Oxidation of hydroxyacetone (acetol) with hydrogen peroxide in acetonitrile solution catalyzed by iron(III) chloride

Article abstract of DOI:10.1016/j.molcata.2016.02.011

α-Hydroxyacetone (acetol) which is easily produced from glycerol can be oxidized to other products of industrial interest. In this work the acetol oxidation by homogeneous cheap and green catalytic system FeCl₃/H₂O₂ has been studied. Acetonitrile or water was used as solvent. Acetol (0.5?M) gave acetic acid (0.25?M) and formic acid (0.35?M) as the main products. Some amount of CO₂ was also detected. For quantification of the CO₂ amount, a novel method has been developed which uses GC–MS for monitoring the signals produced by the CO₂ and argon (used as internal standard) present in the headspace of the reaction vessel. The formation of 0.028?M CO₂ after 4?h under typical conditions was demonstrated. The effects of reactant concentration on the initial reaction rate were studied. The experiments in atmosphere of ¹⁶O₂ and ¹⁶O₂?+?¹⁸O₂ led to the conclusion that molecular oxygen from atmosphere takes part in the reaction and these atoms are incorporated into the products.

Full text of DOI:10.1016/j.molcata.2016.02.011

Accepted Manuscript
Title: Oxidation of hydroxyacetone (acetol) with hydrogen
peroxide in acetonitrile solution catalyzed by iron(III) chloride
´
Author: Marcos L.de Araujo Dalmo Mandelli Yuriy N.
Kozlov Wagner A. Carvalho Georgiy B. Shul’pin
PII:
S1381-1169(16)30045-0
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.02.011
MOLCAA 9776
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
23-10-2015
8-2-2016
9-2-2016
´
Please cite this article as: Marcos L.de Araujo, Dalmo Mandelli, Yuriy N.Kozlov,
Wagner A.Carvalho, Georgiy B.Shul’pin, Oxidation of hydroxyacetone (acetol) with
hydrogen peroxide in acetonitrile solution catalyzed by iron(III) chloride, Journal of
Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2016.02.011
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Oxidation of hydroxyacetone (acetol) with hydrogen peroxide in acetonitrile solution catalyzed by
iron(III) chloride
Marcos L. de Araújoa, Dalmo Mandellia*, Yuriy N. Kozlovb,c, Wagner A. Carvalhoa, Georgiy B. Shul’pin
b,c* Shulpin@chph.ras.ru
aCenter of Natural and Human Sciences, Federal University of ABC (UFABC), Santa Adélia Street, 166,
Bangu, Santo André, SP, 09210-170, Brazil
bSemenov Institute of Chemical Physics, Russian Academy of Sciences, Ulitsa Kosygina, dom 4,
Moscow 119991, Russia
cPlekhanov Russian University of Economics, Stremyannyi pereulok, dom 36, Moscow, 117997 Russia
*Corresponding author. Fax: (+7499) 1376130
This paper is dedicated with admiration to Professor Ulf F. Schuchardt in recognition of his notable
contributions to catalytic chemistry.
1

Graphical Abstract:
Oxidation of acetol by homogeneous cheap and green catalytic system FeCl3/H2O2 gave acetic acid and
formic acid as the main products.
OH
O
C
O
C
O
C
H2O2/FeCl3
OH
+
+
CO2
OH
18O2
H3C
OH
H
OH
H3C
CH2
Acetol
OH
Glycerol
Acetic acid
Formic acid
2

Highlights
- Acetol is oxidized by H2O2 under mild conditions
- Cheap and green FeCl3 is a catalyst
- Acetic and formic acids are the main products
3

ABSTRACT
α-Hydroxyacetone (acetol) which is easily produced from glycerol can be oxidized to other products of
industrial interest. In this work the acetol oxidation by homogeneous cheap and green catalytic system
FeCl3/H2O2 has been studied. Acetonitrile or water was used as solvent. Acetol (0.5 M) gave acetic acid
(0.25 M) and formic acid (0.35 M) as the main products. Some amount of CO2 was also detected. For
quantification of the CO2 amount, a novel method has been developed which uses GC-MS for monitoring
the signals produced by the CO2 and argon (used as internal standard) present in the headspace of the
reaction vessel. The formation of 0.028 M CO2 after 4 h under typical conditions was demonstrated. The
effects of reactant concentration on the initial reaction rate were studied. The experiments in atmosphere
of 16O2 and 16O2+18O2 led to the conclusion that molecular oxygen from atmosphere takes part in the
reaction and these atoms are incorporated into the products.
Keywords: Acetic acid; Alcohols; Formic acid; Oxidation.
4

