Kinetic study of triphenylphosphine addition to para-benzoquinone

Article abstract of DOI:10.1002/kin.20016

Kinetics of the addition reaction of triphenylphosphine to para-benzoquinone in 1,2-dichloroethane as solvent was studied. Initial rate method was used to determine the order of the reaction with respect to the reactants. Pseudo-first-order method was als

Full text of DOI:10.1002/kin.20016

Kinetic Study
of Triphenylphosphine
Addition to
para-Benzoquinone
DAVOOD NORI-SHARGH,1,2 NASRIN SAROOGH FARAHANI2
1Chemistry Department, Science and Research Campus, Islamic Azad University, Hesarak, Poonak, Tehran, Iran
2Chemistry Department, Graduate Faculty, Arak Branch, Islamic Azad University, Arak, Iran
Received 3 March 2003; accepted 12 March 2004
DOI 10.1002/kin.20016
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Kinetics of the addition reaction of triphenylphosphine to para-benzoquinone in
1,2-dichloroethane as solvent was studied. Initial rate method was used to determine the or-
der of the reaction with respect to the reactants. Pseudo-first-order method was also used to
calculate the rate constant. This reaction was monitored by UV-vis spectrophotometry at 520
nm by variable time method. On the basis of the obtained results, the Arrhenius equation of
this reaction was obtained:
5.701
log k = 7.38145 −
2.303RT
#
#
#
The activation parameters, E , ꢀH , ꢀG , and ꢀS at 300 K were 5.701, 6.294, 19.958 kcal mol−1
a
and −45.853 cal mol−1
K
−1, respectively. This reaction is first and second order with respect
to triphenylphosphine and para-benzoquinone, respectively. ꢀ 2004 Wiley Periodicals, Inc. Int
C
J Chem Kinet 36: 472–479, 2004
tween the two types might be quite difficult. From the
evidence available it may be concluded that there is a
good deal of charge delocalization and it is quite likely
that these addition compounds are the resonance hy-
brid of the zwitterionic phosphonium compound and
the phosphinemethylene, having a larger contribution
of the former [3–6].
Previously, the kinetics of reactions of 1,4-
benzoquinone with thiourea dioxide, sodium hydrox-
ymethanesulfinate, hydroxymethanesulfunate [7], and
aromatic amines have been studied [8]. Also, the ki-
netics of interactions of some primary aliphatic amines
with chloranil have been investigated by UV spec-
troscopy [9,10].
INTRODUCTION
The phosphorus of triphenylphosphine attacks a carbon
of para-benzoquinone and forms an ylide or phospho-
betaine [1]. On the basis of the obtained results, it may
be assumed that the structure of the addition compound
is such that there is substitution in the quinone ring and
that there is quaternization of the phosphorus atom.
The structure of the compound formed may be either
zwitterionic or of the ylide type [2]. A distinction be-
Correspondence to: Davood Nori-Shargh; e-mail: nori ir
@yahoo.com.
c
ꢀ
2004 Wiley Periodicals, Inc.

KINETIC STUDY OF TRIPHENYLPHOSPHINE ADDITION TO para-BENZOQUINONE
473
Figure 1 Plot of the absorbance vs time.
Figure 2 Plot of the ln rate vs ln[triphenylphosphine]. (1) [para-benzoquinone] = 0.015 M, [triphenylphosphine] = 0.045,
0.06, 0.075, 0.09, 0.105 M, y = 1.000x − 5.496, R2 = 1.000; (2) [para-benzoquinone] = 0.030 M, [triphenylphosphine] =
0.045, 0.06, 0.075, 0.09, 0.105 M, y = 1.000x − 4.109, R2 = 1.000; (3) [para-benzoquinone] = 0.045 M, [triphenylphos-
phine] = 0.045, 0.06, 0.075, 0.09, 0.105 M, y = 1.000x − 3.299, R2 = 1.000; (4) [para-benzoquinone] = 0.060 M, [triph-
enylphosphine] = 0.045, 0.06, 0.075, 0.09, 0.105 M, y = 1.000x − 2.716, R2 = 1.000; (5) [para-benzoquinone] = 0.075 M,
[triphenylphosphine] = 0.045, 0.06, 0.075, 0.09, 0.105 M, y = 1.000x − 2.281, R2 = 1.000.

