Effect of a Nitrogen-Containing Base on the Kinetics of Formation of the Zinc–Octa(m-trifluoromethylphenyl)porphyrazine Complex in Benzene

Article abstract of DOI:10.1134/S0036024419060244

Abstract: The effect additions of n-butylamine, tert-butylamine, piperidine, and morpholine have on the kinetics of the complexation of zinc acetate with octa(m-trifluoromethylphenyl)porphyrazine in benzene is studied. A possible scheme of the complexatio

Full text of DOI:10.1134/S0036024419060244

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2019, Vol. 93, No. 6, pp. 1049–1053. © Pleiades Publishing, Ltd., 2019.
Russian Text © O.A. Petrov, G.V. Osipova, P.S. Kharlamova, 2019, published in Zhurnal Fizicheskoi Khimii, 2019, Vol. 93, No. 6, pp. 840–844.
CHEMICAL KINETICS
AND CATALYSIS
Effect of a Nitrogen-Containing Base on the Kinetics of Formation
of the Zinc–Octa(m-trifluoromethylphenyl)porphyrazine
Complex in Benzene
O. A. Petrova,*, G. V. Osipovaa, and P. S. Kharlamovaa
aIvanovo State University of Chemical Technology, Ivanovo, 153000 Russia
*е-mail: poa@isuct.ru
Received September 17, 2018; revised October 15, 2018; accepted October 15, 2018
Abstract—The effect additions of n-butylamine, tert-butylamine, piperidine, and morpholine have on the
kinetics of the complexation of zinc acetate with octa(m-trifluoromethylphenyl)porphyrazine in benzene is
studied. A possible scheme of the complexation reaction is proposed. It is established that the rate of the reac-
tion slows with the branching of the hydrocarbon chain in the amine, and it grows along with the pKa of the
nitrogen-containing base.
Keywords: porphyrazines, nitrogen-containing bases, zinc acetate, complexation, kinetics
DOI: 10.1134/S0036024419060244
INTRODUCTION
R
R
N
Porphyrazines, being aromatic macrocyclic com-
pounds, find ever wider use as catalysts, liquid crystal-
line materials, and photosensitizers, due to their
unusual electronic and geometrical structure. They
exhibit semiconductor properties and are considered
promising materials for use in sensor devices [1].
Comprehensive study of the physicochemical proper-
ties of these macrocycles allows their range of practical
application to be expanded.
R
R
R
R
NH
N
N
N
HN
N
N
R
R
R =
Among the most important properties of porphyr-
azines is their ability to participate in molecular com-
plexation reactions with metal salts, among which zinc
plays an important role. Its essential properties allow it
to regulate a number of vital processes [2, 3].
CF3
with (Zn(OAc)2) in benzene.
The formation of porphyrazine complexes with
metal salts is strongly influenced by the properties of
the medium. The effect of the proton-acceptor nature
of a medium has been studied in detail for porphyra-
zines using the example of the formation of a magne-
sium complex [4–7]. In contrast, the effect a nitro-
gen-containing base has on the kinetics and mecha-
nism of introducing zinc ions into porphyrazine
macrocycles is still far from completely clear.
EXPERIMENTAL
Octa(m-trifluoromethylphenyl)porphyrazine was
synthesized as described in [8]. Zinc acetate, nitro-
gen-containing bases, and benzene were purified
according to [9, 10]. A freshly prepared solution of
H2Pa(C6H4CF3)8 in benzene with a constant concen-
tration was placed in the thermostatted cuvette of a
SHIMADZU-UV-1800 spectrophotometer and zinc
acetate dissolved in a mixture of benzene with nitro-
gen-containing base with variable concentration of the
latter was added. The rate of the complexation reac-
tion was determined from the drop in optical density at
The aim of this work was to demonstrate the effect
adding nitrogen-containing bases (B)-n-butylamine
(BuNH2), tert-butylamine (ButNH2), piperidine
(Pip), and morpholine (Mor) has on the complex- a wavelength of λ = 660 nm, since the maximum of the
ation of octa(m-trifluoromethylphenyl)porphyrazine first H2Pa(C6H4CF3)8 absorption band coincides with
(H2Pa(C6H4CF3)8)
the minimum in the electronic absorption spectrum of
1049

