Conditions for manifestation of approachment and orientation effect at the oxidation of ferrocenylacetic acid and its methyl ester by molecular oxygen in organic Solvents

Article abstract of DOI:10.1134/S1070363211010129

By comparison of reactivity of the ferrocene derivatives differing in the nature of the substituents the conditions were revealed of their participation as Bronstedt and Lewis acidic centers in the process of the metallocomplex molecular oxidation with oxygen in terms of manifestations of the effects of rapproachment and orientation. From this standpoint were analyzed the experimental data obtained in the oxidation of methyl ferrocenylacetate. A probable mechanism of the process is proposed that includes the molecular and radicalchain macro steps.

Full text of DOI:10.1134/S1070363211010129

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 1, pp. 81–90. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.M. Fomin, A.E. Shirokov, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 1, pp. 83–92.
Conditions for Manifestation of Approachment
and Orientation Effect at the Oxidation
of Ferrocenylacetic Acid and Its Methyl Ester
by Molecular Oxygen in Organic Solvents
V. M. Fomin and A. E. Shirokov
Lobachevskii Nizhnii Novgorod State University, pr. Gagarina 23, Nizhnii Novgorod, 603950 Russia
e-mail: niih325@bk.ru
Received January 12, 2010
Abstract―By comparison of reactivity of the ferrocene derivatives differing in the nature of the substituents
the conditions were revealed of their participation as Brønstedt and Lewis acidic centers in the process of the
metallocomplex molecular oxidation with oxygen in terms of manifestations of the effects of rapproachment
and orientation. From this standpoint were analyzed the experimental data obtained in the oxidation of methyl
ferrocenylacetate. A probable mechanism of the process is proposed that includes the molecular and radical-
chain macro steps.
DOI: 10.1134/S1070363211010129
It is known that ferrocene can be oxidized in a
solution by molecular oxygen, but only in the presence
of a strong Brønsted acid [1, 2]. The known
characteristic of ferrocenylacetic acid (I) is abnormally
analysis of the causes of this phenomenon has led us
[5] to the conclusion that it is based on the ability of
compound I to act as a bifunctional reagent in the
reaction with O , as shown in Scheme 1.
2
high reactivity toward O as compared not only with
2
ferrocene, but also with a model system Cp Fe +
This scheme is a revised version [5] of the
previously suggested scheme of oxidation of molecular
compound I [4] and takes into account only one route
2
RCOOH, where RCOOH is a carboxylic acid of the
strength comparable with that of I (pK ≈ 5) [3, 4].
a
This is manifested in the ability of ferrocenylacetic
acid to be readily oxidized by oxygen at 20–50ºC in
low-polar solvents such as dioxane, in the absence of
any additional acid. Under the same conditions a
model system remains unchanged for a long time. The
of complex A transformation leading to the formation
•
of internal ferricenyl salt and the radical HO
, which
2
initiates the radical-chain oxidation of the complex.
The oxidation of compound I in accordance with
Scheme 1 leads to a substantial gain in entropy of
Scheme 1.
CH COO
CH COOH
2
2
K
Fe
+ O2
Fe
O2
H
A
_
CH COO
2
Fe +
+ HO2
A
8
1

8
2
FOMIN, SHIROKOV
the amount of the oxygen absorbed in the reaction
mixture per 1 mol of the taken metallocomplex. It is
evident from Fig. 1 that the replacement in the
compound I of the hydroxy substituent by the methoxy
group reduces significantly the reactivity of the
metallocomplex with respect to oxygen under these
conditions. The rate of oxidation of compound II
significantly increased in the presence of a Brønsted
acid, therewith the positive kinetic effect of the latter
depends on the acid strength: the effect of
trifluoroacetic acid (III, pK = 0) is significantly higher
a
than that of benzoic acid (IV, pK = 4.2). It should be
a
noted that the addition of acid III leads also to strong
acceleration of the oxidation of compound I, whereas
acid IV taken in the same ratio to compound I has no
influence on this process, like in the oxidation of
compound II [8].