1. Introduction
The oxidation of alcohols to obtain aldehydes, ketones or carboxylic acids is of great importance
in organic synthesis [1,2.]. Containing hydroxyl groups glycerol is a by-product from biodiesel
manufacturing [3]. It is also a co-product in the production of fatty acids, alcohols and soap using fats and
oils as a feedstock. Oxidative transformations of glycerol are especially important from the practical point
of view (Scheme 1) [4]. For example, dihydroxyacetone (DHA) is a very valuable and important
compound, being the first product in the chain of consecutive glycerol oxidation reactions. DHA does not
damage the skin and it is thus widely used in cosmetics as a safe skin coloring agent as well as a
nutritional supplement. Besides, DHA is a versatile building block for the synthesis of a variety of fine
chemicals. Glyceric acid, another primary product of glycerol oxidation, is used as biochemical
intermediates being liver stimulant, cholesterolytic and anti-inflammatory and also a base material for
functional surfactants. Glycolic acid that is formed from glycerol finds applications in skin care products.
Glycerol is a very reactive compound and 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. Many heterogeneous catalysts
lead to the predominant formation of the products of deep oxidation that are not very valuable (formic
acid, formaldehyde and even CO2). Unfortunately, DHA was either not produced at all in many aerobic
heterogeneous oxidations or its yields were very low (4%). One of the main problems existing in this field
is the over-oxidation of the initially formed reactive products. It is thus very difficult to produce primary
oxygenates (e.g., DHA) in appropriate yields. Only a few reports on the homogeneously catalyzed
oxidation of glycerol with peroxides were reported in recent years (see, for example, [5]).
Glycerol can be easily dehydrated to α-hydroxyacetone (acetol) which can also be oxidized,
potentially leading to the formation of products of industrial interest (Scheme 1), for example lactic acid.
Acetol is used to produce products such as propylene glycol via hydrogenation reaction and acrolein
through dehydration. It is also used to synthesize compounds such as propionaldehyde, acetone and furan
5

derivatives. Acetol has been extensively used in food industry, to give aroma to foods. Acetol can be used
as a substituent to sodium dithionite which is usually used to reduce dye to a water soluble compound.
Cheap and green oxidation of acetol opens the way to the preparation of acetic and formic acid from
glycerol (acetol made from biomass via glycerol costs only USD 1.25 per kilogram).
Acetol has a significantly higher market value than acetic and formic acid. However, the
formation of acetic acid from acetol becomes interesting if the whole process is performed only in one
industrial plant for biodiesel production. Approximately 300,000 tons of glycerol is produced in Brazil.
The idea developed here is the following: in one biodiesel plant, rejected glycerol could be easily
dehydrated to acetol which, after purification by distillation, could be converted into acetic acid. In the
same plant acetic acid could be esterified, also with glycerol, yielding triacetin, which is a fuel and/or
biodiesel additive (Scheme 3) [6a] and is also an additive to the biodiesel [6b]. Therefore, an important
compound could be obtained only using waste from the same company. Formic acid already has a market
value greater than acetic acid and can be used as a bactericide in the manufacture of leather and other
applications [6c].
Use of hydrogen peroxide as green oxidant, together with a cheap easily available catalyst is very
attractive. In 1922, Evans and Hoover showed that acetol under the action of KMnO4 is oxidized to acetic
acid and carbon dioxide in a neutral solution [6d]. Later it has been found that the oxidation of acetol in
the presence of salts of copper, cobalt and iron leads to the products shown in Scheme 2. More recently it
has been demonstrated that methylglyoxal is oxidized to give acetic acid, formic acid and other products
[7].
In this work we studied the acetol oxidation catalyzed by the FeCl3/H2O2 system which affords
acetic acid, formic acid and CO2 (Scheme 4) . Iron complexes are known to induce the decomposition of
hydrogen peroxide to afford hydroxyl radicals which then oxidatively functionalize various organic
compounds [8].
6

