Qing Zhang, Li-Sheng Wang,* Rui-Lan Fan, Xian-Zhao Shao, and Xiao-Fang Wang
School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing 100081, People’s Republic of China
Diphenylphosphinic acid (DPPA) was synthesized and characterized by infrared spectroscopy (IR), nuclear
magnetic resonance (1H NMR), mass spectroscopy (MS), and elemental analysis. The melting point and the
enthalpy of fusion of DPPA were measured by a differential scanning calorimeter (DSC), and the thermal
stability of DPPA was measured by thermogravimetric analysis (TGA). The solubility data of DPPA in
nine solvents were measured and correlated with an empirical equation. The estimated uncertainty of all the
solubility values based on error analysis and repeated observations was within 2.0 %.
Introduction
Diphenylphosphinic acid (here after abbreviated as DPPA;
its formula is shown in Figure 1) (CASRN 1707-03-5) and its
anhydride have been widely used as a reactive flame-retardant
in epoxy resin based laminates for printed circuit boards.1,2
Recently, it has been used as an efficient promoter for the
palladium catalytic systems.3–6 Attention has also been given
Figure 1. Structure of diphenylphosphinic acid.
to the chemistry of molecular assemblies including host-guest
complexes between the DPPA derivative and amine-containing
hosts.7 In the preparation of DPPA, according to the literature,8
Table 1. Mass Fraction Purity (ω), Density (G), and Refractive
Index (nD) for the Organic Solvents used in This Work at T )
the product was finally isolated from its aqueous sodium
hydroxide solution by acidification with dilute hydrochloride
293.15 K
solvent
ethanol
isopropyl alcohol
2-ethoxyethanol
acetic acid
ethyl acetate
acetone
benzene
ω/%
F/g·cm-3
nD
acid and then washed with water. To improve its purity, it was
necessary to carry out the recrystallization of DPPA in organic
solvents. Knowledge of the solubilities of DPPA in solvents is
important for its preparation and purification. These data were
not available in the literature.
In this study, DPPA was synthesized and characterized. The
solubilities of DPPA in different solvents as required in the
purification process were measured.
99.7
99.7
99.5
99.5
99.5
99.5
99.5
99.5
0.789
0.785
0.929
1.049
0.900
0.790
0.879
0.866
1.3619
1.3993
1.4065
1.3718
1.3588
1.3590
1.5011
1.4967
methylbenzene
A jacketed equilibrium cell was used for the solubility
measurement with a working volume of 120 mL and a magnetic
stirrer, as described by Wang et al.9,10 A circulating water bath
was used with a thermostat (type 50 L, made from Shanghai
Laboratory Instrument Works Co., Ltd.), which is capable of
maintaining the temperature within ( 0.05 K. An analytical
balance (type TG328B, Shanghai Balance Instrument Works
Co.) with an uncertainty of ( 0.1 mg was used during the mass
measurements.
Experimental Section
Materials. All the chemicals in the synthesis and measurement
were analytical grade reagents, which were purchased from
Beijing Chemical Factory. They were used without further
purification. The mass fraction purities for the organic solvents
used in this work are listed in Table 1. Their mass fraction
purities were all higher than 99 %.
Apparatus and Procedure. The melting points and enthalpy
of fusion were determined with a DSC Q100 differential
scanning calorimeter (DSC) in flowing nitrogen at a heating
rate of 10 K ·min-1. The elemental analysis was performed on
an Elementar Vario EL element analyzer. IR spectra (Fourier
transform infrared (FTIR)) were recorded on a Magna-IR 750
using KBr pellets. Mass spectra were recorded by a VG-ZAB-
HS. 1H NMR and 31P NMR spectra were obtained with a
BrukerARX-400 and JEOL ECA-600, respectively. Thermo-
gravimetric analysis (TGA) was carried out with an SDT Q600
thermogravimetric analyzer at a heating rate of 10 K ·min-1
under nitrogen from (298.15 to 973.15) K.
