Hydrogen-peroxide epoxidation of natural olefins catalyzed by a dinuclear manganese complex

Article abstract of DOI:10.1023/A:1020475810141

The complex of Mn(IV) with the macrocyclic N-containing ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (L) [L₂Mn₂O ₃](PF₆)₂ catalyzes epoxidation of (+)-limonene in CH₃CN solution at room temperature. Adding CH₃COOH accelerates the reaction. The products are isomers of limonene epoxide with predominance of that with an epoxified ring double bond. Epoxidation of α- and β-pinene by this system is less effective, apparently due to extensive steric shielding of the double bonds in the pinenes.

Full text of DOI:10.1023/A:1020475810141

Chemistry of Natural Compounds, Vol. 38, No. 3, 2002
HYDROGEN-PEROXIDE EPOXIDATION OF NATURAL OLEFINS
CATALYZED BY A DINUCLEAR MANGANESE COMPLEX
D. Mandelli,1 K. B. Voitiski,1 U. Schuchardt,2
and G. B. Shul′pin3
UDC 547.918
The complex of Mn(IV) with the macrocyclic N-containing ligand 1,4,7-trimethyl-1,4,7-triazacyclononane
(L) [L Mn O ](PF ) catalyzes epoxidation of (+)-limonene in CH CN solution at room temperature. Adding
2
2
3
6 2
3
CH COOH accelerates the reaction. The products are isomers of limonene epoxide with predominance of
3
that with an epoxified ring double bond. Epoxidation of α- and β-pinene by this system is less effective,
apparently due to extensive steric shielding of the double bonds in the pinenes.
Key words: terpenes, limonene, pinene, epoxidation, catalysis, hydrogen peroxide, manganese complexes.
Oxidation, in particular, the epoxidation of terpenes that is observed in many Brazilian tropical and subtropical plants,
is an important process from a practical viewpoint because the products are valuable starting materials for the synthesis of
fragrances and drugs [1]. The dinuclear complex of Mn(IV) with the macrocyclic N-containing ligand 1,4,7-trimethyl-1,4,7-
triazacyclononane (L) [L Mn O ](PF ) (1) catalyzes oxidation of saturated hydrocarbons, secondary alcohols, and sulfides by
2
2
3
6 2
H O in CH CN at room or even reduced temperature [2-7]. An organic acid, in particular, acetic, is mandatory.
2
2
3
α
β
We investigated oxidation by the above system of certain natural terpenes such as (+)-limonene (2) and - and -pinene
(6 and 9, respectively). We have found that the hydrocarbon is practically inactive in the absence of a small quantity of acetic
acid.
Epoxidation of limonene, which contains two different double bonds, gives products of addition to both the internal
ring double bond and the double bond in the side chain (Table 1). The first product dominates. The ratio 3/4 varies from 1.4
(expt. No. 7), to 3.5 (expt. No. 9) depending on the reagent concentrations and the reaction time. The unoptimized maximum
yield of both monoepoxides was almost 50% based on starting limonene. Use of an excess of H O and a short reaction time
2
2
formed in significant quantities the product of double epoxidation at both double bonds (5) (expts. No. 8, 9, and 10). The overall
yield of epoxides was >75% based on starting limonene. Another product of unknown structure (the concentration of which
x
in Table 1 is denoted by [ ]) was formed in several experiments (4, 8, 9, 10). However, the amount of it was much less than
those of the target epoxides (GC).
O
O
+
+
O
O
2
3
4
5
1) Institute of Biology and Chemistry, Catholic University, Campinas, Sao Paolo, 13020 904, Brazil, e-mail:
dalmo.mandelli@uol.com.br; 2) Institute of Chemistry, State University, Campinas, Sao Paolo, 13083 970, Brazil, e-mail:
ulf@iqm.unicamp.br; 3) N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow 119991, fax
(7095) 137 61 30, e-mail: shulpin@chph.ras.ru. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 203-205, May-
June, 2002. Original article submitted May 23, 2002.
0009-3130/02/3803-0243$27.00 ©2002 Plenum Publishing Corporation
243