τ, min
τ, h
Such a large difference in the rates of oxidation of
compound II and I in the absence of acids confirms the
mechanism of oxidation of the latter described by the
Scheme 1 and strongly suggests that it is the effect of
rapproachment and orientation which determines the
high reactivity of this compound with respect to
oxygen.
Fig. 1. Comparative kinetic curves of oxidation of com-
pounds (1, 2) I and (3–5) II in dioxane at T = 50ºC and
4
p(O
2
) = 4×10 Pa: (1–3) no acid, (2, 5) in the presence of
0
0
acid III, (4) in the presence of acid IV, CI,II = 0.005, CIII,IV
.05 M.
=
0
As is known, also another complex, the ferro-
cenylacetone (V), shows an abnormally high reactivity
activation and thus to a decrease in the free activation
energy compared with the activation parameters at the
ferrocene oxidation in the model system, in which the
same reaction centers belong to different molecules, as
is shown in the following equation:
toward O in comparison with ferrocene: It is readily
2
oxidized at room temperature to diketone C H Fe·
5
5
C H C(O)C(O)CH in the absence of acids [9]. Like
5
4
3
the case of the oxidation of compound I, the reason for
this, in our opinion, is the participation of the
substituent in the oxidation of complex V due to the
presence of electrophilic carbon atom of carbonyl
group, as shows Scheme 2.
•
–
Cp
2
Fe + O
2
+ RCOOH → Cp
2
Fe + + HO
2
+ RCOO
In the reactions involving multifunctional enzyme
systems such gain in free activation energy, which can
reach 10–11 kcal mol [6], is known as a mani-
festation of the rapproachment and orientation effect.
–
1
The electron transfer from the metal atom to the O2
molecule driven by bonding of the latter with the
In this connection it is interesting to perform a
comparative analysis of the oxidation features of
compound I and its methyl ester II under the same
conditions. Replacing the hydroxy groups by methoxy
one affects slightly the electron-acceptor properties of
substituent in the metal complexes (–CH COOH and
CH COOCH both are weak electron-acceptors [7]),
but compound II loses the ability to coordinate a
molecule of O by the way characteristic of compound
electrophilic carbon atom converts O
nucleophile (in the limit, this is O
into a
) which is strong
2
2
•–
enough for adding to the carbonyl group.
The formed peroxide radicals can initiate radical-
chain oxidation of compounds V to the above α-
diketone. We found that in a model system Cp Fe–O –
2
–
2 3
2
2
0
0
CH CH C(O)CH [C (Cp Fe):C (C=O) = 1:10] the
3
2
3
2
2
oxidation of the complex with an appreciable rate does
not occur for a long time. Compound V, like
compound I, behaves as a bifunctional reagent that
makes possible the manifestation of rapproachment
and orientation effect in the process of molecular
oxidation.
I. It certainly should affect the compound II reactivity
and the mechanism of its interaction with oxygen as
well.
Figure 1 shows the comparative kinetic curves of
oxidation of compounds I and II. Hereinafter, N(O ) is
2
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CONDITIONS FOR MANIFESTATION OF APPROACHMENT
83
Scheme 2.
O
O
C
CH2
C
CH3
CH2
O2
CH3
Fe
+ O2
Fe
OO
CH2
C
O
CH3
Fe+
_
B
Based on the above it would be expected that
compound II could in principle be oxidized in
accordance with the Scheme 2, as its substituent also
contains electrophilic carbon atom of carbonyl group
which is not in conjugation with the Cp ligand being
separated from it by the methylene fragment, like the
carbonyl group in compound V.
than zero (being evaluated from the standard redox
potentials of reagents), but they apparently are not
large enough to prevent these reactions completely.
(
2) The ability of electron-acceptor center of
substituent to coordinate the oxygen molecule, locate it
in the bridge position between this center and the metal
atom. Such coordination should provide a high stat-
ionary concentration of the adduct with oxygen and
facilitate the electron transfer from the metal atom to
the oxygen. Either Brønsted, or Lewis acid center can
act as the coordination center.
