A facile synthesis of stable phosphorus ylides derived from 3,6-dibromocarbazole and kinetic investigation of the reactions by UV spectrophotometry technique

Article abstract of DOI:10.1002/hc.20501

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of NH-acid, such as 3,6-dibromocarbazole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond, resulting from the conjugation of the ylide moiety with the adjacent carbonyl group. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometry. The second-order fits were drawn, and the values of the second-order rate constant (k₂) were calculated using standard equations within the program. At the temperature range studied, the dependence of the second-order rate constant (ln k₂) on reciprocal temperature was in a good agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reactions. The proposed mechanism was confirmed according to the obtained results and a steadystate approximation and the first step (k ₂) of reaction was recognized as a rate-determining step on the basis of the experimental data.

Full text of DOI:10.1002/hc.20501

Heteroatom Chemistry
Volume 19, Number 7, 2008
A Facile Synthesis of Stable Phosphorus
Ylides Derived from 3,6-Dibromocarbazole and
Kinetic Investigation of the Reactions by UV
Spectrophotometry Technique
Sayyed Mostafa Habibi-Khorassani, Malek Taher Maghsoodlou,
Mohammad zakarianezhad, Mahmoud Nassiri,
Mohammad Amin Kazemian, and Puya Karimi
Department of Chemistry, University of Sistan and Baluchestan,
P.O. Box 98135-674, Zahedan, Iran
Received 19 February 2008; revised 24 June 2008
rate of reactions. The proposed mechanism was con-
ABSTRACT: Stable crystalline phosphorus ylides
firmed according to the obtained results and a steady-
state approximation and the first step (k2) of reaction
were obtained in excellent yields from the 1:1:1 addi-
tion reaction between triphenylphosphine and dialkyl
acetylenedicarboxylates, in the presence of NH-acid,
was recognized as a rate-determining step on the ba-
ꢀ
C
sis of the experimental data. 2008 Wiley Periodicals,
such as 3,6-dibromocarbazole. These stable ylides ex-
Inc. Heteroatom Chem 19:723–732, 2008; Published on-
ist in solution as a mixture of two geometrical isomers
line in Wiley InterScience (www.interscience.wiley.com).
as a result of restricted rotation around the carbon–
DOI 10.1002/hc.20501
carbon partial double bond, resulting from the conju-
gation of the ylide moiety with the adjacent carbonyl
group. To determine the kinetic parameters of the re-
actions, they were monitored by UV spectrophotom-
etry. The second-order fits were drawn, and the val-
ues of the second-order rate constant (k2) were calcu-
lated using standard equations within the program.
At the temperature range studied, the dependence of
the second-order rate constant (ln k2) on reciprocal
temperature was in a good agreement with the Arrhe-
nius equation. This provided the relevant plots to cal-
culate the activation energy of all reactions. Further-
more, useful information was obtained from studies
of the effect of solvent, structure of reactants (differ-
ent alkyl groups within the dialkyl acetylenedicarboxy-
lates), and also the concentration of reactants on the
INTRODUCTION
Development of simple synthetic routes for widely
used organic compounds from readily available
reagents is one of the major tasks in organic chem-
istry [1]. Phosphorus ylides are reactive systems,
which take part in many valuable reactions of the
organic synthesis [2–11], and they are most often
prepared by the treatment of a phosphonium salt
with a base. Most of the phosphonium salts are pre-
pared from the reaction of phosphine and an alkyl
halide [3–7], though they can be obtained also by
the Michael addition of phosphorus nucleophiles to
activated olefins [2,3]. Herein, we describe an effi-
cient synthetic route to, and kinetic study of, sta-
ble phosphorus ylides, using triphenylphosphine,
dialkyl acetylenedicarboxylates, and NH-acid such
as 3,6-dibromocarbazole. As noted earlier, the car-
bazole moiety and its derivatives are widely used in
Correspondence to: Sayyed Mostafa Habibi Khorassani;
e-mail: smhabibi@chem.usb.ac.ir.
Contract grant sponsor: University of Sistan & Baluchestan,
Zahedan, Iran.
c
ꢀ
2008 Wiley Periodicals, Inc.
723

724 Habibi-Khorassani et al.
FIGURE 1 The reaction between triphenylphosphine 1, di-
alkyl acetylenedicarboxylate 2 (2a, 2b, or 2c), and 3,6-
dibromocarbazole 3 for generation of stable phosphorus
ylides 4(4a, 4b, or 4c).
FIGURE 2 Two geometrical isomers (major and minor) of
stable phosphorus ylides 4 (4a or 4b).
13C, and 31P NMR spectra. Their mass spectra dis-
played molecular ion peaks at appropriate m/z val-
ues, and initial fragmentations involve the loss of
parts or complete side chains and scission of the
the preparation of medicines [12]. With respect to
the importance of the recent purposes, the present
work was undertaken for the generation of stable
phosphoranes. Accordingly, the reaction of triph-
enylphosphine 1 with dialkyl acetylenedicarboxy-
lates 2 (2a, 2b, or 2c) in the presence of a NH-acid
3 led to the corresponding stable heterocyclic phos-
phorus ylides 4 (4a, 4b, or 4c) in excellent yields (see
Fig. 1).
1
heterocyclic ring system. The H, 13C, and 31P NMR
spectra of ylides 4a and 4b are consistent with the
presence of two isomers. The ylides moiety of these
compounds is strongly conjugated with the adjacent
carbonyl group, and rotation around the partial dou-
ble bond in (E)-4 and (Z)-4 geometrical isomers is
slow on the NMR time scale at ambient temperature
1
(see Fig. 2). Selected H, 13C, and 31P NMR chemi-
RESULTS AND DISCUSSION
cal shifts and coupling constants in the major (M)
and minor (m) geometrical isomers of compounds
4a and 4b are presented in Table 1. As can be ob-
served, only one geometrical isomer (Z)-4 was ob-
served for 4c, presumably, because of the bulky tert-
butyl groups.
Reactions of 3,6-dibromocarbazole 3 with dialkyl
acetylenedicarboxylates 2 in the presence of triph-
enylphosphine 1 were carried out in acetone at room
temperature and were completed within a few hours.
