Kinetic studies of acenaphthene oxidation catalyzed by N-Hydroxyphthalimide

Article abstract of DOI:10.1002/kin.20790

The acenaphthene oxidation with molecular oxygen in the presence of N-hydroxyphthalimide (NHPI) has been investigated. It is shown that the main oxidation product is acenaphthene hydroperoxide. The phthalimide-N-oxyl (PINO) radical has been generated in situ from its hydroxyimide parent, NHPI, by oxidation with iodobenzenediacetate. The rate constant of H-abstraction (k _H) from acenaphthene by PINO has been determined spectroscopically in acetonitrile. The kinetic isotope effect and the activation parameters have also been measured. On the basis of the results of our studies and available published literature data, a plausible mechanism for the oxidation process of acenaphthene with dioxygen catalyzed by NHPI was discussed.

Full text of DOI:10.1002/kin.20790

Kinetic Studies
of Acenaphthene
Oxidation Catalyzed by
N-Hydroxyphthalimide
I. O. OPEIDA, YU. E. LITVINOV, O. V. KUSHCH, M. O. KOMPANETS, O. M. SHENDRIK
L. M. Litvinenko Institute of Physico-Organic and Coal Chemistry of NASU, Donetsk 83114, Ukraine
Received 14 September 2012; revised 7 February 2013; accepted 9 February 2013
DOI 10.1002/kin.20790
Published online 21 June 2013 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: The acenaphthene oxidation with molecular oxygen in the presence of N-
hydroxyphthalimide (NHPI) has been investigated. It is shown that the main oxidation product
is acenaphthene hydroperoxide. The phthalimide-N-oxyl (PINO) radical has been generated
in situ from its hydroxyimide parent, NHPI, by oxidation with iodobenzenediacetate. The rate
constant of H-abstraction (kH) from acenaphthene by PINO has been determined spectroscop-
ically in acetonitrile. The kinetic isotope effect and the activation parameters have also been
measured. On the basis of the results of our studies and available published literature data,
a plausible mechanism for the oxidation process of acenaphthene with dioxygen catalyzed by
NHPI was discussed. ꢀC 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 515–524, 2013
Polycyclic aromatic hydrocarbons with secondary
INTRODUCTION
–
C H bonds, for example, acenaphthenes (AcNph) are
oxidized by using dioxygen to their corresponding
oxygenated derivatives, naphthalic acid and naphthalic
anhydride, which are used as intermediates for the syn-
thesis of the important raw materials (such as esters,
amides, and imides) for the manufacture of dyes, phar-
maceuticals, pesticides, plastics, fibers, curing agents,
plasticizers, pigments, fluorescent whiteners, and many
other items [9]. Polynuclear hydrocarbons were oxi-
dized during catalysis of NHPI [10], [11], but no litera-
ture report has been published on the efficient oxidation
of acenaphthene except [10], where authors used the
NHPI/anthraquinone system. In this paper, we have re-
ported the kinetic study of the acenaphthene oxidation
by molecular oxygen in the presence of NHPI, to bet-
ter understand the mechanism of the NHPI-catalyzed
aerobic oxidation of alkylbenzenes. We have described
Aerobic oxidation of alkylbenzenes is a promising
process in industrial chemistry. One of the most
active and selective catalysts in liquid-phase oxi-
dation of alkylbenzenes using molecular oxygen is
N-hydroxyphthalimide (NHPI) and its mixture with
cobalt and manganese salts [1–8]. It has been used to
produce hydroperoxides, carboxylic acids, and other
oxygen-containing products under moderate condi-
tions in a high yield. In oxidation processes, NHPI
acts as a precursor of the phthalimide-N-oxyl (PINO)
radical, which is the effective species in the reaction of
H-atom abstraction from RH.
Correspondence to: Yu. E. Litvinov; e-mail: nhpi@rambler.ru.
2013 Wiley Periodicals, Inc.
C
ꢀ

516
OPEIDA ET AL.
the use of NHPI, in which it acts as a catalyst in the
absence of a transition metal compound.
