Kinetic and mechanistic analysis of oxidation of 2-furoic hydrazide by hexachloroirradate(IV) in a wide pH range

Article abstract of DOI:10.1007/s11243-019-00347-x

Oxidation of 2-furoic hydrazide (FH) by hexachloroiridate(IV) ([IrCl₆]^2?) was studied kinetically in a wide pH range in aqueous solution of 1.0?M ionic strength. The oxidation reaction followed well-defined second-order kinetics: ? d[IrCl₆ ^2?]/dt = k′[FH]_tot[IrCl₆ ^2?], where [FH]_tot denotes the total concentration of FH and k′ stands for the observed second-order rate constants. The established k′–pH profile displays that k′ increases drastically with pH and a plateau region exists between pH 4 and 6. A stoichiometric ratio of Δ[FH]_tot/Δ[IrCl₆ ^2?] = 1/4?was revealed by spectrophotometric titrations. ¹H NMR spectroscopic studies indicated that FH was cleanly oxidized to 2-furoic acid. The kinetic data suggest a reaction mechanism in which all the three protolysis species of FH react with [IrCl₆]^2? in parallel, forming the rate-determining steps. Two stabilized hydrazyl radicals are generated in the rate-determining steps, in which a single electron is transferred to [IrCl₆]^2?. The two hydrazyl radicals react rapidly in consecutive steps requiring 3?mol of Ir(IV) to form 2-furoic acid as the final product. Rate constants of the rate-determining steps were deduced through a simulation of the rate expression to the k′–pH dependency data. Values of these rate constants demonstrate that the three protolysis species of FH have a huge reactivity span, changing by about 10⁹ times toward reduction in [IrCl₆]^2? and that FH can be readily oxidized in neutral and basic media. Rapid scan spectra and the measured activation parameters suggest that an outer-sphere electron transfer is probably taking place in each of the rate-determining steps. This is the first kinetic study on the oxidation reactions of FH and provides concurrently the protolysis constants of FH (pK_a1 = 3.04 ± 0.08 and pK_a2 = 11.6 ± 0.1) at 25.0?°C and 1.0?M ionic strength.

Full text of DOI:10.1007/s11243-019-00347-x

Transition Metal Chemistry
https://doi.org/10.1007/s11243-019-00347-x
Kinetic and mechanistic analysis of oxidation of 2‑furoic hydrazide
by hexachloroirradate(IV) in a wide pH range
Haiping Yao1 · Hongwu Tian1 · Liyao Xu1 · Yanqing Xia2 · Li Zhou2 · Chunli Liu2 · Tiesheng Shi1,2
Received: 6 June 2019 / Accepted: 25 July 2019
© Springer Nature Switzerland AG 2019
Abstract
Oxidation of 2-furoic hydrazide (FH) by hexachloroiridate(IV) ([IrCl6]2−) was studied kinetically in a wide pH range in
aqueous solution of 1.0 M ionic strength. The oxidation reaction followed well-defned second-order kinetics: −d[IrCl62−]/
dt=k′[FH]tot[IrCl62−], where [FH]tot denotes the total concentration of FH and k′ stands for the observed second-order rate
constants. The established k′–pH profle displays that k′ increases drastically with pH and a plateau region exists between pH
4 and 6. A stoichiometric ratio of Δ[FH]tot/Δ[IrCl62−]= 1/4 was revealed by spectrophotometric titrations. 1H NMR spec-
troscopic studies indicated that FH was cleanly oxidized to 2-furoic acid. The kinetic data suggest a reaction mechanism in
which all the three protolysis species of FH react with [IrCl6]2− in parallel, forming the rate-determining steps. Two stabilized
hydrazyl radicals are generated in the rate-determining steps, in which a single electron is transferred to [IrCl6]2−. The two
hydrazyl radicals react rapidly in consecutive steps requiring 3 mol of Ir(IV) to form 2-furoic acid as the fnal product. Rate
constants of the rate-determining steps were deduced through a simulation of the rate expression to the k′–pH dependency
data. Values of these rate constants demonstrate that the three protolysis species of FH have a huge reactivity span, changing
by about 109 times toward reduction in [IrCl6]2− and that FH can be readily oxidized in neutral and basic media. Rapid scan
spectra and the measured activation parameters suggest that an outer-sphere electron transfer is probably taking place in each
of the rate-determining steps. This is the frst kinetic study on the oxidation reactions of FH and provides concurrently the
protolysis constants of FH (pKa1 =3.04 0.08 and pKa2 =11.6 0.1) at 25.0 °C and 1.0 M ionic strength.
