ESI-MS study of copper chloride/phase-transfer catalytic systems for oxidation of cumene with 1-methyl-1-phenylethyl hydroperoxide

Article abstract of DOI:10.1007/s00706-009-0238-z

Oxidation of cumene with 1-methyl-1-phenyl- ethyl hydroperoxide in the presence of copper chloride/ phase transfer catalytic systems was investigated by ESI- MS. For catalytically active copper(II) chloride/crown ethers, copper(II) chloride/crown ethers/alkaline metal salts, and copper(II) chloride/tetrabutylammonium chloride systems, the presence of a few kinds of copper complexes in the organic phase was detected by use of ESI-MS. When copper(II) chloride/podand systems were used, the conversion of hydroperoxide and the yield of oxidation product were close to zero, although the concentration of copper complexes in the organic phase was high. Addition of bis(2-hydroxyethyl) ether to the catalytically active copper(II) chloride/18-crown-6 system resulted in an inhibition effect. Springer-VerIag 2010.

Full text of DOI:10.1007/s00706-009-0238-z

Monatsh Chem (2010) 141:143–147
DOI 10.1007/s00706-009-0238-z
ORIGINAL PAPER
ESI–MS study of copper chloride/phase-transfer catalytic
systems for oxidation of cumene with 1-methyl-1-phenylethyl
hydroperoxide
•
Danuta Gillner Jan Zawadiak Roman Mazurkiewicz
•
•
•
Joanna Kurczewska Grzegorz Schroeder
•
´
Beata Orlinska
Received: 18 March 2009 / Accepted: 1 December 2009 / Published online: 22 January 2010
Ó Springer-Verlag 2010
Abstract Oxidation of cumene with 1-methyl-1-phenyl-
ethyl hydroperoxide in the presence of copper chloride/
phase transfer catalytic systems was investigated by ESI–
MS. For catalytically active copper(II) chloride/crown
ethers, copper(II) chloride/crown ethers/alkaline metal
salts, and copper(II) chloride/tetrabutylammonium chloride
systems, the presence of a few kinds of copper complexes
in the organic phase was detected by use of ESI–MS. When
copper(II) chloride/podand systems were used, the con-
version of hydroperoxide and the yield of oxidation
product were close to zero, although the concentration of
copper complexes in the organic phase was high. Addition
of bis(2-hydroxyethyl) ether to the catalytically active
copper(II) chloride/18-crown-6 system resulted in an
inhibition effect.
(RH) possessing an active hydrogen with tertiary hydro-
peroxides (Eq. 1) [1, 2].
2ROOH þ R0H ! ROOR0 þ ROH þ H2O
ð1Þ
Symmetric and unsymmetric di-tertiary organic
peroxides [3]—important components in the polymer
industry—are the most desired products of such reactions.
According to Kharasch’s proposal [2], the main steps of
the reaction can be described by Eqs. 2–7:
ROOH þ Cuþ ! ROꢀ þ Cu2þ þ ꢁOH
ROꢀ þ R0H ! ROH þ R0ꢀ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ð6Þ
ð7Þ
R0ꢀ þ ROOH ! R0 ꢀ HOOR
ROOH þ Cu2þ ! ROOꢀ þ Cuþ þ Hþ
ROOꢀ þ R0H ! R0 ꢀ HOOR
Keywords Copper(II) chloride ꢀ Crown ethers ꢀ
Catalytic systems ꢀ ESI–MS ꢀ Oxidation ꢀ Peroxides
R0 ꢀ HOOR þ Ox ! R0OOR þ ðOx þ eÞ þ Hþ
where R = (CH3)3C–, R0 = Ph(CH3)2C–, and Ox is Cu2?
or hydroperoxide.
Introduction
Kochi [1] suggested that copper catalyst was involved in
the formation of intermediate complexes (Eqs. 8–11):
Catalytic oxidation of hydrocarbons by various oxidizing
agents in the presence of copper(I), copper(II), cobalt(II),
or manganese(II) salts has been widely investigated for
many years. Salts of copper(I) and copper(II) have been
used as effective catalysts in the oxidation of hydrocarbons
ROOH þ Cuþ ! ROꢀ þ ½CuOHꢂþ
½CuOHꢂþ þ ROOH ꢀ ½CuOORꢂþ þ H2O
ROꢀ þ R0H ! ROH þ R0ꢀ
ð8Þ
ð9Þ
ð10Þ
ð11Þ
R0ꢀ þ ½CuOORꢂþ ! R0OOR þ Cuþ
where R = (CH3)3C– and R0 = Ph(CH3)2C–.
´
D. Gillner (&) ꢀ J. Zawadiak ꢀ R. Mazurkiewicz ꢀ B. Orlinska
Faculty of Chemistry, Silesian University of Technology,
ul. Krzywoustego 4, 44-100 Gliwice, Poland
e-mail: Danuta.Gilner@polsl.pl
It has been found that the oxidation process is much
more efficient and can be performed under milder condi-
tions when systems composed of transition metal salts and
phase-transfer catalysts, for example onium salts or crown
ethers, were used [4–9].
J. Kurczewska ꢀ G. Schroeder
Faculty of Chemistry, A. Mickiewicz University,
Grunwaldzka 6, 60-780 Poznan, Poland
123

