Carboxylate phosphabetaines based on tertiary phosphines and unsaturated dicarboxylic acids

Article abstract of DOI:10.1134/S1070428007020091

By reaction of triorganylphosphines with unsaturated dicarboxylic acids adducts of betaine structure were synthesized whose stability depended on the character of substituents at phosphorus and on the structure of acid. The betaine obtained from phosphine

Full text of DOI:10.1134/S1070428007020091

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 2, pp. 207−213. © Pleiades Publishing, Ltd. 2007.
Original Russian Text © Yu.V. Bakhtiyarova, R.I. Sagdieva, I.V. Galkina, V.I. Galkin, R.A.Cherkasov, D.B. Krivolapov, A.T. Gubaidullin,
I.A. Litvinov, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 2, pp. 215−221.
Carboxylate Phosphabetaines based on Tertiary Phosphines
and Unsaturated Dicarboxylic Acids
Yu. V. Bakhtiyarovaa, R. I. Sagdievaa, I. V. Galkinaa, V. I. Galkina, R. A.Cherkasova,
D. B. Krivolapovb,A. T. Gubaidullinb, and I. A. Litvinovb
aButlerov Chemical Institute at Kazan State University, Kazan,420008 Russia
e-mail: Julia.Bakhtiyarova@ksu.ru
bInstitute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, Kazan,Russia
Received December 19, 2005
Abstract—By reaction of triorganylphosphines with unsaturated dicarboxylic acids adducts of betaine structure
were synthesized whose stability depended on the character of substituents at phosphorus and on the structure of
acid. The betaine obtained from phosphines and maleic and fumaric acids redily underwent decarboxylation into
the corresponding monoacyl phosphonium derivatives. The structure of the latter was established by means of
X-ray crystallography. The adduct prepared from phosphines and itaconic acid was stabilized by intramolecular
hydrogen bond between the acylate anionic center and the "second" carboxy group.
DOI: 10.1134/S1070428007020091
Phosphabetaines are internal phosphonium salts where
cthe cationic phosphonium and anionic centers are linked
by a system of covalent bonds.
It was established that proton-donor reagents and
solvents play an important part in stabilization of
phosphabetaine structures with separated charges.
Betaines I readily undergo alkylation and acylation
with haloalkyles and acyl halides to give the corresponding
phosphonium salts II.
X = C, S, O, N.
_
_
+
+
[Ph3PCH2CH2COOR]Hlg
Ph3PCH2CH2COO + RHlg
These substances frequently arise as intermediates in
many reactions of organophosphorus compounds; they
are besides analogs of a certain kind of organic amino
acids, and they are endowed with a wide range of
chemical [1] and biological properties [2, 3].
II
I
R =Alk,Acyl; Hlg = Cl, Br, I.
Phosphonium salts in contrast to betaine proper do
not require proton-donor reagents to stabilize their crystal
structure.
We formerly systematically investigated synthetic
procedures for preparation, structures, and reactivity of
phosphabetaines I obtained by addition of tertiary
phosphines to unsaturated monocarboxylic acids. [4–6].
In the present article we report on the results of study-
ing reactions between tertiary phosphines (triphenyl-,
methyldiphenyl-, and tributylphosphines) with unsaturated
dicarboxylic acids (maleic, fumaric, and itaconic) whose
second carboxy group we hope to be able to function as
an internal proton-donor center facilitating the stabilization
of the arising betaines.
_
+
1
1
R3P + R2CH
[R3P_CHCCOOH]
C COOH
R3
R2 R3
R2
_
1+
R3P_CHCHCOO
Maleic acid reacted with triphenylphosphine under mild
conditions in ethyl ether solution giving an adduct insoluble
in organic solvents [mp 67–72°C (decomp.)] that
represents according to IR spectum dicarboxylate betaine
III.
R3
I
R1 = Ph, Bu; R2 = H, Ph, ï -CH3OC6H4; R3 = H, Me.
207

