Dialkyl peroxides decomposition in the presence of quaternary ammonium halides

Article abstract of DOI:10.1023/A:1012405413649

Decomposition of dicumyl peroxide and cumyl tert-butyl peroxide was studied in the presence of tetraethylammonium halides in acetonitrile, dimethylformamide, 2-propanol, and acetic acid. The tetraethylammonium halides accelerate the decomposition of dialkyl peroxides in 2-propanol and acetic acid, but do not affect the reaction velocity in dimethylformamide and acetonitrile. The decomposition products character depends on the solvent nature.

Full text of DOI:10.1023/A:1012405413649

Russian Journal of Organic Chemistry, Vol. 37, No. 6, 2001, pp. 814 818. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 6, 2001,
pp. 861 865.
Original Russian Text Copyright
2001 by Maksyuta, Suprun, Opeida, Turovskii.
Dialkyl Peroxides Decomposition in the Presence
of Quaternary Ammonium Halides
1
2
1
1
N. V. Maksyuta , V. Ya. Suprun , I. A. Opeida , and N. A. Turovskii
1
Litvinenko Institute of Physical Organic and Coal Chemistry, Ukrainian Academy of Sciences, Donetsk, 183114 Ukraine
2
Martin-Luther Universitat, Halle-Wittenberg, Merseburg, BRD
Received November 12, 1998
Abstract Decomposition of dicumyl peroxide and cumyl tert-butyl peroxide was studied in the presence of
tetraethylammonium halides in acetonitrile, dimethylformamide, 2-propanol, and acetic acid. The tetra-
ethylammonium halides accelerate the decomposition of dialkyl peroxides in 2-propanol and acetic acid, but
do not affect the reaction velocity in dimethylformamide and acetonitrile. The decomposition products
character depends on the solvent nature.
In a number of publications [1] was reported on
considerable acceleration of diacyl peroxides de-
composition effected by quaternary onium salts
chlorides, bromides, iodides, picrates of tetraethyl-
ammonium, triethylbenzylammonium, etc.).
The decomposition thereof was already studied in
cumene and chlorobenzene [5] where the products
composition was limited to acetophenone and
2-phenylpropan-2-ol. Yet it is known [6] that at
induced decomposition of dialkyl peroxides (tert-
butyl peroxide) arise epoxy derivatives which can
produce quite a few secondary products depending
on the experiment conditions. Besides the quaternary
ammonium halides are sparingly soluble in the
solvents of low polarity. Therefore we chose a series
of solvents with different properties that were
sufficiently good solvents both for peroxides and
quaternary ammonium salts.
(
The investigation of effect of the quaternary
ammonium salts on the benzoyl peroxide decomposi-
tion established that the rate of reaction became
3 orders of magnitude greater than the thermolysis
velocity, and therefore it was possible to carry out
the peroxide decomposition at lower temperature
2
(
298 303
K).
The
process
activation
is
effected by anion as shows the increase of the reaction
rate in the halide series I > Br > Cl. The role of
cation consists in electrophilic assistance to the per-
oxide decomposition. The acceptor characteristics of
the solvent notably affect the rate of the activated de-
composition [2]. It is also known that the oxidation
of hydrocarbons in the presence of the quaternary
onium salts is accelerated [3] due to the interaction of
the forming hydroperoxides with the salts.
The thermal decomposition of peroxides was
studied at 90 C. We chose this temperature to reduce
the contribution from the thermal decomposition. The
curves of peroxide I consumption are given on Fig. 1.
The initial rates of the thermal and activated decom-
positions were evaluated by graphical differentiation
of the curves c vs time till conversion 10% (Table 1).
It turned out that the rate of the thermal decom-
position considerably depended on the character of
solvent and changed in the series AcOH> i-PrOH>
MeCN > DMF. This fact is well consistent with the
literature data. For instance, in [5] was established
that the rate of thermal decomposition of the tert-
butyl peroxide in the temperature range 120 135 C
decreased in the solvent series acetic acid > aceto-
nitrile > 2-propanol. The alteration of the thermal
decomposition rate corresponds to the change in the
electrophilicity factor and dielectric constant [7].
Thus just the electrophilic characteristics of the
solvent influence the most the rate of thermal decom-
position.
Thus obviously the decomposition of peroxides of
RC(O)OO(O)CR and ROOH type is significantly
affected both by the structure of salts and the medium
characteristics.
Under thermolysis conditions dialkyl peroxides
are more stable than hydroperoxides and diacyl
peroxides [4]. The target of this study was evaluation
of the possibility to activate the decomposition of
dialkyl peroxides with quaternary ammonium halides
and investigation of the medium effect on the kinetic
parameters and mechanism of the process. As objects
of the study we selected the most accessible dicumyl
peroxide (I) and cumyl tert-butyl peroxide (II).
1
070-4280/01/3706-0814$25.00 2001 MAIK Nauka/Interperiodica