1050
PETROV et al.
630
D4h
C2v
D2h
A
N
N
N
N
N
N
N
N
N
N
N
N
N
H
N
H
660
2−
N
N
N
N
N
H
N
N
N
595
N
N
*
π2
*
π1
π2
500
600
700 λ, nm
Fig. 1. Changes in the electronic absorption spectrum of
H Pa(C H CF ) in the presence of Zn(OAc) in the n-
2
6
4
3 8
2
butylamine–benzene system over 17 min at 298 K and
°
= 0.10 mol/L.
C
π1
BuNH2
Fig. 2. Changes in the energies of HOMO and LUMO
during the acid ionization of a porphyrazine macrocycle.
the reaction mixture. The difference between the max-
ima of the absorption bands of H2Pa(C6H4CF3)8 and
its zinc complex allowed us to determine the current
and final concentrations of ZnPa(C6H4CF3)8 accord-
ing to the formula
the intensity of the absorption band at λ = 630 nm and
a simultaneous drop in the intensity of absorption
bands λI and λII were recorded in the EAS of
H2Pa(C6H4CF3)8, regardless of the nature of the base
over time (Fig. 1). The spectral changes accompany-
ing the complexation reaction (Fig. 1) were identical
to those observed during the acid–base interaction
between porphyrazines [11], where there was an
increase in the energy of the lowest free molecular
(1)
C = C°(A∞ – Aτ)/(A∞ – A0),
where A0, Aτ, A∞ are the optical densities of the solu-
tions at the initial moment in time, at moment in time
τ, and after the reaction is complete (τ∞); C° and C are
the initial and current concentrations of
H2Pa(C6H4CF3)8. All measurements were made under
pseudo-first order reaction conditions, so the effective
(observed) reaction rate constant for the formation of
ZnPa(C6H4CF3)8 was calculated using the formula
ln(C°/C)
1
(2)
k = 1/τ ln(C°/C).
(
)
e
1.5
1.2
0.9
The error in the kinetic parameters was determined
according to Student.
RESULTS AND DISCUSSION
It was preliminarily established that due to the lim-
ited solubility of the metal salt, the complexation of
H2Pa(C6H4CF3)8 with Zn(OAc)2 is not observed in
benzene. There is also no spectrally fixed interaction
2
0.6
0.3
of H2Pa(C6H4CF3)8 and Zn(OAc)2 when
°
<
C
BuNH2
0.10 and °
< 0.11 mol/L in benzene. The charac-
C
ButNH2
0
5
10
15
20
25
30
ter of the initial electronic absorption spectra (EAS)
for H2Pa(C6H4CF3)8 (λI = 660, λII = 595 nm)
remained unchanged for ∼95 h at 318 K. However, in
τ, min
Fig. 3. Dependences of ln(C°/C) on the reaction time of
the formation of ZnPa(C H CF ) in the system n-butyl-
amine (tert-butylamine)–benzene at 298 K and concen-
6
4
3 8
the ranges of concentration
°
= 0.10–0.58 and
C
BuNH2
°
= 0.11–6.77 mol/L in benzene, an increase in
C
°
ButNH2
trations
= (1) 0.10 and (2) 1.13 mol/L.
C
BuNH2
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EFFECT OF A NITROGEN-CONTAINING BASE ON THE KINETICS
1051
−logke
−logke
2
4.5
3.5
4.0
3.0
2.5
2.0
3.5
1
3.0
2.5
2
1
3.0
3.5
−logCZn(OAc)
2
Fig. 4. Dependences of logk on log
for the for-
Zn(OAc)2
C
−0.9 −0.6 −0.3
0
0.3
0.6
0.9
e
mation of ZnPa(C H CF ) in the system n-butylamine
logCB
6
4
3 8
(tert-butylamine)–benzene at (1) 298 and (2) 318 K, and at
Fig. 5. Dependences of logke on logCB for the formation of
ZnPa(C H CF ) in the system n-butylamine (tert-butyl-
°
concentrations
= (1) 0.20 and (2) 0.11 mol/L.
C
BuNH2
6
4
3 8
°
amine)–benzene at 298 K and
10 mol/L.
= 1.08 ×
C
Zn(OAc)2
‒4
*
orbital (LUMO)
and the highest filled molecular
π1
orbital (HOMO) π1, while the HOMO π2 and LUMO
*
energies did not change appreciably. A reduction in
π2
As can be seen from the data in Table 1, the intro-
duction of Zn2+ into the coordination center
H2Pa(C6H4CF3)8 is facilitated by an increase in the
benzene concentration of n-butylamine and tert-
butylamine, and by the temperature of the reaction.
The catalytic effect adding these bases has on reac-
tion (3) is illustrated by the straight line dependences
logke = f(log CB) (Fig. 5) with a slope tangent close to
unity. Consequently,
the difference between the HOMO π1 and π2 energies,
*
π
and the degeneration of LUMOs 1,2 (Fig. 2), raises sym-
metry π of the molecule’s chromophore from D2h to D4h.
This testifies to the deprotonation of the porphyrazine
macrocycle during complexation and the emergence of
Zn2+ in the coordination center of H2Pa(C6H4CF3)8 with
the formation of ZnPa(C6H4CF3)8.
Kinetic studies have shown that the reaction
(4)
(5)
ke = kCZn(OAc) CB,
2
–dCH Pa(C H CF ) /dτ = kCH Pa(C H CF ) CZn(OAc) CB,
H2Pa(C6H4CF ) + Zn(OAc)2 + B
3 8
2
6
4
3
8
2
6
4
3
8
2
(3)
ke
where k is the rate constant of the third-order reaction
⎯→ ZnPa(C6H4CF ) + 2HOAc + B
3 8
of ZnPa(C6H4CF3)8 formation.
has an order equal to the unit of H2Pa(C6H4CF3)8
(Fig. 3) and close to that of Zn(OAc)2 (Fig. 4).
Based on our data, one possible scheme of
reaction (3) could be:
B
H
N
N
N
N
H
N
k1
N
N
N
N
N
+ B
k−1
N
N
N
N
N
N
H
H
+ Zn(OAc)2
k2
N
N
N
Zn
+ 2HOAc + B
N
N
N
N
N
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 6 2019