1
The H and 13C NMR spectra of the crude products
clearly indicated the formation of stable phospho-
rus ylides 4. Any products other than 4 could not
be detected by NMR spectroscopy. The structures of
The structural assignment of (E)-4 and (Z)-4
rotamers as the major or minor form in phospho-
rus ylides has been previously established and is re-
ported in the literature [13–16]. Herein, the 1H NMR
1
compounds 4a–c were deduced from their IR, H,
TABLE 1 Selected 1H, 13C, and 31P NMR Chemical Shifts (δ in ppm) and Coupling Constants (J in Hz) for H-2, OR, CO2R,
C-2, and C-3 in the Major (M) and Minor (m) Geometrical Isomers of Compounds 4a–c
1H NMR Spectroscopy Data
13C NMR Data
C-2 (2JPC
Compound
R in 4
Isomer (%)
H-2 (3JPH
)
OR
CO2R
)
C-3 ( 1JPC
)
31P NMR
4a
4a
4b
4b
4c
Me
Me
Et
M(69)
m(31)
M(73)
m(27)
M
5.34 (16.2)
5.26 (18.6)
5.29 (16.7)
5.21 (19.3)
5.08 (18.1)
3.24
3.74
4.20
3.78
1.04
3.76
3.81
4.29
3.88
1.60
58.5 (15.1)
58.6 (15.3)
58.6 (15.4)
58.34 (14.9)
59.15 (15.7)
41.46 (122.9)
41.99 (131.7)
41.23 (122.7)
41.74 (133.6)
40.6 (123.1)
23.38
24.34
23.42
24.73
23.17
Et
tBu
Heteroatom Chemistry DOI 10.1002/hc

Facile Synthesis of Stable Phosphorus Ylides and Kinetic Investigation of the Reactions 725
absorption at 1735–1624 cm−1 for these compounds.
Conjugation with the negative charge appears to be
a plausible factor in the reduction of the wave num-
bers of the carbonyl absorption bands.
On the basis of the well-established chemistry of
trivalent phosphorus nucleophiles [2–6], it is reason-
able to assume that phosphorus ylide 4 results from
the initial addition of triphenylphosphine 1 to the
acetylenic ester 2 (rate constant k2) and subsequent
protonation of the 1:1 adduct (I1) by the NH-acid
3 (rate constant k3) to form phosphoranes 4 (rate
constant k4) (see Fig. 3).
spectrum of compound 4a exhibits two single sharp
lines (δ 3.74 and 3.81) arising from the metoxy group
in the E−rotamer and two single sharp resonances
at 3.24 and 3.76 ppm for methoxy groups in the Z-
rotamer. The shift at 3.24 of methoxy group of the
Z-rotamer is shielded, due to the anisotropic effect
of the phenyl group of triphenylphosphine. This ef-
fect confirms that the (E)-4 and (Z)-4 rotamers could
appear as the minor and major forms, respectively,
with respect to the experimental abundance percent-
age of both isomers that have been reported in the
experimental section. Also signals for methine pro-
tons at δ = 5.34 and 5.26 ppm, which appear as two
doublets for the N CH group, respectively, for the
major and minor geometrical isomers. The 13C NMR
spectrum of 4a exhibited 44 distinct resonances that
are in a good agreement with the mixture of two ro-
tational isomers. Although the presence of the 31P
nucleus complicates both the 1H and 13C NMR spec-
tra of 4a, it helps in assignment of the signals by
long-range couplings with the 1H and 13C nuclei (see
the experimental section). The 1H and 13C NMR spec-
tra of (4b–c) are similar to those of 4a, except for
the ester groups, which exhibited characteristic res-
onances with appropriate chemical shifts (see the
EXPERIMENTAL
Melting points, IR, and UV spectra of all com-
pounds were measured on an Electrothermal 9100
apparatus, a Shimadzu IR-460 spectrometer, and
a Cary UV–vis spectrophotometer model Bio-300
with a 10-mm light-path quartz spectrophotometer
1
cell, respectively. In addition, the H, 13C, and 31P
NMR spectra were obtained from a Bruker DRX-300
Avance instrument with CDCl3 as a solvent at 300.1,
121.4, and 75.5 MHz, respectively. The mass spec-
tra were recorded on a Shimadzu QP 1100 EX mass
spectrometer, operating at an ionization potential of
70 eV. Elemental analyses for C, H, and N were per-
formed using a Heraeus CHM-O-Rapid analyzer. Di-
alkyl acetylenedicarboxylates, triphenylphosphine,
and 3,6-dibromocarbazole were purchased from
Fluka (Buchs, Switzerland) and were used without
further purification.
1
experimental section). The H and 13C NMR spec-
tral data for compounds (4a–b) are consistent with
the geometrical isomers. The structural assignments
made on the basis of the 1H and 13C NMR spectra of
compounds (4a–c) were supported by the IR spectra.
The carbonyl region of the spectra exhibited two dis-
tinct absorption bands for each compound (see the
experimental section). Of special interest is the ester
Preparation of Dimethyl
2-(3,6-dibromocarbazole -1-yl)-3-
(triphenylphosphoranylidene)-butanedioate (4a)
General Procedure. To a magnetically stirred so-
lution of triphenylphosphine (0.26 g or 1 mmol) and
3,6 dibromocarbazole (0.33 g or 1 mmol) in 10 mL
of acetone, a solution of dimethyl acetylenedicar-
boxylate (0.14 g or 1 mmol) in 4 mL of acetone at
−5◦C for more than 10 min was dropwise added.
After approximately 8 h stirring at room tempera-
ture, the product was filtered and recrystallized from
acetone. Colorless crystals. mp 205–207◦C, yield
0.67 g, 94%. IR (KBr) (νmax, cm−1): 1735 and 1626
(C O). MS (m/z, %): 729 (M, 20), 467 (M-PPh3, 34),
407 (M-C12H6NBr2, 7), 262 (PPh3, 60), 183 (PPh2, 79),
108 (PPh, 52). Anal. calcd for C36H28Br2NO4P (729):
C, 59.16; H, 3.86; N, 1.92%. Found: C, 59.26; H, 3.84;
N, 1.92%.