BAKHTIYAROVA et al.
208
as salt IV unlike betaine III is well soluble in organic
solvents, its IR and NMR spectra also proved this
structure (see EXPERIMENTAL).
O
C
O _
+
Ph3P CH
CH2
C
H
O
O
III
CH CH
Δ
_CO2
+
C
O
Ph3PCH2CH2COOH
O
C
_
O
O
H
IV
Asymmetrical part of the unit cell of the crystal of
salt IV is formed by an ion pair of phosphonium cation
and monoanion of maleic acid. The phosphorus atom
coordination is a common one for a four-coordinated
phosphonium atom. The bond distances and bond angles
are consistent with the values found in the alkylation
products of phosphabetaine I [7]. Conformation of the
fragment P1C1C2C3 is close to transoid [torsion angle ϕ
156.2(2)°], of the fragment C1C2C3O1, to eclipsed one
[torsion angle ϕ –24.7(4)°]. The CO distances in the
molecule correspond to a double and an ordinary bonds
(Table 1). As a result of deprotonation of the acid in one
of the carboxy groups the CO bond lengths are equalized
like in betaine I (Table 1). In the crystal intermolecular
Fig. 1. Molecular structure of β-carboxyethyltriphenyl-
phosphonium maleate (IV).
Betaine III is unstable and at heating or short storage
easily suffers decarboxylation to form a phosphonium salt
IV which may be regarded as a product of betaine I
protonation with a molecule of maleic acid.
...
hydrogen bonds O2–H O301 (3/2 – x, 1/2 + y, 3/2 – z)
were found linking the anion to the cation. Parameters
of the hydrogen bonds are as follows: O2–H2 1.07(3),
O
C O_
°
...
...
H2 O301 2.37(3), O2 O301 3.422(3) A , angle
COOH
+
...
O2H2 O301 167(2)° (Fig. 2). Besides in the anion an
Ph3P CH
Ph3P +
...
intramolecular hydrogen bond O–H O is present with
CH2
C O
H
COOH
...
the following parameters: O332–H332 1.15(2), H332 O302
°
...
1.27(3), O332–H332 O302 2.420(3) A, angle 175(2)°.
O
.The similarity of the crystal structures of triphenyl-
β-carboxyethylphosphonium maleate and alkylation
products of phosphabetaine [7] is also seen in the packing
of the molecules: channels are formed parallel to 0a axis
where the acid anions are located (Fig. 3).
III
The decomposition pathway of betaine III resulting
in phosphonium salt IV we proved by a special experiment:
the heating of a sample of zwitter-ion III at 70°C for 1 h
led to its quantitative decarboxylation. The high basicity
of the “anionic moiety” of betaine I caused virtually
complete proton transfer from the molecule of maleic
acid. Thus forming β-carboxyethyltriphenylphosphonium
cation and maleate anion are bound by a strong hydrogen
bond. A similar bond in the maleate anion ensured its
cyclization. These features of an uncommon structure of
new quasiphosphonium salt IV were unambiguously
revealed by X-ray diffraction analysis (Fig.1). Inasmuch
The complete proton transfer from maleic acid to
betaine I (R1 = Ph, R2 = R3 = H) in adduct IV resulted in
its inertness in previously studied reactions of alkylation
with haloalkyles.
Triphenylphosphine reacted with fumaric acid only at
heating in acetonitrile. Under these conditions we failed
to isolate or detect the intermediate containing the initial
dicarboxylic acid. Only betaine I was obtained stabilized
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

CARBOXYLATE PHOSPHABETAINES BASED ON TERTIARY PHOSPHINES
209
by an aceto-nitrile molecule. Its structure was confirmed
by IR and NMR spectroscopy, and also by X-ray
crystallography (Fig. 4).
Phosphonium salts are prone to include in the unit cell
a molecule of solvent [7]. We established that in the unit
cell of phosphabetaine I was present a molecule of
acetonitrile. The geometry of a phosphorus atom in the
phosphabetaine is usual, The conformation of the fragment
P1C1C2C3 is transoid [torsion angle ϕ 171.7(2)°], of the
fragment C1C2C3O1 is close to eclipsed [torsion angle ϕ
31.1(4)°]. The lengths of CO bonds in the molecule are
equalized and are the same within the experimental
accuracy.
Fig. 2. Hydrogen bonds in the crystal of b-carboxyethyl-
triphenylphosphonium maleate (IV).
Reaction of methyldiphenyl- and tributylphosphines
with maleic acid occurred in the same manner as with
triphenyl-phosphine with preliminary formation of
Table 1. Selected geometrical parameters of compounds I and
IV
d,
Bond
I
IV
P1–C1
1.793(2)
1.789(2)
1.784(3)
1.788(3)
1.523(4)
1.495(3)
1.200(3)
1.300(3)
1.247(3)
1.249(3)
1.207(3)
1.303(3)
1.810(3)
1.795(2)
1.796(2)
1.792(2)
1.535(4)
1.543(4)
1.220(5)
1.241(5)
P1–C4
P1–C10
P1–C16
C1–C2
C2–C3
O1–C3
O2–C3
O301–C30
O302–C30
O331–C33
O332–C33
Fig. 3. Packing in the crystal of compound IV. Projection
along 0a axis.
ω, deg
Bond angle
C1P1C4
I
IV
110.5(1)
109.5(1)
C1P1C10
C1P1C16
C4P1C10
C4P1C16
C10P1C16
P1C1C2
C1C2C3
O1C3O2
O1C3C2
O2C3C2
109.0(1)
108.9(1)
107.8(1)
109.9(1)
110.8(1)
113.8(2)
113.0(2)
124.3(2)
124.1(2)
111.5(2)
111.1(1)
109.1(1)
107.5(1)
110.7(1)
109.0(1)
112.2(2)
112.7(3)
124.4(3)
118.7(3)
116.9(3)
Fig. 4. Molecular structure of phosphabetaine I obtained by
reaction of triphenylphosphine and fumaric acid.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