In addition, due to this position of carbonyl group
the –I (inductive) effect of the substituents in the
compared compounds is reduced to almost zero [10],
which acts in favor of reducing their standard redox
potentials. In fact, oxidation of compound II proceeds
very slowly. This suggests that for a substantial
increase in reactivity of the ferrocene derivatives with
respect to oxygen due to the effect of rapproachment
and orientation it is necessary that several conditions
were fulfilled:
(
3) The high reactivity of the electron-acceptor
center of substituent toward the reduced form of the
oxygen. The fact of conjugation of the electron-donor
(
metal atom) and electron-acceptor centers of the
metallocomplex through the O molecule allows an
2
assumption that the stage of electron transfer to O and
2
subsequent interaction of the reduced form of the latter
with Brønsted or Lewis acidic center occur as a single
synchronous process. In this case the maximum
compensation of energy consumed in the step of
electron transfer can be achieved, and the formation of
relatively stable reaction intermediates. This will work
in favor of reducing the activation energy of the
reaction making the reaction energetically more
favorable. The above Schemes 1 and 2 of oxidation of
compounds I and V are based on the conditions (1)–(3).
(
1) The molecular reaction of the metal complexes
with oxygen should not be forbidden thermo-
dynamically. Such forbidding would make impossible
the reaction course that includes generation of radicals.
To confirm this statement, we compare reactivity of
the compounds in the following pairs: (a) complex I,
ferrocenylcarboxylic acid VI, (b) complex V,
acetylferrocene VII. The substituents in compounds I
and V are characterized by nearly zero –M (mesomeric)
and –I effects [10]. In contrast, the substituents in
compounds VI and VII show strong –M and –I effects.
This is a significant, if not the main, reason for the
oxidative stability of the latter two compounds, which
can be oxidized only in the presence of strong
It should be noted that the products of molecular
oxidation of both metallocomplexes are internal
ferricenyl salts with the cation and anion stabilizing
each other, which leads to an additional energy gain. In
nonpolar solvents the stabilization energy of the ion
pair by electrostatic interactions can reach 90–
Brønsted acids [11]. Note that the values of standard
Gibbs free energy Δ G for the reactions of molecular
oxidation of compounds I and V certainly are larger
0
r
–
1
100 kJ mol [12]. The reason for the low reactivity of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

8
4
FOMIN, SHIROKOV
compound II compared with I is obvious: the methoxy
group does not possess the properties of a Brønsted
omerism, and its reactivity is considerably lower com-
pared with ketones. For this reason, electrophilicity of
carbonyl carbon atom and its affinity for the neutral
center in the reaction with O . Therefore, in terms of
2
condition 3 it is important to understand the reasons
for the large difference in the reactivity of compounds
II and V, while both include substituents posessing
electrophilic carbon atom of the carbonyl group
located in the β-position to the Cp-ligand, and their
inductive and mesomeric effects differ little [7, 10].
From the thermodynamic and kinetic points of view,
the preference in molecular oxidation of compound V
over II is likely based on the difference in the
reactivity of the carbonyl group in these compounds
with respect to the reduced form of the oxidizer, and
the stability of the intermediates formed, which,
naturally, differ by nature. It is known [13] that
carbonyl group in esters is stabilized due to the mes-
and reduced form of O molecules are lower in com-
2
pound II than in V. In the tetrahedral intermediates
formed at the addition of nucleophilic species to esters
such stabilization is not the case. Therefore, their
formation is energetically unfavorable and they are so
labile that cannot be isolated, in contrast to related
products derived from ketones. Suggesting that the
reaction of oxidation of compound II, like the
oxidation of compound V, proceeds by Scheme 3, we
have to conclude that despite the formal similarity in
the structure of intermediates B (Scheme 2) and C
(Scheme 3), the latter intermediate certainly must be
much less stable, which leads to a certain kinetic and
thermodynamic ban on the oxidation of compound II.
Scheme 3.
O
C
O
CH2
OCH3
CH2
O2
C
OCH3
Fe
+ O2
Fe
OO
CH2
C
O
OCH3
Fe+
_
C
(
4) Favorable steric factors that depend both on the
protonation of the carbonyl group, or through a stage
of formation of hydrogen bond between it and the acid.
