A facile synthesis of vicinal cis-diols from olefins catalyzed by in situ generated MnxOy nanoaggregates

Article abstract of DOI:10.1039/c5ra01646k

A novel protocol for the practical and green synthesis of vicinal cis-diols from 10.0 mmol olefins by using 5.0 mmol KMnO₄ as oxidant and 30.0 mmol H₂O₂ as co-oxidant is reported. The presented procedure is easy to carry out and enables the direct transformation of linear and cyclic alkenes to the corresponding vicinal cis-diols. The synthesis of vicinal cis-diols by dihydroxylation of olefins with a KMnO₄/H₂O₂ system was catalyzed by in situ generated Mn_xO_y nanoaggregates. The use of H₂O₂ as a co-oxidant is the key for the protocol to synthesize vicinal cis-diols in high yields, because it assists the oxidation of Mn_xO_y nanoaggregates, which have an active role in the oxidation reaction medium.

Full text of DOI:10.1039/c5ra01646k

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A facile synthesis of vicinal cis-diols from olefins
catalyzed by in situ generated MnxOy
Cite this: RSC Adv., 2015, 5, 20751
nanoaggregates†‡
a
Digdem Dalmizrak,a Haydar Goksuab and Mehmet Serdar Gultekin
Received 27th January 2015
Accepted 9th February 2015
*
˘
¨
¨
DOI: 10.1039/c5ra01646k
www.rsc.org/advances
A novel protocol for the practical and green synthesis of vicinal cis- NaIO4, (iii) excess KMnO4, and (iv) organometallic complexes,
diols from 10.0 mmol olefins by using 5.0 mmol KMnO4 as oxidant and have been used in the synthesis of vicinal cis-diols.4 Among
30.0 mmol H2O2 as co-oxidant is reported. The presented procedure these protocols, OsO4/co-oxidant catalyzed olen oxidation is
is easy to carry out and enables the direct transformation of linear and one of the most powerful routes.
cyclic alkenes to the corresponding vicinal cis-diols. The synthesis of
In spite of the widespread application of this type of reaction
vicinal cis-diols by dihydroxylation of olefins with a KMnO4/H2O2 in synthetic organic chemistry, the high cost, volatility and
system was catalyzed by in situ generated MnxOy nanoaggregates. The hazardous toxicity of OsO4, along with the problem of
use of H2O2 as a co-oxidant is the key for the protocol to synthesize contamination, are the main drawbacks for use in industry,
vicinal cis-diols in high yields, because it assists the oxidation of MnxOy when the principles of green chemistry are considered.5 Given
nanoaggregates, which have an active role in the oxidation reaction the economic and environmental restrictions, a protocol that
medium.
uses more environmentally-friendly reactants such as KMnO4,
H2O2 and molecular oxygen in the oxidation of olens is highly
desired.6 KMnO4 has been used as a strong oxidant not only in
medicinal applications,7 but also in several specic organic
reactions, such as cis-dihydroxylation,8 epoxidation,9 and deox-
idisation10 at low temperatures. In the green synthesis of vicinal
cis-diols by dihydroxylation of olens, KMnO4 was generally
used in more than one equivalent, and several undesired by-
products were produced.11 These previous studies revealed
that various manganese oxide derivatives could be formed
during oxidation reactions in the presence of KMnO4 as
oxidant.12
In this study, we report a novel protocol for the practical and
green synthesis of vicinal cis-diols. The dihydroxylation of
olens was performed in the presence of 5.0 mmol of KMnO4
(0.5 eq.) as oxidant and 30.0 mmol of hydrogen peroxide (3.0
eq.) as co-oxidant in a water–acetone mixture (v/v ¼ 1 : 2).