DIALKYL PEROXIDES DECOMPOSITION
815
Table 1. Initial decomposition rates of dialkyl peroxides
From the above data may be constructed the following
in various solvents, 90 C
hypothetical scheme of peroxide I decomposition.
a
8
a
Peroxide [Et NBr], Solvent
E
W0 10 ,
mol l s
4
1
1 1b
mol l
(1)
CumOOCum
MeCN 37.5 5.2 4.1 0.7
DMF 36.7 2.6 5.2 1.1
i-PrOH 18.3 8.7 10.8 0.5
i-PrOH 11.6 0.6
AcOH 6.15 14.6 26.5 3.6
0
0
0
.1
.1
.1
AcOH
MeCN
MeCN
i-PrOH
AcOH
92.9 4.1
0.97 0.12
1.93 0.43
10.8 0.6
286 22
(
2)
3)
CumOOBu-t
a
b
Data from [7]. W was determined up to 10% conversion.
0
(
Note the significant difference in products arising
at peroxide I decomposition in various solvents
(
Table 2). In the literature as the main products of
peroxide I decompositions were described 2-phenyl-
propan-2-ol and acetophenone, however we detected
in the reaction mixture also 2-phenylpropene, 2-
phenyl-1,2-epoxypropane, and 1-acetoxy-2-phenyl-
propan-2-ol. The selectivity of decomposition product
formation we calculated in moles per 1 mole of
decomposed peroxide.
(4)
In 2-propanol and dimethylformamide the main
decomposition product is 2-phenylpropan-2-ol, in
acetic acid alongside this compound and acetophenone
arise 2-phenylpropene, 2-phenyl-1,2-epoxypropane,
and also 1-acetoxy-2phenylpropan-2-ol.
(5)
(
6)
7)
(
(
8)
9)
Fig. 1. DEcomposition of dicumyl peroxide in acetic acid,
9
0 C. (1) Thermal decomposition; (2) Decomposition in
(
the presence of tetraethylammonium bromide.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 6 2001

8
16
MAKSYUTA et al.
1
Table 2. Selectivity of products formation in decomposition of dialkyl peroxides, 90 C, c 0.1 mol l
0
1
Decomposition products, mol mol of decomposed peroxide
Solvent [Et NBr], X, %
4
mol/l
aceto- 2-phenylpro- 2-phenyl- 2-phenyl-1,2- 1-acetoxy-2-phe-
2-phenylpro-
phenone
pan-2-ol
propene epoxypropane
nylpropan-2-ol
pane-1,2-diol
a
Dicumyl peroxide
DMF
DMF
0
0.1
0
4
0.25
0.22
1.55
0.19
0.35
0.11
0.69
0
1.75
1.78
0.45
1.81
0.63
1.89
0.13
1.5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
7.8
0.9
11
6.4
9.7
21.5
17
MeCN
i-PrOH
i-PrOH
i-PrOH
AcOH
AcOH
0
b
0.1
0.1
0
1.01
0
0.98
0.041
0
0
0.15
0.41
0.06
0.05
0.1
c
Cumyl tert-butyl peroxide
MeCN
i-PrOH
AcOH
AcOH
0
0
0
0.1
2.5
0.78
0.12
0.11
0.14
0.22
0.1
0.05
0.14
0
0
0
0.31
0.23
0
0
0.2
0.29
0
0.29
45.5
100
100
0.49
0.34
0.2
0
a
b
c
Conversion in 29 h. Et N Cl. Conversion in 60 h.
4
It is expectable that the primary product of peroxide solvents in the course of reaction was sufficient for
I decomposition would be cumyloxy radical III that
can undergo fragmentation into acetophenone IV and
a methyl radical or can abstract hydrogen atom from
solvent or another species. This hydrogen abstraction
provides 2-phenylpropan-2-ol (V) [8]. The ratio of
compounds IV and V shows the rate ratio of the two
processes; the latter is governed by the temperature
and energy of rupture of the C H or O H bonds in
the solvent molecules [9]. For instance, at peroxide I
decomposition in 2-propanol alcohol V forms con-
siderably faster than occurs fragmentation of radical
III (Table 2). In acetonitrile the fragmentation rate is
higher than that of alcohol V formation, and aceto-
phenone becomes the major product of the reaction.
ring opening along this path. Aldehyde VIII, product
of epoxy ring rearrangement, was not detected in the
reaction mixture.
The dehydration of alcohol
-phenylpropene [reaction (9)] as is confirmed by the
V
furnishes
2
form of product accumulation curves (Fig. 2).
The composition of products of peroxide II
thermolysis (expressed in mol mol 1 of peroxide
decomposed) is given in Table 2. We did not
investigate the volatile products originating from the
tert-butyl part of the molecule.
The peroxide decomposition in the presence of
quaternary ammonium halides was carried out at
equimolar concentration of peroxide and salt. We
established that the solvent character considerably
affected the salt activity in the peroxide decomposi-
tion.
When alkoxy radical attacks the peroxide molecule
may occur hydrogen abstraction from a methyl group
resulting in a -peroxy radical (A) [reaction (4)]
[
6, 9]. The intermolecular homolytic substitution
within -peroxy radical affords 2-phenyl-1,2-epoxy-
propane (VI). The epoxy ring is unstable and depend-
ing on the solvent and temperature it may open to
provide secondary products: 2-phenyl-2-methyl-
propanal, 1-acetoxy-2-phenylpropan-2-ol, and also
The presence of tetraethylammonium bromide
(Et N Br) during the decomposition of peroxide I in
4
dimethylformamide does not affect the process rate
or products composition. The difference in the reac-
tion rates is within the accuracy of gas-chromato-
graphic analysis. The qualitative composition and
ratio of reaction products are identical to the data
obtained with thermal degradation. In the presence of
2
-phenylpropane-1,2-diol [reactions (6, 7, 8)]. Ester
VII readily forms in acetic acid at 60 C within 1 h as
show special experiments. Diol IX can arise in the
presence of water; thus the water content in the
Et N Cl in 2-propanol the ratio of degradation
4
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 6 2001

