Alkylation of alkali metal salts of hydroperoxides with haloalkanes in dipolar nonhydroxyl solvents

Article abstract of DOI:10.1134/S1070363207120031

The possibility of alkylation with chloroalkanes of cumyl hydroperoxide sodium salt hexahydrate in dopolar nonhydroxyl solvents with high donor numbers was examined. The kinetic featutes of the process in hexamethylphosphoric triamide were studied.

Full text of DOI:10.1134/S1070363207120031

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 12, pp. 2096 2100.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
1954.
A.F. Choban, I.S. Abramyuk, A.S. Lyavinets, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 12, pp. 1950
Alkylation of Alkali Metal Salts of Hydroperoxides
with Haloalkanes in Dipolar Nonhydroxyl Solvents
A. F. Choban, I. S. Abramyuk, and A. S. Lyavinets
Fed’kovich National University,
ul. Kotsyubinskogo 2, Chernovtsy, 58012 Ukraine
Received March 28, 2007
Abstract The possibility of alkylation with chloroalkanes of cumyl hydroperoxide sodium salt hexahydrate
in dopolar nonhydroxyl solvents with high donor numbers was examined. The kinetic featutes of the process
in hexamethylphosphoric triamide were studied.
DOI: 10.1134/S1070363207120031
One of the most widely used procedures for prepar-
ing dialkyl peroxides is based on the nucleophilic
substitution of the halogen atom in the corresponding
organic compound [1]:
anions. The solvent effect was examined using as
example the alkylation of peroxy anions with halo-
alkanes, which is a route to various functionalized
peroxides.
We showed previously [4] that the system of a
dipolar nonhydroxyl solvent and an alkali allows the
preparation of ROOM and subsequent alkylation to be
performed as one-pot synthesis. However, the kinetic
features of the alkylation of hydroperoxide salts virtu-
ally were not examined. Therefore, the goal of this
study was to examine the possibility of preparing
ROOR from hydrated hydroperoxide salts in dipolar
nonhydroxyl solvents and to elucidate the kinetic
relationships of the process.
RX + R OOM
ROOR + MX,
M = K, Na.
This procedure requires the use of an anhydrous
alkali metal salt of a hydroperoxide, which is prepared
by the reaction of ROOH with an alkali metal amide
or hydride [2]. However, this route involves certain
problems. Therefore, in later studies the reactions
were performed with hydrated hydroperoxide salts,
which are formed by reactions of ROOH with aqueous
alkalis [2]. However, in this case the yield of dialkyl
peroxides is lower, and the process is often accom-
panied by side reactions of the hydroperoxide salt
with the solvent.
As hydroperoxide salt we used cumyl hydroper-
oxide sodium salt hexahydrate (Na-CHP), which is
readily prepared by the reaction of ROOH with NaOH
[2]. The initial rate of consumption of Na-CHP (W0)
was considered as the alkylation rate, because no
other (side) pathways of the hydroperoxide consump-
tion were observed. In particular, a correlation is
observed between the salt conversion and the ROOR
yield (Fig. 1). Certain differences between these quan-
tities may be associated with the loss of peroxides in
the course of their isolation.
In this study we examined the reactions of hydrated
alkali metal salts of hydroperoxides with haloalkanes
in some dipolar nonhydroxyl solvents. The nucleo-
philic reactions of hydroperoxides and their salts in
such solvents have been studied inadequately. At the
same time, the reactivity of a charged nucleophile
strongly depends on the degree of its solvation. The
use of dipolar nonhydroxyl solvents is one of the
ways to enhance the reactivity of the nucleophile,
because in such media it is mainly solvated by the
mechanism of dispersion interactions. Therefore, such
solvents substantially enhance the efficiency of nu-
cleophilic reactions [3]. In this connection, we at-
tempted to realize the advantages of dipolar nonhy-
droxyl solvents in nucleophilic reactions of peroxy
As alkylating agents we chose chloroalkanes,
which are more readily available and cheaper than
bromoalkanes. Among dipolar nonhydroxyl solvents
for the alkylation of Na-CHP we used hexamethyl-
phosphoric triamide (HMPA), dimethylformamide
(DMF), propylene carbonate (PC), and trimethyl
phosphate (TMP).
The results of studying the effect of dipolar non-
hydroxyl solvents on the alkylation of ROONa 6H2O
2096

