PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
5
‡
‡
‡
ꢁ
Table 3. Activation parameters (DH , DS , DG , Ea and A) at 20 C for the reaction a between (1), (2).
‡
ꢀ1
‡
ꢀ1 ꢀ1
‡
ꢀ1
‡
ꢀ1
ꢀ1
ꢀ1
ꢀ1
DH kJ mol
DS J mol
K
TDS kJ mol
DG kJ mol
E
a
kJ mol
A M min
b
5
Acetonitrile (e ¼ 37.5 D)
19.7 ± 0.7
9.7 ± 0.3
ꢀ143.48 ± 2.26
ꢀ184.49 ± 1.07
[34]
ꢀ41.77
ꢀ53.71
61.53 ± 1.35
63.38 ± 0.6
22.3 ± 0.7
12.2 ± 0.3
5.51 ꢃ 10
3.98 ꢃ 10
3
Methyl ethyl ketone (e ¼ 18.22 D)
b
error standard was calculated corresponding to Lente method.
Table 4. The substituents effects on the rate constant ka of the reaction a, Since, reactants (1, 2) and (3) are components of overall
obs
between para-substituted benzoyl isthiocyanate (1) and 1-naphthylamine (2)
reaction and P is the product that generated in the reaction
a and subsequently consumed in the reaction b, thus a com-
ꢁ
1
at 20 C.
a
ꢀ1
ꢀ1
p-substituted benzoyl isocyanate (1)
k
M
min
obs
bination of rate and rate can be expressed:
a
a
b
Cl
H
104.8± (0.0012)
59.90± (0.001)
42.93± (0.0016)
Rateexp ¼ kobs½1ꢂ½2ꢂ½3ꢂ
(10)
CH
3
a
SD.
Therefore, the reaction is third-order kinetics, and kobs
refers to observational rate constant for three component
reaction among components (1, 2) and (3).
absorbance has been seen for the formation of P in the
1
same approximately range in reaction a, Figure 1).
ꢁ
In the other experiment at 20 C, the change in absorbance
Effects of solvent, temperature and substituent in the
reaction b
We also tested the effect of electron-donating and withdrawing
substitutions such as 4-methyl and 4-chloro on para position
was monitored against time in 395 nm under same condition
with previous experiment, Figure 9. The second-order fitting
curve (solid curve) was exactly fitted on the experimental
absorbance curve (dotted curve) by the associated software
of 1-benzoyl-3-(naphthalene-1-yl) thiourea (P ). The chloro
[
33]
1
ꢀ1
within the program.
A good fitting curve showed that the
ꢀ1
substituent increased the rate constant (4.67 M min ), but
methyl substituent approximately did not effect on the rate
reaction follows second-order kinetics (d þ c ¼ 2).
The rate laws can be written in the following form
ꢀ1
ꢀ1
ꢀ1
ꢀ1
constant (2.03 M min ) versus (1.94 M min , unsub-
c
d
k
Rate ¼ kove½P ꢂ ½3ꢂ ½Et Nꢂ
(7) stituent of (P ) compound) (see Table 5).
1
1
3
Herein, electron-withdrawing groups (EWS) on benzoyl
Triethylamine is a typical catalyst for this reaction, so its
concentration is constant;
group of (P ) (in addition to both carbonyl and thio-groups)
1
reduce the N -H strength (near the EWS) and subsequently
1
c
d
k
b
obs
k
increase the nucleophilicity of sulfur atom to facilitate the rate
Rate ¼ kove½P ꢂ ½3ꢂ ½Et Nꢂ
k
¼ kove½Et Nꢂ
1
3
3
of nucleophilic reaction between reagents (P ) and (3) in the
1
presence of catalyst (4) (step , reaction b, Scheme 3). On the
contrary, electron-donating groups (EDS) tend to reduce the
b
c
d
2
Rate ¼ k ½P ꢂ ½3ꢂ
(8)
obs
1
The overall order of the reaction b is the sum rate of nucleophilic reaction, since relatively increase the N
of c þ d ¼ 2.
strength and reduce the nucleophilicity of sulfur atom.
refer to overall rate constant of reaction b among
Herein, higher polar solvent stabilized the charges in
transition state (TS , step ) more than the reactants with the
refer to observational rate constant of reaction b lack of charge ((P1) and (3)), so high polar solvent and tem-
-H
1
k
ove
(
P ), (3) and Et N.
2
2
1
3
b
k
obs
between (P ) and (3), Equation (8).
perature increased the nucleophilic reaction rate, the results
1
Under pseudo-order condition [([3] ¼ 10ꢀ M) and were reported in Table 6.
2
ꢀ
3
0
[
P ] ¼ 5 ꢃ 10 M)], Equation (8) is convert to Equation (8 ):
The activation parameters evaluated according to the
Arrhenius and Eyring plots (Figure 11) and shown in Table 7.
The reaction is entropy-controlled in methyl ethyl ketone and
1
b
½3ꢂ ¼ k and then Rate ¼ kb' ½P1ꢂ
d
b'
c
(80Þ
k
obs
obs
obs
‡
enthalpy-controlled in acetonitrile. Evaluation of (DH ) and
The experimental absorbance curve shown in Figure 10
‡
0
(DS ) values indicate that activation enthalpy in the aceto-
(dotted), is relevant to the mathematical Equation (8 ) which
nitrile solvent is more than the methyl ethyl ketone, and the
is properly fitted on the first-order fitting curve (solid). It
‡
activation entropy in the acetonitrile solvent DS ¼ (ꢀ48
means that partial order of (P ) is one (c ¼ 1). In the previ-
1
ꢀ
1
ꢀ1
‡
Jmol
K
) is considerably positive in relation to methyl ethyl
ous experiment, the sum of d þ c was 2 (d þ c ¼ 2), there-
fore partial order of bromoacetate (3) is one (d ¼ 1).
ꢀ1 ꢀ1
‡
ketone DS ¼ (ꢀ143.48 Jmol
K ), thus low enthalpy, DH ,
value is favorable in methyl ethyl ketone solvent and compen-
Herein, although the twofold excess of (P ) was practically
1
‡
sates the unfavorable negative entropy, DS , value, while high
enthalpy, DH , value is unfavorable in acetonitrile solvent and
used in this experiment, it was too enough to achieve pseudo-
order condition, since changes in absorbance was considerably
high (DA ¼ 0.4) to record properly absorbance data (Figure 10).
So the rate law can be written for the reaction b as:
‡
can be compensated by the favorable (positive in comparison
‡
with methyl ethyl ketone) entropy value (DS ).
Ea
b
b
lnðk Þ ¼ lnA ꢀ
Rateb ¼ k ½P ꢂ ½3ꢂ
(9)
obs
obs
1
RT
In section 1, demonstrated that rate low for the reaction
b
DH‡ DS‡
k
kB
a
obs
a, can be written as rate ¼ k [1] [2]. In this section, the
ln
¼ ꢀ
þ
þ ln h
a
obs
T
RT
R
b
obs
rate low obtained for the reaction b as rate ¼ k [P ][3].
b
1