Catalytic oxidative cleavage of terminal olefins by chromium(III) stearate

Article abstract of DOI:10.1016/j.molcata.2007.02.007

A new synthetic methodology for the preparation of carbonyl compounds from the oxidative cleavage of terminal olefins has been developed. With the use of TBHP in combination with chromium(III) stearate, selective oxidation of double bonds conjugated with aromatic ring or carbonyl group could be achieved at ambient temperature in moderate to excellent yield. The oxidative cleavage of electron rich α-methylstyrene derivatives proceeded in good to excellent yield whereas lower yields were observed in α-methylstyrene derivatives containing an electron withdrawing group. This developed oxidation reaction was believed to undergo via free radical process and high valent chromium oxo species.

Full text of DOI:10.1016/j.molcata.2007.02.007

Journal of Molecular Catalysis A: Chemical 270 (2007) 289–294
Catalytic oxidative cleavage of terminal olefins by chromium(III) stearate
a
a
b,∗
Suekanya Jarupinthusophon , Uthumporn Thong-In , Warinthorn Chavasiri
a
Program of Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
b
Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
Received 28 July 2006; received in revised form 8 February 2007; accepted 8 February 2007
Available online 16 February 2007
Abstract
A new synthetic methodology for the preparation of carbonyl compounds from the oxidative cleavage of terminal olefins has been developed.
With the use of TBHP in combination with chromium(III) stearate, selective oxidation of double bonds conjugated with aromatic ring or carbonyl
group could be achieved at ambient temperature in moderate to excellent yield. The oxidative cleavage of electron rich ␣-methylstyrene derivatives
proceeded in good to excellent yield whereas lower yields were observed in ␣-methylstyrene derivatives containing an electron withdrawing group.
This developed oxidation reaction was believed to undergo via free radical process and high valent chromium oxo species.
©
2007 Elsevier B.V. All rights reserved.
Keywords: Oxidative cleavage; Terminal olefins; Chromium(III) stearate; Homogeneous catalysis
1
. Introduction
compounds using aqueous H2O2 as an oxidant and 6-molybdo-
-tungstophosphoric acid (PMWA) on either magnesium or
6
The C C double bond cleavage is one of synthetically useful
aluminium or zinc oxide as a catalyst; 1-octene was stoichio-
metrically converted to heptanoic acid [23]. In 2001, Yang
and colleagues utilized RuCl3-oxone-NaHCO3 to oxidize ␣-
methylstyrene to acetophenone in 78% yield. More recently,
RuCl3/NaIO4 was shown to cleave cyclohexene to adipaldehyde
(70%)andcouldoxidize1-dodecenesmoothlytoundecenalwith
95% yield [24].
With the ability of being solubilized in organic media, metal
ester complexes have been extensively investigated to use in
conjunction with oxygen [25]. For ester part in these aforemen-
tioned metal complexes, a cheap fatty acid has been generally
employed. Metal stearates and metal acetates [26,27] have
nonetheless been less used. Additionally, in particular metal tri-
fluoroacetates, metal naphthenates, and metal octanoates [28]
have been rarely utilized.
reactions to degrade large compounds or to introduce oxygen
functionality into molecules [1,2] such as to ketones [3,4], alde-
hydes [5–7] or carboxylic acids [8,9]. Numerous efforts have
been addressed to convert olefins to versatile and valuable raw
materials for other chemical industries, for example, production
of acetophenone and ␣-keto acid [10–12]. Acetophenone is used
in fragrance industries as a perfume head, while ␣-keto acids,
especially those analogues to the naturally occurring amino
acids, are of major importance in intermediary metabolism. In
addition, they have been used in the therapy of certain condi-
tions, e.g., uremia and nitrogen accumulation disorders and have
been reported continually as intermediates in chemical synthe-
ses, in the development of enzyme inhibitors and drugs and as
model substrates of enzymes [13,14].
Many synthetic methodologies for oxidizing double bonds
have been widely reported, including ozonolysis [15,16], oxi-
dation with KMnO4 [17], with OsO4 [18], RuO4 [19,20] and
combination of oxidant and a catalyst [8,21,22]. In 1999,
Brooks and colleagues achieved rapid and complete conver-
sion in the oxidative cleavage of terminal olefins to carbonyl
The most popular reagent for oxidative cleavage of double
bonds was Jones’ reagent which is the combination of CrO3,
H2SO4 and acetone [29]. A major drawback of this reagent was
however poor solubility in organic solvents. In this paper, we aim
to increase the solubility of chromium salts by using different
hydrophobic ligands. Thus, the scope of this work is to develop
of a new synthetic methodology for the preparation of carbonyl
compounds from the oxidative cleavage of terminal olefins by
the use of transition metal stearate complexes.
∗
Corresponding author. Tel.: +66 2 218 7625; fax: +66 2 218 7598.
E-mail address: warintho@yahoo.com (W. Chavasiri).
1
381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.02.007