BAKHTIYAROVA et al.
210
centers: that of the carboxy group at 1700 cm–1, and that
of carboxylate anion in the region 1600 cm–1.
dicarboxylate betaines Va and Vb which already under
the reaction condition suffer decarboxylation into
phosphabetaines VIa and VIb.
However also in this case the bipolar adduct VII,
although more stable than betaines based on maleic and
fumaric acids, still is not very heat-resistant. Its melting
or boiling in chloroform is accompanied with clear signs
of decomposition with CO2 liberation. In a special
experiment we performed its decaboxylation leading to a
product of its thermal decomposition, phosphabetaine
VIII (δP 22.45 ppm, mp 53–57°C ) that was readily
hydrated with the air moisture giving the corresponding
phosphonium salt. Its IR spectrum lacks the absorption
band of the carboxylate anion, and the strong band at
1720 cm–1 corresponds to the absorption of a single
carboxy group.
O
C O_
COOH
+
R3P +
R3P CH
CH2
C O
H
COOH
O
Va, Vb
_
+
Δ
R3PCH2CH2COO
_CO2
VIа, VIb
R3 = Ph2Me (a), Bu3 (b).
The analysis of stability of adducts formed from
triorganylphosphines and unsaturated dicarboxylic acids
showed that the geminal position of the phosphonium
cation and acylate anion results in destabilization of the
betaine structure promoting decarboxylation and leading
to appearance of more thermodynamically favorable
zwitter-ion with a β-location of its anionic and cationic
parts. Apparently, this spreading of charges alongside
with the betaine stabilization by proton-donor solvent
molecules or by specially added acidic substances serves
as a factor of stabilization for the structure of bipolar
ions.
Ph3P + CH2 C CH2COOH
COOH
+
Ph3P CH2 CH
O_ C
CH2
Δ
_CO2
O
C O
.
.
.
H O
VII
_
+
Ph3PCH2CH2CH2COO
H OH
VIII
This conclusion is well consistent with published data
[8] on failed attempts to obtain triphenylphos-phonium
methylcarboxylate by reaction of triphenyl-phosphine
with chloroacetic acid. Here also decarboxyla-tion
occurred giving triphenylmethylphosphonium chloride.
Methyldiphenylphosphine reacted with the itaconic acid
leading to the formation of a single crystalline substance,
betaine IX [δP 24.5 ppm, mp 132°C (decomp.)].
CCH2COOH
COOH
R2R'P + CH2
_
+
[Ph3PCH2COOH]Cl
+
R2R'P CH2 CH
_
O
+
Ph3+PCH2C
B
_
[Ph3PCH3]Cl
O_ C
CH2
_CO2
_HCl
O
O
C O
.
.
.
To support these assumptions we involved into the
reaction with the tertiary phosphine itaconic acid hoping
that these reaction products unlike analogous products
obtained from fumaric and maleic acids would be more
stable for in the arising betains the nearest carboxy group
should be located not in the α-, but in the β-position with
respect to the phosphonium center.
H O
IX, X
R = Ph, R' = Me (IX); R, R' = Bu (X).
In its IR spectrum absorption bands appeared both
from the carboxy group in the region 1700 cm–1 and from
the carboxylate anion in its characteristic region 1600
cm–1. According to elemental analysis compound IX is a
stable dicarboxylate phosphonium betaine. Analogous
reaction of tributylphosphine with itaconic acid gave rise
to dicarboxylate phosphabetaine X (δP 34.0 ppm),
The reaction between triphenylphosphine and itaconic
acid occurs with the formation of a single crystalline
compound VII [δP 23.9 ppm, mp 58–60°C (decomp.)].
Its IR spectrum contains absorption bands of both carboxy
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

