Oxidation reactions catalyzed by osmium compounds. Part 4. Highly efficient oxidation of hydrocarbons and alcohols including glycerol by the H 2O2/Os3(CO)12/pyridine reagent

Article abstract of DOI:10.1039/c3ra41997e

Triosmium dodecacarbonyl cluster Os₃(CO)₁₂ catalyzes oxidation of linear (n-heptane) and cyclic alkanes (cyclohexane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexanes) to the corresponding cycloalkyl hydroperoxides by hydrogen peroxide in acetonitrile solution. Addition of pyridine leads to the acceleration of the process. Turnover numbers in the case of cyclooctane attain 60 000 and turnover frequencies are up to 24 000 h^-1. The alkyl hydroperoxide partly decomposes in the course of the reaction to afford cyclooctanone and cyclooctanol. Selectivity parameters obtained in oxidations of various linear and branched alkanes as well as kinetic features of the reaction indicated that the alkane oxidation occurs with the participation of hydroxyl radicals. A similar mechanism operates in transformation of benzene into phenol and styrene into benzaldehyde. The system also oxidizes 1-phenylethanol to acetophenone. Glycerol is oxidized to produce dihydroxyacetone, glycolic acid and hydroxypyruvic acid. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra41997e

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Oxidation reactions catalyzed by osmium compounds.
Part 4.3 Highly efficient oxidation of hydrocarbons and
alcohols including glycerol by the H2O2/Os3(CO)12/
pyridine reagent{
Cite this: DOI: 10.1039/c3ra41997e
Georgiy B. Shul’pin,*a Yuriy N. Kozlov,a Lidia S. Shul’pina,b Wagner A. Carvalhoc
and Dalmo Mandellic
Triosmium dodecacarbonyl cluster Os3(CO)12 catalyzes oxidation of linear (n-heptane) and cyclic alkanes
(cyclohexane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexanes) to the correspond-
ing cycloalkyl hydroperoxides by hydrogen peroxide in acetonitrile solution. Addition of pyridine leads to
the acceleration of the process. Turnover numbers in the case of cyclooctane attain 60 000 and turnover
frequencies are up to 24 000 h21. The alkyl hydroperoxide partly decomposes in the course of the reaction
to afford cyclooctanone and cyclooctanol. Selectivity parameters obtained in oxidations of various linear
and branched alkanes as well as kinetic features of the reaction indicated that the alkane oxidation occurs
with the participation of hydroxyl radicals. A similar mechanism operates in transformation of benzene
into phenol and styrene into benzaldehyde. The system also oxidizes 1-phenylethanol to acetophenone.
Glycerol is oxidized to produce dihydroxyacetone, glycolic acid and hydroxypyruvic acid.
Received 23rd April 2013,
Accepted 11th June 2013
DOI: 10.1039/c3ra41997e
www.rsc.org/advances
catalytic reagent to the oxidation of saturated and unsaturated
hydrocarbons as well as alcohols including glycerol.
1. Introduction
Transition metal complexes are known to catalyze oxidation
reactions of hydrocarbons (see reviews1) and some other
organic compounds, for example, alcohols (see reviews2) with
molecular oxygen and peroxides, especially with hydrogen
peroxide. Iron compounds are very often used as catalysts in
the oxidation reactions.3 Much less is known about catalytic
properties of compounds of osmium, which is an iron analog.
Thus, osmium compounds catalyze dihydroxylations and
cleavage of olefins,4 oxygenation reactions of saturated
hydrocarbons and other C–H compounds by peroxides and
NaIO4,5 oxidation of alcohols.6
Continuing our studies of osmium-catalyzed oxidation
reactions,7,8 in the present work we carried out an investiga-
tion of the oxidation of various organic substrates in
acetonitrile by the very efficient ‘‘H2O2/Os3(CO)12 (compound
1)/pyridine’’ system. We describe here the application of this
2. Results and discussion
2.1. Oxidation of alkanes
We studied the oxidation of alkanes in acetonitrile solution
with hydrogen peroxide catalyzed by complex 1 in the presence
of pyridine. The oxygenation of cyclohexane gives rise to the
formation of the corresponding alkyl hydroperoxide as the
main primary product. To demonstrate the formation of
cyclohexyl hydroperoxide in this oxidation and to estimate its
concentration in the course of the reaction we used a simple
method developed earlier by Shul’pin.7b,8f,9 If an excess of
solid PPh3 is added to the sample of the reaction solution
before GC analysis, the alkyl hydroperoxide present is
completely reduced to the corresponding alcohol. In recent
years, our method was employed by other chemists for the
aSemenov Institute of Chemical Physics, Russian Academy of Sciences, ulitsa
Kosygina, dom 4, Moscow 119991, Russia. E-mail: Shulpin@chph.ras.ru;
gbsh@mail.ru; Fax: +7499 1376130; Fax: +7495 6512191; Tel: +7 495 9397317
bNesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
ulitsa Vavilova, dom 28, Moscow 119991, Russia
cCenter of Natural and Human Sciences, Federal University of ABC (UFABC), Santa
´
´
Adelia Street, 166, Bangu, Santo Andre, SP 09210-170, Brazil
For parts 1–3, see ref. 7a–c, respectively.