2
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S. Jarupinthusophon et al. / Journal of Molecular Catalysis A: Chemical 270 (2007) 289–294
2
. Experimental
Table 1
The effect of metal stearate complexes on the oxidative cleavage of 1a
2
.1. General
1
The H NMR spectra were obtained in CDCl3 with Varian
model Mercury 400 spectrometers. The Shimadzu gas chro-
matograph GC-14A (capillary column: DB-WAX, 30 m, i.d.
0
.25 mm) was employed for both qualitative and quantitative
analysis of the target product. All organic substrates were pur-
chased from Fluka.
Entry
Metal stearate
1 recovery (%)
% Yield
Mass
balance
2
3
1
2
3
4
5
6
7
Chromium(III)
Manganese(II)
Iron(III)
Cobalt(II)
Nickel(II)
9
40
37
9
19
31
46
85
57
59
71
66
63
42
2
2
4
18
15
3
96
99
100
98
100
97
98
2
.2. Preparation of metal stearate complexes [30]
Stearic acid (22 mmol) was dissolved in 1 M NaOH solution
◦
at 80 C. After the mixture was heated and transmuted homoge-
neously, a solution of metal (III) chloride (7.3 mmol) dissolved
in distilled water 10 mL was added dropwise. The mixture was
continuedheatingatabout80 Cforabout30 min, theprecipitate
was collected and dried in vacuo.
Copper(II)
Zinc(III)
10
◦
a
Reactions conditions: 1 (5 mmol), metal stearate (0.2 mmol), isooctane
◦
(5 mL) and TBHP (9 mmol) at 70 C for 24 h.
2
2
.3. Syntheses of starting materials
catalyst affording the best yield of acetophenone (2) (85%, entry
1). In all cases, the only by-product was the corresponding epox-
.3.1. Preparation of terminal olefins [31]
Into a 250 mL three-necked round bottom flask was placed
ide (3) and some unreacted ␣-methylstyrene (1) was observed.
A series of controlled experiments was conducted and
observed that in the absence of chromium(III) stearate, the oxi-
dation with only TBHP gave a small amount of 2. Addition of
4 mol% (0.2 mmol) of chromium(III) stearate raised the yield to
85%. This observation strongly supported the concept of metal
catalysis in the oxidation reaction as well as TBHP was no doubt
essential for the reaction as the oxidant.
methyltriphenylphosphonium iodide (4.85 g, 12 mmol) sus-
pended in 25 mL dry THF. The suspension was cooled to 0 C
with an ice bath. The reaction mixture was charged slowly with
n-BuLi (1.6 M in hexanes, 7.5 mL, 12.1 mmol) to give an orange
solution. After an hour, the solution of a carbonyl compound
◦
(
10 mmol) in 15 mL dry THF was added slowly to the flask from
the additional funnel, the ice bath was removed and the flask was
gradually warmed to room temperature. After the reaction mix-
ture was stirred overnight, TLC showed complete consumption
of the starting material. HCl 1N was added to the reaction mix-
ture, and the aqueous layer (pH 5) was extracted with EtOAc,
washed with brine, dried, filtered and concentrated in vacuo. The
crude residue was purified by silica gel column and analyzed by
At low catalyst loading (0.4–1 mol%), though the reaction
gave a fair yield of 2 (69% and 61%, respectively), incom-
plete conversion was observed along with the detection of a
small amount of 3. The optimum catalyst loading was 4 mol%.
Accounting on turnover number (TON), using the catalyst
0.01 mmol provided interesting result to gain over 200 TON.
From all above results, it was observed that not only type of
catalyst but also amount of catalyst affected the production of
the desired product.
1
H NMR.
2
.4. The general procedure for the oxidative cleavage of
The effect of solvent on the oxidative cleavage of 1 was also
carefully scrutinized as accumulated in Table 2. Isooctane and
acetonitrile (entries 1 and 3) were found to be ideal solvents.
Reactions in acetone, acetonitrile/pyridine 3:1, butanol and 1,2-
DCEallgave2ingoodyield(entries8, 10, 14and15). Itwasvery
interesting to note that the reaction carried out in pyridine/acetic
acid 3:1 resulted in almost quantitative amount of product with
excellent selectivity. However, the workup of reaction was quite
complicated and highly exothermic. Thus, isooctane is the sol-
vent of choice because of the availability, cheapness and being
able to solubilize chromium(III) stearate catalyst.
terminal olefins
A solution of substrate (5 mmol) in isooctane (5 mL) con-
taining chromium(III) stearate (0.2 mmol) in a round bottom
flask and 70% TBHP (9 mmol) was added. The mixture was
◦
stirred at 70 C for 24 h. After the reaction finished, 1 mL of
the reaction mixture was taken and extracted with Et2O. The
combined extracts were washed with 25% H2SO4 and saturated
NaHCO3, respectively. The organic layer was dried over anhy-
drous Na2SO4 and analyzed by GC with the addition of an exact
amount of appropriate internal standard.
3.1. Kinetic study on the oxidative cleavage of 1 catalyzed
3
. Results and discussion
by chromium(III) stearate
Table 1 reveals the oxidative cleavage of ␣-methylstyrene
1) performed in isooctane in the presence of different metal
stearates and TBHP. Chromium(III) stearate emerged as a viable
Fig. 1 exhibits the kinetic study on the oxidative cleavage of
1 catalyzed by chromium(III) stearate. Fifty percentage conver-
sion was observed at 3 h and the reaction reached completion
(