Synthesis of DPPA. DPPA was prepared according to the
literature (Scheme 1).8 The product was then purified by
recrystallization from ethanol. The melting point of DPPA was
466.12 K (lit. (463.15 to 465.15) K,11 (465.15 to 467.15) K12).
IR (KBr): 2615 (O-H); 1129 (PdO); 964 (P-O); 1438 (P-Ph);
1
1589, 1485, 729, 695 cm-1 (Ph). MS (EI) m/z: 218(M)+. H
NMR (400 MHz, DMSO) ppm: δ ) 7.43 to 7.53 (m, 6H), 7.68
to 7.74 (m, 4H). 31P NMR (600 MHz, DMSO-d6) ppm: δ )
22.74 (s) (lit. 25.8113). Elemental analysis (%, calcd): C ) 65.76
% (66.05 %); H ) 5.35 % (5.09 %). Based on the above
analysis, the purity of DPPA used in this work was higher than
99.0 %.
ThermograWimetric Analysis. An SDT Q600 Simultaneous
DTA-TGA thermogravimetric analyzer was employed for
* Corresponding author. Fax: +86-10-68911040. E-mail: lishengwang@
btamail.net.cn.
10.1021/je800049b CCC: $40.75
2008 American Chemical Society
Published on Web 04/23/2008

Journal of Chemical & Engineering Data, Vol. 53, No. 5, 2008 1193
Scheme 1
Table 2. Results of Differential Scanning Calorimeter Measurement
of DPPA
thermogravimetric analysis (TGA) at a heating rate of 10
K·min-1 under nitrogen from (298.15 to 973.15) K. The
thermogravimetric curve of DPPA is shown in Figure 2. The
initial decomposition temperature of DPPA was around 572.98
K; the temperature at 92.63 % mass loss was 639.60 K; and
the char yield at 973.15 K was 5.478 %. Figure 3 shows the
results of differential scanning calorimeter (DSC) measurement
melting point/K
466.12
100.4
enthalpy of fusion/J ·g-1
of DPPA. The enthalpy of fusion of DPPA was 100.4 J ·g-1
.
The results of DSC measurement of DPPA are summarized in
Table 2.
Solubility Measurement. The solubilities were measured by
a gravimetric method.9,10 For each measurement, an excess mass
of DPPA was added to a known mass of solvent. Then the
equilibrium cell was heated to a constant temperature with
continuous stirring. After at least 2 h (the temperature of the
water bath approached constant value, then the actual value of
temperature was recorded), the stirring was stopped and the
solution was kept still until it was clear. A preheated injector
withdrew 2 mL of the clear upper portion of the solution to
another previously weighed measuring vial (m0). The vial was
quickly and tightly closed and weighed (m1) to determine the
mass of the sample (m1 - m0). Then the vial was uncovered
with a piece of filter paper to prevent dust contamination. After
the solvent in the vial had completely evaporated, the vial was
dried and reweighed (m2) to determine the mass of the constant
residue solid (m2 - m0). Thus, the solid concentration of the
sample solution in mole fraction, x, could be determined from
eq 114
Figure 2. Experimental mass fraction x of DPPA from thermogravimetric
analysis.
(m2 - m0) ⁄ M1
(m2 - m0) ⁄ M1 + (m1 - m2) ⁄ M2
x )
(1)
where M1 is the molar mass of DPPA and M2 is the molar mass
of the solvent.
Different dissolution times were tested to determine a suitable
equilibrium time. It was found that 2 h was enough for DPPA
in all solvents to reach equilibrium. During our experiments,
three parallel measurements were performed at the same
composition of solvent for each temperature, and an average
value is given. The maximum standard deviation of each
triplicate data is 0.25 %, and the minimum is 0.15 %. The
estimated relative uncertainty of the solubility values based on
error analysis and repeated observations was within 0.02.