3
{ Electronic supplementary information (ESI) available: Fig. S1–S7, Tables S1
and S2. See DOI: 10.1039/c3ra41997e
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the reaction solution indicate the formation of a complex
mixture of various compounds in low concentrations. Alkyl
hydroperoxides as well as ketones and alcohols decompose
with C–C bond rupture to produce inter alia derivatives of
linear short-chain alkanes. A remarkable peculiarity of the
reaction is the possibility to use the catalyst in very low
concentrations, which gives high turnover numbers (TONs up
to 60 000; Fig. 1B) and turnover frequencies (TOFs up to
24 000 h21) (for TON and TOF, see below and ref. 12). Total
yields of primary oxygenates (alkyl hydroperoxides, ketones
and alcohols) were in some cases about 50%. It is important to
note that when precatalyst 1 is used in a very low concentra-
tion (5 6 1026 and 1 6 1026 M, see, for example, Fig. 1B)
cyclooctyl hydroperoxide is formed as a sole product.
We checked also the catalytic activity of some other amines
(4-picoline, pyrazine, 2,29-bipyridine, and imidazole). Only
4-picoline showed activity comparable with that of pyridine.
All other amines are very poor cocatalysts (Table S1, ESI{).
Acetonitrile and pyridine are known to replace CO ligands in 1
(see experimental section).
Using cyclooctane as
a model substrate we studied
dependences of the initial reaction rate W0 (based on the
sum of cyclooctanol and cyclooctanone concentrations mea-
sured after reduction of the reaction sample with PPh3) on the
initial concentration of each reactant at fixed concentrations
of all other components of the reaction solution. Further, in
our kinetic analysis we will operate with the initial rate of the
formation of cyclooctyl hydroperoxide, W0 = (d[ROOH]/dt)0,
which is equal to the initial rate of the oxygenates formation.
This initial rate W0 was determined from the slope of a dotted
straight line which is tangent to the kinetic curve (two
examples are presented by the dotted lines in Fig. 1). A dotted
line in Fig. S1, ESI{ corresponds to the maximum initial rate in
the case when the reaction proceeds with auto-acceleration.
The dependence of W0 on the initial concentration of H2O2
(straight line) is shown in Fig. 2. In addition, Fig. S2, ESI{
demonstrates the dependence of the yield of oxygenates after 4
and 8 h on initial concentration of hydrogen peroxide. Water
does not dramatically affect the initial reaction rate (Fig. S3,
ESI{).
Fig. 1 Oxidation of cyclooctane with H2O2 catalyzed by 1 in the presence of
pyridine. Accumulation of cyclooctyl hydroperoxide, cyclooctanone, and
cyclooctanol with time is shown. Conditions: [cyclooctane]0 = 0.5 M, [py] = 0.1
M. Graph A: [1]0 = 1 6 1024 M, [H2O2]0 = 1.5 M (70% aqueous). Graph B: [1]0
=
5 6 1026 M, [H2O2]0 = 2.0 M; solvent MeCN, 60 uC. Concentrations of the three
products (cyclooctyl hydroperoxide, cyclooctanol and cyclooctanone) were
calculated comparing concentrations of cyclooctanol and cyclooctanone
measured before and after reduction with PPh3 (for this method, see ref. 7b, 8f
and 9 and experimental section).
The initial reaction rate W0 (Fig. 3) does not practically
depend on concentration of pyridine at its concentration .
