Specificity of the reaction of β-carboxyvinyl(triphenyl)phosphonium chloride with azoles

Article abstract of DOI:10.1134/S107036320704010X

Reactions of pyrazole, 3,5-dimethylpyrazole, 1,2,4-triazole, 5-aminotetrazole, and imidazole with β-carboxyvinyl(triphenyl)phosphonium chloride in boiling acetonitrile are accompanied by elimination of azole with formation of the initial salt and eliminat

Full text of DOI:10.1134/S107036320704010X

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 4, pp. 566 569.
Original Russian Text R.Dzh. Khachikyan, N.V. Tovmasyan, G.V. Asratyan, M.G. Indzhikyan, 2007, published in Zhurnal Obshchei Khimii, 2007,
Vol. 77, No. 4, pp. 607 609.
Pleiades Publishing, Ltd., 2007.
Specificity of the Reaction
of -Carboxyvinyl(triphenyl)phosphonium Chloride with Azoles
R. Dzh. Khachikyan, N. V. Tovmasyan, G. V. Asratyan, and M. G. Indzhikyan
Institute of Organic Chemistry, National Academy of Sciences of Armenia,
ul. Zakariya Kanakertsi 167A, Yerevan, 375091 Armenia
fax: (3741)283511
e-mail: nazotov2004@mail.ru
Received December 23, 2005
Abstract Reactions of pyrazole, 3,5-dimethylpyrazole, 1,2,4-triazole, 5-aminotetrazole, and imidazole with
-carboxyvinyl(triphenyl)phosphonium chloride in boiling acetonitrile are accompanied by elimination of
azole with formation of the initial salt and elimination of triphenylphosphine to give the corresponding azole
hydrochloride and -azolylacrylic acid. In all cases, ethylenebis(triphenylphosphonium) dichloride was
formed, and the reactions with the most nucleophilic 3,5-dimethylpyrazole and imidazole also led to their
adducts with -azolylacrylic acid. In the reactions of pyrazole and 3,5-dimethylpyrazole with -carboxyvinyl-
(triphenyl)phosphonium chloride at room temperature, the corresponding addition products were isolated in
almost quantitative yield.
DOI: 10.1134/S107036320704010X
We previously studied reactions of nucleophiles
with quaternary phosphonium salts having -allenic,
- and -acetylenic, and vinyl groups. These studies
revealed unusually high electrophilicity of triphenyl( -
phenylallenyl)phosphonium bromide [1] and unusual
transformation of , -unsaturated phosphonium salts
into their , -isomers [2]; O-betaines with a positively
charged onium center were isolated [3]; published
data on the inertness of (E)- -carboxyvinylphospho-
nium bromide with respect to triphenylphosphine and
its hydrobromide [4] were shown to be erroneous, etc.
azolylphosphonium salt was 43%, while 5-aminotetra-
zole failed to react under analogous conditions and
was recovered from the reaction mixture.
Interesting results were obtained when the same
reactions were carried out in boiling acetonitrile. The
reaction of salt I with pyrazole gave a mixture of ad-
duct II and ethylenebis(triphenylphosphonium) di-
chloride (III) [4] in 75 and 12% yield, respectively.
We succeeded in isolating 50% of II as individual
substance, while the remaining amount of II was ob-
tained as a mixture with salt III, and the composition
1
In continuation of our previous studies, in the
present work we examined the behavior of -carboxy-
vinyl(triphenyl)phosphonium chloride (I) toward
azoles. It is known that some organophosphorus com-
pounds, especially phosphine oxides, are effective and
very selective extractants for noble and transition
metals; therefore, they have found wide application in
practice. We believed that a combination of azole
and phosphonium moieties in a single molecule could
give rise (after appropriate transformations) to com-
pounds possessing a number of useful properties.
of that mixture was determined on the basis of the H
NMR data. Our results indicated that adduct II un-
derwent decomposition by the action of pyrazole,
which involved elimination of triphenylphosphine,
pyrazole hydrochloride, and -(1H-pyrazol-1-yl)ac-
rylic acid. Triphenylphosphine thus formed reacted
with initial salt I to give diphosphonium dichloride
III according to the scheme given below. We failed to
isolate -(1H-pyrazol-1-yl)acrylic acid.
An alternative pathway of formation of salt III, de-
carboxylation before addition of triphenylphosphine,
is unlikely to occur, for in no case the corresponding
vinylphosphonium salt was detected by 1H NMR
spectroscopy. An analogous pattern was observed in
the reaction of salt I with 3,5-dimethylpyrazole; the
only difference was that 2,3-bis(3,5-dimethyl-1H-
pyrazol-1-yl)propionic acid (IVa) was isolated in ad-
The results of our studies showed that pyrazole and
3,5-dimethylpyrazole smoothly react with phospho-
nium salt I at room temperature to give the corre-
sponding addition products II and IV in almost quan-
titative yields. In the reaction of I with less nucleo-
philic 1,2,4-triazole, the yield of the corresponding
566