CARBOXYLATE PHOSPHABETAINES BASED ON TERTIARY PHOSPHINES
211
yellowish oily substance.Also in this case the IR spectrum
contained the absorption bands of carboxylate anion at
1600 cm–1 and of carboxy group at 1720 cm–1.
Table 2. Parameters of crystals of compounds I and IV, and
conditions of X-ray crystallographic experiments
Parameter
I
IV
Thus the investigation performed showed the essential
features of behavior inherent to the unsaturated di-
carboxylic acids in phosphabetaines formation originat-
ing from the thermodynamical instability of the struc-
tures with the α-position of phosphonium and carboxylate
sites.
Crystal system
Empirical formula
monoclinic
C21H19O2P
C2H3N
C21H20O2P+
–
C4H2O4
Molecular weight
Space group
375.39
450.4
P21/n
Parameters of unit cell,
a
b
c
EXPERIMENTAL
9.151(2),
12.759(2),
16.375(4)
98.54(3)°
1891.23
4
9.671(2),
18.537(6),
13.327(2),
105.82(2)°
2298.55
IR spectra were recorded on a spectrophotometer
Specord M80 in the frequency range 700–3600 cm–1 from
thin films or mulls in mineral oil between KBr plates.
1H and 31P spectra were registered from solutions in
CDCl3 on a spectrometer Varian Unity-300 at operating
frequencies 300 (1H, internal reference HMDS) and
121.64 MHz (31P, external reference H3PO4).
β
3
Volume,
Z
Density (calc), g/cm3
Extinction coefficient, μ,
cm–1
1.32
1.42
1.6
26.30
4277
20.97
22.76
3247
X-ray diffraction study on single crystals of compounds
I and IV was carried out at 20°C on an automatic four-
circle diffractometer Enraf-Nonius CAD-4 using λMoKα-
θ
max, deg
Reflections measured
Number of observed
reflections with I > 3σ(I)
Scanning type
Accounting for extinction
Conditions of revealing Revealed from Revealed from
°
radiation, λ 0.71073 A(graphite monochromator, variable
2023
2200
scanning rate, 1–16.4 deg/min by θ, Table 2). Unit cell
parameters were estimated from 25 reflections. The
stability of crystals in the course of the experiment was
checked every 2 h by measuring three reference reflec-
tions, the crystal orientation was controlled by measuring
two reflections after every 200 reflections. The structures
were solved by the direct method using SIR software
[7]. All calculations were carried out applying software
package MolEN [9] on a computer DEC Alpha Station
200.
ω/2θ
empirical
and refining of hydrogen difference of
atoms
difference of
electron density,
refined
isotropically
R 0.034,
electron
density, not
refined
R 0.049,
Rw 0.057
Final values of
divergence factors
Number of reflections
used in refining
Rw 0.046
2023
2200
3-Triphenylphosphoniopropanoate (I). To a solu-
tion of 2.110 g of triphenylphosphine in 5 ml of acetonitrile
was added dropwise at stirring 0.935 g of a solution of
fumaric acid. The reaction mixture was boiled on a water
bath at 70°C for 18 h, and the solution turned brown. The
solvent was removed in a vacuum, the crystal substance
was washed with ether, the crystals were filtered off
and dried in a vacuum to obtain 1.614 g (60%) of colorless
crystals of compound I including acetonitrile molecules,
mp 145–148°C, δP 25 ppm, νCOO– 1605 cm–1. The
structure was proved by X-ray diffraction study,
(Fig. 4).
Number of refined
parameters
244
381
an ether solution of 1.372 g of maleic acid. After 15 min
a colorless precipitate of betaine III separated and was
filtered off, mp 67–73°C (decomp.). Compound III is
insoluble in organic solvents, unstable to heat, and readily
decomposed with CO2 liberation even at short storage;
the decomposition product was soluble in acetonitrile.
Thermal decomposition of betaine III. At 70°C
was heated on a water bath 3.045 g of betaine III for
1 h in a flask equipped with a gas-outlet tube. The reaction
mixture was dissolved in 5 ml of acetonitrile, to a solution
anhydrous ether was added. The separated colorless
precipitate was filtered off, washed with ether, and dried
2-(Triphenylphosphonio)hydrosuccinate (III).
Into a solution of 3.094 g of triphenylphosphine in 5 ml of
anhydrous ether at constant stirring was added dropwise
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