0.04 M (for the dependence of yield of the products, see Fig.
S4, ESI{). The mode of the dependence of W0 on the initial
concentration of precatalyst 1 shown in Fig. 4 testifies that the
order of the reaction rate relative to Os3(CO)12 is lower than
first order. In accord with data of Fig. 4 the order in 1
determined as DlogW0/Dlog[1]0 in the studied interval of
concentrations is close to 0.65. The order value lower than
unity apparently indicates that the catalytically active species
contains less than three osmium atoms, that is in the process
of active species generation starting complex Os3(CO)12
dissociates with the loss of one or two osmium atoms.
Assuming that the order 0.65 corresponds to the true order
of the reaction rate and that the extent of 1 dissociation is not
high we will come to the conclusion that the catalytically active
species ‘‘Os2’’ contains two Os atoms and is formed as a result
of the following consecutive transformations:
analysis of reaction products and detection of alkyl hydroper-
oxides in various oxidations of C–H compounds by molecular
oxygen, hydrogen peroxide and other peroxides.10,11 For more
details, see ref. 7b, 8f and 9 and supplementary data.{
Examples of the kinetic curves for the oxidation of
cyclooctane are shown in Fig. 1. Graphs A and B demonstrate
that the oxidation affords predominantly cyclooctyl hydroper-
oxide as well as some amounts of cyclooctanol and cycloocta-
none. In the absence of pyridine the reaction occurs with auto-
acceleration (Fig. S1, ESI{) due to a relatively slow process of
the generation of a catalyst active form. If pyridine in a low
concentration is added to the reaction solution (Fig. 1) the lag
period disappears, which indicates that in the presence of
pyridine the formation of the catalytically active species is fast.
Fig. 1A demonstrates that at relatively high concentration of
precatalyst ([1]0 . 5 6 1025 M) the over-oxidation occurs and
1
the product concentration drops after 2 h. H NMR spectra of
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Fig. 2 Dependence of initial reaction rate W0 on initial concentration of
hydrogen peroxide in the cyclooctane oxidation. Conditions: [cyclooctane]0
=
0.5 M, [py] = 0.1 M, [1]0 = 1 6 1025 M, H2O2, 70% aqueous, solvent MeCN, 60
uC. Concentration of water in the reaction was maintained constant [H2O] =
const by adding necessary amounts of H2O. The initial rate W0 was determined
from the slope of tangent to the kinetic curve of accumulation of the sum of
cyclooctyl hydroperoxide, cyclooctanone, and cyclooctanol (concentration of the
sum cyclooctanol + cyclooctanone was measured after reduction of the sample
with PPh3).
Fig. 4 Oxidation of cyclooctane with H2O2 (2.0 M) in the presence of pyridine
(0.1 M) ([cyclooctane]0 = 0.5 M, solvent MeCN, 60 uC). Graph A: dependence of
W0 oxidation in on initial concentration of precatalyst 1. Graph B: linearization
of dependence shown in graph A using coordinates log[1]0 2 logW0.
(1)
(2)
The analysis of this scheme in
approximation gives rise to eqn (3).
a
quasi-equilibrium
(3)
[‘‘Os2’’] = K2(K1[‘‘Os3’’])O
Assuming that W0 is proportional to [‘‘Os2’’] we obtain the
dependence:
W0 # v[‘‘Os3’’]O
(4)
Fig. 3 Dependence of initial reaction rate W0 on initial concentration of added
pyridine in the cyclooctane oxidation. Conditions: [cyclooctane]0 = 0.5 M, [1]0
1 6 1025 M, [H2O2]0 = 0.24 M, solvent MeCN, 60 uC. The initial rate W0 was
=
Here v is a coefficient. The exponent O at concentration
[‘‘Os3’’] is practically equal to the experimental value 0.65.
Decreasing the concentration of catalyst 1 we were able to
significantly increase TONs (i.e., turnover numbers; mols of
determined from the slop of tangent to the kinetic curve of accumulation of the
sum of cyclooctyl hydroperoxide, cyclooctanone, and cyclooctanol (concentra-
tion of the sum cyclooctanol + cyclooctanone was measured after reduction of
the sample with PPh3).
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products per one mol of the catalyst; see ref. 12) and initial
TOFs (i.e., turnover frequencies; mols of products per one mol
of the catalyst obtained during the first hour of the reaction). It
is necessary to note here that the very high turnover numbers
attained by our system for the alkane oxidation are due to the
order of the reaction in the catalyst 1, which is less than unity.