Major isomer (Z)-4a (69%), 1H NMR (300.1
MHz, CDCl3) δ: 3.24 and 3.76 (6H, 2s, 2OCH3),
5.34 (1H, d, JPH = 16.2 Hz, P C CH), 7.25–7.49
FIGURE 3 Proposed mechanism for the reaction between
1, 2 (2a, 2b, or 2c), and 3 for generation of phosphorus ylides
4 (4a–4c).
3
Heteroatom Chemistry DOI 10.1002/hc

726 Habibi-Khorassani et al.
(19 Harom, 3C6H5, and C12H4N), 8.01(1Hbro, Ha), 8.08
3C6H5, and C12H4NBr), 8.05 (1H, Ha), 8.06 (1H,
(1Hbro, Hb): 13C NMR (75.5 MHz, CDCl3) δ: 41.46
Hb). 13C NMR (75.5 MHz, CDCl3) δ: 14.99 and
1
1
(d, JPC = 122.9 Hz, P C), 49.53 and 52.87 (2OCH3),
15.33 (2OCH2CH3), 41.74 (d, JPC = 133.6 Hz, P C),
2
2
58.50 (d, JPC = 15.1 Hz, P C CH), 111.90, 112.02,
58.34 (d, JPC = 14.9 Hz, P C CH), 58.94 and
112.30, 122.35, and 123.81 (10C, C12H8N), 125.88 (d,
1 JPC = 91.7 Hz, Cipso), 128.81 (d, 3 JPC = 12.3 Hz, Cmeta),
132.19 (Cpara), 133.31 (d, 2 JPC = 9.7 Hz, Cortho), 138.96
(1C, C12H6N), 169.39 (d, 3 JPC = 12.2 Hz, C O), 171.93
61.38 (2OCH2CH3), 111.97, 122.42, and 123.96 (6C,
C12H8N), 125.58 (d, 1 JPC = 92.0 Hz, Cipso), 128.45 (2C,
3
C12H6N), 128.78 (d, JPC = 12.2 Hz, Cmeta), 132.00
(2C, C12H6N), 132.08 (Cpara), 133.44 (d, 2 JPC = 9.7 Hz,
Cortho), 139.42 (2C, C12H6N), 169.83 (d, 3 JPC = 13.5 Hz,
2
(d, JPC = 15.7 Hz, P C C). 31P NMR (121.5 MHz,
CDCl3) δ: 23.38 (Ph3P+ C).
C O), 171.09 (d, JPC = 14.2 Hz, P C C). 31P NMR
2
Minor isomer (E)-4a (31%), 1H NMR (500.1
MHz, CDCl3) δ: 3.74 and 3.81 (6H, 2s, 2OCH3),
(121.5 MHz, CDCl3) δ: 24.73 (Ph3P+ C).
3
5.26 (1H, d, JPH = 18.6 Hz, P C CH), 7.25–7.49
Di-tert-buthyl 2-(3,6- dibromocarbazole -1-yl)-3-
triphenylphosphoranylidene)-butanedioate (4c)
(19 Harom, 3C6H5, and C12H4N), 8.04(1Hbro, Ha), 8.09
(1Hbro, Hb). 13C NMR (75.5 MHz, CDCl3) δ: 41.99
1
(d, JPC = 131.7 Hz, P C), 50.67 and 52.60 (2OCH3),
Colorless crystals. mp 135–137◦C, yield 0.77 g, 95%.
IR (KBr) (νmax, cm−1): 1735 and 1628 (C O). MS (m/z,
%): 549 (M-PPh3, 31), 347 (M-PPh3 and CO2Me3, 7),
262 (PPh3, 77), 183 (PPh2, 77), 108 (PPh, 58). Anal.
calcd for C42H40Br2NO4P (813): C, 62.12; H, 4.88; N,
1.68. Found: C, 61.99; H, 4.92; N, 1.72.
2
58.64 (d, JPC = 15.3 Hz, P C CH), 111.95 and
112.07, 112.33, 122.47, and 123.96 (10C, C12H8N),
125.27 (d, 1 JPC = 91.9 Hz, Cipso), 128.76 (d, 3 JPC = 11.8
2
Hz, Cmeta), 132.15 (Cpara), 133.44 (d, JPC = 9.7 Hz,
Cortho), 139.28 (1C, C12H8N), 169.97 (d, 3 JPC = 17.1 Hz,
2
C O), 170.83 (d, JPC = 14.9 Hz, P C C). 31P NMR
Major isomer (Z)-4c 1H NMR (300.1 MHz, CDCl3)
δ: 1.04 and 1.60 (18H, 2s, 2CMe3), 5.08 (1H, d,
3 JPH = 18.1 Hz, P C CH), 7.23–7.56 (19Harom, 3C6H5,
and C12H4NBr), 8.01 (1H, Ha), 8.04 (1H, Hb): 13C
NMR (75.5 MHz, CDCl3) δ: 28.22 and 28.44 (2CMe3),
40.60 (d, 1 JPC = 123.1 Hz, P C), 59.15 (d, 2 JPC = 15.7
Hz, P C CH), 77.67 and 81.09 (2OCMe3), 111.78,
118.01, 122.17, and 123.82 (8C, C12H8N), 126.57 (d,
1 JPC = 91.2 Hz, Cipso), 128.32 (1C, C12H6N), 128.52 (d,
3 JPC = 12.2 Hz, Cmeta), 131.97 (d, 4 JPC = 2.1 Hz, Cpara),
133.44 (d, 2 JPC = 9.7 Hz, Cortho), 139.61 (2C, C12H6N),
168.60 (d, 3 JPC = 11.8 Hz, C O), 169.61 (d, 2 JPC = 14.7
Hz, P C C). 31P NMR (121.5.4 MHz, CDCl3) δ: 23.17
(Ph3P+ C).
(121.5 MHz, CDCl3) δ: 24.34 (Ph3P+ C).
Diethyl 2-(3,6- dibromocarbazole -1-yl)-3-
(triphenylphosphoranylidene)-butanedioate (4b)
Colorless crystals. mp 177–179◦C, yield 0.69 g, 92%.
