1
098
Liu et al.
R
N
Results and Discussion
R
Liquid Phase Reaction Oxidation of Cyclohexene
NaO H NH
E tOH
.H
O
3 2
In order to test the catalytic performance of the impact of dif-
ferent substituent group to the catalyst, five types of mononu-
clear Mn(II)/terpyridine complex were investigated in the
oxidation of cyclohexene. The results showed that the main
oxidation products of the cyclohexene were 2-cyclohexene-1-
one, 2-cyclohexene-1-ol, and cyclohexene epoxide (Scheme
2).
N
O
O
R
N
N
Com plex (Ligand) 1: R=NO 2
Com plex (Ligand) 2: R=Cl
Com plex (Ligand) 3: R=H
M nCl .
2
2
4H O
EtO H
Com plex (Ligand) 4: R=CH3
Reflux
Com plex (Ligand) 5: R=O CH
3
Effect of different oxidant
N
N
N
The effect of different oxidants on the catalytic activity of
mononuclear Mn(II)/terpyridine complex in the oxidation of
styrene was studied. We chose different oxidant such as
TBHP (65%), H O (30%), molecular oxygen, and air in the
oxidation of cyclohexene. The catalysis results were summa-
rized in Table 1. In the case of TBHP, the reaction showed
Mn
Cl
Cl
2
2
Sch. 1. Synthesis of ligands and Mn(II) complexes.
1
554 (-NO str.), 1610 (CHN str.), CHC ꢁꢁ H (3019 str.). UV- the highest conversion ratio.
2
vis [H O, λ/nm]: 230, 284, 302. Anal. Calcd. for
2
C H N O Cl Mn: C, 52.52; H, 2.94; N, 11.67%. Found: C,
2
1
14
4
2
2
Effect of different solvent
5
2.81; H, 3.18; N, 11.87%.
In the catalytic oxidation of cyclohexene, acetonitrile, tetra-
hydrofuran (THF), N,N-dimethylformamide (DMF),
CH Cl , and CH ClCH Cl were used as solvent. As shown
Complexes (2–5) were prepared in similar way with the
corresponding ligands and were obtained as yellow powders.
¡
1
2
2
2
2
Complex 2, yield 82%. IR (KBr, y/cm ): 1567, 1479
CHC str.), 1607 (CHN str.), 3065 (CHC ꢁꢁ H str.). UV-vis
in Table 2, the highest conversion was obtained in presence
of acetonitrile. It was observed that the catalytic activity of
the Mn(II) complex decreased in the order: acetonitrile >
(
[
H O, λ/nm]: 249, 281, 316. Anal. Calcd. for
2
C H N Cl Mn: C, 53.70; H, 3.00; N, 8.95%. Found: C,
ꢀ
2
1
14
3
3
CH ClCH Cl > DMF > THF > CH Cl at 50 C. Then, all
2
2
2
2
5
3.99; H, 2.81; N, 9.02%.
Complex 3, yield 77%. IR (KBr, y/cm ): 1616 (CHC
experiments will be performed in acetonitrile.
–
1
str.), 1600 (CHN str.), 3055 (CHC ꢁꢁ H str.). UV-vis [H O,
2
Effect of reaction temperature
λ/nm]: 246, 267, 286. Anal. Calcd. for C H N Cl Mn: C,
2
1
15
3
2
5
9
7.95; H, 3.47; N, 9.66%. Found (%): C, 57.47; H, 3.29; N, Effect of temperature on the oxidation of cyclohexene as a
.58%.
function of time has been plotted in Figure 1. A series of
¡
1
Complex 4, yield 82%. IR (KBr, y/cm ): 1426(-CH str.), experiments were carried out in order to test the temperature
3
ꢀ
1
544, 1473 (CHC str.), 1659 (CHN str.), 3058 (CHC ꢁꢁ H str.). effect at different temperatures of 35, 60, 70, and 80 C. As
UV-vis [H O, λ/nm]: 226, 289, 312. Anal. Calcd. for shown in Figure 1, the best conversion ratio was observed at
2
ꢀ
C H N Cl Mn: C, 58.82; H, 3.81; N, 9.35%. Found: C, 80 C. Diminishing conversion ratios were generated when
2
2
17
3
2
ꢀ
5
9.02; H, 3.72; N, 9.44%.
Complex 5, yield 81%. IR (KBr, y/cm ): 1427(-CH str.),
the reaction temperatures were lower than 80 C.
¡
1
3
1
553 (CHC str.), 1599 (CHN str.), 1471, 1545 (CHC ꢁꢁ H str.). Effect of the amount of catalyst
UV-vis [H O, λ/nm]: 230, 285, 308. Anal. Calcd. for
C H N OCl Mn: C, 56.80; H, 3.68; N, 9.03%. Found: C,
2
The effect of the amount of catalyst on the oxidation of cyclo-
hexene as a function of time is illustrated in Figure 2. The
data revealed that the conversion of cyclohexene decreased
with the increase of the catalyst amount from 0.5 to 2 mol%.
2
2
17
3
2
5
6.29; H, 3.58; N, 8.79%.
8
8
8% conversion of cyclohexene was observed after 6 h at
0 C using 0.5 mol% of catalyst 3. An increase of the amount
ꢀ
General Procedure for Oxidation of Substrate
of catalyst would obtain a lower conversion of cyclohexene
from the Figure 2. The possible reason is that the decomposi-
tion of TBHP which resulted from the excess Mn(II)
complex.
Substrate, TBHP and metal complex were introduced in the
5
0 mL two-necked round-bottomed flask placed in an appro-
priate temperature controlled by water bath under vigorous
stirring. After oxidation, the reaction mixture was passed
quickly through a short pad of silica gel and reaction solvent
was used as eluent. The solution was placed in a GC sample
vial, then a quantitative of internal standard (p-xylene) was
added for quantitative analysis by GC (Agilent 6810 chro-
matograph, Agilent DB-5ms capillary column 0.25 mm £
O
OH
Mn(II) Com plex
O xidant
O
3
0 m £ 0.25 mm, FID detector).
Sch. 2. Oxidation of cyclohexene by Mn(II) complex.