Introduction
Hydrazides fnd wide applications as drugs [1, 2]; repre-
sentative drugs incorporating hydrazide scafold include iso-
niazid, marplan, iproniazid, and indolylglyoxyl hydrazide [1,
2]. In addition, hydrazides are used for manufacturing poly-
Electronic supplementary material The online version of this
mers and glues in industry and used as chemical preserv-
article (https://doi.org/10.1007/s11243-019-00347-x) contains
ers for plants [2]. In organic chemistry, acid hydrazides are
potent reagents for synthesis of oxygen-, nitrogen-, and/or
sulfur-containing heterocyclic rings [2]. Of the hydrazides,
2-furoic hydrazide (FH) has been employed (1) as analytical
reagent in sugar analysis [3] and a complexing agent with
β-cyclodextrin in mass spectrometric analysis [4]; (2) as a
fuorescent chemosensor for detection of Al3+ and pyroph-
osphate [5]; (3) as coordinating ligand for formation of com-
plexes with Cu(II), Pd(II), Pt(II), and Ru(II) ions [6–10].
These complexes have also been tested and shown to have
antimicrobial and antitumor properties [6–10]. Additionally,
the vibrational and NMR spectra of FH have been measured
and simulated theoretically [11].
supplementary material, which is available to authorized users.
* Li Zhou
zhouli@uzz.edu.cn
* Chunli Liu
liuchunli@uzz.edu.cn
* Tiesheng Shi
rock@hbu.edu.cn
1
College of Chemistry and Environmental Science, the MOE
Key Laboratory of Medicinal Chemistry and Molecular
Diagnostics, Hebei University, Baoding 071002,
Hebei Province, People’s Republic of China
2
College of Chemistry, Chemical Engineering, and Materials
Science, Zaozhuang University, Zaozhuang 277160,
Shandong Province, People’s Republic of China
Vol.:(0123456789)
1 3

Transition Metal Chemistry
1
However, the kinetic and mechanistic aspects for the FH
reactions have not been exploited so far. The oxidation of
FH by hexachloroiridate(IV) ([IrCl6]2−) was thus carried
out in this work. [IrCl6]2− is a well-known single-electron
oxidizing agent [12–16] and has been utilized as a redox
probe for obtaining chemical information of oxidative stress
[17], since many oxidation reactions are taking place in
biologically and/or biomedically relevant processes involv-
ing a single electron transfer. It is stable in solutions from
pH 0 to about 10.5, and thus, the kinetic data can be col-
lected in a wide pH range [18–20]. Our previous work had
demonstrated that the reduction in the Ir(IV) complex by
hydrazides and hydrazines followed second-order kinetics,
and we were able to evaluate protolysis constants kinetically
[18–20]. This work provides the kinetic data for the oxida-
tion of FH species by Ir(IV), with the hope of revealing the
reactivity diferences among the FH species.
spectrometer. H NMR spectra were run on an AVANCE
NEO 400 MHz NMR spectrometer (Bruker, Switzerland).