Indeed, we can use a very low concentration of 1. Another
reason why we can reach such high TONs is the remarkable
stability of the catalytically active system during a long period
of the reaction. Values TON and TOF for the cyclohexane
oxidation by the 1/py/H2O2 reagent in acetonitrile as well as by
other most efficient catalytic systems are summarized in Table
S2, ESI{ (see ref. 9a and 13–16). These data allow us to
conclude that organometallic osmium complexes in the
combination with pyridine oxidize alkanes with the highest
TON and TOF values (entries 1 and 2). Very active mono-
nuclear vanadate in the form of salt (n-Bu4N)VO3 in combina-
tion with pyrazine-2-carboxylic acid (PCA; for this reagent, see
ref. 9a, 13b–d, 14 and 15) affords oxygenates with slightly lower
TON = 20 000 and TOF = 2100 values (entries 3 and 4). It
should be noted that when we decrease the catalyst concen-
tration we can increase TON and TOF parameters; however, at
least for relatively short reaction times the yield of oxygenates
dramatically drops. It can be seen from the data of Table S2,
ESI{ that other meal complex catalysts (entries 5–11) exhibit
noticeably lower TONs and TOFs.
We measured the selectivity parameters in oxidations of
certain alkanes (Table S3, ESI,{ entries 1 and 2) in order to
determine the nature of the alkane oxidizing species.
Parameters determined previously9a,13–17 for other systems
are also given in Table S3, ESI.{ It can be seen that these
parameters are close to the selectivities determined previously
for the systems generating free hydroxyl radicals (entries 3–24)
and noticeably lower than parameters determined for the
systems oxidizing either without the participation of reactive
hydroxyl radicals or in narrow cages (entries 25–31).
Approaching ‘‘a plateau’’ in the dependence of W0 on initial
concentration of cyclooctane, [RH]0 (Fig. 5A), indicates that
there is a competition between RH and another component of
the reaction mixture for a transient oxidizing species.14a,16d,17b
Indeed, at high concentration of the hydrocarbon all oxidizing
species are accepted by RH and the maximum possible
oxidation rate is attained. This rate does not depend on
[RH]0 in the interval 0.25 , [RH]0 , 0.5 M. Three components
of the reaction solution which can compete with cyclooctane
are pyridine, hydrogen peroxide and solvent acetonitrile. The
concurrence can be described by the following kinetic scheme:
Fig. 5 Oxidation of cyclooctane with H2O2 (2.0 M) in the presence of pyridine
(0.1 M), [1]0 = 5 6 1025 M, solvent MeCN, 60 uC. Graph A: dependence of W0
oxidation in on initial concentration of cyclooctane. Graph B: linearization of
dependence shown in graph a using coordinates 1/[cyclooctane]0 2 1/W0.
where Wi is the rate of generation of oxidizing species X. The
analysis of this scheme in a quasi-stationary approximation
relative to species X leads to eqn (10).
d½ROOHꢀ
dt
Wi
W0~
~
(10)
k2½pyꢀzk3½H2O2ꢀzk4½MeCNꢀ
k1½RHꢀ
1z
In accord with eqn (10) we can see the linear dependence of
the experimentally measured reciprocal parameter 1/W0 on
reciprocal concentration 1/[RH]0 (Fig. 5B). The tangent of this
straight line slope angle corresponds to the value (k2[py] +
k3[H2O2] + k4[MeCN])/k1Wi. The segment which is cut off by the
line on Y-axis is equal to 1/Wi. Using these data we can
calculate the following value:
k2½pyꢀzk3½H2O2ꢀzk4½MeCNꢀ
H2O2 + catalyst A X (rate Wi)
X + RH A products (constant k1)
X + py A products (constant k2)
X + H2O2 A products (constant k3)
X + MeCN A products (constant k4)
(5)
(6)
(7)
(8)
(9)
~0:14
(11)
k1
As the selectivity parameters summarized in Table 2 indicate
that the oxidizing species X is hydroxyl radical it is reasonable
to use known from the literature rate constants of the
?
interaction between HO and pyridine, hydrogen peroxide,
and acetonitrile. The comparison of the term values in the
numerator of the fraction given above (11) can evaluate the
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Table 1 Oxidation of benzene with H2O2 catalyzed by Os3(CO)12 in the
presence of pyridinea
Entry
Os3(CO)12 (M)
Time (h)
Phenol (M)
TON
1
5 6 1025
1
3
5
8
1
3
0.025
0.050
0.058
0.049
0.03
500
2
1000
1160
980
3000
8000
3b
4
5
1 6 1025
6c
0.08
a
Conditions: [benzene]0 = 0.5 M; [H2O2 (50%)]0 = 2.0 M; [py] = 0.05
b
M; 40 uC. Maximum yield of phenol was 12% based on benzene
(conversion of benzene was 48%). Maximum yield of phenol was
c
16% based on benzene (conversion of benzene was 35%).
dominating reaction which competes with the alkane oxida-
tion.
