Solubilities of 2-carboxyethylphenylphosphinic acid and 4-carboxyphenylphenylphosphinic acid in water

Article abstract of DOI:10.1021/je0340396

The solubilities of 2-carboxyethylphenylphosphinic acid (CEPPA) and a potential reactive flame retardant, 4-carboxyphenylphenylphosphinic acid (CPPPA), in water were measured. The concentration of the solution was determined by sodium hydroxide titration with phenolphthalein as the indicator. The solubilities of CEPPA were measured from 25.10 °C to 76.32 °C with an uncertainty of 2.2%, and the solubilities of CPPPA were measured from 26.70 °C to 94.52 °C with an uncertainty of 2.1%.

Full text of DOI:10.1021/je0340396

J . Chem. Eng. Data 2003, 48, 1073-1075
1073
Solu bilities of 2-Ca r boxyeth ylp h en ylp h osp h in ic Acid a n d
4-Ca r boxyp h en ylp h en ylp h osp h in ic Acid in Wa ter
Zh on g-Wei Wa n g, Qi-Xin Su n , J u n -Sh en g Wu , a n d Li-Sh en g Wa n g*
School of Chemical and Environment Engineering, Beijing Institute of Technology,
Beijing 100081, People’s Republic of China
The solubilities of 2-carboxyethylphenylphosphinic acid (CEPPA) and a potential reactive flame retardant,
4-carboxyphenylphenylphosphinic acid (CPPPA), in water were measured. The concentration of the
solution was determined by sodium hydroxide titration with phenolphthalein as the indicator. The
solubilities of CEPPA were measured from 25.10 °C to 76.32 °C with an uncertainty of 2.2%, and the
solubilities of CPPPA were measured from 26.70 °C to 94.52 °C with an uncertainty of 2.1%.
In tr od u ction
Exp er im en ta l Section
Ma ter ia ls. DCPP was purchased from ACROS with a
purity of 97%; anhydrous AlCl3, toluene, KMnO4, NaOH,
and phenolphthalein were all analytical reagents from
Beijing Chemical Factory. The aqueous NaOH solution of
n1 ) 0.1004 mol/L for titration of CPPPA and that of n2 )
1.0034 mol/L for titration of CEPPA were prepared.
2-Carboxyethylphenylphosphinic acid (CEPPA) is a bi-
functional copolymerizable phosphorus monomer disclosed
by U.S. patent.1,2 It can be polycondensed with ethylene
glycol (EG) and terephthalate (TPA) to form flame-
retardant poly(ethylene terephthalate) (FR-PET)3 and
renders the alternated PET and the resulting plastics and
fibers good fire-resistance properties, antistatic properties,
and excellent dyeing characters. As attention was focused
on a reactive phosphorus flame retardant,4-6 a novel
bifunctional copolymonomer for PET, namely, 4-carbox-
yphenylphenylphosphinic acid (CPPPA), in which the
2-carboxyethyl moiety of CEPPA was replaced by a 4-car-
boxyphenyl group, was synthesized. The melting point of
CPPPA is about 90 °C higher than that of CEPPA, which
might make it a potential advantageous flame retardant.
In addition to the fire-resistance property, a higher melting
point is favorable for spinning properties of the FR-PET.
In str u m en ta l An a lysis a n d Mea su r em en ts. Melting
points (mp’s) were obtained from an X4 Micromelting point
meter, and the temperature was uncorrected. The C, H
elemental analysis was performed on a Yanaco CHN FOER
MT-3 element analyzer. IR spectra (Fourier transform
infrared (FTIR)) were recorded on a Perkin-Elmer 2000
FTIR spectrometer using KBr pellets. 1H NMR spectra
were recorded with a Varian Unity 200 MHz spectrometer
with (CD3)2SO as the solvent. Mass spectra were obtained
on a HP-5989 mass spectrometer.
Syn th esis of CEP P A. CEPPA was prepared according
to the literature1,2 with a yield of 90.2%, a mp of 158 °C,
and acidity of 372.71 mg NaOH/g (calculated: 373.83 mg
NaOH/g, purity 99.7%).
In industry, CEPPA is obtained by hydrolyzing the
acrylation intermediate prepared from dichlorophenylphos-
phine (DCPP) and acrylic acid, and it then crystallizes from
water. The amount of water added in the preparation of
CEPPA is important for its purification. According to our
experiment, CPPPA was also precipitated in water. There-
fore, knowledge of the solubilities of CEPPA and CPPPA
in water is important for their preparation and purification.
But the solubilities of CEPPA and CPPPA in water were
not available in the literature. In this study, the solubilities
of CEPPA and CPPPA in water were measured.
Elemental analysis (%, calculated): C, 50.39 (50.47); H,
4.73 (5.14). IR (KBr): 3310 (O-H), 1720 (CdO), 1603, 1430
1
(Ar-P), 1150 (PdO) cm-1. H NMR (200 MHz, (CD3)2SO):
δ13.42 (1H, s, O-H), 7.62 to 8.14 (5H, m, Ar-H), 3.0 to
4.2 (4H, m, -CH2CH2-H). MS (FAB): 213 (M+ - 1).
Syn th esis of CP P P A. Toluene (0.4 mol) was added
dropwise to 0.33 mol DCPP and 0.33 mol anhydrous AlCl3
at 110 °C; the reaction went on for 8 h at 150 °C. The
reaction mixture was then cooled to room temperature,
hydrolyzed with 200 mL of 5 mol/L cold hydrochloric acid,
and then extracted with 100 mL of toluene twice. The
combined organic layer was washed with water and dried
with anhydrous CaCl2. The toluene was removed at re-
duced pressure to get the intermediate, which was then
dissolved by an appropriate amount of sodium hydroxide
(1 mol/L). About 1.2 mol KMnO4 was added partially to
the solution, and the mixture was kept at 80 °C for 8 to 10
h. An appropriate amount of sodium metabisulfite was
added to decolorize the solution and then filtered. The
filtrate was acidified by 2 mol/L hydrochloric acid until no
further precipitation occurred and then was cooled and
filtered one more time to get the solid product. The product
was then dissolved in 1 mol/L sodium hydroxide and
* Corresponding author. Fax: 86-10-68912660. E-mail: lishengwang@
btamail.net.cn.
10.1021/je0340396 CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/18/2003