1052
PETROV et al.
Table 1. Kinetic parameters of the reaction for the formation of ZnPa(C6H4CF3)8 in the nitrogen-containing base system
= 1.03 × 10−5 mol/L,
= 1.08 × 10−4 mol/L)
Zn(OAc)2
°
°
C
(benzene
C
H2Pa(C6H4CF )8
3
ke × 103, s−1
k, L2/(mol2 s)
−∆S≠, J/(mol K)
Ea, kJ/mol
°
CB
Т, K
, mol/L
n-Butylamine
0.10
298
308
318
1.80
2.15
2.60
10.80
12.90
15.50
15
255
0.20
0.33
0.58
298
308
318
298
308
318
298
308
318
2.50
3.10
3.90
4.60
5.50
6.85
8.40
10.50
12.90
7.50
9.30
11.70
8.35
9.90
12.60
8.70
10.80
13.20
17
15
17
246
250
236
tert-Butylamine
0.11
0.52
1.13
3.38
6.77
298
308
318
298
308
318
298
308
318
298
308
318
0.03
0.07
0.20
0.16
0.40
1.00
0.30
0.75
1.85
1.00
2.50
6.10
2.60
6.40
16.30
2.90
7.20
18.05
2.50
6.20
15.20
2.74
6.85
16.70
74
72
72
71
70
91
84
78
72
69
298
308
318
2.05
4.90
12.15
2.80
6.70
16.60
≠
The error in determining k did not exceed 5%. The error in determining E and ∆S was 10%.
e
a
At the final stage of the process, Zn2+ is incorpo-
According to [12], intracyclic NH bonds in cyclic
macrocycles have greater NH acidity than porphyrin rated into the coordination center of the acid–base H-
complex, which requires less energy to break NH
bonds than the molecular form of H2Pa(C6H4CF3)8. It
is assumed that k1 ≫ k−1 and k1 < k2, since the inter-
mediate H-complex is not observed in the spectrum.
It should be noted that according to the data of [14], a
similar scheme for the formation of ZnPa(C6H4CF3)8
is also observed with cyclic nitrogen-containing bases
piperidine and morpholine in benzene.
bonds. As a result, they are delocalized (i.e., linked to
two nitrogen atoms through twin-center hydrogen
bonds). Porphyrazines thus easily participate in kinet-
ically controlled acid–base interactions with nitrogen-
containing bases in inert low-polar solvents (benzene,
chlorobenzene) [13]. This suggests that at the first
stage of complexation, the base molecule interacts
with one of the two protons in the NH groups of
H2Pa(C6H4CF3)8, forming an H-complex in which
the hydrogen atom, bound with a base molecule and
two intracyclic nitrogen atoms through hydrogen
bonds, should be located above the macrocycle plane.
Judging from kinetic equation (5), the complete trans-
fer of the NH proton, which leads to the formation of
an ionic structure, in this case seems unlikely [13].
CONCLUSIONS
The results from our experiment (Table 1) show
that replacing n-butylamine (pKa = 10.60 [15]) with
tert-butylamine, which is similar in basicity (pKa =
10.68 [15]), slows the rate of complexation by a factor
of ~5, judging from the k298 values. At the same time,
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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EFFECT OF A NITROGEN-CONTAINING BASE ON THE KINETICS
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1053
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Translated by M. Aladina
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 6 2019