Copper (II) chloride / tetrabutylammonium bromide catalyzed oxidation of 2,6-diisopropylnaphthalene and 4,4′-diisopropylbiphenyl

Article abstract of DOI:10.2478/s11532-009-0134-8

The oxidation processes of 2,6-diisopropylnaphthalene and 4,4′-diisopropylbiphenyl with oxygen in the presence of a catalyst, composed of copper(II) chloride and tetrabutylammonium bromide, were investigated. It was found that, in essence, only one isopropyl group undergoes oxidation, and obtained mixtures contained mainly peroxide, alcohol, ketone and only small amounts of hydroperoxide.

Full text of DOI:10.2478/s11532-009-0134-8

Cent. Eur. J. Chem. • 8(2) • 2010 • 285–290
DOI: 10.2478/s11532-009-0134-8
Central European Journal of Chemistry
Copper (II) chloride / tetrabutylammonium bromide
catalyzed oxidation of 2,6-diisopropylnaphthalene
and 4,4’-diisopropylbiphenyl
Research Article
Beata J. Orlińska*, Jan M. Zawadiak
Department of Chemical Organic Technology and Petrochemistry,
Silesian University of Technology, Gliwice 44-100, Poland
Received 9 July 2009; Accepted 26 September 2009
Abstract: The oxidation processes of 2,6-diisopropylnaphthalene and 4,4’-diisopropylbiphenyl with oxygen in the presence of a catalyst,
composed of copper(II) chloride and tetrabutylammonium bromide, were investigated. It was found that, in essence, only one
isopropyl group undergoes oxidation, and obtained mixtures contained mainly peroxide, alcohol, ketone and only small amounts of
hydroperoxide.
Keywords: Catalytic oxidation • 2,6-Diisopropylnaphthalene • 4,4’-Diisopropylbiphenyl • Peroxides
© Versita Sp. z o.o.
synthesis of liquid crystal polymers, epoxy resins, crop
protection chemicals and pharmaceuticals [11].
1. Introduction
Oxidation of DIPN to hydroperoxides was conducted
The oxidation of isopropylaromatic hydrocarbons with
mostly within the temperature range of 80-110°C, under
oxygen in the liquid phase is one step in the synthesis of
a pressure of 0.1 to 0.5 MPa. The use of solvents like
hydroxyaromatic compounds and acetone. Every year,
acetonitrile, heptane, methylisobutyl ketone or alkaline
more than 7 million tonnes of phenol is synthesized by
aqueous emulsion has been described [7]. For instance,
the Hock method consisting of alkylation of benzene
oxidation of DIPN at 105°C in the presence of an azo
with propylene, oxidation of cumene to hydroperoxide
initiator leads to hydroperoxides with a selectivity of 82%
and acid decomposition of hydroperoxide to phenol and
and a conversion of 50% [8]. Similar conditions have
acetone [1]. Due to the problem of acetone surplus on
been applied to DIPB oxidation [9]. Uses of solvents,
the market alternative methods of phenol synthesis are
alkalis and surfactants have been described. Thus, non-
needed, which avoids the co-production of acetone. The
catalytic oxidation of DIPB carried out at 110°C in tert-
methods of direct benzene oxidation to phenol using
butylbenzene as the solvent leads to hydroperoxides
N2O, H2O2 or O2/H2 were described [1-4].
with a selectivity of 90% and a conversion of 66% [10].