S. Jarupinthusophon et al. / Journal of Molecular Catalysis A: Chemical 270 (2007) 289–294
291
Table 2
The effect of solvents on the oxidative cleavage of 1 catalyzed by chromium(III) stearatea
Entry
Solvents
1 recovery (%)
% Yield
Mass balance
2
3
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
Isooctane
Dichloromethane
CAN
Chloroform
Methanol
Ethanol
9
85
31
80
17
7
10
34
59
12
61
97
31
3
2
4
6
96
102
104
98
97
93
85
73
109
74
97
103
98
98
97
99
b
67
18
81
90
83
51
12
97
13
Trace
68
95
26
16
99
Trace
Trace
Trace
Trace
2
Trace
Trace
Trace
4
0
2
4
0
Pyridine
b
Acetone
CCl4
1
1
1
1
1
1
1
Acetonitrile:pyridine (3:1)
Pyridine:acetic acid (3:1)
DMSO
DMF
n-Butanol
1,2-DCE
THF
70
77
Trace
a
◦
Reactions conditions: 1 (5 mmol), chromium(III) stearate (0.2 mmol), solvent (5 mL) and TBHP (9 mmol) at 70 C for 24 h.
Refluxing temperature of solvent.
b
after 24 h. If the reaction was left on for 48 h, the yield deterio-
rated.
trolled by appropriate reaction time and amount of TBHP for
the production of either 5 or 6.
3
.2. Oxidative cleavage of selected terminal olefins
3.2.2. Oxidative cleavage of α-methylstyrene derivatives
The oxidative cleavage of various ␣-methylstyrene deriva-
tives was performed to observe the structure–reactivity
relationship of this developed reaction. The outcomes are tabu-
lated in Table 4.
catalyzed by chromium(III) stearate
3
.2.1. Oxidative cleavage of 1,3-diisopropenylbenzene (4)
,3-Diisopropenylbenzene (4) was selected as another chem-
1
ical model. The results are tabulated in Table 3.
Apparently, the oxidative cleavage of monosubstituted ␣-
methylstyrene gave a good mass balance. ␣-Methylstyrene
containing electron donating groups cleanly produced good
When 4 was treated with 0.1 mmol chromium(III) stearate
◦
and 9 mmol TBHP in isooctane 5 mL at 70 C for 24 h, 5 was
formed in 71% yield. In entries 1–4, the effect of reaction time
was explored in order to improve the yield. It was found that
the longer the reaction time, the more 6 was produced. This
was indicative of the further oxidation of 5 took place. On the
other hand, 6 could be obtained as a major product when the
reaction was carried out with 0.25 mmol chromium(III) stearate
Table 3
The oxidative cleavage of 4a
◦
and 18 mmol TBHP in isooctane 5 mL at 70 C for 48 h (entry
1
1). Therefore, the oxidative cleavage conditions could be con-
Entry
Chromium(III)
stearate (mmol)
Time (h)
% Yield
Mass
balance
5
6
1
2
3
4
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.2
0.2
0.25
12
18
24
48
24
12
18
24
24
48
48
21
39
71
60
47
32
44
46
41
23
13
Trace
Trace
12
19
35
Trace
16
29
48
57
97
95
101
103
96
100
101
99
b
5
6
7
8
b
9
0
1
97
95
99
b
1
1
b
62
a
Reactions conditions:
4
substrate (5 mmol), chromium(III) stearate
◦
(
0.1–0.25 mmol), isooctane (5 mL) and TBHP (9 mmol) at 70 C for 12–48 h.
b
TBHP (18 mmol).
Fig. 1. The kinetic study of the oxidative cleavage of 1.