474
NORI-SHARGH AND FARAHANI
Figure 3 Plot of the ln kꢁ vs ln[para-benzoquinone].
There is no published experimental data on the
kinetics of the above addition reaction. In this
work, we want to report the kinetic of the addi-
tion of triphenylphosphine to para-benzoquinone re-
action such as the rate constant, the order of the
reaction with respect to the reactant, and thermo-
dynamic activation parameters (Ea, ꢀH#, ꢀG#, and
ꢀS#).
EXPERIMENTAL
Materials and Instrumentation
para-Benzoquinone (Merck), triphenylphosphine
(Merck) and dichloromethane (Merck) were used with-
out additional purification. UV-visible spectra were
recorded on a Shimadzu 160A spectrophotometer.
Figure 4 Plot of the ln(A∞ − At ) vs t(s). (1) [para-benzoquinone] = 0.070 M, [triphenylphosphine] = 0.007 M,
y = −0.000441x + 0.369490, R2 = 0.998; (2) [para-benzoquinone] = 0.084 M, [triphenylphosphine] = 0.007 M, y =
−0.000635x + 0.457253, R2 = 0.999; (3) [para-benzoquinone] = 0.098 M, [triphenylphosphine] = 0.007 M, y =
−0.000864x + 0.631861, R2 = 1.000; (4) [para-benzoquinone] = 0.105 M, [triphenylphosphine] = 0.007 M, y =
−0.000992x + 0.642607, R2 = 0.999; (5) [para-benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M, y =
−0.001129x + 0.709668, R2 = 0.998.

KINETIC STUDY OF TRIPHENYLPHOSPHINE ADDITION TO para-BENZOQUINONE
475
Figure 5 Plot of the ln kꢁ vs [para-benzoquinone].
which is one of the absorption wavelength of the prod-
uct in which reactants do not present any absorption.
For each of the above concentrations, the progress
curve were obtained and for which, the reaction rates
were then calculated (see Fig. 1).
RESULT AND DISCUSSION
The order of reaction with respect to the reactants was
determined using initial rate method. For this purpose,
the reaction was monitored for constant concentra-
tion of para-benzoquinone (0.015 M) but with differ-
ent concentrations of triphenylphosphine: 0.045, 0.06,
0.075, 0.09, and 0.105 M, respectively, at λ = 520 nm
rate = k[para-benzoquinone]n
× [triphenylphosphine]m
(1)
[A]t [B]0
[A]0[B]t
1
1
1
[A]t
1
Figure 6 Plot of the y vs t(s). y =
(
−
) +
ln(
); (1) [para-benzoquinone] = 0.070 M,
([A]0−2[B]0)2
[A]0−2[B]0 [A]0
[triphenylphosphine] = 0.007 M, y = 0.090052x, R2 = 0.995; (2) [para-benzoquinone] = 0.084 M, [triphenylphosphine] =
0.007 M, y = 0.090068x, R2 = 0.998; (3) [para-benzoquinone] = 0.098 M, [triphenylphosphine] = 0.007 M, y = 0.090040x,
R2 = 0.999; (4) [para-benzoquinone] = 0.105 M, [triphenylphosphine] = 0.007 M, y = 0.090003x, R2 = 0.999; (5) [para-
benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M, y = 0.090026x, R2 = 0.998.

476
NORI-SHARGH AND FARAHANI
Figure 7 Plot of the ln(A∞ − At ) vs t(s). (1) [para-benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M at 288 K,
y = −0.000954x + 0.504091, R2 = 0.998; (2) [para-benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M at 293 K,
y = −0.001131x + 0.652017, R2 = 0.997; (3) [para-benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M at 298 K,
y = −0.001333x + 0.759626, R2 = 0.997; (4) [para-benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M at 303 K,
y = −0.001563x + 0.764988, R2 = 0.989; (5) [para-benzoquinone] = 0.112 M, [triphenylphosphine] = 0.007 M at 308 K,
y = −0.001820x + 1.056199, R2 = 0.978.
enylphosphine and kꢁ were then determined. Again the
rate = kꢁ[triphenylphosphine]m
kꢁ = k[para-benzoquionone]n
(2)
(3)
same procedure was repeated for each of the following
constant concentrations of para-benzoquinone (0.03,
0.045, 0.06, and 0.075 M), where a ln kꢁ value was ob-
tained for each para-benzoquinone concentration (see
Fig. 2). Using Eqs. (3) and (4):
ln rate = ln kꢁ + m ln[triphenylphosphine] (4)
The calculated neperian logarithm of the rate vs
neperian logarithm of triphenylphosphine curve was
plotted. The order of the reaction with respect to triph-
ln kꢁ = ln k + n ln[para-benzoquinone]
(5)
Figure 8 Plot of the ln k vs 1/T (K).