Analogous industry scale syntheses based on
Recently, application of N-hydroxyphtalimide (NHPI)
the Hock method are compiled for hydroquinone,
as a catalyst in oxidation reactions of DIPN and DIPB
resorcinol, cresols and 2-naphthol [5,6]. In the
literature, we can also find information about oxidation
processes for 2,6-diisopropylnaphthalene (DIPN)
has been described [12-15]. Oxidation of DIPN in
the presence of NHPI and AIBN followed by acid
decomposition led to 2,6-dihydroxynaphthalene, with a
[7,8] and 4,4’-disopropylbiphenyl (DIPB) [9,10] with
yield of 90% [12,13]. On the other hand, oxidation of
oxygen to form hydroperoxides (Schemes 1 and 2).
both compounds in the presence of a catalytic system
They are subsets of research on the synthesis of
consisting of NHPI and Co(OAc)2 led to 2,6-di(1-hydroxy-
2,6-dihydroxynaphthalene, 2-hydroxy-6-(1-methylethyl)
1-methylethyl)naphthalene
or
4,4’-di(1-hydroxy-1-
naphthalene, 4,4’-dihydroxybiphenyl and 4-hydroxy-
4’-(1-methylethyl)biphenyl, which can be used in the
methylethyl)biphenyl in high yields, 90%, from which
* E-mail: beata.orlinska@polsl.pl
285

Copper (II) chloride / tetrabutylammonium bromide
catalyzed oxidation of 2,6diisopropylnaphthalene
and 4,4’diisopropylbiphenyl
Varian Unity Inova-300 spectrometer. The melting points
were determined in capillary tubes on SMP 3 (Stuart
Scientific) apparatus.
2.1. Catalytic oxidation of DIPN and DIPB with
oxygen
DIPN and DIPB were oxidized in a glass reactor (ø
2.8 cm; H 6.5 cm) supplied with a mechanical stirrer
(1800 rpm), bubbler, thermometer, reflux condenser
and heating jacket. The hydrocarbon was placed in
the reactor and heated up to reaction temperature.
Subsequently, oxygen was passed through and catalyst
was added. The content of peroxides bis(1-methyl-1-
(2-(6-isopropylnaphthyl))ethyl) peroxide (1P) and bis(1-
methyl-1-(4-(4’-isopropylbiphenyl))ethyl) peroxide (2P)
was determined iodometrically according to the method
described by Zawadiak et al. [21], and the contents
Scheme 1. 2,6-Dihydroxynaphthalene and 2-hydroxy-6-(1-methyl-
ethyl)naphthalene synthesis by the Hock method.
Scheme 2. 4,4’-Dihydroxybiphenyl and 4-hydroxy-4’-(1-methyl-
ethyl)biphenyl synthesis by the Hock method.
of
2-(1-hydroperoxy-1-methylethyl)-6-(1-methylethyl)
2,6-dihydroxynaphthalene and 4,4’-dihydroxybiphenyl
were synthesized in a simultaneous process of oxidation
with hydrogen peroxide and acid decomposition
[14,15].
naphthalene (1MHP), 2-(1-hydroxy-1-methylethyl)-6-(1-
methylethyl) naphthalene (1MH), 1-(6-(1-methylethyl)
naphthalene-2-yl)ethanone (1MAc), 2,6-bis(1-hydroxy-
1-methylethyl) naphthalene (1DH), 4-(1-hydroperoxy-
The present paper deals with investigations
concerning the oxidation of hydrocarbons, DIPN and
DIPB, in the presence of a catalytic system consisting
of copper(II) chloride and tetrabutylammonium bromide
(TBAB).Thiscatalystwaspreviouslyusedintheoxidation
of aromatic hydrocarbons with one isopropyl group,
such as cumene [16,17] and 2-isopropylnaphtalene
[18], and products contained considerable amounts of
alcohol, ketone and peroxide, and only small amounts of
hydroperoxide were obtained. The aim of this research
was to determine whether oxidation of DIPN and DIPB
in the presence of Cu(II)/TBAB catalyst can be used in
the synthesis of corresponding peroxides, mono- and
di-alcohols and ketones, which can potentially be used
as initiators, flavour compounds and monomers for
polymers with special abilities.
1-methylethyl)-4’-(1-methylethyl)biphenyl
4-(1-hydroxy-1-methylethyl)-4’-(1-methylethyl)biphenyl
(2MH), 1-(4’-(1-methylethyl)biphenyl-4-yl)ethanone
(2MAc), 2,6-bis(1-hydroxy-1-methylethyl) biphenyl
(2DH) were determined by HPLC according to previously
elaborated methods [19,20].