144
D. Gillner et al.
H C
CH
H C
3
3
3
CH
CH
3
CH
3
3
3
70oC
cat.
CH
CH
CH
O
3
3
3
OH
OOH
+
2
+
H2O
+
O
CH
1
4
2
3
Scheme 1
In our previous papers [10, 11] we presented some results
concerning the oxidation of isopropyl arenes with tertiary
hydroperoxides in the presence of copper salt/crown ether/
alkali metal salt catalytic systems (CuCl2ꢀH2O/12-crown-4/
LiCl, CuCl2ꢀH2O/15-crown-5/NaCl, CuCl2ꢀH2O/18-crown-
6/KCl). Clear evidence was provided of the occurrence
phase-transfer catalysis (PTC) in the reactions investigated.
We proposed that copper was transferred to the organic phase
in the form of complexes with crown ethers and, sometimes,
alkali metal cations, with copper being transferred in the
form CuCl42- or CuCl3- counterions, or even as Cu[CuCl3]
or Cu[CuCl4] complexes. Moreover, the essential role of
water in the catalytic process was discussed.
Results and discussion
The oxidation of cumene (2) with 1-methyl-1-phenylethyl
hydroperoxide (1) was chosen as model reaction because it
is used for the large-scale production of dicumyl peroxide,
an initiator of many free radical processes. Another reason
for this selection was the availability of reactants and
simple analytical methods for monitoring the course of the
reaction. Catalysts consisting of CuCl2ꢀ2H2O and alkyl-
ammonium salts, crown ethers, or podands were used
(Scheme 1).
Table 1 presents the results of the reaction of hydro-
peroxide 1 with 2 in the presence of different catalytic
systems.
Murahashi [12] and Komiya et al. [13] reported iso-
lation of a few types of copper/crown ether systems and
their application in oxidation of cyclohexane with
molecular oxygen, in the presence of acetaldehyde in
CH2Cl2 at room temperature. The use of CuCl2 with 18-
crown-6 gave the best results. The structure of the
complex of CuCl2 with 18-crown-6 was established by
single-crystal X-ray structure determination. The complex
consisted of tetrameric (CuCl2)4, two molecules of crown
ethers, and two water molecules. The complex of CuCl2
with 18-crown-6 and KCl, which consisted of a dinuclear
[Cu2Cl6]2- anion and two [K(18-crown-6)]? cations,
was much more efficient [14]. A similar complex with
15-crown-5/NaCl was also effective. Such observations
are in good agreement with data obtained during our
study on the oxidation of isopropyl arenes with tertiary
hydroperoxides.
The total concentration of Cu ions in cumene solution
was about 10-5 mol dm-3 for all the catalytic systems
studied except for CuCl2/12-crown-4, for which it was
below 10-6 mol dm-3 (determined by ICP). Distribution
of copper salts formed in the cumene phase was determined
by ESI–MS. In negative-ion ESI–MS spectra obtained
from the cumene phase we observed the following peaks
-
for ion complexes with copper: m/z = 133 for CuCl2
,
m/z = 168 for CuCl3-, m/z = 196 for Cu2Cl2-, m/z = 231
for CuCuCl3-, and m/z = 266 for CuCuCl4-, calculated
for isotopes 63Cu (69%) and 35Cl (75%) (Table 1). Typical
spectra are presented in Figs. 1 and 2, possible combina-
tions of the oxidation states for the observed copper
complexes are presented in Table 2 [15]. The mechanism
of reduction of Cu(II) observed in ESI–MS was described
by Gianelli et al. [16].
In this paper we present experimental evidences,
obtained by ESI–MS, that crown ethers in the presence
of alkali metal salts, and some other phase-transfer cat-
alysts, are able to transfer copper containing complexed
anions, and sometimes Cu? or Cu2?/crown ether com-
plexes also, to the organic phase. ESI–MS can be used
for ionization of molecules and ionic chemical species,
and to form charged ions from relatively non-volatile,
thermally labile compounds up to a concentration of
10-7 mol dm-3. ESI–MS is therefore a perfect tool for
determination of the formulae and concentrations of the
different ions and complexes of catalysts present in the
investigated reaction mixture.
For the system CuCl2ꢀ2H2O/12-crown-4, for which the
conversion of hydroperoxide 1 and the yield of peroxide 3
were very low, only traces of copper complexes were
observed in the cumene phase. On the other hand, a very
-
intense signal of the CuCl2 ion (Fig. 1) occurred when
LiCl was added to the system. In that case high conversion
of hydroperoxide 1 and relatively high yield of peroxide 3
were observed. In the positive-ion ESI–MS spectrum there
were signals of a (12-crown-4/Li)? complex. Analogous
results were also obtained for the systems with other crown
ethers. For the systems with 15-crown-5 or 18-crown-6
additional signals of (crown ether/Cu)? complexes were
observed. The stability constants (log K) of Cu(II) with 15-
123