Reaction media
The acidic reaction media were prepared by combinations
of 1.00 M HClO4 and 1.00 M NaClO4 solutions, where
[H+]=[HClO4]; their pH values were estimated using the
equation: pH=−log[H+]+0.11, which is based on a mean
activity coefcient of 0.77 in solutions of 1.00 M NaClO4
[21]. For bufer solutions in the pH range of 3.47–12.68,
combinations of AcOH/NaOAc, NaH2PO4/Na2HPO4,
NaHCO3/Na2CO3, and Na2HPO4/Na3PO4 (all around 0.2 M)
were employed and all the bufers contained 2 mM PDCA
[16]. The ionic strengths (μ) of these bufers were all tuned
to 1.00 M with NaClO4. The pH of the bufer solutions was
measured immediately before use.
Stoichiometric investigation
Experimental
Spectrophotometric titration method was used to investigate
the reaction stoichiometry [22–24]. The reaction was stud-
ied in two reaction media: one in [H+] = 0.020 M and the
other in a pH 6.30 bufer. In each medium, a series of solu-
tion mixtures were prepared in which [IrCl62−]=0.40 mM
was remained constant and [FH]tot was varied from 0 to
0.40 mM, where [FH]tot stands for the total concentration
of FH. Each of the reaction mixtures was aged for about
3 min in the pH 6.30 bufer and for about 2 h in the acidic
medium, and the absorbance was then measured at 488 nm.
Materials
Sodium hexachloroiridate(IV) hexahydrate (Na2IrCl6·6H2O,
99.9%), 2-furoic hydrazide (FH), and 2,4-pyridinedicarbox-
ylic acid (PDCA) were purchased from Sigma-Aldrich. The
purity of FH was checked by 1H NMR spectroscopy in D2O
(vide infra). Acetic acid, sodium acetate, sodium dihydro-
gen phosphate, disodium hydrogen phosphate, trisodium
phosphate, sodium bicarbonate, sodium carbonate, sodium
chloride, hydrochloric acid, perchloric acid, and sodium per-
chlorate were obtained either from Alfa Aesar or from Fisher
Scientifc; these chemicals were all of analytical grade and
used without further purifcation. Standard bufers of pH
4.00, 7.00 and 10.00, also from Fisher Scientifc, were used
to calibrate the electrode. Doubly distilled water was utilized
to prepare all the solutions.
NMR product analysis
In order to identify the oxidation product of FH, 1H NMR
spectra were run for 2 samples: (a) 1 mM FH in D2O which
contains 0.05% TSP (3-(trimethylsilyl)propionic acid-d4
sodium salt, Alpha Aesar) and (b) a reaction mixture of
1 mM FH and 5 mM [IrCl6]2− after a reaction time of about
5 h.
Instrumentation
Kinetic measurements
The pH values of bufer solutions (when pH>3) were meas-
ured with an Accumet Basic AB15 Plus pH meter equipped
with an Accumet combination pH electrode (Fisher Scien-
tifc, Pittsburgh, PA). The UV–Vis spectra and absorption
measurements were performed on a TU-1950 spectropho-
tometer (Persee Inc., Beijing, China) using 1.00-cm quartz
cells. Kinetic runs and rapid scan spectra were recorded on
an Applied Photophysics SX-20 stopped-fow spectrometer
(Applied Photophysics Ltd., Leatherhead, UK). The tem-
perature was controlled to 0.1 °C using a water bath cir-
culation from a thermostat of Lauda Alpha RA8 (Lauda,
Germany) for both spectrophotometer and the stopped-fow
Stock solutions of 1.0 mM [IrCl6]2− were prepared daily
fresh by dissolving the required amount of Na2IrCl6·6H2O
in a solution containing 0.90 M NaClO4, 0.09 M NaCl, and
0.01 M HCl. Stock solutions of FH were prepared by add-
ing the desired amount of FH into a medium of specifc
pH and then fushed for 10 min with nitrogen. Solutions of
[IrCl6]2− and FH for kinetic measurements were prepared
by dilution of these stock solutions with the same medium
and then fushed for about 10 min with nitrogen. Reactions
were initiated by mixing equal volumes of the [IrCl6]2− and
FH solutions directly on the stopped-fow spectrometer.