EXPERIMENTAL
NHPI was purchased from Fluka (Sigma-Aldrich
Chemie GmbH) and was used as received. Azodi-
isobutyronitrile (AIBN) and acenaphthene were pu-
rified by recrystallizing twice from ethanol. Ethylben-
zene, toluene, cumene were purified using a described
procedure [12]. An acetic acid was distilled over P2O5.
Iodobenzenediacetate (PhI(OAc)2) was synthesized as
described [13]. Acenaphthenone-9, acenaphthenole-
9, and acenaphthene quinone were used as received.
9,9,10,10-Tetradeuterated acenaphthene (AcNph-d4)
was synthesized from acenaphthene by means of
hydrogen–deuterium exchange with NaH in (CD3)SO-
Figure 1 Time dependence curves of O2 uptake for the
oxidation of AcNph (0.1 M) in chlorobenzene (2 mL) at 75◦C
under atmospheric pressure (1 atm) of dioxygen: 1, [AIBN] =
2.5 × 10−3 M, [NHPI] = 5 × 10−3 M; 2, [AIBN] = 2.5 ×
10−3 M; 3, [NHPI] = 5 × 10−3 M.
performed on precoated silica gel ‘‘Silufol” plates. A
mixture of toluene and ethyl acetate (5:1, v/v) was
used as an eluent. Plates were developed by the UV
light (365 nm) or KJ treatment.
The concentration of hydroperoxide was measured
by the standard iodometric titration.
1
D2O by following a literature method [14], and H
NMR spectroscopy was used to confirm that 99.8% of
acenaphthene was converted into AcNph-d4.
Oxidation kinetics was studied at constant oxygen
pressure (1 atm) with the gas-volumetric method by
measuring the volume of the absorbed oxygen. The in-
tensity of agitation of a reaction vessel was enough to
conduct the reaction in kinetic regime. The initial reac-
tion rates were calculated from the slope of the linear
plots of the volume of oxygen consumption against
time. All kinetic measurements were carried out by
using freshly prepared samples.
The rate constant of H-abstraction from ace-
naphthene by PINO was measured in acetonitrile
by UV–vis spectrophotometry, using an Analytic
Jena SPECORD S300 spectrophotometer equipped
with a thermostated cell holder. PINO was gener-
ated by the oxidation of NHPI (7.15 × 10−3 M)
with PhI(OAc)2 (7.15 × 10−4 M) in deoxygenated
acetonitrile. A solution of the acenaphthene was added
into the PINO solution in the cuvette (the acenaphthene
concentration is varied in the range (1.35–3.48) ×
10−3 M), and the absorbance change was monitored
at 382 nm. In all cases, each kinetic trace obeyed a
first-order kinetics. Second-order-rate constants were
obtained by the plot of the observed rate constant kobs
versus the substrate concentration. It was verified that
the self-decomposition of PINO, generated by the ox-
idation of NHPI with PhI(OAc)2 in acetonitrile (10–
25◦C) was slow enough to allow the study of the reac-
tion of PINO with acenaphthene.
KINETICS
The oxidation of acenaphthene was carried out in liq-
uid phase under mild reaction conditions (75◦C, atmo-
spheric pressure) both in the presence of NHPI and in
the absence of NHPI. The oxidation was followed by
monitoring the oxygen consumption in a monostatic
system built in our laboratory. The experiments were
carried out at 75◦C in chlorobenzene solutions contain-
ing acenaphthene (0.02–1.54 M), AIBN (0–0.05 M) as
an initiator, and NHPI (0–0.005 M). Figure 1 shows,
as an example, the time-dependence curves of the O2
uptake during the oxidation of acenaphthene.
After an initial induction period of several min-
utes, the oxygen absorption is observed (Fig. 1). In
the oxidation of substrate by NHPI or AIBN alone, the
rates of oxidation were low, or almost no O2 uptake
was observed. The oxidation in the presence of the
NHPI/AIBN system discloses a synergistic effect.
In the following experiments, the influence of the
concentration of the catalyst, initiator, and substrate on
the maximum reaction rate was studied. The oxidation
was carried out at 75◦C in chlorobenzene solutions
containing AIBN (2.5 × 10−3 M), NHPI (5 × 10−3 M),
and variable amounts of acenaphthene (Fig. 2).