Results and Discussion
The mole fraction solubility data of DPPA, x, in selected solvents
are summarized in Table 3 and plotted as ln x vs temperature in
Figures 4 to 6. From these figures, it can be seen that a trend of
Figure 3. Experimental heat flow Q from differential scanning calorimeter
(DSC) measurement of DPPA.

1194 Journal of Chemical & Engineering Data, Vol. 53, No. 5, 2008
Table 3. Mole Fraction Solubilities (x) and Activity Coefficients (γ) of DPPA in the Selected Solvents
solvent
ethanol
T/K
x
γ
(x - xcalcd)/x
solvent
T/K
x
γ
(x - xcalcd)/x
283.15
288.15
293.10
298.07
303.07
308.15
313.16
318.16
322.84
327.94
333.10
337.97
342.90
288.15
293.15
297.98
303.09
308.05
313.15
318.06
323.08
328.12
332.97
338.17
342.94
347.80
288.15
293.18
298.17
303.04
308.11
313.15
318.20
323.16
328.20
332.96
338.03
343.24
348.24
353.25
358.29
363.10
0.00575
0.00671
0.00774
0.00889
0.01020
0.01170
0.01340
0.01520
0.01730
0.01980
0.02310
0.02640
0.03020
0.00426
0.00503
0.00594
0.00696
0.00803
0.00931
0.01070
0.01230
0.01440
0.01650
0.01890
0.02230
0.02570
0.00619
0.00716
0.00810
0.00924
0.01060
0.01180
0.01350
0.01510
0.01720
0.01960
0.02230
0.02520
0.02850
0.03210
0.03600
0.04010
4.506
4.540
4.593
4.647
4.670
4.705
4.713
4.733
4.712
4.661
4.524
4.441
4.350
7.148
7.078
6.933
6.874
6.850
6.791
6.758
6.652
6.463
6.306
6.218
5.882
5.690
4.922
4.980
5.114
5.166
5.187
5.346
5.353
5.431
5.392
5.326
5.272
5.254
5.174
5.125
5.068
5.013
0.030
0.021
0.007
acetic acid
293.23
303.15
313.03
323.15
333.21
343.04
293.06
298.15
303.15
308.17
313.23
318.04
323.10
328.13
333.25
337.95
293.25
298.18
303.12
308.23
313.19
318.21
323.24
293.15
303.19
313.17
322.95
333.21
343.12
293.15
303.16
313.18
323.08
333.17
343.25
352.95
362.65
303.14
313.17
323.13
333.00
343.05
353.05
0.00426
0.00604
0.00827
0.01120
0.01510
0.02090
0.00052
0.00060
0.00075
0.00098
0.00121
0.00144
0.00176
0.00208
0.00247
0.00318
0.00051
0.00068
0.00091
0.00120
0.00156
0.00203
0.00244
0.00070
0.00112
0.00183
0.00291
0.00459
0.00706
0.00049
0.00074
0.00107
0.00157
0.00232
0.00326
0.00462
0.00651
0.00005
0.00008
0.00011
0.00014
0.00018
0.00023
8.374
7.924
7.622
7.307
6.937
6.291
68.08
69.29
63.85
56.34
52.31
49.82
46.59
44.68
42.50
36.91
70.68
61.20
52.69
45.99
40.68
35.57
33.63
51.15
42.88
34.57
28.07
22.85
18.67
72.96
65.21
59.38
52.24
45.17
40.58
35.30
30.63
888.6
781.8
760.3
773.2
750.7
713.0
0.011
0.007
-0.010
-0.022
-0.020
0.032
-0.006
-0.013
-0.022
-0.026
-0.032
-0.028
-0.019
0.010
0.027
0.045
0.023
0.013
ethyl acetate
0.052
-0.044
-0.038
0.015
0.018
0.001
0.001
isopropyl alcohol
-0.022
-0.036
0.048
-0.015
-0.007
0.010
0.014
0.012
0.024
-0.039
0.033
-0.022
-0.022
-0.011
-0.001
0.023
0.015
0.005
acetone
-0.010
-0.020
-0.032
-0.033
-0.019
-0.010
-0.012
0.030
0.048
0.043
0.033
0.009
benzene
2-ethoxyethanol
0.000
methylbenzene
0.045
0.010
-0.003
-0.032
-0.032
-0.046
-0.037
-0.024
-0.012
-0.008
0.009
-0.037
-0.038
-0.016
-0.025
0.008
0.049
-0.045
0.043
water
0.019
0.031
0.042
0.034
-0.016
-0.020
0.001
increasing solubility with temperature is observed. The solubilities
were correlated as a function of temperature by
as solvent in order to remove the 2-ethoxyethanol from the slurry
so as to quickly filtrate and dry.