1074 J ournal of Chemical and Engineering Data, Vol. 48, No. 4, 2003
Ta ble 1. Mea su r ed a n d Ca lcu la ted Solu bilities (Mole
F r a ction ) of CEP P A a n d CP P P A in Wa ter
103s (measured)
titration titration titration
103s
(calcd)
t/°C
1
2
3
av
CEPPA 25.10
35.51
1.765
3.625
6.756
1.773
3.683
6.656
1.807
3.667
6.706
1.782
3.658
6.706
1.809
3.630
6.811
44.92
54.02 13.36
64.40 24.89
69.60 33.91
71.91 41.18
76.32 56.85
13.31
24.92
33.89
41.22
13.33
24.95
33.84
41.22
13.32
24.92
33.88
41.21
12.52
25.07
35.49
41.42
56.83
56.78
56.82
55.63
CPPPA 26.70
0.2223
0.2257
0.2526
0.3016
0.3499
0.4706
0.6334
0.7954
0.9829
0.2250
0.2513
0.3044
0.3499
0.4741
0.6306
0.7974
0.9843
0.2243
0.2526
0.3030
0.3492
0.4727
0.6313
0.7954
0.9822
0.2325
0.2456
0.2958
0.3683
0.4732
0.6361
0.7857
0.9905
34.21
45.08
54.40
64.15
75.71
84.38
94.52
0.2546
0.3030
0.3479
0.4734
0.6300
0.7934
0.9794
reprecipitated by acidification with 2 mol/L hydrochloric
acid to pH 3. The white solid was collected by filtration,
washed with water until the washings were neutral, and
dried to get CPPPA (37.6 g): yield, 33.1% (based on DCPP);
mp, 249 to 250 °C; the acidity was 303.51 mg NaOH/g
(calculated: 305.34 mg NaOH/g, purity 99.4%).
F igu r e 1. Solubility (mole fraction) of CEPPA in water: [,
measured; s, calculation (eq 1).
Elemental analysis (%, calculated): C, 59.07 (59.54); H,
4.43 (4.20). IR (KBr): 3180 (-OH), 1725 (CdO), 1613, 1437
1
(Ar-P), 1096 (PdO) cm-1. H NMR (200 MHz, (CD3)2SO):
δ11.32, 13.15 (2H, 2s, O-H), 7.71 to 8.34 (9H, m, Ar-H).
MS (FAB): 261 (M+ - 1).
Appa r a tu s for Solu bility Mea su r em en t. The setup for
the solubility measurement was the same as that described
in the literature.6 The equilibrium cell was a sealed 120
mL glass measuring flask. The flask was immersed in a
constant-temperature water bath. The bath temperature
control uncertainty is within (0.1 °C. A magnetic stirrer
was utilized for solution preparation. The precision of the
analytical balance was 0.1 mg. The mass of sample of
CEPPA taken for titration ranged from 5.01 g to 16.02 g,
and that of CPPPA ranged from 0.31 g to 0.82 g.
Solu bility Mea su r em en t. At each selected tempera-
ture, an excessive amount of CEPPA or CPPPA was added
to 100 g of distilled water and constant stirring was
applied. At an interval of 30 min, the stirrer was stopped
and then the solution was settled for 30 min; the excess
solid could be observed to settle in the lower portion of the
equilibrium cell. The clear upper portion of the solution
was withdrawn from the cell to another measuring flask
and weighed with an analytical balance; the flask was then
immersed in the same bath. The concentration of the
solution was determined by sodium hydroxide titration
with phenolphthalein as the indicator. Repeated measure-
ments were performed for different dissolution times to
determine how long it would take to reach equilibrium. It
was found that 120 min was sufficient for CPPPA and 150
min for CEPPA in distilled water within the measuring
temperature ranges. For each temperature, the titration
operation was conducted three times and an averaged value
was taken.
F igu r e 2. Solubility (mole fraction) of CPPPA in water: [,
measured; s, calculation (eq 2).
adopting a logarithmic formula.
ln sCEPPA ) -26.2623 + 6.6882 × 10-2(T/K) (1)
The solubility (mole fraction) of CPPPA was correlated
as a function of temperature (T/K) by adopting a second-
order polynomial:
sCPPPA ) 1.4128 × 10-2 - 9.3254 × 10-5(T/K) +
1.5644 × 10-7(T/K)2 (2)
The measured solubility and the smoothed data based
on eq 1 for CEPPA in the temperature range of 25.10 to
76.32 °C and that based on eq 2 for CPPPA in the
temperature range of 26.70 to 94.52 °C are presented in
Table 1. The absolute average deviation (AAD%) of the
measured solubilities from the smoothed data is defined
as
The solubility of CEPPA in water at temperatures
ranging from 25.10 °C to 76.32 °C and that of CPPPA at
temperatures ranging from 26.70 °C to 94.52 °C are
summarized in Table 1 and plotted in Figure 1 and Figure
2. The estimated accuracy of the solubility values, based
on error analysis and repeated observations, was within
2%.
1
AAD% )
|sei xptl - sci alcd|/|siexptl| × 100
Cor r ela tion . The solubility (mole fraction) of CEPPA
was correlated as a function of temperature (T/K) by
∑
N
i