Compared to methods reported in the literature, our protocol
provides shorter reaction times, higher yields and a greener
approach, by using a smaller amount of KMnO4 for the
synthesis of vicinal cis-diols.12,13 Various cyclic and linear olens
were oxidized using our new protocol. Besides the high-yield
synthesis of vicinal cis-diols, various manganese oxide deriva-
tives were formed in situ during the oxidation reaction, among
which Mn3O4 nanoaggregates were determined to be the main
component. The Mn3O4 nanoaggregates were characterized
using several advanced analytical techniques (TEM, SEM, XRD,
XPS, EDX, BET and BJT). The results revealed that the use of
Polyhydroxyl alcohols are industrially important compounds, as
some of their derivatives are used in the production of several
natural products and drugs.1 The cyclitols, especially molecules
bearing three or more hydroxyl groups, constitute an important
class of compounds in synthetic organic chemistry. Vicinal cis-
diols are the most important functional group in cyclitols, as
they are an important component of many drugs and show
signicant biological activities.1 Besides their biological activi-
ties, they can also be used as solvents in the cleaning, cosmetic
and pharmaceutical industries.2 Therefore, studies on the
practical and green synthesis of vicinal cis-diols have gained
great importance. Although various methods have been devel-
oped for the synthesis of vicinal cis-diols, the most convenient
method is the oxidation of olens in the presence of a suitable
oxidant.3 Oxidation systems including (i) stoichiometric OsO4,
(ii) a metal oxide and a co-oxidant such as OsO4/NMO or RuCl3/
a
¨
Department of Chemistry, Faculty of Science, Ataturk University, 25240 Erzurum,
Turkey. E-mail: gultekin@atauni.edu.tr; digdem.dalmizrak@ogr.atauni.edu.tr; Tel:
+90 422 2314428
bKaynasli Vocational College, Duzce University, 81900 Duzce, Turkey. E-mail:
adar_gok@hotmail.com
¨
¨
† Dedicated to Prof. Dr Metin Balci in recognition of his contribution to organic
chemistry, on the occasion of his retirement.
‡ Electronic supplementary information (ESI) available: General procedure for
synthesis of vicinal cis-diols. See DOI: 10.1039/c5ra01646k
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Table 1 Vicinal cis-dihydroxylation of various olefins (10.0 mmol) by Table 1 (Contd.)
5.0 mmol KMnO4 in the presence of 30.0 mmol H2O2 as co-oxidanta
Isolated yields (%),
2 h
Isolated yields (%),
2 h
Entry Olen
Vicinal cis-diol
RT
0
ꢀC 0 ꢀC, N2
Entry Olen
Vicinal cis-diol
RT
51
50
0
ꢀC 0 ꢀC, N2
17
52
63
73
70
82
1
2
77
78
75
82
95
90
18
19
62
3
4
5
6
67
56
33
58
65
43
73
52
85
73
73
47
65
79
60
72
20
a
Reaction conditions: all dihydroxylation reactions were performed in
aqueous acetone (20.0 mL, water–acetone ¼ 1 : 2 v/v) using 5.0 mmol
KMnO4, 10.0 mmol olen, and 30.0 mmol H2O2.
H2O2 as a co-oxidant is the key for the protocol to synthesize
vicinal cis-diols in high yields, because it assists the oxidation of
Mn3O4 nanoaggregates, which have an active role in the
oxidation reaction medium. We thought that the oxidation
reaction continues because the transformation of manganese
oxide derivatives into manganese dioxide is delayed in the
hydrogen peroxide reaction medium.
7
58
65
72
8
62
31
43
75
42
52
83
65
75
9
The amount of H2O2 in the oxidation reaction was optimized
by performing dihydroxylation reactions using different amounts
of H2O2 with 5.0 mmol KMnO4 in a water–acetone (v/v ¼ 1 : 2)
mixture (see methods and Table S1 in the ESI‡). Acetone and
water are especially applicable for these oxidation reactions.
Acetone is immiscible with water and serves as an important
solvent, so an acetone–water solvent mixture is a useful solvent
for the KMnO4 oxidation reaction, and tap water is used in our
protocol for practical purposes. Under the optimized reaction
conditions, maximum yields were obtained using 10.0 mmol of
olen, 5.0 mmol of KMnO4 and 30.0 mmol of H2O2 in aqueous
10
11
41
50
63
12
13
47
49
58
60
62
66
ꢀ
acetone (H2O–acetone, v/v ¼ 1 : 2) at 0 C and under a nitrogen
atmosphere (Table 1, entries 1–20). Additionally, in our protocol,
hydrogen peroxide is the driving force for the dihydroxylation of
olens, and should be used carefully in this reaction medium. It
is important to note that the nitrogen atmosphere and low
14
45
54
60
15
16
60
50
66
57
76
68
ꢀ
temperature (0 C) conditions greatly inuence the yield of the
dihydroxylation reaction. The results of this study show that the
presence of O2 is closely related to the yields of the dihydrox-
ylation reaction, as can be seen from Table 1.