(2MHP),
2.2. Peroxides separation
The peroxides 1P and 2P were isolated by crystallization
of 5 g of oxidation product with a corresponding
amount of ethanol. The contents of the peroxides were
determined iodometrically [21]. Obtained results are
collected in Table 2.
Peroxides 1P and 2P were also purified by column
chromatography (Kieselgel 60 / Merck 0.063 ÷ 0.200
mm). During purification of peroxide 1P, by column
chromatography, traces of bisperoxide 2,6-bis(1-
methyl-1-(1-methyl-1-(6-isopropylnaphthyl-2-yl)ethyl)
ethyldioxy) naphthalene were isolated. 1H and 13C NMR
analyses of purified peroxides were done.
2. Experimental Procedure
2,6-Diisopropylnaphthalene (DIPN) > 99%, m.p. 66.8°C;
4,4’-diisopropylbiphenyl (DIPB) > 99%, m.p. 66°C.
The catalysts (CuCl2•2H2O, TBAB) and solvents are
commercially available.
Bis(1-methyl-1-(2-(6-isopropylnaphthyl))ethyl)
peroxide 1P
5 g of DIPN oxidation product (80°C, 10 h, Cu(II)
6.7 mmol mol-1 DIPN, TBAB 0.27 mmol mol-1 DIPN)
containing 25% of 1P (1.25 g; 2.75 mmol) and 19 cm3
(15 g) of EtOH were quickly boiled. The hot mixture was
decanted from green precipitate of catalyst and cooled.
Precipitated product was filtered off and dried. Crude
1P (0.58 g) with purity of 80% (0.46g, 1.01 mmol) was
A
Waters Alliance 2690 HPLC equipped
with an autosampler and UV detector (Waters
photodiode array) was used. Column Nova-Pak
Silica 60 Å 4 μm (150 mm×3.9 mm; Waters) was
applied with a gradient elution of a mixture of
hexane and 2-propanol as a mobile phase [19,20].
1H and 13C NMR spectra were recorded in CDCl3 on a
286

B. J. Orlińska, J. M. Zawadiak
obtained (crystallization yield 37%). Crude 1P (0.18 g)
was purified by column chromatography (hexane/
acetone 15/1 (v/v), 70 cm3 of silica gel) giving 0.11 g
of still contaminated peroxide which was purified again
by column chromatography (hexane/acetone 25/1
(v/v), 12 cm3 of silica gel). 0.037g of pure 1P and about
0.005 g of bisperoxide was obtained (the procedure was
repeated to obtain bisperoxide for analysis).
1P: Mp 123,5-126°C
1H NMR (300MHz, CDCl3) δH ppm: 7.73-7.78 (m, 6H,
HAr), 7.55-7.62 (m, 4H, HAr), 7.37 (dd, 2H, HAr, J=8.7,
1.8), 3.06 (m, 2H, C(CH3)2H), 1.62 (s, 12H, C(CH3)2OO),
1.33 (d, 12H, C(CH3)2H, J=7.2).
Scheme 3. Products of DIPN oxidation in the presence of
CuCl2•2H2O and TBAB.
13C NMR (75MHz, CDCl3) δC ppm: 146.1, 143.0, 132.6,
131.7, 128.1, 127.0, 125.7, 124.7, 123.7, 123.7 (Ar),
81.6 (CCH3)2OO), 34.2 (CCH3)2H), 26.9 (CCH3)2OO),
24.0 (CCH3)2H).
2 , 6 - B i s ( 1 - m e t h y l - 1 - ( 1 - m e t h y l - 1 - ( 6 -
isopropylnaphthyl-2-yl)ethyl)ethyldioxy)
naphthalene
Scheme 4. Products of DIPB oxidation in the presence of
CuCl2•2H2O and TBAB.