Identification of oxidation products was per-
formed by comparing their chromatograms with
those of the authentic samples of acenaphthenenone-
9, acenaphthenenole-9, and acenaphthene quinone.
Analytical thin layer chromatography (TLC) was
The influence of the initiator concentration on the
oxidation rate at 75◦C was studied. The variation of
the AIBN concentration at constant concentrations of
acenaphthene (0.1 M) and catalyst NHPI (5 × 10−3 M)
show that the rate of oxidation increases linearly
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KINETIC STUDIES OF ACENAPHTHENE OXIDATION CATALYZED BY N-HYDROXYPHTHALIMIDE
517
Figure 5 Dependence of the induction period of oxidation
rates of AcNph in chlorobenzene (2 mL) at 75◦C on the
concentration of the inhibitor; [AcNph] = 0.1 M; [AIBN] =
2.5 × 10−3 M; [NHPI] = 5 × 10−3 M.
Figure 2 Dependence of the oxygen consumption rates for
the oxidation of AcNph catalyzed by NHPI (5 × 10−3 M)
and AIBN (2.5 × 10−3 M) in chlorobenzene (2 mL) at 75◦C
on the AcNph concentration.
The rate of initiation was determined using the in-
hibitor method, using butylated hydroxytoluene (BHT)
as the inhibitor: Wi = 2[BHT]/τ, where τ, the induction
period, is taken to be a time obtained using extrapo-
lation of the oxygen consumption rates—a time curve
at zero of the oxygen consumption rates. The rate of
acenaphthene oxidation after complete consumption of
the inhibitor is equal to the rate of acenaphthene ox-
idation in the absence of the inhibitor. As illustrated
in Fig. 5 the induction period linearly depends on the
concentration of the inhibitor.
Analysis of the data of Fig. 5 provides the Wi =
(2.71 0.11) × 10−7 M s−1. The initiation rate calcu-
lated using the equation Wicalc = 2kd[AIBN] (where kd
is the rate constant of the AIBN decomposition at 75◦C
and [AIBN] is the AIBN concentration) agrees with
the experimental initiation rate Wi (Wicalc = (2.66
0.11) × 10−7 M s−1). This fact shows that PINO does
not participate in the initiation stage.
Figure 3 Dependence of the oxygen consumption rates
for the NHPI (5 × 10−3 M) catalyzed oxidation of AcNph
(0.1 M) in chlorobenzene (2 mL) at 75◦C on the AIBN
concentration.
with the square root of the initiator concentration
(Fig. 3).
A series of experiments were performed where the
catalyst concentration was changed at constant con-
centrations of acenaphthene and AIBN. As illustrated
in Fig. 4 a plot of the oxidation rates versus the NHPI
concentration is linear.
REACTION PRODUCTS
The iodometric titrations of reaction mixtures during
acenaphthene oxidation catalyzed by NHPI showed
the presence of peroxides. Acenaphthene was oxi-
dized easily to the corresponding hydroperoxide in
high yield, by the NHPI/AIBN system. Acenaphthene-
9-hydroperoxide is the main oxidation product, but as
shown in Fig. 6 the change in the concentration of
hydroperoxide does not follow the curve of the ab-
sorption of O2. The yield of hydroperoxide decreases
with time. NHPI does not accelerate the hydroperox-
ide decomposition reaction [15], but it is found that
the oxidation of acenaphthene for 5 h leads to the
formation of a mixture of acenaphthenone, acenaph-
thenole, acenaphthene quinone, and acenaphthene-9-
hydroperoxide. The products were separated by TLC.
Figure 4 Dependence of the oxygen consumption rates for
the AIBN (2.5 × 10−3 M) initiated oxidation of AcNph
(0.1 M) at 75◦C in chlorobenzene (2 mL) on the NHPI
concentration.
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518
OPEIDA ET AL.
Scheme 1 The mechanism of H-abstraction from molecule
of substrate by PINO.
(trace 1). Following the addition of 7.15 × 10−4
M
of PhI(OAc)2 in acetonitrile at 25◦C, a new and broad
absorption band in the 360–460 nm develops (trace 2),
having λmax at 382 nm and ε = 1360 M−1 cm−1. The
λ382 absorption decreases according to an exponential
first-order curve (kd = 1.3 × 10−3 s−1 in acetonitrile
at 25◦C). The same value of kd we obtained by gener-
ating PINO by Pb(OAc)4 in acetic acid at 25◦C [26].