BAKHTIYAROVA et al.
212
mixture was dissolved in 5 ml of acetonitrile, to a solution
anhydrous ether was added. The separated colorless
precipitate was filtered off, washed with ether, and dried
in a vacuum. We isolated 0.280 g (70%) of 4-(triphenyl-
phosphonio)butanoate (VIII), mp 55°C, δP 24 ppm,
in a vacuum. We isolated 2.441 g (67%) of colorless
crystals of (2-carboxyethyl)triphenyl-phosphonium
hydromaleate (IV), mp 144–148°C, δP 21 ppm, νCOO
–
1600 cm–1. The liberated gas was passed through a solu-
tion of calcium hydroxide.Awhite precipitate of calcium
carbonate separated, The structure of compound IV was
ν
COOH 1720 cm–1. On passing the liberated gas through
31
proved by 1H and P NMR spectroscopy, and also by
the calcium hydroxide solution white precipitate of calcium
carbonate was obtained.
X-ray diffraction study, (Fig. 1).
2-(Methyldiphenylphosphoniomethyl)hydro-
succinate (IX). To a solution of 0.512 g of methyl-
diphenylphosphine in 5 ml of acetonitrile was added
dropwise a solution of 0.335 g of itaconic acid in 5 ml of
acetonitrile. On storage of the solution at room tempera-
ture after several days a fine colorless precipitate separat-
ed that was washed with ethyl ether, filtered off, and
dried in a vacuum. We obtained 0.549 g (65%) of betaine
IX that was stable in air, insoluble in most organic solvents,
soluble in DMF. mp 132°C, νCOO– 1600 cm–1, νCOOH 1700
cm–1, δP 24.5 ppm. Found, %: C 65.39; H 5.72; P 8.98.
C18H19O4P. Calculated, %: C 65.45; H 5.76; P 9.39.
3-(Methyldiphenylphosphonio)propanoate (VIa).
To a solution of 0.539 g of methyldiphenylphosphine in
5 ml of acetonitrile at constant stirring was added
dropwise a solution of 0.341 g of maleic acid in 5 ml of
acetonitrile, the reaction mixture was kept at room
temperature for several hours, the solvent was removed
in a vacuum. The formed colorless crystals of 2-(methyl-
diphenylphosphonio)hydrosuccinate (Va) are
insoluble in organic solvents and are stable only under a
layer of solvent. Compound Va is unstable in air and easily
suffered decarboxylation to phosphabetaine VIa, oily
substance, νCOO– 1615 cm–1, δP 24.9 ppm
2-(Tributylphosphoniomethyl)hydrosuccinate
(X). To a solution of 1.510 g of tributylphosphine in 5 ml
of acetonitrile was added a solution of 1.080 g of itaconic
acid in 5 ml of acetonitrile. The reaction mixture was
kept for 24 h at room temperature. The solvent was
removed in a vacuum. We obtained betaine X as an oily
yellowish substance . 31P NMR spectrum: δ 34 ppm. IR
spectum, cm–1: 1730 (νCOOH), 1600 (νCOO–).
The study was carried out under a financial support
of the program of the Ministry of Education and Science
of the Russian Federation “Universities of Russia, funda-
mental research” and of joint program of the Ministry of
Education and Science of the Russian Federation and
CRDF “Basic Research & Higher Education” (grant no.
REC-007).
3-(Tributylphosphonio)propanoate (VIb). To
a solution of 3.062 g of tributylphosphine in 5 ml of
anhydrous ether at constant stirring was added dropwise
a solution of 1.761 g of maleic acid. The reaction mixture
was kept for 1 month. First in the course of the reaction
formed 2-(tributyl-phosphonio)hydrosuccinate (Vb),
δP 56 ppm, that under the reaction conditions easily
suffered decarboxylation into betaine VIb, δP 35 ppm. In
the IR spectrum of betaine VIb appear absorption bands
both of carboxylate anion at 1600 cm–1 and of carboxy
group involved in a hydrogen bond (νC=O 1720, νOH 800–
3200 cm–1).
2-(Triphenylphosphoniomethyl)hydrosuccinate
(VII). To a solution of 0.901 g of triphenylphosphine in
5 ml of acetonitrile was added dropwise at stirring a solu-
tion of 0.472 g of itaconic acid in 5 ml of acetonitrile. The
reaction mixture was kept for 24 h. The solvent was
removed in a vacuum, the crystalline residue was washed
with ether, filtered off, and dried in a vacuum to obtain
0.863 g (64%) of colorless crystals, mp 58–60°C
(decomp.), δP 23.92 ppm, νCOO– 1605, νCOOH 1720 cm–1.
Betaine VII is stable in air, well soluble in polar
solvents.
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