SPECIFICITY OF THE REACTION OF -CARBOXYVINYL(TRIPHENYL)PHOSPHONIUM CHLORIDE 567
+
+
+
(C6H5)3P CH2 CH COOH
(C6H5)3P CH=CH COOH
N
Cl
N
H
Cl
N
N
I
II
HN
N
+
+
CH2=C COOH
(C6H5)3P
N
HCl
N
H
N
N
+
+
(C6H5)3P CH2 CH2 P(C6H5)3
Cl Cl
I + (C6H5)3P + HCl
III
dition to salts III and IV. Obviously, acid IVa was
weakest and strongest among the above nucleophiles,
1,2,4-triazole and 3,5-dimethylpyrazole. In the first
case, we isolated a mixture of initial salt II and salt
III (71 and 26%, respectively), and in the second, a
mixture of compounds II, III, IV, and IVa (52, 22,
16, and 6%, respectively).
formed by addition of highly nucleophilic 3,5-dime-
thylpyrazole to
acrylic acid.
-(3,5-dimethyl-1H-pyrazol-1-yl)-
Unlike pyrazole and 3,5-dimethylpyrazole, the
conversion of salt I in the reactions with less nucleo-
philic 1,2,4-triazole and 5-aminotetrazole was incom-
plete even in boiling acetonitrile. In both cases, 20%
of initial salt I was recovered from the reaction mix-
tures. As products we isolated mixtures of phospho-
nium chlorides V and VI with salt III. The yields of
V and VI were 51 and 48%, and the yield of III was
25 and 23%, respectively.
N
HN
+
N
(C6H5)3P CH2 CH COOH
III
Cl
N
N
II
CH3
N
Among the examined azoles, imidazole is the most
basic and nucleophilic. Therefore, it was not surpris-
ing that imidazole reacted with salt I to give a mixture
of VII and III (yield 52 and 25.6%, respectively). As
in the reaction with 3,5-dimethylpyrazole, 2,3-bis(1H-
imidazol-1-yl)propionic acid (VIIa) was also isolated;
compound VIIa was formed as a result of nucleophilic
addition of imidazole to -(1H-imidazol-1-yl)acrylic
H3C
N
H
III + IV + IVa
acid.
These data show that adduct II, as well as com-
pounds IV VI, undergoes both dissociation and
1,2-elimination to give the corresponding azole and
initial salt.
+
(C6H5)3PCH2CH COOH + III
I + RH
Cl
R
IV VII
+
CH2=C COOH + RH
R
R CH2CH COOH
(C6H5)3P CH2 CH COOH
Cl
R
R
+
IVa, VIIa
RH
(C6H5)3P CH=CH COOH
Cl
IV, R = 3,5-dimethyl-1H-pyrazol-1-yl; V, R = 1,2,4-1H-
triazol-1-yl; VI, R = 5-amino-1H-tetrazol-1-yl; VII, R =
1H-imidazol-1-yl.
An alternative pathway of formation of salt IV via
nucleophilic replacement in adduct II seems to be less
probable. Our results also indicate that 1,2,4-triazole
is not competitive in nucleophilic addition reactions.
To elucidate processes occurring in the above reac-
tions, we examined the reactions of adduct II with the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 4 2007