ALKYLATION OF ALKALI METAL SALTS OF HYDROPEROXIDES
2097
Table 1. Effect of dipolar nonhydroxyl solvents on the alkylation of CHP sodium salt hexahydrate with chlorohexane.
Composition of the system: (Na-CHP) = (HexCl) = 3 mmol, V(solvent) 15 ml, T 298 K
W0 103,
Na-CHP
conversion, %
ROOR
yield, %
Reaction
time, min
Solvent
DN
1
moll 1 s
HMPA
DMF
TMP
PC
38.8
26.6
23.0
15.1
30.0
36.1
20.6
69.0
1.52
0.06
66
60
53
50
30
90
Na-CHP is insoluble in TMP
0
0
0
240
with 1-chlorohexane are summarized in Table 1. As
can be seen, the alkylation occurs only in HMPA and
DMF, which are known as effective donor solvents
well solvating cations. Anions in these solvents re-
main virtually nonsolvated. HMPA is one of the
strongest donor solvent as judged from its donor
number DN [5]. We found that in this solvent the
alkylation of ROONa 6H2O is the most efficient with
respect to both the reaction rate and product yield.
In dimethylformamide, which is inferior to HMPA in
the electron-donor power, these parameters are consid-
erably lower. Thus, only dipolar nonhydroxyl solvents
with high donor numbers favor alkylation of hydrated
sodium salt of cumyl hydroperoxide with chloroal-
kanes.
n, %
80
1
2
60
40
20
0
0
0.2
0.4 0.6
0.8 1.0
1.2
[HexCl], M
Fig. 1. (1) Conversion of Na-HPC and (2) yield of hexyl
cumyl peroxide as functions of the initial concentration
of 1-chlorohexene.
(Na-CHP) 3 mmol, V(HMPA)
0
The decisive role of solvent in the reaction under
consideration was additionally confirmed in a series of
experiments in which the alkylation of Na-CHP was
performed in a binary solvent, HMPA methanol
(MeOH). The dependence of the main process param-
eters on the methanol volume fraction is presented in
Table 2. As can be seen, the initial rate drastically
decreases on adding even minor amounts of MeOH.
For example, even at (MeOH) 5% the rate decreases
by a factor of 1.5, and at 15%, by more than an order
of magnitude. The conversion of ROONa 6H2O also
depends on the MeOH concentration, drastically de-
creasing even at (MeOH) 15%. Thus, the strong
inhibiting effect of methanol, which is capable to
solvate both cations and anions, on the alkylation of
Na-CHP confirms the decisive role of the medium in
the process.
15 ml, T 298 K, reaction time 90 min.
In going from primary to secondary haloalkanes,
the Na-CHP conversion and dialkyl peroxide yield
decrease (Table 3). We attribute this effect to a change
in the mechanism of nucleophilic substitution of the
halogen atom in haloalkane by ROO . However, we
have not examined the alkylation of Na-CHP with
secondary haloalkanes in detail.
Table 2. Dependence of the initial consumption rate and
conversion of Na-CHP on the composition of the binary
solvent HMPA methanol. Composition of the system:
0(Na-CHP) = 0(HexCl) = 3 mmol; V(solvent) 15 ml;
T 298 K
(MeOH),
%
W0 103,
Na-CHP
conversion, % yield, %
ROOR
1
Then we performed a series of experiments on
alkylation of Na-CHP in HMPA with various halo-
alkanes (Table 3). As expected, higher rates were
observed with bromoalkanes. However, chloroalkanes
also ensure relatively high degrees of conversion of
the hydroperoxide salt and, correspondingly, relatively
high ROOR yields. Thus, these experiments show
that, in the synthesis of dialkyl peroxides from hydro-
peroxide salts in HMPA, expensive bromoalkanes can
be replaced by cheaper chloroalkanes.
moll 1 s
0
5
1.52
0.98
0.35
0.083
0.080
0.080
0.073
66
68
60
6
5
6
53
52
48
10
15
30
50
100
No data
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 12 2007