1 3

Transition Metal Chemistry
Reactions were followed under pseudo-frst-order conditions
with [FH]tot ≥10·[IrCl62−], and the reaction solutions were
only used for a couple of hours.
Empirical rate law
The influence of varying [FH]tot on the reaction rate
was investigated within the concentration range
0.50 mM≤[FH]tot ≤5.00 mM at diferent pHs, and variation
of [FH]tot at a fxed pH did not cause any change in pH of
the media. The kobsd–[FH]tot plots at diferent pHs are shown
in Fig. 2; clearly, the plots are linear without any signif-
cant intercepts, indicating that the reaction is frst order in
[FH]tot. Therefore, the reaction follows overall second-order
kinetics and an empirical rate law is as written in Eq. (2),
where k′ denotes observed second-order rate constants and
kobsd =k′[FH]tot.
Results and discussion
Rapid scan spectra
Rapid scan spectra were recorded on the stopped-fow spec-
trometer for the oxidation of FH by [IrCl6]2− under a set of
reaction conditions; the acquired spectra are displayed in
Fig. 1. The disappearing bands around 428 and 488 nm origi-
nate from [IrCl6]2−, whereas FH has essentially no absorption
contribution in these two bands. Clearly, there were neither
signifcant shifts of the two absorption bands, nor did new
absorption bands emerge, suggesting that there were no sub-
stitution reaction on Ir(IV) complex or a strong association
between the [IrCl6]2− and FH before the rate-determining
step(s). Under the pseudo-frst-order reaction conditions, the
kinetic traces could be well described by Eq. (1), where kobsd
is the pseudo-frst-order rate constant, and At, A0, and A∞
represent the absorbances at time t, zero, and infnity, respec-
tively. Figure S1 in Electronic supplementary material (ESM)
shows good fts of the kinetic traces acquired at
−d[IrCl26−]∕dt = kobsd[IrCl62−] = k�[FH]tot[IrCl26−
]
(2)
The kinetics was studied over a wide pH range
(0.16≤pH≤9.53); when pH>9.6, the reaction became too
fast to follow even by the technique used. Values of k′ were
evaluated from the linear plots of kobsd versus [FH]tot at vari-
ous pHs and are summarized in Table S1 in ESM. The data
(Table S1 and plotted in Fig. 3) reveal a drastic increase (ca.
(
)
(
)
At = A0−A∞ exp −kobsdt + A∞
(1)
428 and 488 nm; moreover, the values of kobsd obtained at
these two wavelengths are identical within experimental
error. All the above features indicate that the reaction is
indeed frst order in [IrCl62−].
Fig. 1 Rapid scan spectra for the oxidation of FH by [IrCl6]2− under
the reaction conditions: [Ir(IV)]=0.20 mM, [FH]tot =2.00 mM, phos-
phate bufer of pH 6.30, μ=1.0 M and 25.0 °C. The spectra were
acquired at 3, 25, 51, 75, 101, 125, 151, 175, 200, 225, 251, 275, 300,
323, 350, 375, and 400 ms after mixing
Fig. 2 Plots of kobsd versus [FH]tot at 25.0 °C and diferent pHs with
the numbers around the lines indicating the pH values
1 3

Transition Metal Chemistry
106 times) in k′ as pH is increased from 0.16 to about 9.6
Reaction mechanism and rate expression
with no indication of saturation of the plot in alkaline media.
In aqueous solution, there exist three protolysis species
for FH being described as I–III in Fig. 5 [19, 25]. The k′
versus pH profle established in this work (Fig. 3) is simi-
lar in shape to that we obtained earlier for the oxidation of
isoniazid by the Ir(IV) complex [19], suggesting that the
reactivities of the three species of FH toward reduction in
[IrCl6]2− difer drastically. When all the kinetic data (i.e.,
the rapid scan spectra for the reaction, overall second-order
kinetics and the reaction stoichiometry) are put together, a
reaction mechanism is proposed as delineated in Fig. 5 in
which the generations of two types of hydrazyl radicals are
the rate-determining steps expressed by k1–k3 [19]. The free
radical generated from species I and II is on the nitrogen
atom that is distal from the carbonyl group as a result of
Stoichiometry and oxidation product
Plots of absorbance at 488 nm as a function of [FH]tot
are given in Figure S2 in ESM; the data points fol-
low clearly two crossing straight lines in both media.