?
The constant values for reactions (7), (8), and (9) (X = HO )
are known (M21 21): k2 = 2.3 6 109 or 4.5 6 109; k3 = (4.5 ¡
s
1.4) 6 107; k4 = 3.6 6 106 or 2.2 6 107 (see ref. 14a, 16d and
17b). Taking into account that under conditions of the
experiments presented in Fig. 5 concentrations [py] = 0.1 M,
[H2O2] = 2.0 M, and [MeCN] # 18 M we can calculate the
following parameters (s21): k2[py] = 2.3 6 108 or 4.5 6 108;
k3[H2O2] = (9 ¡ 2.8) 6 107, and k4[MeCN] = 6.4 6 107 or 3.9 6
108. This estimation shows that the most probable competitors
of cyclooctane for hydroxyl radicals are pyridine and acetoni-
trile. The rate constant k1 (M21 21) for reaction (6) can be
s
calculated using eqn (11) and given above values k2[py] and
k2[MeCN]. The minimum value of constant k1 equals to 1.4 6
Fig. 6 Graph A: oxidation of cyclooctane (accumulation of a sum of oxygenates)
109 and maximum value is 5.0 6 109 M21 21. Taking into
s
at different temperatures. Conditions: [1]0 = 1 6 1025 M, [py] = 0.1 M, [H2O2]0
=
0.24 M, [cyclooctane]0 = 0.5 M. Graph B: The Arrhenius plot based on data is
presented in Graph A.
account the experimental errors in determination of rate
constants we can see that the minimum value of k1 is typical
for the reactions of hydroxyl radicals with alkanes (see ref.
16d): k1 = 1.2 6 109 for cyclopentane, k1 = 1.3 6 109 for
cyclohexane, and k1 = 1.6 6 109 M21 s for cycloheptane in
aqueous solution. Therefore, the experimentally found com-
petition is in good agreement with the assumption that the
oxidizing species in our system is hydroxyl radical. Radical
of the catalytically active Os-containing species which are
involved into the alkane oxygenation with H2O2 is at present
unknown. We can, however, assume that manifold OsIII–OsII
operates in this system,7a which is analogous to the pairs FeIII–
FeII and VV–VIV (ref. 14 and 15). In this case the catalytic cycle
of the alkane hydroperoxidation can involve the following
steps:
?
?
HO attacks the hydrocarbon RH to generate alkyl radical R
which very rapidly reacts with molecular oxygen. Produced
+
?
peroxyl radical, ROO , can be reduced in the presence of H by
a low-valent form of Os-containing species to lead to the
formation of the first product alkyl hydroperoxide. The nature
+
OsIII + H2O2 A OsII + HOO + H
?
(12)
II
OsIII + HOO A Os + H+ + O2
?
(13)
OsII + H2O2 A OsIII + HO2 + HO
Table 2 Oxidation of styrene with H2O2 catalyzed by Os3(CO)12 in the presence
of pyridinea
?
(14)
?
?
RH + HO A R + H2O
(15)
(16)
(17)
(18)
(19)
Entry
Os3(CO)12 (M)
Time (h)
Benzaldehyde (M)
TON
1
2
3
4
5
6
5 6 1025
1
3
5
8
1
3
0.028
0.039
0.046
0.040
0.027
0.066
560
780
920
800
2700
6600
?
?
R + O2 A ROO
ROO + Os A ROO2 + OsIII
II
?
1 6 1025
ROO2 + H+ A ROOH
a
Conditions: [styrene]0 = 0.5 M; [H2O2 (50%)]0 = 2.0 M; [py] = 0.05
?
?
ROO + HOO A ROOH + O2
M; 40 uC.
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In the sequence (15)–(19), stage (15) is the reaction limiting
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the rate of alkyl hydroperoxide formation. We carried out the
oxidation of cyclooctane at different temperatures (Fig. 6).
Estimated effective activation energy is 12 ¡ 3 kcal mol21
.