2. Experimental
The oxidation of acetol in acetonitrile was carried out in air in thermostated vessels under vigorous
stirring. Typically, the reactions were performed in a 20-mL glass reactor to 60 °C and atmospheric
pressure, with the reagents in the following concentrations: FeCl3, 1 × 10‒3 M; acetol, 0.5 M; H2O2, 0.5
M; and acetonitrile up to 5 mL. The reaction was started by the addition of hydrogen peroxide to the
mixture containing substrate, catalyst and solvent. The total volume of the reaction mixture was 5 mL,
60% aqueous H2O2 was used as the oxidant. CAUTION: the combination of air and H2O2 with organic
compounds at elevated temperatures may be explosive! To each aliquot removed (2 drops) were added to
1 mL of acetonitrile and then triphenylphosphine to reduce H2O2 and stop the reaction. The values of
initial rates W0 were measured (see Fig. 1) from the slope of tangents (shown by dotted straight lines
denoted by symbol “a”) to the kinetic curves in the initial period of the reaction.
The analysis of acetic acid was done by GC-FID. The analysis of formic acid was done by GC-MS,
injecting the samples directly from the reaction medium without prior dilution or chemical treatment. The
analysis of the CO2, was also made by GC-MS by injecting the headspace samples with a syringe air
tight and comparing the signals from the mass spectrum with those of a calibration curve previously CO2
standards prepared (using air as the internal standard argon). The kinetics of acetic acid and formic acid
showed that after 6 hours of reaction 0.25 M of acetic acid and 0.35 M of formic acid are produced.
Samples of the reaction mixture were analyzed by GC (Agilent 6890, N2 was carrier gas, FID) and
GC-MS (Shimadzu QP-2010 Plus, He was carrier gas); in both instruments the column was BP-20 (SGE;
polyethyleneglicol – 30 m × 250 μm × 0.25 μm). Attribution of peaks was made by comparison with
chromatograms of authentic samples and by GC-MS.
3. Results and discussion
3.1. Main features of the acetol oxidation
7

The oxidation of acetol by the FeCl3/H2O2 combination in acetonitrile solution leads to the formation
of acetic and formic acids as well as carbon dioxide (Scheme 4). Fig. 1 represents kinetic curves for the
accumulation of acetic and formic acid and carbon dioxide with time. In this work and in the kinetic
analysis we will operate using initial reaction rates of the product formation. The values of these rates W0
we measured from the slope of tangents to the kinetic curves in the beginning of the reaction. In Fig. 1
these tangents are shown by dotted straight lines denoted by symbol “a”. As shown in the inset,
accumulation of acetic acid during first 11 min is linear. It can be seen that the accumulation of formic
acid starts only after some induction period and the initial rate for the formation of acetic acid in the
beginning is much higher than the initial rate for formic acid. It also follows from Fig. 1 that the amount
of CO2 (recalculated to its concentration in the reaction solution) is noticeably lower than amount of
acetic acid. These two observations allowed us to neglect formic acid and CO2 in measuring the initial
oxidation rate in the kinetic consideration (that is only concentration of acetic acid was taken into
account). Assuming that one acetol molecule is required to form one molecule of acetic acid, one formic
acid and one CO2 we can calculate that after 4 h yields of acetic, formic acids and CO2 are equal to 48, 68
and 6%, respectively. Turnover number (TON) is 600 at mass balance 110.
Iron chloride plays the role of catalyst and is obligatory component of the reaction mixture. In the absence
of catalyst only 0.01 M of acetic acid is produced after 6 h. Increase of the FeCl3 concentration leads to
the enhancement of both the initial reaction rate and final yield of acetic acid (Fig. 2). The oxidation
reaction deceases when concentration of hydrogen peroxide is close to zero. The iodometric titration
showed that in a typical reaction 99.6% of H2O2 is consumed after 6 h. However, if a new portion of H2O2
is added after 3 h to the reaction solution the reaction proceeds further (see Supplementary data, Fig. S1).
It is noteworthy that yield of acetic acid is higher and reaches ca. 70% (Fig. 3) if water is used as solvent.
Yield in acetonitrile solution is about 50%.
3.2. Dependences of acetic acid formation initial rate
8

