Kinetic regularities of reactions of O,O-diaryl phosphorohydrazidothioates with phenyl isothiocyanate in benzene

Article abstract of DOI:10.1007/s11176-005-0330-y

The effect of the temperature on the rate of reactions of O,O-diaryl phosphorohydrazidothioates with phenyl isothiocyanate in benzene is studied, and the activation parameters of the reactions are calculated. It is established that the reaction series under study obeys the isokinetic relationship with an enthalpy control and an isokinetic temperature of 690±24 K. The effect of electronically diverse substituents on phosphorus on the reactivity of O,O-diaryl phosphorohydrazidothioates is additive. It is described by the Hammett equation with σ^P constants.

Full text of DOI:10.1007/s11176-005-0330-y

Russian Journal of General Chemistry, Vol. 75, No. 6, 2005, pp. 841 844. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005,
pp. 893 896.
Original Russian Text Copyright
2005 by Yanchuk, Ivanets.
Kinetic Regularities of Reactions
of O,O-Diaryl Phosphorohydrazidothioates
with Phenyl Isothiocyanate in Benzene
N. L. Yanchuk and L. N. Ivanets
Gnatyuk Ternopol State Pedagogical University, Ternopol, Ukraine
Received January 8, 2004
Abstract The effect of the temperature on the rate of reactions of O,O-diaryl phosphorohydrazidothioates
with phenyl isothiocyanate in benzene is studied, and the activation parameters of the reactions are calculated.
It is established that the reaction series under study obeys the isokinetic relationship with an enthalpy control
and an isokinetic temperature of 690 24 K. The effect of electronically diverse substituents on phosphorus
on the reactivity of O,O-diaryl phosphorohydrazidothioates is additive. It is described by the Hammett equa-
P
tion with
constants.
In the present work we present the results of a ki-
netic study of reactions of O,O-diaryl phosphorohyd-
razidothioates with phenyl isocyanate, aimed at asses-
sing structure reactivity relationship for the hydra-
zides in hand.
evidenced by the fact that the reciprocal current
concentration linearly varies with time.
The effect of substituents of different electronic
nature in the aromatic rings of O,O-diaryl phosphoro-
hydrazidothioates on the rates of their reactions with
phenyl isothiocyanate was studied in the temperature
range 25 55 C. The resulting reaction rate constants
are listed in Table 1.
The reactions of O,O-diaryl phosphorohydrazido-
thioates with phenyl isothiocyanate proceed quanti-
tatively and irreversibly to form thiosemicarbazides.
The reactions under study are described by the
Arrhenius equation. The polytherms of the log rate
constants of phosphorus-containing thiosemicarbazide
formation are linear, as evidenced by high correlation
coefficients of the Arrhenius equation [Table 2, Eqs.
(1) (7)]. This allowed the activation parameters of the
reactions (Table 3) to be found from the temperature
dependences of the rate constants measured at four
temperatures and known relationships [1]. The activa-
tion entropy ( S ), enthalpy ( H ) and Gibbs energy
( G ) were calculated for 25 C.
S
RC H O
6
4
P NHNH + S=C=N C H
6 5
2
R C H O
6
4
S
RC H O
6
4
P NHNHCSNH C H
6
5
R C H O
6
4
The kinetics of these reactions are described by an
irreversible second-order reaction equation (partial
first order in hydrazide and phenyl isothiocyanate), as
Table 1. Rate constants of reactions of O,O-diaryl phosphorohydrazidothioates I VII with phenyl isothiocyanate in
benzene at various temperatures
Comp. no.
R
R
298 K
308 K
318 K
328 K
I
II
p-CH3
p-CH3
p-CH3
H
H
p-Cl
m-Cl
p-CH3
H
p-CH3
H
p-Cl
p-Cl
m-Cl
0.390 0.024
0.239 0.017
0.248 0.019
0.0958 0.0029
0.0920 0.0025
0.0465 0.0014
0.0372 0.0011
1.36 0.10
0.631 0.033
0.716 0.037
0.559 0.016
0.370 0.021
0.129 0.005
0.123 0.009
4.71 0.24
2.94 0.16
3.24 0.30
2.09 0.13
1.47 0.11
0.611 0.028
0.662 0.014
9.75 0.23
6.74 0.27
5.76 0.21
6.29 0.19
2.74 0.12
2.40 0.18
1.36 0.11
III
IV
V
VI
VII
1
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842
YANCHUK, IVANETS
Table 2. Parameters of the equation log k = logA +
stituents decreases the activation energy, enthalpy, and
Gibbs energy. Therewith, the activation entropy de-
creases in absolute value. Electron-acceptor substi-