2
92
S. Jarupinthusophon et al. / Journal of Molecular Catalysis A: Chemical 270 (2007) 289–294
Table 4
The oxidative cleavage of ␣-methylstyrene derivativesa
Instead, it should be from the presence of a new benzylic carbon
which could be readily oxidized, giving out other products from
a competitive reaction.
To investigate the effect of electron-withdrawing sub-
stituents, o-, m-, and p-NO2 substituted ␣-methylstyrenes were
separately subjected to the oxidative cleavage. The lowest yield
in this series (32%) was observed for o-NO2. The p-NO2 substi-
tuted substrate gave a slightly higher yield (41%). This observed
difference may be the result of the ortho electronic effect.
Oxidative cleavage of m-NO2-␣-methylstyrene gave the desired
product in 46% yield. The m-substituent has obviously less deac-
tivating effect than o- and p-ones, probably derived from only
inductive effect.
3.2.3. Oxidative cleavage of other selected terminal olefins
Entry
Substrate
Acetophenone
Substrate
Mass
derivative (% yield)
recovery (%)
balance
Toshedsomelightontheapplicabilityofthisreaction, further
study on the oxidative cleavage reaction of other terminal olefins
were examined. The results are shown in Table 5.
1
2
3
4
5
6
7
8
9
1
7
8
2 (85)
15 (89)
16 (85)
17 (81)
18 (67)
19 (65)
20 (32)
21 (46)
22 (41)
9
9
96
98
96
92
97
101
99
96
11
11
30
36
67
50
57
The oxidative cleavage of styrene 23 gave benzaldehyde
9
24 in 69% yield. It is slightly lower than the reaction of ␣-
10
11
12
13
14
methylstyrene of which methyl group helped stabilization of the
intermediate. The reaction of 1,1-diphenylethylene 25 gave the
benzophenone 26 in good isolated yield (76%). For the oxidative
cleavage of 1,1-diphenylethylene 25 a drop in the product yield
is probably the result from steric congestion in the cyclization
98
a
Reactions conditions: substrate (5 mmol), chromium(III) stearate
V
◦
of Cr O species into the proposed intermediate. The reaction
(
0.2 mmol), isooctane (5 mL) and TBHP (9 mmol) at 70 C for 24 h.
of MMA 27 proceeded to give methyl pyruvate 28 in 55% yield.
Surprisingly, diethyl itaconate 29 did not give the correspond-
ing oxidative cleavage product, diethyl oxalacetate 30 and the
starting material 29 was recovered quantitatively (entry 4). Cam-
phene 31 and 1-dodecene 32 were also unreactive towards this
oxidation. The oxidation of 4-vinyl-1-cyclohexene 33 resulted
in an unexpected allylic oxidation to give a diketone product 34
in 17% yield. This obtained product 34 could be gained from
the direct isolation from the reaction mixture.
yield of the corresponding acetophenone slightly increasing
with the electron donating ability of the substituent (81% for p-
Cl < 85% for p-Br < 89% for p-OMe). These derivatives showed
similar reactivity to the unsubstituted ␣-methylstyrene.
For alkyl substituted ␣-methylstyrenes, the oxidative cleav-
age surprisingly gave a somewhat lower yield (65% for p-Me and
6
7% for p-Et). This lower product yield was not the direct result
of the alkyl group on the electronic property of ␣-methylstyrene.
Table 5
The oxidative cleavage of selected terminal olefinsa
Entry
Substrate
Product
% Yield
Substrate recovery (%)
Mass balance
1
2
3
4
5
6
7
23
25
27
29
31
32
33
24
26
28
69
76
55
–
–
–
28
24
14
100
100
100
43
97
100
69
100
100
100
60
No reaction
No reaction
No reaction
34
17
a
◦
Reactions conditions: substrate (5 mmol), chromium(III) stearate (0.2 mmol), isooctane (5 mL) and TBHP (9 mmol) at 70 C for 24 h.

S. Jarupinthusophon et al. / Journal of Molecular Catalysis A: Chemical 270 (2007) 289–294
293
Scheme 1. Proposed mechanism for the oxidative cleavage of terminal olefins catalyzed by chromium(III) stearate.
Therefore, based upon the results attained this developed
oxidative cleavage was selective for conjugated double bonds
and could not use with the substrates containing a nonconjugated
methyl or methylene protons, respectively.
the ␣-methylstyrene derivatives. Compounds bearing electron
donating substituents on the aromatic ring are more reactive
towards oxidative cleavage than those containing electron with-
drawing substituents.
3
.3. Proposed mechanism
Acknowledgement
The mechanism for the oxidative cleavage of activated double
bonds by TBHP catalyzed by Cr(III) stearate is proposed in
Scheme 1.
This work was supported in part by the Graduate School,
Chulalongkorn University.
The chromium(III) complex was transformed to the corre-
sponding high valent (formally) CrV O species by interaction
with TBHP. In similar fashion to Barton’s theory for the for-
mation of high valent iron oxo species [32], the addition of the
Cr O species to the double bond followed by cleavage to the
ketone and a methylene carbene. There are experiments which
confirmed the detection of formaldehyde [32].
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