DIALKYL PEROXIDES DECOMPOSITION
products changes, and arises additionally olefin X
817
originating from dehydration of alcohol V. However
in the presence of Et N Br the set of decomposition
4
products of peroxide I remains the same.
Et N Br considerably affects the rate and de-
4
composition products when the reaction is carried out
in acetic acid. In the presence of the salt grows the
rate of alcohol V formation as compared to the rate of
fragmentation, decreases the fraction of olefin X,
increases the amount of ester VII, and that of epoxide
VI is reduced. The rate of the activated decomposi-
tion is similar to that of thermolysis (Table 1).
Thus the data of this study show that the solvent
character significantly affects the activity of tetra-
ethylammonium halides in the decomposition process
of dialkyl peroxides. The series of alteration in the
thermal decomposition rate is in agreement with the
change in the solvent electrophilicity.
Fig. 2. Accumulation of 2-phenylpropene (1) and
2-phenylpropan-2-ol (2) at the thermal decomposition
of dicumyl peroxide in acetic acid, 90 C.
The solutions of the peroxides under study were
maintained at constant temperature in the sealed
ampules. The temperature 90 C was maintained with
The effect of salts on the kinetic parameters and
decomposition mechanism in dimethylformamide and
acetonitrile is negligible, and only the decomposition
in acetic acid and 2-propanol is accelerated in the
presence of salts. The presence of salts considerably
affects the reaction products composition indicating
that the transformation of the cumyloxy radical shifts
in the direction of proton abstraction.
the accuracy 0.05 C. The initial reagents concentra-
1
tions were as follows: ROOR, 0.1 mol l ; Et N Hlg,
.1 mol l .
4
1
0
The consumption of peroxides and accumulation of
decomposition products was determined by GLC
using a capillary column CP-Sil 5CB Film-0.12 m,
1
0 m long, internal diameter 0.25 mm. It was pre-
liminary shown at that the use of capillary columns at
evaporator temperature less than 200 C the chromato-
graphic separation of peroxides was not accompanied
by their thermal decomposition [11]. The analysis
was carried out on a Chrompack chromatograph
equipped with the flame-ionization detector,
evaporator temperature 170 C, detector at 250 C,
oven temperature programmed from 50 till 170 C at
a rate 7 C/min. The reactant concentrations was
evaluated by internal standard method, biphenyl
standard.
EXPERIMENTAL
Acetonitrile (Aldrich, 99.3%) was used without
further purification. 2-Propanol, acetic acid, and
dimethylformamide were purified as in [10].
Tetraethylammonium bromide (Aldrich, 99%) was
dried at reduced pressure at 353 K in Fisher gun.
Tetraethylammonium chloride was purified by
reprecipitation with cold ethyl ether from hot ethanol
solution. The precipitate was collected on glass frit
filter and dried at 329 K in Fisher gun at reduced
pressure over P O . The salts were kept in a glove
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2
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2
5
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