The mechanism of the spontaneous decay of PINO is
unknown. Espenson et al. [27] and Masui et al. [28]
have confirmed the second-order self-decay of PINO
in both acetonitrile and acetic acid. This different ob-
served behavior may be due to different conditions of
experiments: concentrations of PINO and methods of
generation of radicals.
Figure 6 Concentration profiles for hydroperoxide and O2
observed during the oxidation of AcNph (0.1 M) in the pres-
ence of NHPI (5 × 10−3 M) and AIBN (2.5 × 10−3 M) in
chlorobenzene (2 mL) at 75◦C and 1 atm.
FORMATION OF PINO
The formation of the PINO radicals in oxidation pro-
cesses of organic substrates catalyzed by NHPI has
been described [16,17]. PINO can be generated by
treating NHPI with inorganic [15,18–20], organic, and
organometallic [21–23] oxidants. Usually, on a prepar-
ative scale, PINO is generated from a precursor NHPI
by the oxidation with Pb(OAc)4 in the acetic acid so-
lution [24]. It should be noted that lead tetraacetate has
a strong influence on the NHPI reactivity and induces
two different channels for the reaction pathway, radical
and nonradical reactions [25]. As an experimental al-
ternative to use of Pb((OAc)4 for the oxidation of NHPI
to PINO, iodobenzenediacetate ((PhI(OAc)2) was stud-
ied. We report here the generation of PINO from its
precursor NHPI by the oxidation with PhI(OAc)2 in
the acetonitrile solution and show an electron spec-
trum with maximum absorbance at 382 nm. The UV–
vis spectra of the solution of NHPI and PhI(OAc)2 in
acetonitrile are shown in Fig. 7.
RATE CONSTANT OF H-ABSTRACTION
AT 25◦C
The reaction of PINO in the hydrocarbon medium (RH)
under inert atmosphere can be described by the follow-
ing Eqs. (1)–(3) (Scheme 1) [29]– [32].
The contribution from each step to the kinetics of
the process can depend on the structure of R•. It was
necessary to study the effect of each step on the ki-
netics of PINO consumption under our experimental
conditions.
The kinetics of the reaction of the PINO with a se-
ries of alkylarenes with primary, secondary, and tertiary
The absorption spectrum of 7.15 × 10−3 M so-
lution of NHPI in acetonitrile is presented in Fig. 7
–
benzyl C H bonds (toluene, ethylbenzene, acenaph-
thene, and cumene) was studied, and the reaction rate
constants were determined. The scheme of the process
was examined, and the applicability boundaries of the
simplification during the analysis were shown.
Kinetic studies described above were carried out
in chlorobenzene, because a catalytic oxidation based
on NHPI in apolar solvents is expected to be more
effective [33]. However, owing to the low solubility of
acenaphthene in chlorobenzene, the rate of hydrogen
abstraction from the acenaphthene was investigated in
acetonitrile in the presence of an excess of substrate.
PINO was generated in a 3-mL spectrophotomet-
ric quartz cuvette by quickly mixing NHPI (7.15 ×
10−3 M) with PhI(OAc)2 (7.15 × 10−4 M) in acetoni-
trile at 25◦C under an argon atmosphere, and their UV–
vis absorption spectra were recorded at λmax = 382 nm.
Figure 7 UV–vis spectrum of NHPI (7.15 × 10−3 M)
in acetonitrile in the absence of PhI(OAc)2 (1) and in the
presence of PhI(OAc)2 (7.15 × 10−4 M) ((2), 1200 s after
mixing; (3), 7200 s after mixing).
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KINETIC STUDIES OF ACENAPHTHENE OXIDATION CATALYZED BY N-HYDROXYPHTHALIMIDE
519
Figure
8
Decomposition of PINO generated from
Figure 9 Logarithmic anamorphoses of the kinetic curves
of PINO consumption in the reactions with acenaphtene (1),
ethylbenzene (2), toluene (3), and cumene (4) at 25◦C.