ln x ) A + B ⁄ (T ⁄ K)
(2)
Parameters A and B for each solvent are listed in Table 4. The
smoothed data calculated from eq 2 are compared with the data
listed in Table 3. The relative standard deviations (RSD), defined
by eq 3, are also presented in Table 3.
xi - xci alcd
2
1⁄2
N
1
RSD )
(3)
∑
(
)
[
]
Ni)1
xi
where calcd stands for the calculated values and N is the number
of experimental points. The results show that eq 2 can be used
to correlate the solubility data. Within the temperature range
of the measurements, the solubilities of DPPA in all of the
investigated solvents increased with an increase in temperature.
The solubility of DPPA in water shows the lowest value and in
ethanol shows the higher value from (283.15 to 342.90) K.
However, the solubility of DPPA in 2-ethoxyethanol at its
boiling temperature (408.15 K) can be predicted from eq 2, and
the result is 22.5 (g/100 g of solvent). The 2-ethoxyethanol is
recommended as the best solvent for the recrystallization of
DPPA. For the final stage of purification, water is recommended
Figure 4. Mole fraction solubility of DPPA in: (experimental) 9, ethanol;
2, 2-methoxyethanol; b, isopropyl alcohol; (calculated from eq 2) -·-,
ethanol; -, 2-methoxyethanol; - - -, isopropyl alcohol.

Journal of Chemical & Engineering Data, Vol. 53, No. 5, 2008 1195
∆Hf T
m - 1
(4)
1
ln
)
(
)
x1γ1 RTm
T
where ∆Hf refers to the enthalpy of fusion; Tm is the melting
temperature; R is the gas constant; and x1 and γ1 refer to the
mole fraction and activity coefficient of solute in the solution,
respectively. With the experimental x1, T, ∆Hf, and Tm values
known, the activity coefficients of DPPA in different solvents
were obtained. The results are listed in Table 3. From Table 3
it can be seen that the activity coefficients of DPPA in different
solvents are all more than unity. For the DPPA-water system,
very small solubilities and very large activity coefficients were
obtained, and this results in great deviations from the ideal
behavior.
Literature Cited
(1) von Gentzkow, W.; Huber, J.; Kapitza, H.; Epoxy resin mixtures
containing phosphonic/phosphinic acid anhydride adducts. U.S. Patent
5,587,243, 1996.
(2) Huber, J.; Kapitza, H.; Kleiner, H.; Phosphorus-modified epoxy resins,
processes for their preparation and their use. U.S. Patent 5,811,188,
1998.
Figure 5. Mole fraction solubility of DPPA in: (experimental) 9, acetic
acid; b, acetone; 2, ethyl acetate; (calculated from eq 2) - · -, acetic
acid; -, acetone; - - -, ethyl acetate.
(3) Garsperini, M.; Ragaini, F.; Remondini, C.; et al. The palladium-
phenanthroline catalyzed carbonylation of nitrioarenes to diarylureas:
effect of chloride and diphenylphosphinic acid. J. Organomet. Chem.
2005, 690, 4517–4529.
(4) Ragaini, F.; Cognolato, C.; Gasperini, M.; Cenini, S. The carbonylation
reaction of nitrobenzene to methyl phenylcarbamate: Highly efficient
promoters for the palladium-phenanthroline catalytic system based on
phosphorus acids. Angew. Chem., Int. Ed. 2003, 42, 2886–2889.