tuents produce the opposite effect. In this reaction
series, there is an enthalpy entropy compensation
effect: Enhancing electron-donor power of substi-
tuents in O,O-diaryl phosphorohydrazidothioates
decreases the activation enthalpy and increases the
activation entropy. The activation energies of reac-
tions of O,O-diaryl phosphorohydrazidothioates with
phenyl isothiocyanate in benzene are about 6 times
those of reactions of the same substrates with phenyl
isocyanate [2].
b 103
zidothioates I VII with phenyl isothiocyanate in benzene
298 328 K)
T
1
for reactions of O,O-diaryl phosphorohydra-
(
Equa- Hydra-
logA
b
r
s
tion
zide
1
2
3
4
5
6
7
I
II
III
IV
V
12.19 0.92 4.64 0.29 0.996 0.066
12.83 1.17 4.91 0.37 0.995 0.084
12.01 1.51 4.66 0.47 0.990 0.108
15.86 1.53 5.91 0.48 0.994 0.109
12.56 1.46 4.93 0.46 0.992 0.104
14.64 1.25 5.68 0.39 0.995 0.089
VI
The reactivity of O,O-diaryl phosphorohydrazido-
thioates toward phehyl isothiocyanate varies in paral-
lel the basicity constants of the hydrazides. The
dependence of the log reaction constants on the
basicity constants of the hydrazides [2] is described
by the Brønsted equation [Table 4, Eqs. (8) (11)].
VII 13.40 1.52 5.31 0.20 0.992 0.109
Table 3. Activation parameters of reactions of O,O-diaryl
phosphorohydrazidothioates I VII with phenyl isothio-
cyanate in benzene
As follows from the data in Table 1, the reactivity
of O,O-diaryl phosphorohydrazidothioates is much
dependent on the position and nature of substituents
in the aromatic rings. The effect of substituents on the
Comp.
no.
Ea
S
298,
K
H298
kJmol
,
G298
,
kJmol
kJmol 1 Jmol
1
1
1
1
I
II
90.8 4.2
90.7 4.1
91.3 4.0
95.4 4.8
96.2 5.1
98.2 5.3
99.2 3.7
13.8 1.7
18.2 1.4
15.9 2.0
10.1 1.2
7.7 0.8
6.7 0.3
5.2 0.3
88.3 6.2 92.5 8.0
88.2 5.6 93.6 7.8
88.8 6.0 93.6 9.0
92.9 7.0 95.9 6.1
93.7 7.2 96.1 7.4
95.7 6.2 97.8 5.0
96.7 3.4 98.2 3.6
reactivity of O,O-diaryl phosphorohydrazidothioates
P
described by the Hammett equation with
constants
III
IV
V
VI
VII
[
3] [Table 4, Eqs. (12) (15)]. The absolute values of
the reaction constant of 1.94 1.56 in the tempera-
ture range under study suggest enhanced sensi-
tivity of this reaction series to the structure of the
O,O-diaryl phosphorohydrazidothioate compared to
the same reaction with phenyl isocyanate [2].
The log rate constants of the reaction under study
Table 4. Parameters of the equations y = Cx + D for
kinetic characteristics of reactions of O,O-diaryl phospho-
rohydrazidothioates with phenyl isothiocyanate in benzene
P
nicely correlate with the
constants of the substi-
values are
tuents on the phosphorus atom. The
negative, which is characteristic of nucleophilic reac-
tions. As the temperature increases, the reaction
constant only slightly decreases in absolute value,
implying that the isokinetic temperature [4] of these
reactions falls far beyond is the temperature range
studied.
(
n = 7)
y
x
C
D
r
s
8
9
logk298 pKa 5.91 0.73 19.5 2.0 0.961 0.116
logk308 pKa 5.38 0.47 17.8 1.3 0.981 0.075
To find out if there is the isokinetic relationship in
this reaction series in the temperature range studied,
we made use of known criteria [4 6]. Evidence
showing that a given reaction series obeys the iso-
kinetic law [7] is obtained from an analysis of correla-
tion equations of kinetic and activation parameters.
1
1
1
1
1
1
0 logk318 pKa 5.13 0.64 16.5 1.7 0.962 0.101
1 logk328 pKa 4.55 0.59 14.6 1.6 0.960 0.093
2 logk298
3 logk308
4 logk318
5 logk328
P
1.94 0.24 4.03 0.05 0.962 0.115
1.82 0.14 3.46 0.03 0.986 0.064
1.75 0.16 2.85 0.03 0.979 0.077
1.56 0.14 2.47 0.26 0.981 0.065
P
P
P
One of the most reliable criteria for the isokinetic
relationship is a linear dependence of log reaction rate
constants at two different temperatures. According to
the Exner method [4, 8, 9] based on an analysis of the
tangent slope of logk = logk + const dependences,
Substituents of different electronic nature in O,O-
diaryl phosphorohydrazidothioates affect both kinetic
and thermodynamic parameters of the reactions.
Hence, enhancing electron-donor power of the sub-
T
T
1
2
where T > T , the isokinetic temperature is readily
2
1
calculated with known . The isokinetic temperature
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 6 2005