[NHPI] = 7.15 × 10−3 M in the absence (1) and in the
presence (2) of different amounts of AcNph in acetonitrile at
25◦C. Readings were at 382 nm.
At reaction time, the increase in the peak intensity was
observed. This result indicates the formation of PINO
radicals. Fast addition of a solution of acenaphthene
into the PINO solution, at an initial substrate concen-
tration 8–15 times higher than that of PINO, marked
the beginning of the kinetic experiment. The concen-
trations of alkylarenes were selected in such a way that
the half-life of PINO would be 10–60 s. Preliminary
experiments showed that PINO was slowly consumed
in a pure solvent. The half-life of PINO would be 760 s
at 25◦C. The consumption of PINO strongly acceler-
ated in the presence of acenaphthene, following clean
pseudo–first-order kinetics in the presence of an excess
of substrate (Fig. 8).
Figure 10 Pseudo–first-order rate constants of the H-
abstraction from AcNph by PINO at various concentrations
of AcNph. The slope of the plot gives the kH value.
The decay traces are nicely described in Eq. (4)
(Fig. 9), where A is the absorbance, kd is the first-
order-rate constant for spontaneous decay, and kH is
the second-order-rate constant for hydrogen abstrac-
tion from RH:
The experimentally determined values of the
pseudo–first-order rate constant kobs = kd + 2kH for
the decay of the PINO radical are plotted in Fig. 10
as a function of the acenaphthene concentration, and
the second-order rate constants (kH) for the reactions
of PINO with acenaphthene were obtained from the
slopes of these plots. The initial concentrations of RH
was (2.0–3.7) × 10−3 M.
(At − A )
∞
ln
= −(kd + 2kH [RH])t
(4)
(Ao − A )
∞
The factor 2 before kH indicates that PINO takes
part in two reactions: The PINO radical abstracts a hy-
The simulation using differential equations was
chosen to analyze Scheme 1. To apply successfully
this method, one has to estimate the boundaries of
probable variation of the rate constant values for
each of the steps and to choose a reliable method
of integration of the resulting system of differential
equations.
–
drogen atom from a C H bond of hydrocarbon (RH);
this step is followed by a radical recombination reac-
tion of the carbon-centered radical (R•) with the PINO
radical to form a radical adduct PINO-R.
In the O2 atmosphere, alkyl radicals (R•) are cap-
tured by oxygen to form ROO• radicals. In this case,
the chain termination step is the self-reaction of the
peroxyl radical, because there are no likely termina-
tion channels for PINO radicals at high enough [O2] to
capture R• radicals. PINO radicals also do not termi-
nate with peroxyl radicals [34]. Therefore, the factor
before kH in Eq. (4) must be 1 if the reaction is carried
out in the O2 atmosphere.
The data on the k2 values are obtained at 294–298 K
(k2 ∼ 103–104 L mol−1
s
−1) [29,30]. The k3 values
change from 107 to 109 L mol−1 s−1 [35–37]. The kH
values change from 10−4 to 103 L mol−1 s−1 [17]. Thus,
a probable interval of variation of the rate constants of
reactions (1)–(3), considering the obtained estimates
and measured observed rate constants of PINO con-
sumption, is 10−4–109 L mol−1 s−1, and the system of
International Journal of Chemical Kinetics DOI 10.1002/kin.20790

520
OPEIDA ET AL.
differential equations corresponding to reactions (1)–
(3) is stiff. We chose the Gear method for numerical
integration of such systems. We compared the results of
calculations obtained by this method for an ideal case
(when the reaction of PINO with RH is described only
by Eq. (1)) and for the general case (Eqs. (1)–(3)) to
determine the error, which is the result of reaction (2).
It was found out that the error depends on val-
ues of k2, k3, [NHPI]o, and [PINO]o, but the er-
ror is independent of product kH·[RH]. The complete
coincidence of the results of numerical integration
and calculation by algebraic equations was obtained
for Scheme 1 (see reactions (1)–(3)) with integral
equations).