Mp 149-152°C
1H NMR (300MHz, CDCl3) δH ppm: 7.74-7.82 (m, 10H,
HAr), 7.57-7.63 (m, 6H, HAr), 7.38 (dd, 2H, HAr, J=8.7,
1.8), 3.06 (m, 2H, C(CH3)2H), 1.63 (s, 24H, C(CH3)2OO),
1.33 (d, 12H, C(CH3)2H, J=7.2 ).
13C NMR (75MHz, CDCl3) δC ppm: 146.1, 143.0, 132.6,
131.7, 128.1, 127.0, 125.7, 124.7, 123.7, 123.7 (Ar),
81.6 (CCH3)2OO), 34.2 (CCH3)2H), 26.9 (CCH3)2OO),
24.0 (CCH3)2H).
3. Results and Discussion
The present paper reports the oxidation processes of
diisopropylaromatic coumpounds such as DIPN and
DIPB with oxygen in the presence of CuCl2•2H2O and
TBAB as catalyst at temperature range of 90 to 110°C.
The studied oxidation processes proceed according
to a widely known free-radical chain mechanism,
and hydroperoxides are the primary products. In our
previously described non-catalytic oxidation processes
of DIPN and DIPB, hydroperoxides were the main
products; at 110°C, they were obtained with yields
ranging from 40 to 60% and a selectivity of about
80% [8,10]. Application of catalyst, CuCl2•2H2O or
CuCl2•2H2O with TBAB, yielded significantly different
products. A decrease of hydroperoxide content and
increasing amounts of other products were observed.
The composition of obtained products is presented in
Schemes 3 and 4, as well as in Table 1. Courses of
typical catalytic oxidation processes of DIPN and DIPB
are shown in Figs. 1 and 2.
It has been found that, in essence, only one isopropyl
group in DIPN and DIPB undergoes catalytic oxidation.
Alcohols 1DH and 2DH were the only products of
oxidation of two groups detected, but their amount did
not exceed 10% mol.
The composition of the obtained oxidation products
of DIPN and DIPB, consisting mainly of peroxide, alcohol
and ketone, is a result of, among others, the increase
Bis(1-methyl-1-(4-(4’-isopropylbiphenyl))ethyl)
peroxide 2P
5 g of DIPB oxidation product (80°C, 10 h, Cu(II)
13.6 mmol mol-1 DIPB, TBAB 0.27 mmol mol-1 DIPB)
containing 18.9% of 2P (0.95 g; 1.87 mmol) and 19 cm3
(15 g) of EtOH were quickly boiled. The hot mixture was
decanted from green precipitate of catalyst and cooled.
Precipitated product was filtered off and dried. Crude
2P (1.44 g) with purity of 43% (0.62 g, 1.22 mmol) was
obtained (crystallization yield 65%). Crude 2P (1.0 g)
was recrystallized from EtOH (30 cm3) giving product
(0.33 g) with purity of 94% (yield 72%). Recrystallized
2P (0.28 g) was also purified by column chromatography
(CH2Cl2/acetone 20/1 (v/v), 35 cm3 of silica gel) giving
0.2 g of 2P.
2P: Mp 124-131°C
1H NMR (300MHz, CDCl3) δH ppm: 7.20-7.47 (m,
16H, HAr), 2.80-2.97 (m, 2H, C(CH3)2H), 1.54 (s, 12H,
C(CH3)2OO), 1.22 (d, 12H, C(CH3)2H, J=6.9).
13C NMR (75MHz, CDCl3) δC ppm: 147.8, 144.8, 139.6,
138.5, 127.0, 126.8, 126.5, 126.0 (Ar), 81.6 (CCH3)2OO),
33.8 (CCH3)2H), 27.0 (CCH3)2OO), 24.0 (CCH3)2H).
287

Copper (II) chloride / tetrabutylammonium bromide
catalyzed oxidation of 2,6diisopropylnaphthalene
and 4,4’diisopropylbiphenyl
Table 1. Oxidation of DIPN and DIPB in the presence of catalytic system CuCl2•2H2O/TBAB.