TABLE 1. Oxidation of (+)-Limonene by H2O2—1—CH3COOH in CH3CN at 25°C
No.
1
[1]
[H2O2]0
t, min
E, %
[3]
[4]
[3]/[4]
[5]
[x]
ES, %
MB, %
5×10-5 0.25 (anhydr. )
15
60
30
30
30
15
60
15
60
15
60
120
15
60
15
15
5
0.007
0.018
0.017
0.024
0.062
0.000
0.003
0.025
0.032
0.002
0.023
0.021
0.066
0.082
0.094
0.083
0.004
0.010
0.013
0.014
0.029
0.000
0.002
0.011
0.014
0.000
0.014
0.015
0.027
0.030
0.027
0.026
1.8
1.8
1.3
1.7
2.1
0.000
0.000
0.000
0.001
0.080
0.000
0.000
0.000
0.005
0.000
0.000
0.000
0.042
0.068
0.034
0.059
0.000
0.000
0.000
0.002
0.010
0.000
0.000
0.001
0.002
0.000
0.000
0.000
0.006
0.010
0.008
0.004
46
75
92
86
77
98
96
99
98
84
11
33
15
36
0
2
3
4
5
5×10-5 1.25 (anhydr.)
25×10-5 0.25 (anhydr.)
25×10-5 1.25 (anhydr.)
5×10-5 0.11 (30% aq)
2
1.5
2.3
2.3
65
87
86
66
91
59
62
75
81
77
99
98
97
100
99
90
71
83
89
82
6
7
5×10-5 0.43 (30% aq)
14
18
1
5×10-5
1.3 (30% aq)
15
14
37
45
48
44
1.6
1.4
2.4
2.7
3.5
3.2
8
20×10-5 1.3 (30% aq)
9
25×10-5 1.25 (30% aq)
25×10-5 1.25 (70% aq)
10
______
Concentrations (M) of reagents and products are given in square brackets. The index 0 denotes starting concentrations. In all
experiments [2]0 0.25 M, [CH3COOH] = 0.25 M, t is the reaction time in min. The yield of isomeric monoepoxides (E, %) is
calculated using E = 100([3] + [4])/[2]0. The selectivity for formation of all epoxides (ES, %) is measured using ES = 100([3]
+ [4] + [5])/([2]0 - [2]), where [2]0 and [2] are the starting and instantaneous limonene concentrations. Mass balance (MB, %)
was determined using MB = 100([3] + [4] + [5] + [x])/([2]0 - [2]), where [x] is the concentration of an unknown side product
estimated from GC. H2O2 was used as either the anhydrous product obtained by distillation of a 50% aqueous solution with
further drying over anhydrous MgSO4 or aqueous solutions (30 and 70%).
Epoxidation of both pinene isomers was less efficient (Table 2). The yield of target epoxide was <10%. Furthermore,
significant quantities of side products (this product is cyclohexene derivative 8 for oxidation of α-pinene; the structure of the
second product from oxidation of β-pinene was not established) appeared.
O
O
CHO
+
8
6
7
9
10
We propose that the low efficiency of this system for pinene oxidation is due to extensive steric hindrance by the
substituents to approach of the bulky catalytic molecule. This indicates that epoxidation occurs via a mechanism that does not
involve formation of free radicals. Their generation during oxidation of alkanes by t-butylhydroperoxide catalyzed by 1 (in the
absence of CH COOH, although it slightly accelerates oxygenation of saturated hydrocarbon [7]) has been assumed. We
3
observed that 1 does not catalyze epoxidation of limonene by t-butylhydroperoxide even in the presence of CH COOH in
3
CH CN. This also is consistent with oxidation by H O without formation of free radicals.
3
2 2
Thus, the results lead to the conclusion that the described catalytic system is useful for efficient epoxidation of sterically
accessible olefins, including natural compounds.
244

TABLE 2. Oxidation of α- (6) and β-Pinene (9) by H2O2—1—CH3COOH in CH3CN at 25°C
Substrate
[1]
[H2O2]0
t, min
E, %
[7] or [10]
[x]
ES, %
MB, %
α-Pinene
5×10-5
1.3 (30% aq)
15
30
60
15
30
30
x
x
x
0.024
0.019
0.010
0.005
0.004
0.025
0.007
0.013
0.017
0.002
0.003
0.006
97
69
58
64
100
91
87
98
97
94
β-Pinene
5×10-5
0.43 (30% aq)
1.25 ( anhydr.)
x
25×10-5
70
______
Concentration (M) of reagents and products are diven in brackets. The index o denotes starting concentrations. In all
experiments [Pinene]0 = 0.25 M, t is the reaction time in min. The epoxide yield (E, %) is calculated using E = 100[7]/[6]0 and
E = 100[10]/[9]0. The selectivity for formation of epoxide (ES, %) is measured using ES = 100[7]/([6]0 - [6]) and
ES = 100[10]/([9]0 - [9])/ Mass balance (MB, %) was determined using MB = 100([7] + [8])/([6]0 - [6]) and MB = 100([10]
+ [x])/([9]0 - [9]), where [x] is the concentration of an unknown side product estimated from GC.
EXPERIMENTAL
Reactions were performed in cylindrical glass containers surrounded by a jacket through which thermostatted water
was passed. The solution volume was 5 mL. Samples of the reaction mixture (0.5 mL) were taken at certain time intervals.
These were treated (within several minutes) with an excess of solid manganese oxide to decompose unreacted H O and analyzed
2
2
by GC on a Hewlett—Packard Series II 5890 instrument with a reinforced quartz injector and quartz column packed with
Carbowax 20M (25 m × 0.2 mm, 0.2 µm) using He carrier gas.
Complex 1 was synthesized as before [8, 9]. CH CN was distilled before use over P O .
3
2 5
ACKNOWLEDGMENT
The work was supported by the Russian Foundation for Basic Research, project No. 98-03-32015a, and the Brazilian
National Council on Scientific and Technological Development (Conselho Nacional de Desenvolvimento Cientifico e
Tecnologico, CNPq). G. B. Shul′pin thanks CNPq (Grant No. 300601/01-8) and the Institute of Chemistry, State University,
Campanis (Brazil) for support during residency at the university, where part of the work was performed.
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