We measured initial rats W0 of acetic acid formation at varying concentration of each reactant at fixed
concentrations of all other components of the reaction mixture. Concentration of catalyst was varied in
the interval 10‒4‒1.6 × 10‒3 M (Fig. 4). Fig. 5 demonstrates the dependence of W0 on initial concentration
of substrate acetol and Fig. 6A represents the dependence on initial concentration of hydrogen peroxide at
fixed (6.0 M) concentration of water. The reaction rate is not changed when total concentration of water
grows from 6.0 to 7.4 M (Fig. 6B). Similarly, addition of acetic acid does not affect the reaction rate (Fig.
6C).
The activation parameters were determined from the results obtained in the study of variation of
the temperature of the system using the Arrhenius equation. The Arrhenius plot is presented in Fig. 7.
2.3. Kinetic analysis of acetic acid formation from acetol
It is known [1a,d] that the limiting stage of the catalytic cycle which generates active oxidizing
species in the H2O2 decomposition on iron ions is the following transformation:
Fe3+ + H2O2 → Fe2+ + HOO• + H+
The activation energy of this process (Ea) in aqueous solution is 32 kcal mol‒1. If we assume that the
acetol oxidation reaction induced by the catalytic decomposition of H2O2 on iron ions is ion-radical chain
process the activation energy of this step should be more than a half of the Ea value for the generation of
active species (> 16 kcal mol‒1). Indeed, it is known that for chain reactions in solutions a quadratic chain
termination is typical. Since experimentally found value for acetol Ea = 8.8 kcal mol‒1 (see Fig. 7) is
sufficiently lower we can conclude that the ion-radical chain process is impossible in our case. This
conclusion is also in agreement with the reaction order for the reaction which is higher than first order
relative [FeCl3] in the region of low catalyst concentration (see Fig. 4). In the frames of ion-radical chain
mechanism order cannot be so high relative [FeCl3] because if iron ion does not take part in the
propagation stage the order should equal 0.5 and if ions of iron do take part in the propagation step the
9

order can be equal to 1. Thus all kinetic observations do not support the chain mechanism for the acetol
oxidation which is induced by the catalytic decomposition of H2O2 on iron ions.
Experimentally attained yields of products in the acetol oxidation are high (based on one H2O2
molecule yield is ~50%, see Fig. 1). The initial reaction rate linearly depends on acetol concentration in
the whole studied interval of its concentrations (see Fig. 5). In addition, the activation energy of the
oxidizing species generation in the course of H2O2 decomposition is much higher than observed Ea of the
acetol oxidation (32 and 8.8 kcal mol‒1, respectively). These results allow us to exclude the mechanism of
induced acetol oxidation involving the acceptance oxidizing species generated by the Fe/H2O2 system. In
the case if such a path would be realized, the linearity of the rate dependence on the concentration of
acetol indicates that, along with the acceptance of oxidative particles by acetol there is another effective
way. The rate of this second route of oxidizing species consumption should be much higher in
comparison with the rate of the step with acceptance of oxidizing species. It follows from this conclusion
that the rate of H2O2 consumption in the acetol oxidation should be much lower than the total rate of H2O2
consumption in the oxidizing species generation. It means that yields of products in non-chain acetol
oxidation should be noticeably lower than 50%.
As we noted previously, observed dependence of the reaction rate on [FeCl3] (Fig. 4) indicates
that at low concentration of FeCl3 the oxidation rate quadtratically depends on [FeCl3] and at high catalyst
concentration W0 does not depend on its concentration. Independence of W0 on catalyst concentration is
apparently due to attaining the solubility limit of the catalyst in the reaction mixture. Under conditions of
experiments shown in Fig. 4 this limit is close to 6 × 10‒4 M. This result and data presented in Figs. 5 and
6A allow us to assume that in the limiting step of the acetol oxidation a peroxo complex FeCl3•H2O2 (see
Fig. 6A) interacts with FeCl3•CH3COCH2OH. Linear mode of the dependence of W0 on acetol
concentration (Fig. 5) indicates that the equilibrium constant of formation a complex between iron
catalyst and acetol is not high. In accord with this observation we can write:
FeCl3 + H2O2
FeCl3•H2O2
(1)
10