In both cases the positive charge on the carbonyl
carbon atom, and hence its electrophilicity, increase,
favoring addition of the nucleophilic species. The
mechanism of oxidation of compound II in this case
can be represented by Scheme 4.
size and configuration of the oxidant and its reduced
form, as well as its accessibility to the metal atom and
the coordination center of the substituent. Naturally,
the more pronounced steric hindrance in the transition
state, the less favorable the latter is energetically and is
realized more difficultly. For the compounds
containing a carbonyl group as a reaction center, this is
particularly relevant [13].
Although the participation of HX can contribute to
oxidation of compound II, as shown in Scheme 4,
nevertheless, the reaction course through the formation
of a highly labile complex F, which must be con-
sidered as limiting step, makes this route very
problematic from the energetic viewpoint.
From this viewpoint, it becomes clear why acid III
shows strong accelerating effect on the oxidation of
compounds I and II. An acid may be involved in the
oxidation of metal not only as the agent, but also as a
catalyst accelerating addition of nucleophilic species to
the carbonyl group of organic compound [13]. The
reaction takes place either through the stage of
It should be emphasized that, anyway, the
participation of acid in the oxidation of metal complex
makes the route more favorable thermodynamically,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

CONDITIONS FOR MANIFESTATION OF APPROACHMENT
85
Scheme 4.
O
O
C
HX
CH2
C
OCH3
CH2
OCH3
K1
Fe
+ HX
Fe
(1)
D
O
C
HX
OCH3
CH2
O2
K2
D + О2
Fe
(2)
(3)
(4)
E
OH
CH2
C
OCH3
OO
k
_
+
E
Fe X
F
O
CH2
COO
_
+
F
Fe X
+ CH OH
3
due to the increase of the standard redox potential of
oxygen [14]. We must however take into account the
kinetic aspect of the influence of acid on the course of
the process, which is associated with the mechanism of
its participation, influencing activation parameters of
the process. The coordination of acid with compound
II through the carbonyl group (Scheme 4) is typical for
aldehydes and ketones. With carboxylic acid or ester,
the HX coordination can occur through the oxygen
atom of the hydroxy or alkoxy group, which takes
place at the protonation of these compounds by a
strong acid [15] or at the hydrolysis of esters [16]. This
mode of coordination of acid III with compound II
can occur also at the oxidation of the latter (Scheme 5).
Scheme 5.
HX
CH C(O)OCH
CH C(O)OCH3
2
3
K '
2
1
(
1)
Fe
+ HX
Fe
G
HX
CH C(O)OCH3
K '
2
2
(
2)
G + О2
Fe
O2
H
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

8
6
FOMIN, SHIROKOV
Scheme 5. (Contd.)
O
CH2 COO
k '
_
+
H
Fe X
+
CH OH
3
(3)
R'C(O)OO
From the viewpoint of thermodynamics and
kinetics, the mechanisms shown in Schemes 4 and 5
are indistinguishable, since in both cases the process
rate is described by the equation W =k [II][O ][HX],
acid with the metallocomplex, the manifestation of the
effect of rapproachment and orientation is excluded.
Clearly, this mechanism differs from that in
0
0
2
0
Scheme 5 both by the value of Δ G for the overall
r
where k is equal to k K K or k'K'K', which can be
0
1
1
2
1 1 2
reaction and the activation parameters of the limiting
step of the process. Unfortunately, it is impossible to
compare the energy of these two processes due to the
lack of necessary data. Note that complex H is more
preferable than complex J from the viewpoint of the
hydrogen bond energy.
shown using a principle of quasi-equilibrium [17].
Nevertheless, the mechanism in Scheme 5 seems
preferable, since the oxidation of compound II to the
same products as in the Scheme 4 proceeds bypassing
the stage of formation of the labile intermediate F.