DIPN a
1P
Temp.
[oC]
Cu(II)
TBAB x102
[mmol]
1MH
1MAc
1DH
1MHP
[mmol]
Yield [% mol]
80
80
1.28
5.14
2.57
2.57
2.57
2.57
5.1
5.1
5.1
-
5.1
5.1
25.0
23.2
23.2
13.0
14.8
6.7
25.9
25.5
26.8
30.5
24.0
22.2
9.0
11.7
10.0
9.0
14.5
24.0
4.2
6.4
4.9
2.3
4.3
3.5
2.2
1.7
6.2
4.7
5.2
2.7
80
90 c
90
110
DIPB b
Temp.
[oC]
Cu(II)
TBAB x102
[mmol]
2P
2MH
2MAc
2DH
2MHP
[mmol]
Yield [% mol]
80
80
1.00
4.00
2.00
2.00
2.00
2.00
4.0
4.0
4.0
-
4.0
4.0
12.0
26.0
18.9
0.0
26.8
10.6
12.4
18.1
19.8
1.3
21.7
14.0
5.3
13.8
7.8
0.9
12.0
22.7
0.7
5.7
0.4
0.0
3.3
5.4
1.3
1.1
2.8
9.7
2.5
1.8
80
90 c
90
110
Oxygen - 10 dm3 h-1; stirrer – 1000 rpm; reaction time – 10h
a
DIPN – 0.190 mol (40g)
DIPB – 0.147 mol (35g)
4 mmol of 1,1’-azobis(cyclohexanecarbonitrile) was added
b
c
Conversion of DIPN and DIPB can be estimated on sum of the products presented in Table 1, because any other possible products like
2,6-bis(1-hydroperoxy-1-methylethyl)naphthalene, 4,4’-bis(1-hydroperoxy-1-methylethyl)biphenyl), 2-(1-hydroperoxy-1-methylethyl)-6-(1-hydroxy-
1-methylethyl)naphthalene or 4-(1-hydroperoxy-1-methylethyl)-4’-(1-hydroxy-1-methylethyl)biphenyl as well as carboxylic acids were not observed
in amounts of exceeding 1%.
Figure 1. Course of oxidation process of DIPN in the presence Figure 2. Course of oxidation process of DIPB in the presence
of CuCl2•2H2O and TBAB. (0.190 mol DIPN, 90°C,
of CuCl2•2H2O and TBAB. (0.147 mol - DIPB, 90°C,
O2 - 10 dm3 h-1; 1000 rpm.
O2 - 10 dm3 h-1; 1000 rpm).
of hydroperoxide decomposition rate in the presence of by recombination of alkoxyl as well as peroxyl radicals
bothCu(II)andTBAB. Itiswellknownthatcopper(II)ions, generated during the oxidation process. Peroxyl radicals
similar to other transition metal ions, lower the activation can recombine to tetraperoxides, which decompose
energy of the hydroperoxide decomposition reaction with generation of two alkoxy radicals. Some of those
[22]. The catalytic effect of quaternary ammonium salts radicals recombine to peroxide and some undergo
on the hydroperoxide decomposition has also been aforementioned reactions, such as H-abstraction and
described [23]. Free alkylperoxyl or alkoxyl radicals β-scission (Scheme 5) [24].
generated during the decomposition of hydroperoxides
It should also be noted that copper(II) chloride
can initialize further reaction chains. Alkoxyl radicals is slightly soluble in hydrocarbons and remains
undergo typical hydrogen abstraction or β-scission that insoluble in the reaction mixture. Thus, TBAB probably
generate alcohols and ketones. Peroxides can be formed acts also as a phase transfer catalyst of copper
288

B. J. Orlińska, J. M. Zawadiak
Obtained by DIPN and DIPB oxidation symmetrical
peroxides 1P and 2P were separated from post-
oxidation mixtures by crystallization with EtOH (hexane
gave poorer results). Purities of isolated peroxides and
yields of crystallization are given in Table 2.