IR (KBr) (νmax, cm−1): 1730 and 1624 (C O). MS (m/z,
%): 586 (M-2OEt and Br, 33), 557 (M-2OEt and PPh,
76), 493 (M-PPh3, 9), 325 (M-C12H6NBr2 and PPh,
59), 262 (PPh3, 60), 183 (PPh2, 76), 108 (PPh, 40).
Anal. calcd for C38H32Br2NO4P (757): C, 60.14; H,
4.25; N, 1.85. Found: C, 60.24; H, 4.23; N, 1.85.
Major isomer (Z)-4b (73%), 1H NMR (300.1
3
MHz, CDCl3) δ: 0.50 and 1.23 (6H, 2t, JHH = 7.1
Hz, CH3 in 2OCH2CH3), 4.20 and 4.29 (4H, 2 m,
KINETIC STUDIES
2ABX3system, and CH2 in 2OCH2CH3), 5.29 (1H,
3
d, JPH = 16.7 Hz, P C CH), 7.23–7.53 (19Harom
,
The synthetic reactions between triphenylphosphine
1, dialkyl acetylenedicarboxylates 2, and CH, SH,
or NH-acids have been reported earlier [17–34], but
the kinetic study of these reactions has not been yet
investigated. Herein, we describe a kinetic investi-
gation of the current synthesis. Numerous kinetic
investigations over a large area of different reac-
tions have been reported previously using UV analy-
sis [35–40]. To gain further insight into the reaction
mechanism, a kinetic study of the reactions was un-
dertaken by UV spectrophotometric technique. First,
it was necessary to find the appropriate wavelength
to follow the kinetic study of the reaction. For this
purpose, in the first experiment, 3 × 10−3 M solu-
tion of compounds 1, 2c, and 3 was prepared in 1,4-
dioxane as a solvent. Approximately, 3 mL aliquot
from each reactant was pipetted into a 10-mm light
3C6H5, and C12H4NBr), 8.02 (1H, Ha), 8.06 (1H, Hb).
13C NMR (75.5 MHz, CDCl3) δ: 14.08 and 14.22
1
(2OCH2CH3), 41.23 (d, JPC = 122.7 Hz, P C), 58.14
2
(OCH2CH3), 58.57 (d, JPC = 15.4, Hz, P C CH),
61.60 (OCH2CH3), 111.81, 122.27, and 122.42 (6C,
C12H8N), 126.11 (d, 1 JPC = 91.6 Hz, Cipso), 128.33 (2C,
3
C12H6N), 128.71 (d, JPC = 12.3 Hz, Cmeta), 132.04
(2C, C12H6N), 132.11 (Cpara), 133.38 (d, 2 JPC = 9.7 Hz,
Cortho), 139.11 (2C, C12H6N), 168.97 (d, 3 JPC = 12.2 Hz,
C O), 171.25 (d, JPC = 15.5 Hz, P C C). 31P NMR
2
(121.5 MHz, CDCl3) δ: 23.42 (Ph3P+ C).
Minor isomer (E)-4b (27%), 1H NMR (300.1
3
MHz, CDCl3) δ: 1.25 and 1.35 (6H, 2t, JHH = 7.00
Hz, CH3 in 2OCH2CH3), 3.78 and 3.88 (4H, 2
m, 2ABX3system, CH2 in 2OCH2CH3), 5.21 (1H,
3
d, JPH = 19.3 Hz, P C CH), 7.23–7.53 (19Harom
,
Heteroatom Chemistry DOI 10.1002/hc

Facile Synthesis of Stable Phosphorus Ylides and Kinetic Investigation of the Reactions 727
FIGURE 4 The UV spectra of the reaction between 1, 2c,
and 3 with 10−3 M concentration of each compound as reac-
tion proceeds in 1, 4-dioxane with 10 mm light-path cell.
FIGURE 5 Second-order fit curve (full line) accompanied by
the original experimental curve (dotted line) for the reaction
between compounds 1, 2c, and 3 at 368 nm and 12.0◦C in
1,4-dioxane.
path quartz spectrophotometer cell, and the relevant
spectra were recorded over the wavelength range
190–400 nm. In a second experiment, a 1-mL aliquot
from the 3 × 10−3 M solutions of each compound of
1 and 3 was pipetted first into a quartz spectropho-
tometer cell (as there is no reaction between them),
later 1-mL aliquot of the 3 × 10−3 M solution of re-
actant 2c was added to the mixture and the reaction
monitored by recording scans of the entire spectra
every 13 min over the whole reaction time at ambient
temperature. The ultraviolet spectra shown in Fig. 4
are typical. From this, the appropriate wavelength
was found to be 368 nm (corresponding mainly to
product 4c). Because at this wavelength, compounds
1, 2c, and 3 have relatively no absorbance value.
This, then provided the opportunity to fully inves-
tigate the kinetics of the reaction between triph-
enylphosphine 1, di-tert-butyl acetylenedicarboxy-
late 2c, and 3, 6-dibromocarbazole 3 at 368 nm in
the presence of 1,4-dioxane as solvent. Because the
spectrophotometer cell of the UV instrument had
a 10-mm light path cuvette, the UV–vis spectra of
compound 4c were measured over the concentra-
tion range (2 × 10−4 M ≤ M4c ≤ 10−3 M) to check
for a linear relationship between absorbance values
and concentrations. With the suitable concentration
range and wavelength identified, the following pro-
cedure was employed.
action between compounds 1, 2c, and 3 at 12.0◦C.
The infinity absorbance (A∞) that is the absorbance
at reaction completion can be obtained from Fig. 5
at t = 214 min. With respect to this value, zero, first,
or second curve fitting could be drawn automati-
cally for the reaction by the software [41] associ-
ated with the UV instrument. Using the original ex-
perimental absorbance versus time data provided a
second-order fit curve (full line) that fits exactly the
experimental curve (dotted line) as shown in Fig. 5.
Thus, the reaction between triphenylphosphine 1, di-
tert-butyl acetylenedicarboxylate 2c, and 3 follows
second-order kinetics. The second-order rate con-
stant (k2) is then automatically calculated using a
standard equation [41] within the program at 12.0◦C.
It is reported in Table 2.