ESI–MS study of copper chloride/phase-transfer catalytic systems
145
Table 1 Anions observed by negative-ion ESI–MS
Catalytic systema,b,c
Conv.
of 1 (%)
Yield of
3 (%)
Anions observed in negative-ion ESI–MS, and relative intensity (%)
m/z = 133
-
CuCl2
m/z = 168
-
CuCl3
m/z = 196
-
Cu2Cl2
m/z = 231
-
CuCuCl3
m/z = 266
-
CuCuCl4
A
B
C
D
E
F
G
H
I
9d
84d
82d
82d
72d
88d
83
92
79
84
86
0
8d
46d
42d
48d
33d
46d
41
50
32
40
63
0
–
100
–
–
–
Trace
–
–
–
–
–
–
–
–
–
–
–
–
–
–
6
8
8
–
100
20
50
30
40
–
–
100
100
100
100
100
100
100
60
20
20
–
40
20
10
–
20
–
–
20
40
–
–
–
J
–
–
K
L
M
N
a
100
25
20
20
–
100
100
100
40
40
40
10
15
12
0
0
23
5
Catalytic systems used
A
CuCl2ꢀ2H2O ? 12-crown-4,
B
CuCl2ꢀ2H2O ? 12-crown-4 ? LiCl,
C
CuCl2ꢀ2H2O ? 15-crown-5,
D
CuCl2ꢀ2H2O ? 15-crown-5 ? NaCl, E CuCl2ꢀ2H2O ? 18-crown-6, F CuCl2ꢀ2H2O ? 18-crown-6 ? KCl, G CuCl2ꢀ2H2O ? dibenzo-18-
crown-6, H CuCl2ꢀ2H2O ? dibenzo-18-crown-6 ? KCl, I CuCl2ꢀ2H2O ? dibenzo-24-crown-8, J CuCl2ꢀ2H2O ? dibenzo-24-crown-8 ? KCl,
K CuCl2ꢀ2H2O ? Bu4NCl, L CuCl2ꢀ2H2O ? HOCH2CH2OCH2CH2OH, M CuCl2ꢀ2H2O ? CH3OCH2CH2OCH2CH2OH, N CuCl2ꢀ2H2O
? poly(ethylene glycol)-350-monomethyl ether
b
c
d
?
?
?
Ionic diameters, Cu2? 1.38 A; Li 1.20 A; Na 1.90 A; K 2.66 A
˚
˚
˚
˚
˚
˚
˚
˚
Cavity diameters of crown ethers, 12-crown-4 1.171.4 A; 15-crown-5 1.772.2 A; 18-crown-6 2.673.2 A; dibenzo-18-crown-6 2.673.2 A
Refs. [10, 11]
Fig. 1 ESI–MS spectrum
obtained from the CuCl2ꢀ2H2O
and 12-crown-4–LiCl system in
cumene solution
crown-5 and 18-crown-6 are 2.26 and 2.01 in 90% DMSO–
water solvent [17] or 2.04 and 1.85 in 40% ethanol–water
solvent [18]. The stability constants of (crown ether/Cu)?
complexes are smaller.
The highest concentration and variety of different ionic
copper complexes were observed for podands, whereas for
the CuCl2ꢀ2H2O/Bu4NCl system (Fig. 2) the concentration
of copper complexes was approximately a factor of two
123