FeCl3 + CH3COCH2OH
FeCl3•CH3COCH2OH
(2)
FeCl3•H2O2 + FeCl3•CH3COCH2OH → products
(i)
Here i is a limiting stage in the chain of acetol transformation into the products of the reaction. Taking
into account that the equilibrium constant K2 of equilibrium (2) is small and consequently
K2[CH3COCH2OH]0 << 1, and also the equilibrium (1) with K1 we will obtain the equation of the material
balance:
[FeCl3]0 = [FeCl3] + [FeCl3•H2O2]
(3)
where [FeCl3]0 is the analytical concentration of iron chloride introduced into the reaction mixture.
Conditions of equilibrium of peroxo complex concentration and the complex with acetol are given by the
equations (4) and (5), respectively.
K1[FeCl3][H2O2] = [FeCl3•H2O2]
(4)
(5)
K2[FeCl3][CH3COCH2OH] = [FeCl3•CH3COCH2OH]
It follows from eqs. (3)‒(5) that
K1[FeCl3]0[H2O2]
.
[FeCl3 H2O2] =
(6)
(7)
1 + K1[H2O2]
[FeCl3]0
1 + K1[H2O2]
[FeCl3] =
K2[FeCl3]0[CH3COCH2OH]
1 + K1[H2O2]
.
[FeCl3 CH3COCH2OH] =
(8)
Thus, the equation for the reaction rate which coincides with the equation for the limiting stage rate will
be
2
K1K2[FeCl3]0 [H2O2][CH3COCH2OH]
(9)
W = ki
(1 + K1[H2O2])2
Assuming that value K1[H2O2]0 is small in comparison with unity we can simplify equation (9):
2
kiK1K2[FeCl3]0 [H2O2][CH3COCH2OH]
(10)
W =
1 + 2K1[H2O2]
Equation (10) is in accordance with our experimental data. Indeed, first the reaction rate at concentration
[FeCl3]0 < 6 × 10‒4 M is proportional to square of FeCl3 concentration (Fig. 8).
11

Second, the mode of experimental dependence of W on [H2O2] (Fig. 6A) corresponds to equation
(10) because the dependence of [H2O2]/W on [H2O2] shown in Fig. 9 is linear:
[H2O2]
1
2
=
(1 + 2K1[H2O2])
(11)
W
kiK1K2[FeCl3]0 [CH3COCH2OH]
The slope of tangent of dependence (11) to the segment cut on the y-axis gives the ratio which
allows us for the conditions of Fig. 6A to measure the effective equilibrium constant K1 = 0.4 M‒1. This
excuses disregard of the quadratic term relative [H2O2] in the denominator of equation (9) in its
transformation into (10). The value kiK2 is determined from the value of segment cut on the y-axis in Fig.
9 for conditions mentioned for Fig. 6A. This combination is equal to 6 × 104 M‒2 min‒1. In the frames of
the model under discussion the linear dependence shown in Fig. 5 means that K2 << 1 M‒1. In this case
the constant ki can be estimated as a value greatly exceeding 6 × 104 M‒1 min‒1.
3.4. Formation of CO2
As acetol contains three carbon atoms and acetic acid is a compound with only two carbons we
can expect the formation in the reaction one-carbon products including CO2. The determination of the
produced CO2 was carried out using the methodology described below. The CO2 produced in the reaction
was determined by the GC-MS analysis of samples from headspace (HS) of the reaction vessels using
argon from air as internal standard. Therefore the GC-MS was programmed to monitor the molecular ions
m/z 40 and 44 (Ar and CO2, respectively). Retention times of the gases are too close. Thus we obtained
the spectrum of average masses of the signal generated by the gases in the chromatogram and calculated
the ratio of signal intensity of the m/z 44 and the intensity of the signal m/z 40. The determined ratio
(Im/Z=44/Im/Z=40) was then compared with the values obtained from a previously prepared calibration curve.
The calibration curve was obtained by injecting known amounts of CO2 in a standard reactor under
typical reaction conditions (acetol, 0.5 M; FeCl3, 1 × 10‒3 M; acetonitrile up to total volume 5 mL;
stirring at 60 °C) without addition of H2O2. The typical curve of CO2 accumulation average from 3
experiments is shown in Fig. 10.
12