Figure 11 The regions of 5% error in coordinates
[PINO]o − [NHPI]o at different values of k2/k3.
to an error when determining kH, the first-order kinetic
equation is used. In the ideal case, Eq. (8) is simplified:
If [RH] = constant and [NHPI]o = constant (kH
[RH] = kHe and k2[NHPI]o = k2e), Scheme 1 is sim-
plified (as shown below):
[PINO•]
[PINO•]o
ln
= −2kHid[RH]t
(9)
kHe
PINO• −→ R•
(5)
(6)
(7)
k2e
R• −→ PINO•
Thus, the error of experimental determination of kH
is described by the following equation:
k3
PINO• + R• −→ PINOR
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
id
kH − kH
Error =
[PINO•]
kHid
d
= −kHe[PINO•] − k3[PINO•][R•] + k2e[R•]
= kHe[PINO•] − k3[PINO•][R•] − k2e[R•]
t
d
d
[R•]
Taking into account Eqs. (8) and (9), one can obtain
the equation for the error:
t
d
ꢀ
ꢁ
If in our system, the steady-state condition [R•]/
dt = 0 is fulfilled, then
1
1
−
[PINO•] [PINO•]o
k2[NHPI]o
Error =
·
[PINO•]
ln
k3
kHe[PINO•]
k3[PINO•] + k2e
[PINO•]o
[R•] =
(10)
The calculations were conducted taking into ac-
count that [PINO•] = 0.5·[PINO•]o. Conditions for
the 5% experimental error were obtained by the vari-
ation of the values of the ratio k2/k3, [NHPI]o, and
[PINO]o.
In Fig. 11, a line in the coordinate ([NHPI]o/
[PINO]o) at different values of (k2/k3) represents the
border of the area with 5% error. The area above the
line is the area in which the error is ≤5% and the area
under the line is the area of ≥5% error.
Taking into account the latter one, we can obtain the
next equation:
d[PINO•]
= −kHe[PINO•] − k3[PINO•]
dt
kHe[PINO•]
×
k3[PINO•] + k2e
kHe[PINO•]
k3[PINO•] + k2e
+ k2e
The solving of the latter equation gives the next
equation:
ACTIVATION PARAMETERS
ꢀ
ꢁ
Rate constants of H-abstraction from a molecule of
acenaphthene have been measured at various temper-
atures (in the 10–25◦C range). Each second-order kH
value is derived from averaging of five pseudo–first-
order rate constants, determined at different initial con-
centrations of the substrate. The initial concentration
of PINO was 2.5 × 10−4 M and that of acenaphthene
[PINO•]
k2[NHPI]o
1
1
ln
−
−
[PINO•] [PINO•]o
[PINO•]o
k3
= −2kH[RH]t
(8)
The second term of Eq. (8) is related to the contri-
bution of steps (2) and (3) of Scheme 1 and might lead
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KINETIC STUDIES OF ACENAPHTHENE OXIDATION CATALYZED BY N-HYDROXYPHTHALIMIDE
521
Table I Rate Constants kH of H-abstraction from
AcNph by PINO in Acetonitrile at Different Temperatures
strates and obtained large values of KIE. They pro-
posed that quantum mechanical tunneling takes part in
the PINO radical reactions.
T (K)
kH (M−1 s−1
)
The value WH/WD for the oxidation of acenaph-
thene was measured by performing an experiment with
0.1 M AcNph-d4, 2.5 × 10−3 M AIBN, and 5 × 10−3
M NHPI. The value WH/WD = 2.2 indicates that the
catalytic cycle also involves hydrogen abstraction in
the propagation reaction (ROO• + RH).
283
288
293
298
4.6 0.1
5.4 0.1
6.6 0.1
7.7 0.1
ranged between 2 × 10−3 M and 3.7 × 10−3 M. From
the Arrhenius equation (ln kH = ln A − Ea/RT), ln A
and Ea parameters were obtained.
REACTION MECHANISM
The kH values for all temperatures are reported in
Table I.