2.2. Oxidation of benzene
A very important chemical product phenol is utilized in the
fabrication of polycarbonates and epoxy resins with more than
90% produced via the cumene process.18a One of the
alternative methods used for the preparation of phenols from
arenes is the oxidation of arenes with H2O2 catalyzed by metal
complexes.18b Unlike the cumene peroxidation route,18c direct
oxidation of benzene with hydrogen peroxide does not
produce co-products such as acetone. However, usually the
yields of phenol are not high. For example, in the oxidation of
benzene with H2O2 catalyzed by Tp*Cu(NCMe), where Tp* is
hydrotris(3,5-dimethylpyrazolylborate), phenol was detected as
the major product in the reaction mixture, with some 1,4-
benzoquinone as the sole byproduct, as a consequence of
overoxidation of the phenol produced.18d Benzene conversion
was between 15 and 21% and selectivity to phenol was between
73 and 81%. Catalysis by molybdovanadophosphoric hetero-
poly acid H5PMo10V2O40 gave18e phenol with conversion of
34%, the benzene oxidation18f catalyzed by V(acac)3 gave a
mixture of phenol and quinone with conversion to phenol
from 2.7 to 9.0% and the phenol content in this mixture from
76 to 84%, the oxidation with the Fenton-like system18g and
vanadium silicalite zeolite catalysts18h produced phenol in
yields 12% and 11%, respectively.
Our Os-based system oxidizes efficiently benzene to phenol
with maximum attained TON = 8000 (Table 1). The oxidation
of benzene at different temperatures (Fig. 7). evaluated
effective activation energy equal to 9 ¡ 2 kcal mol21
.
Fig. 7 Graph A: accumulation of phenol in the oxidation of benzene at different
temperatures. Conditions: [benzene]0 = 0.5 M, [H2O2]0 = 1.0 M, [Os3(CO)12] = 5
6 1025 M, [py] = 0.05 M. Initial reaction rates were calculated from slops of the
dotted lines. Graph B: The Arrhenius plot based on data presented in Graph A.
2.3. Oxidation of styrene
The oxidation of styrene with H2O2 catalyzed by metal
complexes leads usually to the formation of styrene oxide,
benzaldehyde and benzoic acid in relatively low yields. Thus,
catalysis by [Cu(hmbmz)2] (hmbmz is 2-(a-hydroxymethyl)
benzimidazole) gave these products with selectivity of 16, 65
and 10%, respectively, and with conversion of 42% in addition
to 9% of other products.19a The oxidation of styrene with the
reagent ‘‘H2O2–nBu4NVO3–pyrazinecarboxylic acid’’ gave after
3 h at 60 uC benzaldehyde in 28% yield.19b Our Os-system
under consideration oxidizes styrene to produce benzaldehyde
with TON attained 6600 (Table 2).
point of view.20 For example, dihydroxyacetone (DHA) is a very
valuable and important compound (it is widely used in
cosmetics as a safe skin coloring agent as well as a nutritional
supplement), being the first product in the chain of
consecutive glycerol oxidation reactions. Glycolic acid that is
formed from glycerol via C–C bond rupture finds applications
in skin care products.
As glycerol is a very reactive compound, its oxidation
typically gives rise to the formation of several compounds.
Due to the high reactivity of both glycerol and its oxidation
products, the oxidation of glycerol usually affords desirable
products in low yield and selectivity. Recently we reported on
two first systems which allow us to oxidize glycerol in
homogeneous solution. These catalytic systems are based on
complexes of manganese21a and copper.21b In the present
work, glycerol was oxidized by the H2O2/1/py system to DHA,
glycolic acid and hydroxypyruvic acid (Scheme 1).
Concentrations (determined by 1H NMR; an example of the
typical spectrum is shown in Fig. S5, ESI{) and yields of these
products are summarized in Table 3. The best result was
2.4. Oxidation of 1-phenylethanol
We checked the possibility of oxidation by our system of easily
oxidizable alcohols. The first one is 1-phenylethanol which is
effectively oxidized to acetophenone (Fig. 8). Effective activa-
tion energy was estimated: 11 ¡ 3 kcal mol21
.
2.5. Oxidation of glycerol
The second easily oxidizable alcohol checked here is glycerol.
Glycerol is a by-product from biodiesel manufacturing. It is
also a co-product in the production of fatty acids, alcohols and
soap using fats and oils as a feedstock. Oxidative transforma-
tions of glycerol are especially important from the practical
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obtained at 60 uC after 13 h. In this experiment (entry 6)
glycerol conversion was 32%.