3.5. Experiments with 16O2 and 18O2
In order to determine the participation of molecular oxygen in the acetol oxidation the amount of
oxygen relative to argon was monitored by GC-MS. The used methodology was similar to that employed
in the quantification of CO2: monitoring the signal attributed to 16O2 (Im/z=32) and argon (Im/Z=40) (as
internal standard) and using the intensity ratio Im/z=32/Im/Z=40) we evaluated the profile of changes in
concentration of O2. The result is shown in Fig. 11. The profile shown in the graph matches the expected
behavior for a reaction that consumes oxygen. There is an increase in the amount of oxygen due to some
decomposition of H2O2 to O2 and H2O, followed by a decrease due to consumption of O2 by the reaction
mixture during 2.5 h and then attaining a plateau.
The O2 consumption can be seen more clearly if 18O2 has been introduced into the head space of
the reaction vessel as shown in Fig. 12. Kinetic curves in this Figure demonstrates that 18O2 is consumed
starting from the beginning of the reaction, and both 16O2 and 18O2 take part in the reaction which
deceases after 2 h.
3.6. On the mechanism of oxidation
We can assume that in the rate limiting stage (i) acetol is transformed into the products; one of
them is the radical MeCOCH•(OH) shown in Scheme 5. This radical rapidly reacts with a O2 molecule to
afford performic acid and acetyl radical [7,10,11]. As the acetyl radical may react with O2 to produce
acetylperoxyl radical which in turn can form acetic acid [12], this scheme explains also the formation of
labeled acetic acid in experiments with 18O2. Mass spectra of the products of the reactions with acetol and
methylglyoxal formed after 4 h using 18O2 added to the headspace of the reaction vessel were obtained.
Small amounts of acetic and formic acids containing 18O (m/z 62 and m/z 48, respectively) were detected
when acetol was used as the substrate. The ratio of the intensities of signals of labeled acetic acid (m/z
62) and 16O-acetic acid (m/z 60) is 0.15, and the ratio of the intensities of signals from labeled formic acid
(m/z 48) and 16O-formic acid (m/z 46) is 0.026. Thus, acetic acid incorporates oxygen from atmosphere
much more intensively than formic acid. The spectrum of the formic acid indicates that only the hydroxyl
13

oxygen may be originated from air since the signal at m/z 29 which comes from the loss of a hydroxyl
group is not accompanied by a signal with m/z 31 corresponding to the 18O-labeled fragment. Such type
of analysis can not be implied to acetic acid because the fragment corresponding to the loss of a hydroxyl
group has m/z 43 and the corresponding 18O-labeled fragment with m/z 45 coincides with the fragment
formed via the loss of a methyl which also has m/z 45.
As acetol can be oxidized to methylglyoxal, MeCOCHO, it is important to study the oxidation of
this substrate to acetic acid by the FeCl3/H2O2 system. Figure 13 shows kinetics of the methylglyoxal
oxidation. When methylglyoxal was oxidised in the atmosphere of labeled dioxygen only 18O-labeled
acetic acid was found. It is interesting that when a relatively low concentration of methylglyoxal was used
only acetic acid (0.15 M) was produced after 4 h. The oxidation of 0.5 M of methylglyoxal afforded
acetic acid (0.23) and formic acid (0.35). It is reasonable to assume that methylglyoxal is formed in the
oxidation of acetol to acetic and formic acids.
4. Conclusions
Simple salt FeCl3 may be used as a catalyst in the efficient oxidation of acetol using hydrogen
peroxide as oxidant and acetonitrile as solvent. Acetic acid and formic acid are the main products. It was
also found that some amount of CO2 is formed. The use of water as a green solvent allowed us to enhance
concentration of produced acetic acid. In the course of the oxidation reaction consumption of atmospheric
O2 occurs from the beginning of the reaction and its participation in the reaction includes its incorporation
into acetic and formic acids.
Acknowledgements
The authors thank the “Science without Borders Program, Brazil–Russia”, CAPES (grant A017-2013)
and the Russian Foundation for Basic Research (grant 16-03-00254) for support. D.M. is grateful to
CNPq (grants 303828/2010-2, 311585/2013-2 and 472130/2012-9) for support. G.B.S. expresses his
gratitude to the CAPES and the Center of Natural and Human Sciences, Federal University of ABC
14

(UFABC), Santo André, São Paulo, for making it possible for him to stay at the UFABC, as an invited
Professor and to perform a part of the present work.
15

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17

Figure Captions
0.08
1
0.04
0
8
0
16
0.4
Time (min)
2
1
0.3
0.2
0.1
1a
2a
3a
3
0
0
4
1
2
3
5
6
Time (h)
Fig. 1. Accumulation of acetic acid (curve 1), formic acid (curve 2) and CO2 (curve 3) in the acetol
oxidation. The inset shows the same kinetics in another time scale. Conditions. The reactions were
performed in a glass reactor 20 mL at 60 °C and atmospheric pressure, with the reagents in the following
concentrations: FeCl3, 1 × 10‒3 M; acetol, 0.5 M; H2O2, 0.5 M; acetonitrile, up to 5 mL.
18