568
KHACHIKYAN et al.
EXPERIMENTAL
dimethylpyrazole in 8 ml of acetonirile we isolated
0.06 g (12%) of compound IVa, mp 209 210 C. H
1
1
The H NMR spectra were recorded on a Varian
Mercury-300 spectrometer at 300 MHz using tetra-
methylsilane as internal reference.
NMR spectrum (DMSO-d6), , ppm: 1.8 s, 1.85 s,
2.1 s, and 2.15 s (3H each, CH3); 4.4 4.6 m (2H,
CH2); 5.15 5.2 m (1H, CH); 5.5 s and 5.6 s (2H,
pyrazole). Found, %: C 59.30; H 6.60; N 21.1.
C13H18N4O2. Calculated, %: C 59.50; H 6.90; N 21.4.
Precipitation with diethyl ether from the filtrate gave
0.59 g of a mixture of salts IV and III in a ratio
of 3:1.
2-Carboxyvinyl(triphenyl)phosphonium chlo-
ride (I) was synthesized by the procedure reported in
[5].
Reaction of 2-carboxyvinyl(triphenyl)phospho-
nium chloride (I) with azoles at room temperature.
A mixture of 0.0004 mol of salt I and 0.0004 mol of
the corresponding azole in 7 ml of acetonitrile was
left to stand for 12 days at room temperature. Products
were precipitated from the solution by adding diethyl
ether, and the precipitate was filtered off and dried
under reduced pressure. In the reaction with pyrazole
we isolated 0.16 g (95%) of salt II, mp 205 205 C.
1H NMR spectrum (DMSO-d6), , ppm: 4.5 4.6 m
(1H, CH2), 4.7 4.9 m (1H, CH2), 5.6 5.75 m (1H,
CH), 5.95 t and 7.15 d (2H, pyrazole), 7.6 7.9 m
(16H, C6H5, pyrazole). Found, %: C 65.5; H 5.0; Cl
8.10; N 6.35. C24H22ClN2O2P. Calculated, %: C 65.9;
H 5.04; Cl 8.13; N 6.41.
In the reaction of 0.55 g of salt I with 0.1 g of
1,2,4-triazole in 6 ml of acetonitrile we isolated by
precipitation with diethyl ether 0.56 g of a mixture of
salts I, V, and III in a ratio of 1:3:1.
In the reaction of 0.6 g of salt I with 0.164 g of
5-aminotetrazole in 6 ml of acetonitrile we isolated by
precipitation with diethyl ether 0.59 g of a mixture of
salts I, VI, and III in a ratio of 1:3:1. 1H NMR spec-
trum of VI (DMSO-d6), , ppm: 4.4 4.6 m (2H,
CH2); 5.2 5.4 m (1H, CH); 7.6 8.0 m (15H, C6H5).
In the reaction of 0.3 g of salt I with 0.06 g of
imidazole in 5 ml of acetonitrile we isolated by pre-
cipitation with diethyl ether 0.27 g of a mixture of
compounds VII, III, and VIIa in a ratio of 6:2:1. 1H
NMR spectrum of VII (DMSO-d6), , ppm: 4.4 4.6
m (2H, CH2); 5.4 5.6 m (1H, CH); 6.8 d, 7.3 d, and
In the reaction with 3,5-dimethylpyrazole we iso-
lated 0.176 g (98%) of salt IV, mp 174 175 C. H
1
NMR spectrum (DMSO-d6), , ppm: 1.75 s (3H,
CH3), 1.9 s (3H, CH3), 4.4 4.7 m (2H, CH2), 5.3 5.4
m (1H, CH), 5.5 s (1H, pyrazole), 7.6 8.0 m (15H,
C6H5). Found, %: C 67.0; H 5.4; Cl 7.54; N 6.00.
C26H26ClN2O2P. Calculated, %: C 67.2; H 5.6; Cl
7.60; N 6.02.
1
7.6 s (3H, imidazole); 7.63 8.0 m (15H, C6H5). H
NMR spectrum of VIIa (DMSO-d6), , ppm: 4.4
4.6 m (1H, CH, and 2H, CH2); 8.01 d and 8.02 d;
8.05 d and 8.06 d (4H, imidazole); 8.45 s and 8.46 s
(2H, imidazole).
In the reaction with 1,2,4-triazole we isolated
Reaction of salt II with 3,5-dimethylpyrazole.
A mixture of 0.26 g of salt II and 0.06 g of 3,5-di-
methylpyrazole in 5 ml of acetonitrile was heated for
14 h under reflux. Precipitation with diethyl ether,
followed by drying under reduced pressure, gave
0.26 g of a mixture of compounds II, IV, III, and
IVa in a ratio of 9:2:4:1.
0.65 g of a mixture of salts I and V in a ratio of 5:4.
1
The H NMR spectrum of I coincided with that given
1
in [5]. H NMR spectrum of V (DMSO-d6), , ppm:
4.4 4.8 m (2H, CH2), 5.5 5.6 m (1H, CH), 7.4 s and
8.4 s (2H, triazole).
Reaction of salt I with azoles in boiling aceto-
nitrile. A mixture of salt I and the corresponding
azole in acetonitrile was heated for 17 h under reflux.
The precipitate was filtered off, washed with diethyl
ether, and dried under reduced pressure. In the reac-
tion of 0.7 g of salt I with 0.13 g of pyrazole in 8 ml
of acetonitrile we isolated 0.4 g (50%) of salt II, mp
Reaction of salt II with 1,2,4-triazole. A mixture
of 0.31 g of salt II and 0.05 g of 1,2,4-triazole in 5 ml
of acetonitrile was heated for 14 h under reflux. Pre-
cipitation with diethyl ether, followed by drying under
reduced pressure, gave 0.29 g of a mixture of salts II
and III in a ratio of 3:1.
1
205 205 C. Its elemental composition and H NMR
spectrum coincided with those of a sample obtained in
the reaction at room temperature. Precipitation with
diethyl ether from the acetonitrile filtrate gave 0.27 g
of a mixture of salts II and III in a ratio of 3:1. The
1H NMR spectrum of III coincided with that given
in [4].
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 4 2007

SPECIFICITY OF THE REACTION OF -CARBOXYVINYL(TRIPHENYL)PHOSPHONIUM CHLORIDE 569
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