3. Conclusions
In the present work, the most efficient homogeneous metal–
complex reagent exhibiting very high TON (60 000) and TOF
(24 000 h21) values was used for the oxidation of saturated,
aromatic and olefinic hydrocarbons and alcohols, including
glycerol. This system represents one of the first examples of
homogeneous systems for the oxidation of glycerol. In the
glycerol oxidation the system operates under mild conditions
and shows good selectivity.
4. Experimental
4.1. Reagents
Hydrogen peroxide was used as 70% solution in H2O in the
oxidation of alkanes and 50% solution in H2O in the oxidation
of benzene, styrene and alcohols including glycerol.
Triosmium dodecacarbonyl, Os3(CO)12 (precatalyst 1;
Aldrich) is insoluble in cold acetonitrile. The precatalyst was
introduced into the reaction solution in the form of a stock
solution which was prepared by the following method.
Typically, Os3(CO)12 (9.2 mg) was suspended in CH3CN (40
mL). The mixture was stirred at 60 uC for 1 h. This procedure
led to replacing CO ligands by MeCN and gave a homogeneous
bright yellow stock solution which was used in the oxidations
(typically, concentration [1]0 in the stock solution was from 5
6 1025 to 2.5 6 1024 M). A new weak peak at 2106 cm21
appeared in the IR spectrum of the stock solution (compare
Fig. S6A and S6B, ESI{) which indicates the formation of
complex Os3(CO)11(MeCN).22 The stock solution is stable and
can be stored either at room temperature or in a refrigerator
without loss of activity in alkane oxidation (Fig. S7, ESI{).
Fig. 8 Graph A: accumulation of acetophenone in the oxidation of 1-pheny-
lethanol at different temperatures. Conditions: [1-phenylethanol]0 = 0.5 M,
[H2O2]0 = 1.0 M, [Os3(CO)12] = 5 6 1025 M, [py] = 0.05 M. Initial reaction rates
were calculated from slops of the dotted lines. Graph B: the Arrhenius plot
based on data presented in Graph A.
4.2. Oxidation of alkanes
The reactions of alkanes were typically carried out in air in
thermostated Pyrex cylindrical vessels with vigorous stirring
and using MeCN as solvent. Typically, precatalyst 1 (‘‘Aldrich’’;
used as received) and the cocatalyst (pyridine) were introduced
into the reaction mixture in the form of stock solutions in
acetonitrile. The substrate (hydrocarbon or alcohol) was then
added and the reaction started when hydrogen peroxide was
introduced in one portion. (CAUTION. Compound 1 is toxic by
absorption through the skin and should therefore be handled
with care. All reactions should be carried out in a fume hood.
The combination of air or molecular oxygen and H2O2 with
organic compounds at elevated temperatures may be explo-
sive!). The reactions were stopped by cooling and after
addition of nitromethane as a standard compound analyzed
by GC (instrument ‘HP 5890–Serie-II’; fused silica capillary
columns column Hewlett-Packard; the stationary phase was
polyethyleneglycol: INNOWAX with parameters 25 m 6 0.2
mm 6 0.4 mm; carrier gas was N2 with column pressure of 15
psi). Attribution of peaks was made by comparison with
Scheme 1 Products of glycerol oxidation.
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Table 3 Oxidation of glycerol with the H2O2/1/pyridine systema
Products, concentration, M (yield, %)
Entry
Temperature uC
Time h
Glycerol conversion (%)
DHA
Glycolic, acid
Hydroxo-pyruvic acid
1
2
3
4
5
6
17
60
24
72
144
0.5
5
5
0.007 (4.3)
0.010 (5.0)
0.011 (5.5)
0.0008 (0.4)
0.017 (8.3)
0.015 (7.5)
0 (0)
0 (0)
10
18
4
15
32
0.005 (2.5)
0.010 (5.0)
0 (0)
0.006 (4.0)
0.016 (8.0)
0.006 (3.0)
0.006 (3.0)
0 (0)
0.005 (2.7)
0.003 (1.5)
13
a
Conditions. Solvent was acetonitrile, [glycerol]0 = 0.2 M, [H2O2]0 = 0.3 M, [Os3(CO)12]0
= 5 6 1025 M, [py] = 0.05 M, total volume of the
reaction solution was 2.5 mL. Yields (%) in parentheses are based on starting glycerol.