2098
CHOBAN et al.
3.5
3.0
100
80
3.0
2.5
2.0
1.5
80
60
40
2
2.5
2.0
1
1
60
40
1.5
1.0
2
20
0
0.5
0
1.0
20
0
0.5
0
0
0.1
0.2
0.3
0.5
0.5
[Na-CHP]0, M
0
0.2
0.4
0.7
0.8
1.0
[HexCl]0, M
Fig. 2. (1) Initial rate of consumption of available
oxygen and (2) yield of hexyl cumyl peroxide as func-
Fig. 3. (1) Initial rate of consumption of CHP sodium
salt and (2) yield of hexyl cumyl peroxide as functions
of the initial concentration of 1-chlorohexane;
tions of the initial Na-CHP concentration; (Na-CHP)
0
3 mmol, V(HMPA) 15 ml, T 298 K, reaction time
(Na-CHP) 3 mmol, V(HMPA) 15 ml, T 298 K, reac-
0
90 min.
tion time 90 min.
As the best results in alkylation of ROONa 6H2O
with chlorohexane were obtained in hexamethylphos-
phoric triamide, the kinetic features of the process
were examined in this solvent.
The dependence of the salt alkylation rate on the
chlorohexane concentration is plotted in Fig. 3. As
can be seen, the initial portion of the dependence of
W0 on the chlorohexane concentration is linear, after
which W0 passes through a small maximum and then
starts to slowly decrease. Apparently, large excess of
the haloalkane significantly alters the properties of the
medium, its basicity, and, quite probably, even the
solvation of anions. However, we have not performed
further studies in this direction.
The dependences of the initial consumption rate
and conversion of Na-CHP on its initial concentration
are plotted in Fig. 2. As can be seen, starting from
a Na-CHP concentration of 0.1 M, the dependence of
the initial rate of consumption of available oxygen on
the salt concentration is linear, i.e., the reaction is
first-order with respect to Na-CHP. The constant k
determined from the slope of the linear portion is
The linearity of the ascending portion of curve 1
in Fig. 3 suggests the first order of the reaction with
respect to haloalkane. The constant k determined
3
1
7.3 10 s . We have not examined the reaction
features at Na-CHP concentrations lower than 0.1 M.
At the same time, it can be assumed that at low salt
concentrations, when the kinetic order of the reaction
changes, water of hydration plays a significant role.
3
1
from the slope of this linear portion is 6.8 10 s .
Also, as seen from Fig. 3, the initial rate of the Na-
CHP consumption and the yield of ROOR depend on
the initial haloalkane concentration in the similar
manner.
Table 3. Results of alkylation of Na-CHP with various
haloalkanes. Composition of the system: 0(Na-CHP) =
0(R Hal) = 3 mmol, V(HMPA) 15 ml; T 298 K
Thus, the alkylation of cumyl hydroperoxide sodi-
um salt hexahydrate with chlorohexane in hexameth-
ylphosphoric triamide is a second-order reaction and
is described by the following rate equation:
Na-CHP
conversion, % yield, %
ROOR
W0 103,
R Hal
1
moll 1 s
W0 = k[C6H5C(CH3)2OONa 6H2O] [n-HexCl], (1)
n-HexCl
n-OctCl
n-OctBr
sec-OctCl
sec-OctBr
n-BuBr
66
71
74
20
21
63
37
53
63
67
16
18
56
31
1.52
1.51
3.71
1.20
1.31
2.01
1.30
In the majority of experiments, Na-CHP was dis-
solved in HMPA. Electrical conductivity data show
(Table 4) that dissolution of Na-CHP in HMPA is
accompanied by its partial dissociation:
n-BuCl
C6H5C(CH3)2OONa 6H2O + S
C6H5C(CH3)2OO nH2O + Na+ S + (6 n)H2O, (2)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 12 2007