KINETIC STUDY OF TRIPHENYLPHOSPHINE ADDITION TO para-BENZOQUINONE
477
and the plot of ln kꢁ vs ln[para-benzoquinone] (see
Fig. 3), the order of reaction was to be of second-order
with respect to para-benzoquinone and first-order with
respect to triphenylphosphine.
obtained results:
y = kt
ꢀ
ꢁ
1
1
1
y =
−
According to the following rate equation:
[A]0 − 2[B]0 [A]0
[A]t
ꢀ
ꢁ
Rate = k[triphenylphosphine][para-benzoquinone]2
1
[A]t [B]0
[A]0[B]t
+
ln
([A]0 − 2[B]0)2
A pseudo-first-order method was then used to trans-
form the rate constant, obtained on the basis of the
absorption data to the concentration basis. In this
method by keeping large excess (10-fold or greater)
of para-benzoquinone over triphenylphosphine, the
reaction between para-benzoquinone (0.07 M) and
triphenylphosphine (0.007 M) was carried out at
20◦C. For this reaction the plot of ln(A∞ − At )
vs time was obtained (see Fig. 4) and ln kꢁ val-
ues were calculated for different molar ratio of
para-benzoquinone/triphenylphosphine (0.084/0.007,
0.098/0.007, 0.105/0.007, and 0.112/0.007, see Fig. 5).
Using the following equation:
A = [para-benzoquinone]
B = [triphenylphosphine]
Accordingly, from the slope of the plot of y vs time,
the rate constant was calculated. As it can be seen from
the slope of Fig. 6, the value of k = 0.09 mol−2 s−1
is found in every case, which is a confirmation of the
previously obtained results.
In order to calculate the activation parameters (Ea,
ꢀH#, ꢀS#, and ꢀG#), ln k vs 1/T (Arrhenius equa-
tion) was plotted. Ea/R and ln A were then obtained
∞
from the slope and intercept of this slope (see Figs. 7
and 8):
rate = kꢁ[triphenylphosphine]
kꢁ = k[para-benzoquinone]n
Ln k = ln A∞ − (Ea/RT )
A
= 1.606 × 103
∞
ln kꢁ = ln k + n ln[para-benzoquinone]
E
= 5.701 kcal mol−1
∞
from the plot of ln kꢁ vs ln[para-benzoquinone], the
values of the rate constant k293 = 0.09 and order of re-
action (n = 2) with respect to para-benzoquinone were
obtained from the intercept and slope of this curve,
respectively.
ꢀS# = −45.853 cal mol−1 K−1
ꢀH# = 6.294 kcal mol−1
ꢀG# = 19.959 kcal mol−1
The following integrated third-order rate equation
along with the initial rate and pseudo-first-order data
were also used to confirm the validity of the above
On the base of the experimentally obtained rate
equation of the reaction, the follow mechanism could
be suggested:

478
NORI-SHARGH AND FARAHANI
Table VI Calculated ln kꢁ Values at Various
Tempratures
Table I Initial Rate Method Results for Reaction
Between para-Benzoquinone and Triphenylphosphine
Slope = m
Intercept = ln kꢁ
Slope = kꢁ
(ln Rate = ln kꢁ + m
ln[triphenylphosphine])
(kꢁ = k[para-
Reactions T (K) (kꢁ = k[para-benzoquinone]2)
k
Reactions
benzoquinone]n)
1
2
3
4
5
288
293
298
303
308
0.000954
0.001131
0.001333
0.001563
0.001820
0.076052
0.090163
0.106266
0.124601
0.145089
1
2
3
4
5
1.000
1.000
1.000
1.000
1.000
5.496
4.109
3.299
2.716
2.281
Table VII Calculated E /R and ln A Values
a
∞
Table II Calculated Order of Reaction with Respect to
para-Benzoquinone Concentration
Slope = −Ea/R
−2869.244267
Intercept = ln A
∞
7.381445
Slope = n
(ln kꢁ = ln k + n ln[para-benzoquinone]) Intercept = ln k
2.000
2.905
In the first step, the triphenylphosphine phosphorus
attacks the carbon of the carbonyl group of the para-
benzoquinone and produces the intermediate I.
In the second step, the triphenylphosphine group is
transferred from the intermediate I to a ꢀ-carbon atom
of an another molecule of para-benzoquinone. This
reaction step is reasonable in view of the hard and soft
acid base character of the reactants.
Table III Pseudo-First Order Method Results for
Reaction Between para-Benzoquinone and
Triphenylphosphine
Slope = kꢁ
Reactions
(kꢁ = k[para-benzoquinone]n)
In the third step, an H+ ion is transferred from
the above mentioned ꢀ-carbon of the intermediate
II to the oxygen atom by an intramolecular mech-
anism giving the reaction product. This final ylide
product could also be in resonance with its ylene
from.
1
2
3
4
5
0.000441
0.000635
0.000864
0.000992
0.001129
As the first step is a kinetically controlled reaction,
consequently the produced intermediate I is also a ki-
netic product.
Based on the experimental results, the second step
could be considered as the determining reaction step,
in which two molecule of para-benzoquinone and one
molecule of triphenylphosphine react by a concerted
mechanism.
Table IV Calculated Order of Reaction with Respect to
para-Benzoquinone Concentration
Slope = n
(ln kꢁ = ln k + n ln[para-benzoquinone]) Intercept = ln k
2.000129
2.407674
BIBLIOGRAPHY
Table V Calculated Rate Constant by Third-Order
Equation
1. Ramirez, F.; Dershowitz, S. J Am Chem Soc 1956, 78,
Reactions
Slope = k
5614–5622.
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1
2
3
4
5
0.090052
0.090068
0.090040
0.090003
0.090026
58–60.
3. Ramirez, F.; Dermshowits, S. Chem Ind 1956, 665–
666.
4. Arshad, M.; Bey, A.; Siddiqui, M. S. Tetrahedron 1966,
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KINETIC STUDY OF TRIPHENYLPHOSPHINE ADDITION TO para-BENZOQUINONE
479
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