Biomimetic Oxidations Catalyzed by Transition Metal Complexes,
B. Meunier, Ed., Imperial College, London, 2000; (g) G. A. Olah
chromatograms of authentic samples. Blank experiments with
cyclooctane showed that in the absence of catalyst 1 no
products were formed. The quantification of alkyl hydroper-
oxides and ketones (aldehydes) and alcohols present in the
reaction solution was performed using developed previously by
Shul’pin7b,8f,9 simple GC method with reduction of the
reaction samples with tryphenylphosphine.
´
´
and A. Molnar, Hydrocarbon Chemistry, Wiley, Hoboken, NJ, 2003;
(h) G. B. Shul’pin, Oxidations of C–H Compounds Catalyzed by
Metal Complexes, in Transition Metals for Organic Synthesis, M.
Beller and C. Bolm, ed., 2nd edition, Wiley–VCH, Weinheim/New
York, 2004, vol. 2, Chapter 2.2, pp. 215–242; (i) Aqueous-Phase
Organometallic Catalysis, B. Cornils and W. A. Herrman, ed.,
4.3. Oxidation of benzene, styrene, 1-phenylethanol and
glycerol
´
Wiley-VCH, Weinheim, 2004; (j) J.-M. Bregeault, M. Vennat,
L. Salles, J.-Y. Piquemal, Y. Mahha, E. Briot, P. C. Bakala,
A. Atlamsani and R. Thouvenot, J. Mol. Catal. A: Chem., 2006, 250,
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4217–4228; (l) E. G. Chepaikin, Russ. Chem. Rev., 2011, 80,
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R. A. Periana, Acc. Chem. Res., 2012, 45, 885–898.
2 (a) J. Muzart, Tetrahedron, 2003, 59, 5789–5816; (b) I. E. Marko,
P. R. Giles, M. Tsukazaki, A. Gautier, R. Dumeunier, K. Doda,
F. Philippart, I. Chelle-Regnault, J.-L. Mutonkole, S. M. Brown
Oxidation reactions of benzene, styrene, 1-phenylethanol and
glycerol were carried out as the reactions with alkanes. In
these experiments concentration of the products was mea-
sured using 1H NMR NMR method using instruments ‘‘Bruker
AMX-400’’ and ‘‘Bruker AV-300’’. Solutions were in CD3CN;
signals were integrated using added 1,4-dinitrobenzene in
acetone-d6 as a standard.
´
and C. J. Urch, in Transition Metals for Organic Synthesis, M.
Beller and C. Bolm, ed., second edition, Wiley-VCH,
Weinheim/New York, 2004, vol. 2, pp. 437–478; (c) G. Tojo
and M. Fernandez, Oxidation of Alcohols to Aldehydes and
Ketones Springer Science, Business Media Inc., New York, 2006;
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2006, 309, 270–272.
Acknowledgements
This work was supported by the Russian Foundation for Basic
Research (grants No. 06-03-32344-a and No. 12-03-00084-a), the
˜
˜
State of Sao Paulo Research Foundation (Fundaçao de Amparo
˜
a Pesquisa do Estado de Sao Paulo, FAPESP; grants 2005/
51579-2 and 2006/03996-6), and the Brazilian National Council
on Scientific and Technological Development (Conselho
3 (a) H. B. Dunford, Coord. Chem. Rev., 2002, 233–234, 311–318;
˜
(b) A. Correa, O. G. Mancheno and C. Bolm, Chem. Soc. Rev.,
2008, 37, 1108–1117; (c) Iron Catalysis in Organic Chemistry, B.
Plietker, Ed., Wiley-VCH, Weinheim, 2008; (d) A. A. Shteinman,
´
e Tecnologico,
Nacional de Desenvolvimento Cientifico
CNPq, Brazil; grants Nos. 478165/2006-4; 552774/2007-3,
305014/2007-2 and 303828/2010-2). The authors thank Miss
Mariane K. G. Bizarra and Mr. Nikita V. Shvydkiy for their help
in the experiments.
¨
Russ. Chem. Rev., 2008, 77, 945–966; (e) K. Schroder, K. Junge,
B. Bitterlich and M. Beller, Top. Organomet. Chem., 2011, 33,
83–109; (f) Iron-Containing Enzymes: Versatile Catalysts of
Hydroxylation Reactions in Nature, Edited by S. P. de Visser
and D. Kumar, ed., Royal Society of Chemistry, Cambridge,
2011; (g) E. P. Talsi and K. P. Bryliakov, Coord. Chem. Rev., 2012,
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RSC Adv.
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