This route is shorter and kinetically more favorable if
we compare the activation energy in the limiting steps
In accordance with Schemes 4 and 5, the oxidation
[Scheme 4, Eq. (3)] and [Scheme 5, Eq. (3)]. Note also
of molecular compound II in the presence of acids HX
that hydrogen complexes D and G, reaching
equilibrium concentrations instantaneously, react with
should lead to the formation of peroxide radicals
·
+
·
C
5
H
5
Fe C
H
4
CH
C(O)OO , which can initiate radical-
5
2
O as bifunctional reagents. This suggests a possibility
chain oxidation of the metallocomplex. This is
demonstrated indirectly by the high rate of oxidation of
compound II in the presence of acid III, which is
comparable with the rate of oxidation of compounds I
under similar conditions, and by high consumption of
2
of manifestation in these cases of the effect of
rapproachment and orientation, since the preliminary
coordination of compound II with the acid formally
leads to a decrease in reaction order and hence to a
gain in the activation entropy. For comparison, if the
oxidation of compound II proceeds in accordance with
Scheme 6 which does not include coordination of the
oxygen per 1 mol of oxidized compound II [N(O )]
2
(Fig. 1). Earlier we showed that the radical-chain path
contributes predominantly to the whole process of
Scheme 6.
CH C(O)OCH3
CH C(O)OCH
2 3
2
K ''
1
Fe
Fe
+ O2
Fe
Fe
O2
CH C(O)OCH3
CH C(O)OCH
2 3
2
K ''
2
+ HX
O2
O2
HX
J
CH C(O)OCH
2
3
k ''
_
+
J
Fe X
+
HO2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

CONDITIONS FOR MANIFESTATION OF APPROACHMENT
87
CII, CIII, M
–4
2
p(O )×10 , Pa
τ, min
Fig. 2. Oxidation of compound II in (1, 2) dioxane and (3)
Fig. 3. Dependence of the initial rate of oxidation of
ethanol in the presence of acid III at T = 50ºC and
compound II on the concentration of (1) complex and
4
0
p(O
2
) = 4.1×10 Pa: (1) no inhibitor, (2) in the presence of
(2) acid, and on the oxygen pressure, at T = 50ºC: (1) CIII
=
0
0
0
4
0
o-phenylenediamine (In); CII = 0.005, CIII = 0.05, CIn
=
0.01 M, p(O
2
) = 4.1×10 Pa; (2) CII = 0.01 M, p(O
2
) =
–
4
4
0
0
2
.5×10 M.
4.1×10 Pa; (3) CII = 0.005 M, CIII = 0.01 M.
interaction of O with metal at the oxidation of
compound I in the presence of acid III [5].
plainable by the ability of alcohol to deactivate per-
oxide radicals binding them to low reactive hydrogen
complexes and thus suppresing the chain propagation
2
To verify the validity of the assumptions made
above and to show that the rate of oxidation of the
molecular compound II in the presence of acid III is
described by the equation W = k [II][O ][HX], we
[18]. Thirdly, if the oxidation is carried out in methyl
methacrylate, the latter is polymerized. Previously,
similar effects of o-phenylenediamine, ethanol and
methyl methacrylate were observed at the oxidation of
compounds I [5], ferrocenylmetanol, and ethyl ether of
the latter [19].
0
0
2
have studied the kinetic regularities of the reaction and
the composition of the products. Besides, it was
interesting to compare the compositions of the main
products of the compound II oxidation in the presence
and absence of acid III. The comparison of the kinetic
regularities of these processes presents some
difficulties due to the low reaction rate in the latter
case.
The results of the study of the kinetic regularities of
the compound II oxidation in dioxane in the presence
of acid III indicate that the process is described by the
kinetic equation of first order with respect to the initial
concentrations of the metallocomplex, oxygen and
acid. This follows from the linear increase in the initial
We found that as in the case of oxidation of com-
pounds I, the radical chain route contributes mainly to
the overall oxidation of compound II. This is con-
firmed by several observations. Firstly, the inhibition
of the oxidation at adding o-phenylenediamine, known
as an effective inhibitor of radical chain reactions
rate W of the compound II oxidation with increasing
0
concentration of any of these reagents (Fig. 3).