The liquid-phase oxidation of acenaphthene proceeds
according to a widely known free radical chain mech-
anism, and it is a typical example of consecutive
reaction. Amorati et al. have carried out an in-depth re-
searchonthecatalyticmechanism of NHPI [33]. Onthe
basis of our experimental observations and published
literature data, the following reaction scheme, for the
oxidation process of acenaphthene with dioxygen cat-
alyzed by NHPI, has been suggested. The scheme
shows the oxidation reactions of acenaphthene to its
hydroperoxide on the radical pathway. The initial stage
is being the formation of the PINO radicals in the re-
action of NHPI with initiator radicals:
Analysis of the data of Table I provides the Ea =
24.4
M−1
0.2 kJ/mol and A = (1.47
0.05) × 105
s
−1. It is not easy to explain low pre-exponential
factor for the reaction of PINO with AcNph, and we
do not have the necessary data to explain this problem.
As to our point of view, the most likely cause may be
a specific interaction (hydrogen bond or others) of the
substrate molecules and the radical with the medium
that prevents reaching the required structure (geome-
try) of the transition state.
(11)
(12)
KINETIC ISOTOPE EFFECT
The highly reactive PINO radicals can abstract the
hydrogen atom from the acenaphthene to produce the
carbon-centered radicals of acenaphthene and regener-
ate the NHPI:
The kinetic isotope effect (KIE) was calculated from
the ratio of the kH and kD rate constants of the reac-
tion of acenaphthene and AcNph-d4 with PINO. The
The alkyl radicals react with oxygen to form the
important peroxyl radical (ROO•), which can abstract
hydrogen from the molecule of acenaphthene to form
the alkyl radical and hydroperoxide:
reactions of the PINO radical with acenaphthene show
KIEs (kH/kD) of 11.7 in acetonitrile at 25◦C, which
accounts for a hydrogen atom abstraction mechanism.
Koshino et al. [27] measured the KIE for various sub-
International Journal of Chemical Kinetics DOI 10.1002/kin.20790

522
OPEIDA ET AL.
(13)
(14)
The peroxyl radical can also abstract a hydrogen atom
from the NHPI:
(15)
Amorati et al. report, experimentally, that d[O2]/dt
changes linearly with the low concentration of NHPI,
with the square root of the initiator concentration,
and the rate of catalyzed oxidation does not signif-
icantly depend on the cumene concentration [33]. Such
The chain termination step is the self-reaction of
the peroxyl radical. Secondary peroxyl radicals react
in a nonradical way, leading to the formation of equal
yields of alcohol and ketone [38]. PINO radicals do not
terminate with each other or with peroxyl radicals [34]:
(16)
Secondary alkylbenzenes cannot be selectively con-
verted to their corresponding alcohols or ketones
because the products posses higher reactivity than
the starting hydrocarbons. Acenaphthene quinone can
form consequently of deep product oxidation, for
example,
dependences were observed in acenaphthene oxida-
tion in the presence of NHPI. All these observa-
tions can be described on the basis of the Ishii [1]
mechanism.
(17)
(18)
(19)
International Journal of Chemical Kinetics DOI 10.1002/kin.20790

KINETIC STUDIES OF ACENAPHTHENE OXIDATION CATALYZED BY N-HYDROXYPHTHALIMIDE
523
Table II Results of Oxidation of AcNph by O2 in the
Presence of NHPI at 75◦C and 1 atm in Chlorobenzene
2. Gambarotti, C.; Punta, C.; Recupero, F. Encyclopedia
of Reagents for Organic Synthesis; Wiley: Weinheim,
Germany, 2005.
3. (a) Minisci, F.; Recupero, F.; Pedulli, G. F.; Lucarini,
M. J Mol Catal A: Chem 2003, 204–205, 63–90; (b)
Minisci, F.; Punta, C.; Recupero, F. J Mol Catal A: Chem
2006, 251, 129–149.
Wi × 107 (M s−1
)
2.71 0.11
0.012 0.001
√
k /
p
k
t
√
kf/
k
t
5
0.2
kHꢁ (M−1 s−1
)
7.7 0.1
4. Ishii, Y.; Sakaguchi S. In Modern Oxidation Methods;
Backvall, J.-E., Eds.; Wiley-VCH: New York, 2004;
pp. 119.
According to the proposed kinetic model [33], the
rate of oxidation described by Eq. (20) is
5. Sheldon, R. A.; Arends, I. W. C. E. Adv Synth Catal
2004, 346, 1051–1071.
6. Ishii, Y.; Nakayama, K.; Takeno, M.; Sakaguchi, S.;
Iwahama, T.; Nishiyama, Y. J Org Chem 1995, 60, 3934–
3935.