Furthermore, kinetic studies were carried out us-
ing the same concentration of each reactant in the
continuation of experiments with concentrations of
5 × 10−3 M and 7 × 10−3 M, respectively. As expected,
the second-order rate constant was independent of
concentration and its value was the same as in the
TABLE 2 Values of Overall Second-Order Rate Constant for
the Reaction Between 1, 2c, and 3 in the Presence of Solvents
Such As 1,4-Dioxane, Ethyl Acetate, and 1,2-Dichloroethane,
Respectively, at All Temperatures Investigated
For each kinetic experiment, first a 1-mL aliquot
from each freshly made 3 × 10−3 M solution of com-
pounds 1 and 3 in 1,4-dioxane was pipetted into a
k2 (M −1 min−1
12.0 ◦C 17.0 ◦C 22.0 ◦C 27.0 ◦C
)
quartz cell, and then a 1-mL aliquot of the 3 × 10−3
M
of solution of reactant 2c was added to the mix-
ture, keeping the temperature at 12.0◦C. The reac-
tion kinetics was followed by plotting UV absorbance
against time. Figure 5 shows the absorbance change
(dotted line) versus time for the 1:1:1 addition re-
Solvent
δ
1,4-Dioxane
Ethyl acetate
1,2-Dichloroethane 10 78.8
2
6
56.8
67.0
70.1
81.3
93.1
82.3
93.6
109.3
98.8
109.7
123.6
Heteroatom Chemistry DOI 10.1002/hc

728 Habibi-Khorassani et al.
previous experiment. In addition, the overall order
of reaction was also two.
Effect of Solvents and Temperature
To determine the effect of change in temperature
and solvent environment on the rate of reaction, it
was elected to perform various experiments at dif-
ferent temperatures and solvent polarities but oth-
erwise under the same conditions as for the pre-
vious experiment. For this purpose, ethyl acetate
and 1,2-dichloroethane with 6- and 10-dielectric con-
stants, respectively, were chosen as suitable solvents
because they could not only be dissolved all com-
pounds but also did not react with them. The effects
of solvents and temperature on the rate constant are
given in Table 2. The results show that the rate of
reaction in each case was increased at higher tem-
perature. In addition, the rate of reaction between
1, 2c, and 3 was accelerated in a higher dielectric
constant environment (1,2-dichloroethane) in com-
parison with a lower dielectric constant environment
(1,4-dioxane) at all temperatures investigated. In the
temperature range studied, the dependence of the
second-order rate constant (ln k2) of the reactions on
reciprocal temperature is consistent with the Arrhe-
nius equation, giving activation energies of reaction
between 1, 2c, and 3 (25.8 kJ/mol) from the slope of
Fig. 6.
FIGURE 7 Pseudo-first-order fit curve (full line) for the reac-
tion between 2c and 3 in the presence of excess 1 (10−2 M)
at 368 nm and 12.0◦C in 1,4-dioxane.
of excess 3. Under this condition, the rate equation
may therefore be expressed as
Rate = kobs [1]a [2]β − kobs = k2 [3]γ or
ln kobs = ln k2 + γ ln [3]
(1)
In this case (3 × 10−2 M of 3 instead of 3 × 10−3 M),
using the original experimental absorbance versus
time data provides a second-order fit curve (full line)
against the time at 368 nm that exactly fits the exper-
imental curve. The value of the rate constant was the
same as that of obtained from the previous experi-
ment (3 × 10−3 M). Repetition of the experiments
with 5 × 10−2 M and 7 × 10−2 M concentrations of
3 gave, separately, the same fit curve and the rate
constant. In fact, the experimental data indicated
that the observed pseudo-second-order rate constant
(kobs) is equal to the second-order rate constant (k2),
this is possible when γ is zero in Eq. (1). It is ap-
peared, therefore, that the reaction is zero and sec-
ond order with respect to 3 (NH-acid) and the sum
of 1 and 2 (2c) (α + β = 2), respectively. To de-
termine the reaction order with respect to dialkyl
acetylenedicarboxilate 2 (2c), the continuation of ex-
periment was performed in the presence of excess 1
Effect of the Concentration
To determine the reaction order with respect to
triphenylphosphine 1 and dialkyl acetylenedicar-
boxylate 2 (2c), in the continuation of experiments,
all kinetic studies were carried out in the presence
4.7
4.6
4.5
4.4
k
4.3
4.2
4.1
4
Rate = k´ [3]γ [2]β
obs
k´ = k2[1]α
(2)
obs
The original experimental absorbance versus time
data provides a pseudo-first-order fit curve at
368 nm, which exactly fits the experimental curve
(dotted line) as shown in Fig. 7. As a result, since
γ = 0 (as determined previously), it is reasonable to
accept that the reaction is first order with respect to
the compound 2 (2c) (β = 1).
3.3
3.35
3.4
3.45
3.5
3.55
1000 / T
FIGURE 6 Dependence of second-order rate constant
(ln k2) on reciprocal temperature for the reaction between
1, 2c, and 3 measured at wavelength 368 nm in 1,4-dioxane
in accordance with the Arrhenius equation.
Heteroatom Chemistry DOI 10.1002/hc

Facile Synthesis of Stable Phosphorus Ylides and Kinetic Investigation of the Reactions 729
Because the overall order of reaction is 2 (α +
ions. The solvent thus would stabilize the species
ions more than it does the transition state, and there-
fore Ea would be higher, slowing down the reaction.
However, in practice, 1,2-dichloroethane speeds up
the reaction and for this reason, the fourth step,
which is independent of the change in the solvent
medium, could not be the rate-determining step.
Furthermore, the rate law of formation of the prod-
uct (fourth step) for a proposed reaction mechanism
with application of the steady-state assumption can
be expressed by
β + γ = 2), it is obvious that α = 1 and the order of
triphenylphosphine 1 must be equal to 1. This ob-
servation was also obtained for reactions between
(1, 2b, and 3) and (1, 2a, and 3). Based on the above
results, a simplified proposed reaction mechanism
is shown in Fig. 3. The experimental results indicate
that the third step (rate constant k3) is possibly fast.
In contrast, it may be assumed that the third step is
the rate-determining step for the proposed mecha-
nism. In this case, the rate law can be expressed as
follows:
Rate = k4 [I2] [N−].