Analysis of the composition of the reaction
products indicates that the radical-chain oxidation of
compound II in the presence of acid III leads to the
formation of other ferrocene derivatives, namely
methyl ferrocenylpiruvate C H FeC H C(O)C(O)OCH
3
(
Fig. 2). Secondly, the inhibitory effect of ethanol on
the rate of oxidation of compound II, up to virtually
complete suppression of the process when ethanol is
used as the solvent instead of dioxane (Fig. 2), ex-
5
5
5
4
VIII, which, judging from the results of the analysis, is
the main product, and formylferrocene IX, formed in
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8
8
FOMIN, SHIROKOV
2
–3% yield. In addition to compounds VIII and IX
oxidation of the initial metallocomplex affects only
methylene group. This is quite natural, since the
energy of the C–H bond in a group associated with
aromatic ring, such as the Cp ligand, is known [20] to
methanol, H O, CO, and CO were found as well as
products of oxidative degradation of compound II:
cyclopentadiene, cyclopentadienone dimer, and a
resinous residue containing Fe . Yield of methanol could
not be determined accurately. The maximum yields of
CO and CO [N(O ) ≈ 4] are 0.07 and 0.35 mol,
2
2
3+
–1
be by over 70 kJ mol less than in the methyl ester
group RC(O)OCH . In accordance with the results
3
obtained and the generally accepted scheme of radical-
chain oxidation of hydrocarbons [18], the probable
mechanism of radical-chain oxidation of compound II
reflecting its main stage and explaining the
composition of the reaction products can be
represented by scheme (7). As a radical R leading the
chain in the initial stage of the process the radical
2
2
respectively, per 1 mol of the oxidized metallocomplex.
The oxidation of compound II in the absence of an
acid leads wholly to the products of the same
composition as in the presence of acid III. The main
products are also complexes VIII and IX. But also
methyl ferrocenylhydroxyacetate C H FeC H CH(OH)
C(O)OCH X was found, albeit in a small quantity.
The formation of X, as well as the formation of the
complex VIII, suggests that the radical-chain
•
5
5
5
4
C H FeC H C HC(O)OCH is considered formed in
5
5
5
5
3
·
+
3
the reaction of peroxide radicals C H Fe C H CH C·
(O)OO [R'C(O)OO ] generated in accordance with the
5 5 5 5 2
·
·
Scheme 5 with the compound II to be oxidized.
Scheme 7.
R'C(O)OO + II
R'C(O)OOH + R
RO2
(1)
(2)
R + O2
RO2 + II
ROOH + R
(3)
(4)
C H FeC H C(O)C(O)OCH + H O
5
5
5
4
3
2
HX
VIII
ROOH
C H FeC H CHO + HOC(O)OCH
(5)
5
5
5
4
3
IХ
HOC(O)OCH3
CH OH + CO2
(6)
(7)
3
_
+
II + RO2
[C
5
H
5
Fe C
H
4
CH
C(O)OCH
]OOR
5
2
3
_
+
Fc OOR
CH C(O)OCH3
2
_
_
+
+
Fc OOR
Fe OH
+ VIII
(8)
The reactions (1) and (2) are the typical reaction of
the chain propagation, the reaction (7) corresponds to
the chain termination. Evidences that the chain
respectively, leading to the formation of the found
metallocomplexes and several other reaction products.
termination occurs predominantly by the reaction of
Acids are known [13] to catalyze the decomposition
of secondary hydroperoxides as shows Eq. (4) in
Scheme 7. Obviously, acid III also catalyzes decom-
position of ROOH in accordance with Eq. (5) in
Scheme 7. The difference in the catalysis mechanism
for these two reactions is that in order to accelerate the
•
the radical RO with the initial metallocomplexes at
2
the radical-chain oxidation of some ferrocene
derivatives are given in [21]. Reactions (4), (5), and (8)
describe the main routes of the transformation of
·
+
hydroperoxide ROOH and ion-radical salt Fc OOR,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

CONDITIONS FOR MANIFESTATION OF APPROACHMENT
89
first of them the acid must protonate the hydroperoxide
fragment, while to accelerate the second reaction the
acid should protonate the carbonyl or methoxy group,
or at least form a hydrogen bond. This will increase the
electrophilicity of the carbonyl carbon atom and thereby
facilitate its interaction with the peroxide fragment.