From the intersections, ratios were estimated to
be Δ[FH]tot/Δ[IrCl62−] = (0.105 0.005) mM/0.40
mM = (1.05 0.05)/4 in 0.020 M HClO4 and to be
Δ[FH]tot/Δ[IrCl62−] = (0.095 0.005) mM/0.40
mM = (0.095 0.005)/4 in pH 6.30 bufer, respectively.
Thus, a reaction stoichiometry of Δ[FH]tot:Δ[IrCl62−]=1:4
is established, and the stoichiometric reaction can be
described by Eq. (3):
O
_
_
2
+
(3)
4[IrCl6] + H2O
+ 4[IrCl6] + 4H+ + N2
C-NH-NH2
COOH
O
O
1
The H NMR spectra obtained are shown in Fig. 4 in
which TSP was used as the reference for the NMR shifts.
The assignments of NMR peaks are given in the fgure leg-
end, and no signals were observed between 0 and 6.5 ppm.
The NMR experiment demonstrates that when more than
stoichiometric amount of Ir(IV) was used in the reaction
mixture, all the reactant FH was cleanly transferred to
2-furoic acid. Moreover, we found that the excess of Ir(IV)
could not oxidize the 2-furoic acid that was formed. Thus,
the oxidation product 2-furoic acid was ascertained by the
NMR spectroscopic analysis.
the electron-withdrawing efect of the carbonyl group. The
other free radical is on the nitrogen atom that is close to
the carbonyl group (for species III) owing to the electron-
donating property of enolate. These two types of hydrazyl
free radicals have also been proposed in the oxidations of
INH by enzymes [26–28]. Generation of each type of the
hydrazyl radicals is followed by three consecutive and fast
reactions [19], leading to the formation of 2-furoic acid. In
fact, the present reaction mechanism resembles those pro-
posed earlier for the oxidations of isoniazid and nicotinic
hydrazide by [IrCl6]2− [19].
According to the reaction mechanism in Fig. 5, Eq. (4)
can be derived as the rate law, and clearly conform with the
empirical rate law in Eq. (2), where aH stands for the proton
activity which corresponds exactly to the pH measurements.
4(k1a2H + k2Ka1aH + k3Ka1Ka2)
−d[IrCl26−]∕dt =
[FH]tot[IrCl26−
]
a2H + Ka1aH + Ka1Ka2
(4)
Comparing Eq. (4) with Eq. (2) confers:
4(k1a2H + k2Ka1aH + k3Ka1Ka2)
k� =
(5)
a2H + Ka1aH + Ka1Ka2
Evaluation of the rate constants and pKa values
The protolysis constants Ka1 and Ka2 of FH at 25.0 °C and
μ = 1.0 M appear not available in the literature. The pKa1
value of FH is expected to be between 3 and 4 [19], being
in the pH region used in this work while that of pKa2 is
Fig. 3 Logk′ versus pH profle at 25.0 °C constructed from the data
points for the oxidation of FH by [IrCl6]2−. The solid curve was
produced from the best ft of the experimental data to Eq. (5) by a
weighted nonlinear least-squares method
1 3

Transition Metal Chemistry
Fig. 4 1H NMR spectra obtained for 1 mM FH in D2O (top) and a
reaction mixture of 1.0 mM FH with 5 mM [IrCl6]2− in D2O after a
reaction time of about 5 h (bottom). Peak assignments: δ 7.64 (d) for
5-H, δ 7.13 (d) for 3-H, and δ 6.60 (q) for 4-H for the 5-membered
ring in FH (top spectrum) [11]; δ 7.73 (d) for 5-H, δ 7.31 (d) for 3-H,
and δ 6.64 (q) for 4-H for the 5-membered ring in 2-furoic acid (bot-
tom spectrum)
anticipated to be larger than 10 [25], being beyond the pH
region used. To our experience [20], the pKa value cannot
be evaluated kinetically in good accuracy if the kinetic
data are not collected within a pH region not covering
the pKa value. We thus determined the pKa2 value of FH
spectrophotometrically [25], while the pKa1 value will be
derived from kinetic data below. The UV–Vis spectra were
recorded for 0.10 mM FH in bufer solutions of pH 6.00
and 12.68 and are shown in the top part of Fig. 6, where
the spectra stem predominantly from species II and III
of FH. The absorption peak at 255 nm of species II was
utilized for the subsequent measurements.