Taking these results into account, it might be assumed that
several manganese oxide derivatives are formed in situ during
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the oxidation reaction and catalyze the oxidation of olens. To
The porous structure and surface area of the material were
elucidate this phenomenon, the dark brown/blackish solid further analyzed by BET-surface area measurement and BJT
material was separated from the reaction medium, washed and adsorption analyses. The BET analysis conrmed that the
dried under vacuum, and then characterized by TEM (trans- recovered material had a surface area of 129.6 ꢂ 0.6 m2 gꢃ1; the
mission electron microscopy), SEM (scanning electron micros- average pore radius of the material was measured as 4.6 nm,
copy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray and the cumulative surface area of the pores was found to be
diffraction), EDX (energy-dispersive X-ray spectroscopy), BET 117.4 m2 gꢃ1 by BJT adsorption analysis (see FS-1 in ESI‡). The
(Brunauer Emmett Teller) and BJT (bipolar junction transistor) elemental composition of the MnxOy nanoaggregates was
adsorption analyses. Fig. 1A shows a representative TEM image determined by EDX analysis. EDX spectra showed the presence
of the recovered brown/blackish solid material. The TEM image of manganese as well as oxygen, carbon and potassium atoms.
reveals the formation of nanoaggregates from small spherical (see, FS-2 in ESI‡).
nanoparticles (ꢁ300 nm). The formation of nanoaggregates
Besides the morphology of the material, we studied its XPS
from small nanoparticles can also be seen from a representative spectra to clarify its chemical composition (Fig. 2). The survey
SEM image of the material shown in Fig. 1B. Additionally, the XPS spectrum (Fig. 2A) of the material indicates the presence of
SEM image indicates the porous structure of the material, Mn along with other elements K, Cl and O; the Cl might be due
which is very important for heterogeneous catalysis applica- to the water used in the experiments. Fig. 2B shows the
tions. The Mn3O4 structure can also be identied by the XRD deconvoluted XPS spectra for the Mn2p3/2 and Mn2p1/2 core
pattern of the solid material. Fig. 1C shows representative XRD levels at 641.1 eV and 652.8 eV, respectively. The deconvoluted
spectra for pure Mn3O4 and for the MnxOy nanoaggregates. spectra reveal that the material includes oxidized Mn deriva-
Hence, we concluded that the solid material recovered at the tives and no metallic Mn. The oxide species were found to be
end of the oxidation reaction was formed by the aggregation of mostly Mn3O4 and MnO2, along with the other possible
mostly Mn3O4 nanoparticles, along with other MnxOy deriva- manganese oxide species in small fractions.14 This conclusion
tives. Additionally, Mn3O4 formed in the reaction medium was also supported by the high-resolution XPS spectrum of the
reacted again with H2O2, and the olen was converted to vicinal Mn3s core level (Fig. 2C), in which the distance of 4.8 eV
cis-diol, while some of the Mn3O4 was converted into MnO2, between the two peaks observed for the Mn3s core level indi-
which was observed by a color change from blackish to brown. cates that the material consists mainly of Mn3O4.
Instead of starting with KMnO4, commercial MnO2 (Sigma-
Aldrich code no. 63548), Mn3O4 (Sigma-Aldrich code no.
377473) and the MnxOy nanoaggregates formed in the reaction
medium were tested under the optimized reaction conditions.
In these test reactions, the procedure (0 ꢀC, N2 atm.) was applied
to cylohexene (3), 3-buten-2-one (29) and styrene (33) molecules
in the presence of commercial MnO2, Mn3O4 and in situ
generated MnxOy nanoaggregates. No vicinal cis-diols were
obtained from the reaction of 10.0 mmol olen with 5.0 mmol
MnO2 and 30.0 mmol H2O2, whereas the corresponding vicinal
cis-diols were obtained using Mn3O4. When we used 30.0 mmol
H2O2 in the dihydroxylation reaction together with 5.0 mmol
Mn3O4 and 10.0 mmol olen (3, 29 or 33), the yields of the
corresponding vicinal cis-diols (4, 30 and 34) were low (25, 22
and 20%, respectively). A certain amount of olen was converted
to decomposition products, which were not identied. Because
of the low yields and the decomposition of olens in this test
reaction, we used 10.0 mmol H2O2, 5.0 mmol Mn3O4 and 10.0
mmol olen, and better yields were obtained (about 34% for 4,
30% for 30, and 27% for 34) under the same reaction conditions.
When we used 10.0 mmol olen (3, 29 or 33) with 30.0 mmol
H2O2 and 0.4 g of the dark brown/blackish solid residue material
(MnxOy nanoaggregates) formed in the reaction medium, vicinal
cis-diols (4, 30 and 34) were obtained in yields of about 42% for 4,
40% for 30, and 36% for 34 under the same reaction conditions
(see methods and Table S2 in the ESI‡).