146
D. Gillner et al.
Fig. 2 ESI–MS spectrum
obtained from the CuCl2ꢀ2H2O
and Bu4NCl system in cumene
solution
mentioned compounds occurs. This assumption accounts
for the inhibition effect observed for bis(2-hydroxyethyl)
ether added to the catalytically active CuCl2ꢀ2H2O/18-
crown-6 system.
Table 2 Possible combinations of the oxidation states for the copper
complexes observed [15]
Chemical formula
Description (oxidation states)
-
CuCl2
[Cu(I) ? 2 Cl]-
The ESI–MS method provides new opportunities for
examination of the oxidation of cumene with 1-methyl-1-
phenylethyl hydroperoxide in the presence of catalytic
systems consisting of CuCl2ꢀ2H2O and crown ethers or
other phase-transfer catalysts [19].
-
CuCl3
[Cu(II) ? 3 Cl]-
-
Cu2Cl2
[Cu(0) ? Cu(I) ? 2 Cl]-
[2 Cu(I) ? 3 Cl]-
-
CuCuCl3
-
CuCuCl4
[Cu(I) ? Cu(II) ? 4 Cl]-
Experimental
lower. Unexpectedly, with podands the high concentration
of copper complexes in the organic phase was accompa-
nied by conversion of hydroperoxide 1 and a yield of
peroxide 3 close to zero, whereas for the system with
Bu4NCl both conversion and yield were extremely high.
When bis(2-hydroxyethyl) ether was added to the cata-
lytically active CuCl2ꢀ2H2O/18-crown-6 system, the
conversion and the yield of peroxide decreased signifi-
cantly from 72 to 14%, and from 33 to 5%, respectively.
Materials
1-Methyl-1-phenylethyl hydroperoxide was purchased as
technical product from PKN ‘‘Orlen’’, Płock, Poland. It
was purified using the method described in the literature
[20]. Cumene was purchased from Merck and washed with
concentrated sulfuric acid, neutralized, dried with anhy-
drous magnesium sulfate, and distilled over sodium (152.0-
152.5 °C). Other reagents and catalysts were purchased
from Merck and used as received.
Conclusion
Oxidation of cumene with 1-methyl-1-phenylethyl
hydroperoxide
Our results confirm that the transfer of copper complexes
with crown ethers or crown ethers and alkali metal salts or
Bu4NCl to the cumene phase is responsible for the catalytic
effect in the process of the oxidation of cumene with
1-methyl-1-phenylethyl hydroperoxide.
In a typical procedure a 70% solution of 35 g 1-methyl-1-
phenylethyl hydroperoxide (0.23 mol) in cumene was added
at a rate of 0.27 cm3/min to a mixture of 16.4 g cumene
(0.14 mol), copper(II) chloride dihydrate (4.1 mmol),
phase-transfer catalyst (8.4 9 10-2 mmol) and, in some
It seems that with podands no reaction is observed
because the complexation of copper ions by podands is too
strong, or because specific inhibition caused by above
123

ESI–MS study of copper chloride/phase-transfer catalytic systems
147
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The ESI–MS spectra were recorded on a Waters/Micro-
mass (Manchester, UK) ZQ mass spectrometer equipped
with a Harvard Apparatus syringe pump. A solution of
cumene with alkylammonium salts, podands, or crown
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a concentration of approximately 10-5 mol dm-3. The
samples were infused into the ESI source using a Harvard
pump at a flow rate of 20 mm3 min-1. The ESI source
potentials were: capillary 3 kV, lens 0.5 kV, extractor 4 V.
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