KINETIC REGULARITIES OF REACTIONS OF O,O-DIARYL PHOSPHOROHYDRAZIDOTHIOATES
843
calculated from the logk318 logk308 dependence (16)
is 674 K.
Table 5. Reaction constants ( ) of reactions of O,O-diaryl
phosphorohydrazidothioates with phenyl isothiocyanate in
benzene at various temperatures
logk318 = (0.413 0.021) + (0.942 0.102)logk308, (16)
n 7, r 0.972, s 0.089.
Reaction constant
Temperature, K
The existence of the isokinetic relationship follows
experimental calculated
from the H298
S298 dependence (17):
2
308
318
98
1.94
1.82
1.75
1.56
1.94
1.83
1.73
1.63
0
H298 = (99.8 1.1) + (0.699 0.994) S298
n 7, r 0.962, s 1.08.
,
(17)
0.01
0.02
0.07
3
28
In this case, the isokinetic temperature is 699 K.
Furthermore, the activation parameters of the reaction
fit the linear dependence E logA (18), and the iso-
with phenyl isothiocyanate involve a cyclic transition
complex [11]. The existence of the isokinetic relation-
ship in this series point to a common reaction me-
chanism with all the members of the reaction series
in the temperature range studied.
a
kinetic temperature in these coordinates is 697 K.
Ea = ( 74.2 2.2) + (13.3 1.7)logA,
n 7, r 0.962, s 1.08.
(18)
The average isokinetic temperature
18)] is 690 24 K. As seen, the isokinetic tempera-
[Eqs. (16)
EXPERIMENTAL
(
ture falls far above the temperature range studied and
is thus unavailable for experimental verification.
Benzene for kinetic studies was purified according
to [12]. O,O-Diaryl phosphorohydrazidothioates were
prepared and purified according to [13, 14]. Phenyl
isothiocyanate was distilled in a vacuum directly
before use.
The existence of the isokinetic relationship creates
certain prerequisites for predicting Hammett reaction
constants of reactions of the type in hand. It is known
that the temperature dependence of in cases where
isokinetic relationship is obeyed is given by Eq. (19)
Reaction rate was controlled following the con-
centration of unreacted phenyl isothiocyanate [15, 16].
Each experiment was repeated three times and in-
cluded 6 8 measurements. The conversion was no less
than 80%. The kinetics of the formation of phos-
phorus-containing thiosemicarbazides were studied at
298, 308, 318, and 328 K. The activation parameters
were calculated by known equations [1]. The accuracy
of the resulting data was assessed by mathematical
statistics (confidence probability 0.95) [17].
[5].
=
(1
/T).
(19)
By writing Eq. (19) for two arbitrary temperatures
T and T and dividing the resulting equations term-by-
0
term, we obtain, after simple transformations,
Eq. (20).
T0
T0
T
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