A series of FH solutions with varied pH values were
prepared in which [FH]tot = 0.10 mM was maintained
O
_
[IrCl6]2
_
+
C-NH-NH3
[IrCl6]3 + 2H+
O
I
k1
_
3[IrCl6]2 + H2O
Ka1
O
H+
C-NH-NH
_
3[IrCl6]3 + 4H+
k2
O
O
_
fast
fast
C-NH-NH2
[IrCl6]3 + H+
_
O
[IrCl6]2
II
+ N2
COOH
O
Ka2
H+
_
_
k3
3[IrCl6]3 + 3H+
O
O
C-N-NH2
C=N-NH2
_
O
_
O
[IrCl6]2
_
III
3[IrCl6]2 + H2O
[IrCl6]3
Fig. 5 A reaction mechanism proposed for the oxidation of FH by [IrCl6]2− in which the reactions described by k1–k3 are the rate-determining
steps
1 3

Transition Metal Chemistry
Table 1 Rate constants for
the rate-determining steps and
protolysis constants in Fig. 5 at
25.0 °C and μ=1.0 M
Constant
Value (M−1 s−1
)
k1
k2
k3
pKa1
pKa2
0.05 0.02
620 15
(7.3 0.1)×107
3.04 0.08
11.6 0.1
A weighted nonlinear least-squares simulation provided
an excellent ft shown in Fig. 3 [30]; the values of k1, k2,
k3, and Ka1 were obtained concurrently from the ft and
are listed in Table 1. A good ft of the data to the equation
after simulation in Fig. 3 strongly conforms to the trueness
of the rate expression of Eq. (5) and in turn to the proposed
reaction mechanism. The simulated rate constants of the
oxidation of the FH species (as shown in Fig. 5) are k1:k2:
k3 = 1:1.2 × 104:1.4 × 109 and show huge reactivity difer-
ences of the three species of FH toward the reduction in
[IrCl6]2−; this huge reactivity range is clearly surprising.
The exceptional rapidness to give of an electron for spe-
cies III indicates that FH can be readily oxidized in neutral
and basic media; this nature might be responsible for the
chemical preserving property in general for hydrazides.