By application of steady state for [I−] and [N−], and
replacement of their values in the above equation,
the following equation is obtained:
Rate = k3 [I1]
(3)
The steady-state assumption can be employed
for [I1] that generates the following equation:
k2[1] [2]
[I1] =
k2 k3 [1] [2] [3]
k−2 + k3[3]
Rate =
(4)
k−2 + k3 [3]
The value of [I1] can be replaced in Eq. (3) to obtain
this equation
This equation is independent of the rate constant of
the fourth step (k4) and shows why the fourth step
would not be affected by a change in the solvent
medium. In addition, it has been suggested earlier
that the kinetics of ionic species phenomena (e.g.,
the fourth step) is very fast [42–45]. If the first step
(rate constant k2) were the rate-determining step, in
this case, two reactants (triphenylphosphine 1 and
dialkyl acetylenedicarboxylate 2), as we see (Fig. 3),
have no charge and could not form strong ion–dipole
bonds to the high dielectric constant solvent, 1,2-
dichloroethane. However, the transition state carries
a dispersed charge, which here is divided between
the attacking 1 and 2 and, hence bonding of solvent
to this dispersed charge is much stronger than to the
reactants, which lack the charge. The solvent thus
stabilizes the transition state more than it does the
reactants and, therefore, Ea is reduced that speeds
up the reaction. Our experimental results show that
the solvent with the higher dielectric constant exerts
a powerful effect on the rate of reaction (in fact, the
first step has rate constant k2 in the proposed mecha-
nism), but the opposite occurs with the solvent with
lower dielectric constant (1,4-dioxane, see Tables 2–
4). The results of the present work (effects of the
solvent and the concentration of compounds) have
provided useful evidence for steps 1 (k2), 3 (k3), and
4 (k4) of the reactions between triphenylphosphine
1, dialkyl acetylenedicarboxylate 2 (2a, 2b, or 2c),
and 3,6-dibromocarbazole 3. Two steps involving 3
and 4 are not the rate-determining step although
the discussed effects, taken altogether, are compat-
ible with the first step (k2) of the proposed mecha-
nism and would allow it to be the rate-determining
step. However, a good kinetic description of the
k2 k3 [1] [2] [3]
Rate =
k−2 + k3 [3]
Because it was assumed that k3 is relevant to the
rate-determining step, it is reasonable to make the
following assumption:
k−2 ꢁ k3[3]
so the rate low becomes
k2 k3 [1] [2] [3]
Rate =
k−2
The last equation indicates that the overall reaction
order is three, which is not compatible with the ex-
perimental overall reaction order (two). In addition,
according to this equation, the order of reaction with
respect to 3,6-dibromocarbazole 3 is one, whereas
it was actually shown to be equal to zero. For this
reason, it appears that the third step is fast. If we
assume that the fourth step (rate constant k4) is the
rate-determining step for the proposed mechanism,
in this case, there are two ionic species to consider
in the rate-determining step, namely, phosphonium
ion (I2) and carbazole ion (N−). The phosphonium
and carbazole ions, as we see in Fig. 3, have full
positive and negative charges and form very power-
ful ion–dipole bonds to 1,2-dichloroethane, the high
dielectric constant solvent. However, the transition
state for the reaction between the two ions carries a
dispersed charge, which here is divided between the
attacking carbazole and the phosphonium ions. A
bonding of solvent (1,2-dichloroethane) to this dis-
persed charge would be much weaker than to the
concentrated charge of carbazole and phosphonium
Heteroatom Chemistry DOI 10.1002/hc

730 Habibi-Khorassani et al.
TABLE 3 Values of Overall Second-Order Rate Constant
for the Reaction Between 1, 2b, and 3 in the Pres-
ence of Solvents Such As 1,4-Dioxane, Ethyl Acetate,
and 1,2-Dichloroethane, Respectively, at All Temperatures
Investigated
We can now replace [I1] in Eq. (6) to obtain the fol-
lowing equation:
k2 k3 [1] [2] [3]
ꢀ
ꢁ
[I2] =
k4 [N−] k−2 + k3 [3]
k2(M −1 min −1
12.0 ◦C 17.0 ◦C 22.0 ◦C 27.0 ◦C
)
The value of [I2] can be put into Eq. (5) to obtain the
rate equation (8) for the proposed mechanism
Solvent
δ
k2 k3 k4[1] [2] [3] [N−]
1,4-Dioxane
Ethyl acetate
1,2-Dichloroethane 10 437.5
2
6
319.2
350.2
355.1
387.1
452.6
381.5
423.0
507.3
413.3
452.3
557.4
Rate =
Rate =
or
k4 [N−] [k−2 + k3 [3]]
(8)
k2 k3 [1] [2] [3]
[k−2 + k3 [3]]
experimental result using a mechanistic scheme
based on the steady-state approximation is fre-
quently taken as evidence of its validity. By appli-
cation of this, the rate formation of product 4 from
the reaction mechanism (Fig. 3) is given by
Since the experimental data have indicated that
steps 3 (k3) and 4 (k4) are fast but step 1 (k2) is slow,
it is therefore reasonable to make the following as-
sumption:
k3[3] ꢁ k−2.
So the rate equation becomes
d[4]
d[ylide]
=
= Rate = k4 [I2] [N−]
(5)
d t
d t
We can apply the steady-state approximation to [I1]
and [I2]
Rate = k2 [1] [2]
(9)
This equation, which was obtained from a mechanis-
tic scheme (shown in Fig. 3) by applying the steady-
state approximation, is compatible with the results
obtained by UV spectrophotometry.