J ournal of Chemical and Engineering Data, Vol. 48, No. 4, 2003 1075
where the superscript exptl stands for experimental values
solubility in mole fraction of CPPPA in water increased
and calcd stands for calculated values. The absolute
average deviations of the measured solubilities from the
smoothed data of CEPPA and CPPPA are 2.2% and 2.1%,
respectively.
from 0.2243 × 10-4 at 26.70 °C to 0.9822 × 10-4 at 94.52
°C.
Liter a tu r e Cited
(1) Weinkauff, D. J .; Paulik, F. E. Production of 2-carboxyalkyl-
(phenyl)phosphinic acid. U.S. Patent 6,320,071, 2001.
(2) Weinkauff, D. J .; Paulik, F. E. Process for the preparation of
2-carboxyalkyl (aryl)phosphinic acid and corresponding anhydride-
(s). U.S. Patent 6,399,814, 2002.
Discu ssion
Within the temperature range of the measurements, the
solubilities (mole fraction) in water of both CEPPA and
CPPPA showed an increased trend based on the increased
temperature, but they varied greatly. The solubility for
CEPPA increased more quickly than that of CPPPA.
Because the up-trends were different, a logarithmic equa-
tion was used to correlate the sharply increased solubility
data for CEPPA, and a polynomial equation was used to
correlate the gently increased solubility data of CPPPA.
The solubility of CEPPA is much higher than that of
CPPPA, showing that CEPPA is readily dissolvable in
water, especially in heated water. Thus the solubility in
mole fraction of CEPPA in water increased from 1.782 ×
10-3 at 25.10 °C to 5.682 × 10-2 at 76.32 °C, while the
(3) Wu, B.; Wang, Y.-Z.; Wang, X.-L.; Yang, K.-K.; J in, Y.-D.; Zhao,
H. Kinetics of thermal oxidative degradation of phosphorus-
containing flame retardant copolyesters. Polym. Degrad. Stab.
2002, 76 (3), 401-409.
(4) Wang, L.-S.; Wang, X.-L. Solubilities of dichlorophenylphosphine
sulfide and bis(4-carboxyphenyl)phenylphosphine oxide in water.
J . Chem. Eng. Data 2000, 45, 743-745.
(5) Wang, L.-S.; Wang, X.-L.; Yan, G.-L. Synthesis, characterization
and flame retardance behavior of poly(ethylene terephthalate)
copolymer containing triaryl phosphine oxide. Polym. Degrad.
Stab. 2000, 69, 127-130.
(6) Wu, J .-S.; Cheng, K.-K.; Wang, L.-S. Solubilities of bis(4-meth-
ylphenyl) phosphine sulfide and bis(4-carboxyphenyl)phenylphos-
phine oxide in acetic acid. J . Chem. Eng. Data 2002, 47, 2-3.
Received for review February 23, 2003. Accepted May 15, 2003.
J E0340396