(5) Ragaini, F.; Gasperini, M.; Cenini, S. Phosphorus acids as highly
efficient promoters for the palladium-phenanthroline catalyzed car-
bonylation of nitrobenzene to methyl phenylcarbamate. AdV. Synth.
Catal. 2004, 346, 63–71.
(6) Gasperini, M.; Ragaini, F.; Cazzaniga, C.; et al. Carbonylation of
dinitrotoluene to dimethyl toluenedicarbamate; High efficiency of
phosphorus acids as promoters for the palladium-phenanthroline
catalytic system. AdV. Synth. Catal. 2005, 347, 105–120.
(7) Gasperov, V.; Lindoy, L. F.; Parkin, A.; Turner, P. Structure of host-
guest assemblies involving interaction of cyclen with diphenylphos-
phinic and 4-tert-butylzoic acid. J. Mol. Struct. 2007, 839, 132–136.
(8) Frank, A. W. Synthesis of diarylphosphine oxide by Friedel-Crafts
method. J. Org. Chem. 1959, 24, 966–968.
(9) Wang, Z.-W.; Sun, Q.-X.; Wu, J.-S.; Wang, L.-S. Solubilities of
2-carboxyethyl-phenylphosphinic acid and 4-carboxyphenylphenyl-
phinic acid in water. J. Chem. Eng. Data 2003, 48, 1073–1075.
(10) Wang, L.-S.; Liu, Y.; Wang, R. Solubilities of some phosphaspirocyclic
compounds in selected solvents. J. Chem. Eng. Data 2006, 51, 1686–
1689.
(11) Kosolapoff, G. M. An improved method of preparation of bis-
arylphosphonic acids. J. Am. Chem. Soc. 1942, 64, 2982–2983.
(12) Hunt, B. B.; Saunders, B. C. Esters containing phosphorus. Part XV.
Preparation and reactions of diphenylphosphine oxide. J. Chem. Soc.
1957, 2413-2414.
(13) Rao, H.; Jin, Y.; Jiang, Y. A versatile and efficient ligand for copper-
catalyzed formation of C-N, C-O, and P-C bonds: Pyrrolidine-2-
phosphonic acid phenyl monoester. Chem.-Eur. J. 2006, 12, 3636–
3646.
(14) Zhu, M. Solubility and density of disodium salt hemiheptahydrate of
ceftriaxone in water + ethanol mixtures. J. Chem. Eng. Data 2001,
46, 175–176.
Figure 6. Mole fraction solubility of DPPA in: (experimental) 9, benzene;
b, methylbenzene; 2, water; (calculated from eq 2) - · -, benzene; -,
methylbenzene; - - -, water.
Table 4. Parameters of Equation 3 and Root-Mean-Square
Deviations of the Measured Solubility Calculated from Equation 4
for Ethanol, Isopropyl Alcohol, and 2-Ethoxyethanol
solvent
ethanol
isopropyl alcohol
2-ethoxyethanol
acetic acid
ethyl acetate
acetone
benzene
methylbenzene
water
A
B
RSD
4.2261
4.8420
3.9303
5.3416
6.0228
9.6676
8.6762
5.8252
0.1434
-2665.7
-2974.8
-2610.5
-3170.1
-3995.9
-5056.6
-4684.5
-3956.6
-3009.5
0.024
0.024
0.028
0.019
0.033
0.020
0.021
0.032
0.031
(15) Prausnitz, J. M.; Lichtenthaler, R. N.; Gomes de Azevedo, E. Molecular
Thermodynamics of Fluid-Phase Equilibria, 2nd ed.; Prentice-Hall Inc.;
Englewood Cliffs, 1986.
To obtain the activity coefficients of DPPA in the solvents
from the experimental data, the following equilibrium equation
for solute 1 was derived as a fair approximation15
Received for review January 18, 2008. Accepted March 13, 2008.
JE800049B