d[I1]
= k2 [1] [2] − k−2 [I1] − k3 [I1] [3]
d t
d [I2]
= k3 [I1] [3] − k4 [I2] [N−]
d t
To obtain a suitable expression for [I2] to put into
Eq. (5), we can assume that, after an initial brief
period, the concentrations of [I1] and [I2] become
a steady state with their the rates of formation and
the rates of disappearance are just balanced. There-
fore, d[I1]/dt and d[I2]/dt are zero and we can obtain
expressions for [I2] and [I1] as follows:
Further Kinetic Investigations
Effect of Structure of Dialkyl Acetylenedi-
carboxylates. To confirm the above observations,
further experiments were performed with diethyl
acetylenedicarboxylate 2b and dimethyl acetylenedi-
carboxylate 2a, respectively, under the same condi-
tions used in the previous experiments. The values of
the second-order rate constant (k2) for the reactions
between (1, 2b, and 3) and (1, 2a, and 3) are re-
ported in Tables 3 and 4, respectively, for all solvents
and temperatures investigated. The original exper-
imental absorbance curves (dotted line) accompa-
nied by the second-order fit curves (full line), which
exactly fit experimental curves (dotted line), for both
reactions are shown in Figs. 8 and 9 at 12.0◦C and
368 nm.
d [I2]
= 0
d t
(6)
k3[I1] [3]
[I2]
=
k4 [N−]
d [I1]
d t
= 0
(7)
k2[1] [2]
[I1]
=
k−2 + k3 [3]
As can be seen from Tables 3 and 4, the behavior
of diethyl acetylenedicarboxylate 2b and dimethyl
acetylenedicarboxylate 2a is the same as for di-tert-
butyl acetylenedicarboxylate 2c (Table 2) with re-
spect to the reaction with triphenylphosphine 1 and
3,6-dibromocarbazole 3. The rate of the former reac-
tions was also accelerated in a higher dielectric con-
stant environment and with higher temperatures;
however, these rates under the same condition are
approximately five to seven times more than for the
reaction with di-tert-butyl acetylenedicarboxylate 2c
TABLE 4 Values of Overall Second-Order Rate Constant for
the Reaction Between 1, 2a, and 3 in the Presence of Solvents
Such As 1, 4-Dioxan, Ethyl Acetate, and 1, 2-Dichloroethane,
Respectively, at All Temperatures Investigated
k2 (M −1 min −1
12.0 ◦C 17.0 ◦C 22.0 ◦C 27.0 ◦C
)
Solvent
δ
1,4-Dioxane
Ethyl acetate
1,2-Dichloroethane 10 548.3
2
6
432.1
478.6
475.3
517.8
573.5
505.1
540.2
617.7
541.8
596.7
669.2
Heteroatom Chemistry DOI 10.1002/hc

Facile Synthesis of Stable Phosphorus Ylides and Kinetic Investigation of the Reactions 731
advantage that not only the reaction is performed un-
der neutral conditions but also the substances can be
mixed without any activation or modifications. The
stable phosphorus ylides 4 (4a, 4b, or 4c) are poten-
tially useful synthetic intermediates, and the proce-
dure described here may be acceptable for the prepa-
ration of phosphoranes with variable functionalities.
In addition, kinetic investigation of these reactions
was undertaken using UV spectrophotometry. The
results can be summarized as follows: (1) The ap-
propriate wavelengths and concentrations were de-
termined to follow the reaction kinetics. (2) The
overall reaction order followed second-order kinet-
ics and the reaction orders with respect to triph-
enylphosphine, dialkyl acetylenedicarboxylate, and
3,6-dibromocarbazole were one, one, and zero, re-
spectively. (3) The values of the second-order rate
constants of all reactions were calculated automat-
ically with respect to the standard equation, using
the software associated with the Cary-300 UV equip-
ment. (4) The rates of all reactions were acceler-
ated at higher temperatures. Under the same con-
ditions, the activation energy of the reaction with
di-tert-butyl acetylenedicarboxylate 2c (25.8 kJ/mol)
was higher than that for both the reactions, which
were followed by the diethyl acetylenedicarboxylate
2b (12.04 kJ/mol) and dimethyl acetylenedicarboxy-
late 2a (10.47 kJ/mol) in 1,4-dioxane. (5) The rates
of all reactions were increased in solvents of higher
dielectric constant and this can be related to differ-
ences in stabilization by the solvent of the reactants
and the activated complex in the transition state. (6)
Increased steric bulk in the alkyl groups of the dialkyl
acetylenedicarboxylates, accompanied by the cor-
respondingly greater inductive effect, reduced the
overall reaction rate. (7) With respect to the exper-
imental data, the first step of proposed mechanism
was recognized as the rate-determining step (k2), and
this was confirmed based on the steady-state approx-
imation.
FIGURE 8 Second-order fit curve (full line) accompanied by
the original experimental curve (dotted line) for the reaction
between 1, 2b, and 3 at 368 nm and 12.0◦C in 1, 4-dioxane.
FIGURE 9 Second-order fit curve (full line) accompanied by
the original experimental curve (dotted line) for the reaction
between 1, 2a, and 3 at 368 nm and 12.0◦C in 1, 4-dioxane.
(see Tables 2–4). It seems that both inductive and
steric factors for the bulky alkyl groups in 2c tend to
reduce the overall reaction rate (see Eq. (9)). In the
case of dimetyl acetylenedicarboxylate 2a, the lower
steric and inductive effects of the dimethyl groups
exert a powerful effect on the rate of reaction.
SUPPLEMENTARY MATERIAL
Proposed mechanism for the reaction between 1,
2 (2a, 2b, or 2c), and 3 for generation of phoso-
horus ylides 4 (4a, 4b, or 4c), figures showing the
UV spectrum of 10−3M of 1, 2c, and 3, and the
experimental absorbance change versus time for
the reaction between 2c and 3 in the presence of
excess 1 (10−2 M) at 368 nm and 12.0◦C in 1,4-
dioxane are available from the corresponding author
(smhabibi@chem.usb.ac.ir) on request.
CONCLUSIONS
Briefly, we prepared novel phosphorus ylides us-
ing a one-pot reaction between triphenylphosphine
1 and dialkyl acetylenedicarboxylates 2 (2a, 2b,
or 2c) in the presence of a NH-acid such as 3,6-
dibromocarbazole 3. The present method has the
Heteroatom Chemistry DOI 10.1002/hc

732 Habibi-Khorassani et al.
[23] Yavari, I.; Alizadeh, A.; Anary-Abbasinejad, M. Tetra-
hedron Lett 2002, 43, 9449.
[24] Yavari, I.; Adib, M.; Jahani-Mogaddam, F.; Sayahi,
M. H. Phosphorus Sulphur and Silicon Relat Elem
2002, 177, 545.