− d[O2]/dt = kp·(Wi/2kt)1/2·[RH]
+kf·(Wi/2kt)1/2·[R2NOH]. (20)
where kp is the propagation rate constant, kt is the rate
constant of termination of the peroxyl radicals, Wi is
the rate of initiation, and kf is the rate constant for the
hydrogen atom abstraction from NHPI by the peroxyl
radical.
It is interesting to apply Eq. (20) to our kinetic data
for the oxidation of acenaphthene in the presence of
NHPI. On the basis of this equation, the slope of the
plot reporting –d[O2]/dt against [NHPI] will provide
kf(Wi/2kt)1/2. The results of acenaphthene oxidation
with the NHPI catalyst are listed in Table II.
7. Coseri, S.; Mendenhall, G. D.; Ingold, K. U. J Org Chem
2005, 70, 4629–4636.
8. Shibamoto, A.; Sakaguchi, S.; Ishii, Y. Org Process Res
Dev 2000, 4, 505–508.
9. Dashevskii, M. M. Atsenaphten (Acenaphthene);
Khimiya: Moscow, 1966; 459 pp.
10. Yang, G.; Zhang, Q.; Miao, H.; Tong, X.; Xu, J. Org Lett
2005, 7 (2), 263–266.
11. Tong, X.; Xu, J.; Miao, H. Adv Synth Catal 2005, 347,
1953–1957.
12. Weissberger, A.; Proskauer, E.; Riddick, J.; Toops,
E. Organic Solvents, Physical Properties and Meth-
ods of Purification; Interscience: New York, 1955,
518 pp.
The kt value is unknown, but from Table II it can
be seen that the reactivity of NHPI with the peroxyl
radical (kf) is larger than that of acenaphthene (kp).
13. Sharefkin, J. G.; Saltzmann, H. Org Synth 1973, 5, 660–
663.
14. Schwartz, M. P.; Halter, R. J.; McMahon, R. J.; Hamers,
R. J. J Phys Chem B 2003, 107(1), 224–228.
15. Orlinska, B. Tetrahedron Lett 2010, 51, 4100–4102.
16. Coseri, S. Catal Rev 2009, 51 (2), 218–292.
17. Recupero, F.; Punta, C. Chem Rev 2007, 107, 3800–
3842.
18. Saha B.; Koshino, N.; Espenson, J. H. J Phys Chem A
2004, 108, 425–431.
19. Falcon, H.; Campos-Martin, J. M.; Fierro, J. L. G. Catal
Commun 2010, 12, 5–8.
20. Nechab M.; Einhorn, C.; Einhorn, J. Chem Commun
2004, 1500–1501.
21. Amorati, R.; Lucarini, M.; Mugnaini, V. J Org Chem
2003, 68 (5), 1747–1754.
22. Opeida, I. A.; Kompanets, M. A.; Kushch O.
V.; Yastrebova, E. G. Pet Chem 2009, 49 (5),
389–392.
23. Tong, X.; Xu, J.; Miao, H. Tetrahedron 2007, 63, 7634–
7639.
CONCLUSIONS
We have developed metal-free acenaphthene oxidation
catalyzed by NHPI. The developed catalytic system al-
lows obtaining the desired hydroperoxide in high yield
by the oxidation of the acenaphthene. We also sug-
gested a possible mechanism of this catalytic method,
which undergoes a radical process. Kinetic studies car-
ried out to investigate the catalytic behavior of NHPI
on the oxidation of acenaphthene are consistent with a
simple kinetic model.
The H-abstraction rate constant and KIE for the re-
action of PINO with acenaphthene are determined. The
value of KIE is 11.7. This finding further supports that
quantum mechanical tunneling plays a role in the hy-
drogen abstraction of the PINO radicals. The activation
parameters are determined for this reaction.
24. Kolyakina, E. V.; Grishin, D. F. Russ Chem Rev 2009,
78 (6), 535–568.
25. Coseri, S. J Phys Org Chem 2009, 22, 397–402.
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111.
27. Koshino, N.; Saha, B.; Espenson, J. H. J Org Chem 2003,
68, 9364–9370.
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