OOH
OOH
CH
O
HX
CH C(O)OCH3
C
Fe
+ HX
Fe
OCH3
CHO
Fe
+ HOC(O)OCH + HX
3
The kinetic curves of oxygen consumption in the
reaction (Figs. 1, 2) in the chain-radical oxidation of
compound II evidence the absence of degenerate chain
branching due to homolytic decomposition of peroxide
ROOH. This can be attributed to a significantly higher
rate of conversion of hydroperoxide by the routes (4)
and (5) in Scheme 7 not only due to catalysis, but also
because of the much more favorable energetics of
these reactions.
along the reactions (4) and (5) in Scheme 7.
The formation of products of oxidative degradation
of compound II may result from the oxidation of the
formed ferrocinium ion [22], its disproportionation
[
23] and decay, if it contains a peroxide anion [24].
·
–
·
+
2
II + ROOH + HX → Fe X + H O + RO
SH
·
RO
ROH
–
S
The difference in the yield of CO at the oxidation
2
In accordance with the suggested Scheme 7 and
data of [18], the rate of radical-chain oxidation of
of compounds I and II in the presence of acid III [for
compound I the maximum yield of CO is N(O ) =
2
2
compound II is described by Eq. (1). [k and k below
3
7
0
.62] is due to the fact that the oxidative decar-
correspond to the rate constants of reactions (3) and (7)
in the Scheme 7].
boxylation of the first complex can be procced by two
routes, one similar to the reaction (5) in Scheme 7, and
the other described by the following equation [5]:
·
2
W
0
= k
3
[II][RO
].
(1)
·
Experimentally determined kinetic equation of this
process has the form (2).
C
5
H
5
FeC
R''OOH + C
FeC
5
H
4
CH
2
COOH + R''O
2
·
→
5
H
5
FeC
5
H
4
CH
2
COO
·
W = keff[II][O
2
][HX].
The chain termination rate (W ), which in the steady
t
(2)
→
C
5
H
5
5
H
4
C H
2
+ CO
2
.
•
2
Here R''O is the peroxide radical corresponding to
state is equal to the rate of its initiation (W ), cor-
0
compound I.
responds to Eq. (3).
The ferrocenylcarboxylic acid formed at the
radical-chain oxidation of compound IX in the later
stages of oxidation of compounds I and II can enter
the similar reaction, although in the latter case it was
·
2
W
τ
= W
0
7
= k [II][RO
].
(3)
A comparison of Eqs. (1)–(3) gives an expression
for the rate of chain generation (4).
not detected. To the formation of CO (most likely as
2
W = [(k k )/k ][II][O ][HX] = k '[II][O ][HX]. (4)
0
7
eff
3
2
0
2
at the oxidation of compounds I and II) the oxidative
decarboxylation of acid III may possibly contribute.
The oxidation of compound IX explains the presence
of CO in the reaction products. The absence of methyl
ferrocenylhydroxyacetate X in the reaction product
obtained at the oxidation of compound II in the
presence of acid III, which could be formed in the
same reactions, can be explained by a significantly
higher rate of conversion of hydroperoxide ROOH
Comparing this expression with the above
expression for the rate of the molecular oxidation of
compound II in accordance with the Scheme 5 shows
their complete analogy, which implies Eq. (5):
k
0
' = k
0
= k
1
'K
1
'K
2
'.
(5)
Thus, the Schemes 5 and 7 complement each other
and collectively describe the complete picture of the
oxidation of compound II.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

9
0
FOMIN, SHIROKOV
6. Berezin, I.V. and Martinek, K., Osnovy fizicheskoi
EXPERIMENTAL
khimii fermentativnogo kataliza (Foundations of
Physical Chemistry of Fermentative Catalyst), Moscow:
Vysshaya Shkola, 1977, p. 50.
To measure the kinetics of oxidation of compound
II we used a static vacuum setup with intensive stirring
the reaction mixture. The reaction course was
monitored by measuring the oxygen absorption mano-
metrically.
7
8
. Nesmeyanov, A.N., Khimiya ferrotsena (Chemistry of
Ferrocene), Moscow: Nauka, 1969, p. 9.