Fig. 2: Acetic acid concentration versus time for the catalyzed oxidation of acetol. Conditions. Acetol, 0.5
M; FeCl3; 1 × 10‒4 (curve 1) and 1 × 10‒3 (curve 2) M; H2O2, 0.5 M; H2O, 6.0 M; acetonitrile up to 5 mL;
60 °C.
19

Fig. 3. Acetic acid concentration versus time for the FeCl3-catalyzed oxidation of acetol in water or
acetonitrile. Conditions: acetol, 0.5 M; FeCl3, 1 × 10‒3 M; H2O2, 0.5 M; solvent up to 5 mL; 60 °C.
20

Fig. 4. Dependence of the initial rate of acetic acid accumulation W0 on concentration of FeCl3 for the
oxidation of acetol to acetic acid catalyzed by FeCl3. Conditions: acetol, 0.5 M; H2O2, 0.5 M; acetonitrile
up to 5 mL;. 60 °C.
21

Fig. 5. Dependence of the initial rate of acetic acid accumulation on initial concentration of acetol in the
oxidation of acetol to acetic acid catalyzed by FeCl3. Conditions: FeCl3, 1 × 10‒3 M; H2O2, 0.5 M
(containing 6.0 M H2O); acetonitrile up to 5 mL; 60 °C.
22

Fig. 6. Graph A: dependence of the initial rate of acetic acid accumulation on initial concentration of
hydrogen peroxide for the oxidation of acetol to acetic acid catalyzed by FeCl3. Conditions: FeCl3, 1 ×
10‒3 M; acetol, 0.5 M; acetonitrile up to 5 mL; 60 °C. Graph B: analogous dependence on total
concentration of water (at [H2O2]0 = 0.5 M). Graph C: dependence of W0 on the concentration of initially
added acetic acid.
23

Fig. 7. Arrhenius plot of lnW0 versus 1/T. Conditions. Temperature was varied between 40 °C and 70 °C
(313 K and 343 K); FeCl3, 1 × 10‒3 M; acetol, 0.5 M; H2O2, 0.5 M H2O, 6.0 M; acetonitrile up to 5 mL.
24

6
5
4
102 W (M1/2 min1/2
)
3
2
1
0
1
0
2
3
4
5
6
104[FeCl3]0 (M)
Fig. 8. Dependence of the initial rate of acetic acid accumulation W0 on concentration of FeCl3 for the
oxidation of acetol to acetic acid catalyzed by FeCl3. Conditions: acetol, 0.5 M; H2O2, 0.5 M; acetonitrile
up to 5 mL;. 60 °C.
25

[H2O2]0
(min)
150
W
100
50
0
0.2
0
0.4
0.6 0.8 1.0
[H2O2]0 (M)
1.2
Fig. 9. Dependence of the value [H2O2]0/W on concentration of FeCl3 for the oxidation of acetol to acetic
acid catalyzed by FeCl3. Conditions: FeCl3, 1 × 10‒3 M; acetol, 0.5 M; acetonitrile up to 5 mL; 60 °C.
26

Fig. 10. Concentration of CO2 produced in the oxidation of acetol to acetic acid catalyzed by FeCl3 versus
time. Conditions: FeCl3, 1 × 10‒3 M; acetol, 0.5 M; acetonitrile up to 5 mL; 60 °C.
27

Fig. 11. Plot of intensity of the 16O2 signal compared to the intensity of the Ar signal (Im/z=32/Im/Z=40
)
versus time in the acetol oxidation to acetic acid catalyzed by FeCl3. Conditions: FeCl3, 1 × 10‒3 M;
acetol, 0.5 M; H2O, 6.0 M; acetonitrile up to 5 mL; 60 °C.
28

Fig. 12. Changes of intensities (I) of the signals 16O2 and 18O2 relative to the signal intensity of argon (Im/Z
= 40) with time in the oxidation of acetol to acetic acid catalyzed by FeCl3. Conditions: FeCl3, 1 × 10‒3
M; acetol, 0.5 M; H2O, 6.0 M; acetonitrile up to 5 mL; 60 °C.
29