ALKYLATION OF ALKALI METAL SALTS OF HYDROPEROXIDES
2099
where S = O=P[N(CH3)2]3.
Table 4. Electrical conductivity of solutions in HMPA at
298 K
Quite probably, in the system Na-CHP HMPA
there is an equilibrium between solvated and nonsol-
vated peroxy anions:
(Na-CHP),
mmol
(n-HexCl),
mmol
Specific conductivity
1
103, Scm
C6H5C(CH3)2OO H2O + S
C6H5C(CH3)2OO + S HOH.
1.081
1.114
1.091
2.976
4.324
(3)
3
6
Also, there are some other equilibria. The set of the
equilibria occurring in the system govern the alkyla-
tion of Na-CHP. At the same time, specifically the
occurrence of reaction (3), possible, as we believe,
only in a solvent with very high donor number and
dielectric permittivity, is apparently responsible for
the fact that the alkylation of the hydrated salt of
cumyl hydroperoxide was fairly efficient only in
HMPA. The inhibition or even full suppression of
reactions of peroxy anions by water molecules was
reported in [6].
3
3
3
ture-controlled cell with a magnetic stirrer at 298 K.
The reactor was charged with the required amounts of
cumyl hydroperoxide sodium salt hexahydrate and the
solvent, after which the mixture was brought to the
required temperature over a period of 20 min with
stirring, and haloalkane was added. The instant of its
addition was considered as the start of the reaction.
The reaction progress and kinetics were monitored by
determining available oxygen in samples by iodomet-
ric titration under mild conditions (without heating).
Under these conditions, dialkyl peroxides do not react
with iodide ions. The accumulation of dialkyl perox-
ides was monitored by high-performance liquid chro-
matography following the procedure we developed
previously [7]. Measurements were performed with
a Milikhrom-1A chromatograph equipped with a UV
detector. Chromatographing conditions: 64 2-mm
column packed with Separon-C18 (5.0 m), 5000 TP;
The electrical conductivity data show that the con-
centration of nonsolvated peroxy anions in HMPA is
low; however, we believe that specifically these spe-
cies enter into the nucleophilic reaction with chloro-
hexane:
C6H5C(CH3)2OO + RCl
C6H5C(CH3)2OOR + Cl .
(4)
Taking into account the kinetic relationships ob-
tained, we can conclude that reaction (4) controls the
overall process rate. Thus, alkylation of cumyl hydro-
peroxide sodium salt hexahydrate with chlorohexane
in hexamethylphosphoric triamide solution occurs by
the ionic mechanism and is a second-order reaction
which can be described by the classical SN2 mechan-
ism. The decisive factor providing high rate of Na-
CHP alkylation with chloroalkanes and relatively high
yields of dialkyl peroxides is the high nucleophilic
power of the solvent. In particular, irrespective of
the way used to vary the donor power of the solvent,
replacement of HMPA by DMF or addition of MeOH
or excess HexCl, the result was always similar: The
initial reaction rate, Na-CHP conversion, and dialkyl
peroxide yield decreased.
1
eluent acetonitrile water (9 : 1), feed rate 50 l min ;
sample volume 1 10 l; working wavelength 250 nm.
The consumption of haloalkanes was monitored by
gas liquid chromatography on a Chrom-5 chromato-
graph equipped with a flame ionization detector.
A glass column (length 3 m, inside diameter 3 mm)
was packed with Chromaton N Super (0.16 0.22 mm)
impregnated with 5% SE-30. The vaporizer tempera-
1
ture was 473 K, and the heating rate, 12 K min .
The carrier gas was argon, flow rate 40 ml min .
1
The sample volume was 1 l.
Cumyl hydroperoxide sodium salt hydrate,
ROONa 6H2O, was prepared according to [2]. Halo-
alkanes and solvents were purified by standard pro-
cedures [8].
Relatively high reaction rates and high yields of
ROOR were also observed when hydroperoxides were
alkylated with haloalkanes in superbasic media con-
sisting of a dipolar nonhydroxyl solvent with a high
donor number and an alkali [4].
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EXPERIMENTAL
1952, vol. 22, no. 3, p. 784.
Experiments on alkylation of cumyl hydroperoxide
sodium salt hexahydrate were performed in a tempera-
2. Sokolov, P.A. and Aleksandrov, Yu.A., Usp. Khim.,
1978, vol. 47, no. 2, p. 307.
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CHOBAN et al.
3. Lyavinets, A.S., Zh. Fiz. Khim., 2000, vol. 74, no. 7,
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