. Fomin, V.M., Pukhova, I.V., and Smirnov, A.S., Zh.
Obshch. Khim., 2003, vol. 73, no. 10, p. 1756.
The analysis of reaction products of compound II,
organometallic or organic (cyclopentadienone dimer,
cyclopentadiene) was carried out by gas chromato-
graphy/mass spectrometry. For the analysis we used a
Crystal 5000.1 (SKB Khromatek) gas chromatograph
coupled with a Termo Finnigan mass spectrometer
TRACE DSQ: column RTX-5MS, Tinit = 110ºC, dwell
time 1 min, heating 15º/min to 250ºC, the total analysis
time 30 min, Tevap = 250ºC, discharge 1:30, the sample
volume 1 ml; scan time 30 min, scanning range 50 to
9. Toma, S. and Salisova, M., J. Organometal. Chem.,
vol. 55, no. 2, p. 371.
10. Egorochkin, A.N., Voronkov, A.G., and Kuznetsova, A.V.,
Polyarizatsionnyi effekt v organicheskoi elemento-
organicheskoi i koordinatsionnoi khimii (Polarization
Effect in Organic and Organoelement Chemistry),
Nizhnii Novgorod Univ., 2008, p. 61.
1
1. Fomin, V.M., Shirokov, A.E., Polyakova, N.G., and
Smirnov, P.A., Zh. Obshch. Khim., 2007, vol. 77, no. 4,
p. 698.
1
2. Fialkov, Yu.Ya., Rastvoritel, kak sredstvo upravleniya
khimicheskim protsessom (Solvents As a Means of
Reaction Control), Leningrad: Khimiya, 1990.
5
00 atomic mass units, amplifying 3, scanning
frequency five scans per second, ionizing electrons
energy 70 eV.
1
1
1
1
1
3. Becker, H., Introduction to the Theory of Organic
Reactions, Moscow: Mir, 1965, p. 246.
4. Day, M.C. and Selbin, J., Theoretical Inorganic
Chemistry, Moscow: Khimiya, 1976, p. 330.
Content of methanol was determined by GLC on a
Crystal 5000.1 (SKB Khromatek) chromatograph,
column: ZB-FFAP, length 50 m, diameter 0.32 mm,
with a flame ionization detector.
5. Bethel, D. and Gold, V., Carbonium Ion, Moscow: Mir,
1
970, p. 334.
6. Comprehensive Organic Chemistry, Barton S.D. and
Ollis, W.D., Eds., Moscow: Khimiya, 1983, vol. 4, p. 337.
7. Romanovskii, B.V., Osnovy khimicheskoi kinetiki
Water content was determined by GLC on a
Separone-CHN (detector katharometer), column length
2
m, diameter 4 mm, temperature 120°C, the eva-
(Fundamentals of Chemical Kinetics), Moscow: Ekzamen,
porator temperature 150°C.
2
006, p. 78.
1
8. Emanuel’, N.M., Zaikov, G.E., and Maizus, Z.K., Rol’
sredy v radikal'no-tsepnykh reaktsiyakh okisleniya
organicheskikh soedinenii (The Role of Medium in the
Radical-Chain Reactions of Oxidation of Organic
Compounds), Moscow: Nauka, 1973.
The gaseous products CO and CO were deter-
2
mined by GLC on a Tsvet-100 chromatograph, with
flame ionization detector and rod tap dispenser; the
column length 0.5 m, diameter 4 mm, sorbent activated
carbon (CKT), carrier gas argon, the column tem-
perature 90°C, the reactor catalyst temperature 450°C.
1
9. Fomin, V.M. and Shirokov, A.E., Zh. Obshch. Khim.,
2
009, vol. 79, no. 5, p. 756.
2
0. Energii razryva khimicheskikh svyazei. Potentsialy
ionizatsii i srodstvo k elektronu. Spravochnik (Energy of
Cleavage of Chemical Bonds. Ionization Potentials and
Electron Affinity. Handbook), Kondrat’ev, V.N., Ed.,
Moscow: Nauka, 1974, p. 351.
Compound II was synthesized from compound I
with diazomethane as described in [25].
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2
2
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011