Activation parameters and the electron transfer
mode
Fig. 6 (Top): UV–Vis spectra of 0.10 mM FH in bufers of pH 6.00
and 12.68 at 25.0 °C and µ=1.0 M. (Bottom): absorbance at 255 nm
of 0.10 mM FH as function of pH at 25.0 °C and µ=1.0 M. The
solid curve was obtained from the best ft of the experimental data to
Eq. (6)
The protolysis constants and the rate constants were used
to construct species of FH versus pH distribution diagram
(the top part of Figure S3 in ESM) and the reactivity of
FH species versus pH distribution diagram (the bottom
part of Figure S3 in ESM) [19, 20, 24]. These diagrams
provide a straightforward way to view the distributions of
a specifc species and its reactivity along with pH. Exami-
nation of these diagrams reveals that the neutral species
of FH (species II in Figure S3 in ESM) at pH about 4.5
contributes predominantly in both distributions (96% and
99%, respectively). Thus, the electron transfer reaction was
studied at pH 4.45 and at several temperatures (the top part
of Figure S4 in ESM), where Eq. (5) can be simplifed to
k′≈4k2 (or k2 ≈k′/4). Values of k2 were thus calculated and
are listed in Table 2. The Eyring plot for k2 is given in the
bottom part of Figure S4, and the activation parameters
were calculated from the plot and are listed in Table 2 as
well. Clearly, the middle-ranged negative value of activa-
tion entropy coincides with the nature of the second-order
kinetics, where a compact structure of the transition state
is anticipated. This typical feature together with the reac-
tion characters observed in the rapid scan spectra suggests
that the reaction expressed by k2 probably undergoes an
outer-sphere electron transfer. It is difcult to determine
constant; after those solutions were equilibrated at 25.0 °C
for 10 min, absorption values at 255 nm were measured.
The absorbance at 255 nm versus pH plot (data points) is
given in the bottom part of Fig. 6. The data were simulated
to Eq. (6) by use
ꢀ
−pH)} ꢀ
}
a2−pH)
Abs (255 nm) = [FH]tot ꢀ3 + ꢀ2 ⋅ 10(pK
∕ 1 + 10(pK
a2
(6)
of nonlinear squares method [29], where ε2 and ε3 represent
the molar absorptivities of species II and III, respectively.
The simulation resulted in a good ft (bottom part of Fig. 6),
rendering the values of ε2 = (1.21 0.02) × 104 M−1 cm−
1, ε3 = (8.4 0.2) × 103 M−1 cm−1 and pKa2 = 11.6 0.1 at
25.0 °C and μ=1.0 M.
Equation (5) was then used to simulate the k′–pH
dependency data in Table S1; in the simulation, k1, k2,
k3, and Ka1 were treated as adjustable parameters and the
value of Ka2 determined above was used as a direct input.
1 3

Transition Metal Chemistry
3. Lever M, Walmsley TA, Visser RS, Ryde SJ (1984) Anal Biochem
139:2015–2211
Table 2 Second-order rate constant k2
and the corresponding activa-
tion parameters in the reduction in [IrCl6]2‒ by FH at μ=1.0 M
4. Dotsikas Y, Loukas YL (2003) J Am Soc Mass Spectrom
14:1123–1129
t (°C)
k2 (M−1 s−1
)
ΔHa2 (kJ mol−1
)
ΔSa2 (J·K−1 mol−1
)
5. Hwang SM, Kim MS, Lee M, Lim MH, Kim C (2017) New J
Chem 41:15590–15600
15.0
20.0
25.0
30.0
35.0
323
430
570 15
676 16
870 18
7
9
33.5 1.6
−80
6
6. Fontes APS, Guerra W, Machado FC, de Almeida MV, Alves WA,
da Costa Ferreira AM (2004) Transit Met Chem 29:382–387
7. Silva PP, Guerra W, dos Santos GC, Fernandes NG, Silveira JN,
da Costa Ferreira AM, Bortolotto T, Terenzi H, Bortoluzzi AJ,
Neves A, Pereira-Maia EC (2014) J Inorg Biochem 132:67–76
8. de Souza GD, Rodrigues MA, Silva PP, Pereira-Maia EC, Botelho
FV, de Campos TA, de Faria Franca E, de Almeida KJ, Guerra W
(2013) Croat Chem Acta 86:201–206
aTransition State
9. Rodrigues MA, Marzano IM, Ribeiro GH, Colina-Vegas L, Pivatto
M, Fontes APS, Ribeiro CM, Pavan FR, de Almeida KJ, Batista
AA, Pereira-Maia EC, Guerra W (2015) Polyhedron 98:146–153
10. Mahalingam V, Chitrapriya N, Zeller M, Natarajan K (2009) Poly-
hedron 28:1532–1540
the activation parameters for the reactions expressed by k1
and k3, but the same type of electron transfer is expected
to take place.