[25] Yavari, I.; Hossein Mosslemin, M. Tetrahedron 1998,
54, 9169.
[26] Yavari, I.; Ramazani, A. Synth Commun 1997, 27,
1385.
REFERENCES
[1] Johnson, A. W. Ylied Chemistry; Acadamic Press:
London, 1966.
[2] Cadogan, J. I. G. Organophosphorus Reagents in
Organic Synthesis; Academic Press: New York,
1979.
[3] Engel, R. Synthesis of Carbon-Phosphorus Bond;
CRC Press: Boca Raton, FL, 1988.
[4] Hudson, H. R. The Chemistry of OrganoPhosphorus
Compound Primary Secondary Tertiary Phosphines
Heterocyclic OrganoPhosphorus Compounds; Wiley:
New York, 1990.
[5] Corbridge, D. E. C. Phosphorus an Outline of
Chemistry Biochemistry Uses; Elsevier: Amsterdam,
1995.
[6] Kolodiazhnyi, O. I. Russ Chem Rev 1994, 66, 225.
[7] Cherkasov, R. A.; Pudovic, M. A. Russ Chem Rev
1994, 63, 1019.
[8] Pietrusiewicz, K. M.; Zablocka, M. Chem Rev 1994,
94, 1375.
[9] Maryanoff, B. E.; Rietz, A. B. Chem Rev 1989, 89,
863.
[10] Nicolaou, K. C.; Harter, M. W.; Gunzner, J. L.; Nadin,
A. Liebigs Ann 1997, 1283.
[11] Shen,Y. Acc Chem Res 1998, 31, 584.
[12] Gilchrist, T. L. Heterocyclic Chemistry; Wiley: New
York, 1985.
[13] Eslami, A. A.; Ghereghloo, M.; Islami, M. R.;
Bijanzadeh, H. R. Tetrahedron 2003, 59, 4785.
[14] Islami, M. R.; Yavari, I.; Tikdari, A. M.; Ebrahimi, L.;
Razee, S.; Bijanzadeh, H. R. Russ Chem Bull 2002,
51, 2244.
[15] Bestmann, H. J.; Joachim, G.; Lengyel, T.; Oth, J. F.;
Merenyi, R.; Weitkamp, H. Tetrahedron Lett 1966, 7,
3355.
[16] Hooper, D. L.; Garagan, S. J Org Chem 1994, 59,
1126.
[17] Yavari, I.; Ramazani, A. Phosphorus Sulphur and Sil-
icon Relat Elem 1997, 73, 130.
[18] Yavari, I.; Esmaili, A. A.; Asghari, S.; Bijanzadeh, H.
R. J Chem Res 1999, 368.
[19] Yavari, I.; Islami, M. R. J Chem Res 1998, 166.
[20] Yavari, I.; Bayat, M. Phosphorus Sulphur and Silicon
Relat Elem 2002, 177, 2537.
[21] Yavari, I.; Anary-Abbasinejad, M.; Alizadeh, A.;
Habibi, A. Phosphorus Sulphur and Silicon Relat
Elem 2002, 177, 2523.
[27] Yavari, I.; Esmaili, A. A. J Chem Res 1998, 714.
[28] Ramazani, A.; Shajari, N.; Gouranlou, F. Phosphorus
Sulphur and Silicon Relat Elem 2001, 174, 223.
[29] Yavari, I.; Alizadeh, A.; Anvary-Abbansinejad, M.
Phosphorus Sulphur and Silicon Relat Elem 2002,
177, 81.
[30] Maghsoodlou, M. T.; Habibi-Khorassani, S. M.;
Hazeri, N.; Kakaei, R.; Nassiri, M.; Marandi, G. Phos-
phorus Sulphur and Silicon Relat Elem 2006, 181,
553.
[31] Maghsoodlou, M. T.; Hazeri, N.; Habibi-khorassani,
S. M.; Afshar, G. J Chem Res 2005, 727.
[32] Maghsoodlou, M. T.; Hazeri, N.; Habibi-khorassani,
S. M.; Nassiri, M.; Marandi, G.; Afshari, G.;
Niroumand, U. J Sulfur Chemistry 2005, 26, 261.
[33] Habibi-khorassani, S. M.; Maghsoodlou, M. T.;
Hazeri, N.; Nassiri, M.; Marandi, G. Phosphorus Sul-
fur and Silicon Relat Elem 2006, 181, 567.
[34] Maghsoodlou, M. T.; Habibi khorassani, S. M.;
Hazeri, N.; Nassiri, M.; Kakaei, R. Phosphorus Sulfur
and Silicon Relat Elem 2006, 181, 553.
[35] Nielsen, O. J.; Sehested, J.; Langer, S.; Ljungstro¨m,
E.; Wa¨ngberg, I. Chem Phys Lett 1995, 238, 359.
[36] Langer, S.; Ljungstro¨m, E.; Ellermann, T.; Sehested,
J.; Nielsen, O. J Chem Phys Lett 1995, 240, 53.
[37] Ivanov, V. V.; Decker, C. Polym Int 2001, 50, 113.
[38] Carvalho, R. N.; Moura, L. S.; Rosa, P. T. V.; Angela,
M. Supercrit Fluids 2005, 35, 197.
[39] Fung, P. C.; Sin, K. M.; Tsui, S. M. Color Technol
2000, 116, 170.
[40] Misiti, F.; Castagnola, M.; Zuppi, C.; Giardina, B.;
Messana, I. Biochem 2001, 356, 799.
[41] Schwartz, L. M.; Gelb, R. I.; Anal Chem 1978, 50,
1592.
[42] Treglon, P. A.; Laurence, G. S. Sci Instrum 1956, 42,
869.
[43] Wolff, M. A.; Chem Instrum 1976, 5, 59.
[44] Treglon, P. A.; Laurence, G. S. J Sci Instrum 1965,
42, 869–872.
[45] Okubo, T.; Maeda, Y.; Kitano, J. Phys Chem 1989, 93,
3721–3723.
[22] Yavari, I.; Adib, M.; Hojabri, L. Tetrahedron 2002, 58,
7213.
Heteroatom Chemistry DOI 10.1002/hc