In summary, we can conclude that the MnxOy oxide deriva-
tives, mainly Mn3O4 nanoaggregates, were generated in situ
from KMnO4/H2O2 during the synthesis of vicinal cis-diols from
olens. It is thought that the Mn3O4 formed in the reaction
Fig. 1 (A) TEM image; (B) SEM image; (C) XRD pattern spectrum of the
solid material recovered at the end of the oxidation reaction.
medium has a major role in the further oxidation reaction.
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Fig. 2 XPS spectra of the solid material recovered at the end of the oxidation reaction.
Scheme 1 shows the proposed mechanism for the dihy- entries 1–4 and 18–19) have been demonstrated to be very
droxylation reaction in aqueous acetone. In the rst step of the active, and the respective vicinal cis-diols (2, 4, 6, 8, 36 and 38)
oxidation reaction, olens are oxidized by KMnO4 in aqueous were obtained in high yields (79–95%). On the other hand,
acetone and the expected vicinal cis-diols, along with MnxOy molecules bearing diene groups (9 and 11) were selective for
derivatives, are formed. In the second step, oxygen atoms are mono-dihydroxylation, and the corresponding alkene-diol
transferred from H2O2 to the MnxOy residue having Mn3O4 compounds (10 and 12) were obtained in yields of 60% and
nanoaggregates as a main component.15 Following this, vicinal 72%, respectively. Methyl-, acetoxy- and epoxy-substituted
cis-diols are obtained by ensuring the continuous oxidation of olens (13, 15 and 17) were disposed to dihydroxylation, in
Mn3O4 by H2O2.
which 15 and 17 were converted to stereospecic products (16
Table 1 shows the results of the dihydroxylation of cyclic and and 18) in yields of 83% and 65%, respectively. On the other
linear olens using our novel protocol (see ESI‡ for experi- hand, 4-methyl-1-cyclohexene (13) gave syn and anti-isomer
mental details). Cyclic mono-alkenes (1, 3, 5, 7, 35 and 37, products (ratio syn : anti 45 : 55). Cyclic a,b-unsaturated
carbonyl compounds such as cyclopentenone (19) and cyclo-
hexenone (21) were converted directly to the corresponding
vicinal cis-diols (20 and 22, respectively) in yields of 75% and
63%. Linear olens (Table 1, entries 12–17) were easily trans-
formed to the respective vicinal cis-diols (24–34) in good yields
(60–76%). Norbornene (39) reacted easily and was converted to
the exo-cis-diol 40 in a good yield of 73%. Some of the vicinal cis-
diols were identied by 1H and 13C-NMR spectroscopy by
comparison with the literature data.5
To examine the effect of an inert atmosphere on our
protocol, we performed the dihydroxylation of all olens at 0 ꢀC
under N2 gas. The results revealed that vicinal cis-diols were
obtained in higher yields than when the reactions were carried
out under air. It can be concluded that an inert atmosphere is
more effective for the controlled oxidation of MnxOy derivatives,
especially Mn3O4 nanoaggregates, in the dihydroxylation reac-
tion of olens.
Scheme 1 A proposed mechanism for the dihydroxylation of 10.0
In conclusion, we have developed a novel and facile oxida-
mmol olefins by 5.0 mmol KMnO4/30.0 mmol H2O2 in aqueous
acetone.
tion system for the dihydroxylation of olens to vicinal cis-diols.
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The present KMnO4/H2O2 oxidation system provides many
advantages, such as being eco-friendly,6 using fewer equivalents
of KMnO4, and in situ generation of the catalyst. Moreover, the
reported procedure is easy to carry out and enables the direct
transformation of linear as well as cyclic alkenes to the corre-
sponding vicinal cis-diols. In addition, we believe that this study
will give new insights to materials chemists on the synthesis of
MnxOy nanoaggregates, mainly Mn3O4. Furthermore, the life-
time of the MnxOy by-products obtained from KMnO4 can be
elongated using various oxidants. By delaying the formation of
MnO2 in this way, the functionality of the MnxOy by-product can
be increased.
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Acknowledgements
¨
We thank Assoc. Prof. Dr Onder Metin for his help with the
TEM, SEM, XRD, XPS, EDX, BET and BJT studies and proof-
reading. This work was supported by the Ataturk University
under project no. 2013/82.
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