11. Vimalraj V, Vijayalakshmi S, Umayaparvathi S, Krishnan AR
(2011) Spectrochim Acta A 78:670–675
12. Pelizzetti E, Mentasti E, Baiocchi C (1976) J Phys Chem
80:2979–2982
Conclusions
13. Pelizzetti E, Mentasti E, Pramauro E (1978) Inorg Chem
17:1181–1186
The oxidation of FH by [IrCl6]2− has been studied kinetically
in a wide pH range in this work, and overall second-order
kinetics is well defned, complementing with the nature of
the [IrCl6]2−—hydrazide/hydrazine reaction systems stud-
ied earlier [18–20]. The good reaction nature enables us
to derive the rate constants of rate-determining steps and
the protolysis constants of FH. Rapid scan spectra and the
measured activation parameters suggest that an outer-sphere
electron transfer mechanism probably occurs in the rate-
determining steps. Most intriguingly, the three protolysis
species are shown to have signifcantly diferent reactivity
toward the reduction in Ir(IV), spanning a range of nine
orders of magnitude. Clearly, FH or hydrazides in general
can be oxidized readily in neutral and basic media. To the
best of our knowledge, this is the frst kinetic study on the
oxidation reactions of FH.
14. Stanbury DM (1984) Inorg Chem 23:2879–2882
15. Hubbard CD, Gerhard A, van Eldik R (2001) Dalton Trans
1069–1075
16. Bhattari N, Stanburry DM (2012) Inorg Chem 51:13303–13311
17. Kim E, Winkler TE, Kitchen C, Kang M, Banis G, Bentley WE,
Kelly DL, Ghodssi R, Payne GF (2017) Anal Chem 89:1583–1592
18. Nan C, Dong J, Jiao X, Shi H, Duan J, Shi T (2017) Transt Met
Chem 42:9–15
19. Dong J, Ren Y, Sun S, Yang J, Nan C, Shi H, Xu J, Duan J, Shi T,
Elding LI (2017) Dalton Trans 46:8377–8386
20. Nan C, Dong J, Tian H, Shi H, Shen S, Xu J, Li X, Shi T (2018)
J Mol Liq 256:489–496
21. Kimura M, Yamamoto M, Yamabe S (1982) J Chem Soc Dalton
Trans 423–427
22. Huo S, Dong J, Shen S, Ren Y, Song C, Xu J, Shi T (2014) Dalton
Trans 43:15328–15336
23. Dong J, Ren Y, Huo S, Shen S, Xu J, Tian H, Shi T (2016) Dalton
Trans 45:11326–11337
24. Liu C, Xu L, Tian H, Yao H, Elding LI, Shi T (2018) J Mol Liq
271:838–843
Acknowledgements Financial support of this work by a setup fund
25. Manoussakis G, Haristos D, Youri C (1973) Can J Chem
51:811–814
from Zaozhunag University (1020717) is gratefully acknowledged.
26. Wengenack NL, Rusnak F (2001) Biochemistry 40:8990–8996
27. Aitken SM, Quellet M, Percival MD, English AM (2003) Biochem
J 375:613–621
Compliance with ethical standards
28. Khan SR, Morgan AGM, Michail K, Srivastava N, Whittal RM,
Aljuhani N, Siraki AG (2016) Biochem Pharmacol 106:46–55
29. Huo S, Shen S, Liu D, Shi T (2012) J Phys Chem B
116:6522–6528
Conflict of interest The authors declare no confict of interest.
30. Huo S, Dong J, Song C, Xu J, Shen S, Ren Y, Shi T (2014) RSC
Adv 4:7402–7409
References
1. Narang R, Narasimhan B, Sharma S (2012) Curr Med Chem
19:569–612
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
2. Majumdar P, Pati A, Patra M, Behera RK, Behera AK (2014)
Chem Rev 114:2942–2977
1 3