Peroxide 1P separation from oxidation products of
DIPN, with EtOH used in ratios of 1:1 and 1:2, did not
produce positive results, as the whole mixture solidified.
When higher amounts of EtOH were used, 1P was
obtained with high purity, but with low yields. Purity of
isolated 2Pwas rather low. However, the recrystallization
produced peroxide with a purity of 94% and a yield of
72%.
The results have demonstrated that the oxidation
of DIPN and DIPB in the presence of the CuCl2•2H2O
and TBAB catalyst can be potentially useful as a simple
method for symmetrical peroxide synthesis directly from
hydrocarbons.
Scheme 5. Ketone, alcohol and peroxide formation reactions from
alkoxyl and peroxyl radicals.
ions, transmitting them in the form of complexes -
[Bu4N]+[CuCl3]- or [Bu4N]+[CuCl2]- - to the organic phase
[25]. Similar catalytic system consisting of CoCl2 and
didecyldimethylammonium bromide was recently
described for methylbenzenes oxidation [26].
The results presented in Table 1 have shown that
higher concentrations of mono- peroxides, alcohols and
ketones are obtained in case of using CuCl2•2H2O with
TBAB than only CuCl2•2H2O. Under the same reaction
conditions, higher concentrations of oxidation products
are obtained in cases of DIPN than DIPB. The kinetic
profiles of products formation are similar for DIPN and
DIPB (Figs. 1 and 2). Monoalcohols and peroxides
concentrations pass through the maximum (1MH and
1P after 3 h, 2P after 7 h and 2MH after 10 h). This
suggests that subsequence reactions occurred, e.g.
oxidation of 1MH leading to 1DH or decomposition of
1P to 1MAc or 1MH.
Depending on the applied process conditions, it was
possible to obtain expected peroxides as well as mono-
alcohols and ketones with yields of over 20% (Table 1)
The temperature increase influenced the alcohol to
ketone ratio. This is in agreement with literature data,
which has demonstrated that higher temperatures
favoured the β-scission reaction to ketones [27]. Thus,
for higher yields of ketones, the process must be carried
out at 110°C. On the other hand, higher yields of alcohols
are obtained at 80°C. Due to lower stability of peroxides
at higher temperature, smaller amounts were obtained
at 110°C.
4. Conclusions
It was found that oxidation of hydrocarbons containing
two isopropyl groups, such as DIPN and DIPB, in the
presence of copper(II) chloride and tetrabutylammonium
bromide catalyst gave products containing mainly mono-
peroxide, alcohol, ketone and only small amounts of
hydroperoxide. It is a result of the high activity of catalyst
in increasing the decomposition rate of hydroperoxides
created in this process. The catalytic mechanism is
complicated and includes catalytic influence of copper
ions and TBAB on hydroperoxide decomposition; TBAB
likely also transfers copper ions in the form of complexes
to the organic phase.
The obtained products have different applications,
e.g. peroxides as initiators or cross-linking agents, 1MAc
as raw material for 6-hydroxy-2-naphthoic acid [28].
Theprocessofisopropylaromaticoxidationcatalyzed
by Cu(II)/TBAB can be used as a simple method of
symmetrical peroxides synthesis.
Table 2. Isolation of peroxides from oxidation products by crystallization with EtOH.
Product : EtOH w/w
DIPN a
DIPB b
1P c [%]
Yield d [%]
2P c [%]
Yield d [%]
1 : 1
1 : 3
1 : 6
-
80
97
-
37
12
38
43
45
52
65
63
a 5 g of DIPN oxidation products containing 25% of 1P
b 5 g of DIPB oxidation products containing 18% of 2P
c purity of peroxide after crystallization
d yield of crystallization
289

Copper (II) chloride / tetrabutylammonium bromide
catalyzed oxidation of 2,6diisopropylnaphthalene
and 4,4’diisopropylbiphenyl
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