Specific features of alkylation of organic hydroperoxides with chlorinated hydrocarbons in superbasic media

Article abstract of DOI:10.1023/B:RUGC.0000045866.17932.f7

Alkylation of organic hydroperoxides with chlorinated hydrocarbons in superbasic media (dipolar nonhydroxyl solvent-strong ionic base) was performed.

Full text of DOI:10.1023/B:RUGC.0000045866.17932.f7

Russian Journal of General Chemistry, Vol. 74, No. 7, 2004, pp. 1068 1071. Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 7, 2004,
pp. 1157 1161.
Original Russian Text Copyright
2004 by Lyavinets, Abramyuk, Choban.
Specific Features of Alkylation of Organic Hydroperoxides
with Chlorinated Hydrocarbons in Superbasic Media
A. S. Lyavinets, I. S. Abramyuk, and A. F. Choban
Fed’kovich National University, Chernovtsy, Ukraine
Received August 8, 2002
Abstract Alkylation of organic hydroperoxides with chlorinated hydrocarbons in superbasic media (dipolar
nonhydroxyl solvent strong ionic base) was performed.
Organic peroxides find increasing use as models
and objects in studying numerous basic problems of
natural science. Therefore, it is of interest to find new,
more convenient synthetic routes to them. For this
purpose, it is suggested to use superbasic media con-
sisting of a dipolar nonhydroxyl solvent and a strong
ionic base. Such media promote nucleophilic reac-
tions.
First, we extended the range of reagents used.
Among hydroperoxides, we used cumene hydroperox-
ide I, tert-butyl hydroperoxide II, and 1-(1-methyl-1-
tert-butylperoxyethyl)-4-(1-hydroperoxy-1-methyleth-
yl)benzene III. The alkylating agents were 1-chloro-
hexane (HexCl) and benzyl chloride (BnCl). As super-
basic medium, in most experiments we used HMPA
NaOH, which provides better results in alkylation of
hydroperoxides, compared to the related system with
KOH.
We briefly reported previously that the use of su-
perbasic media [hexamethylphosphoramide (HMPA)
alkali metal hydroxide] significantly improves syn-
thesis of organic peroxides by alkylation of hydroper-
oxides (in particular, cumene hydroperoxide) with
haloalkanes [1].
The results of this experimental series are given in
Table 1. These data show that alkylation with chloro-
hexane in HMPA NaOH (system nos. 1 4) is fairly
efficient. For example, with HexCl as alkylating agent
the yield of dialkyl peroxides was 40 70% or even
higher. The previously known procedures for alkyla-
tion of hydroperoxides with chlorides do not ensure
the yields of dialkyl peroxides higher than 15 30%
[2 4]. Therefore, major attention was given to alkyla-
tion with bromides, which are less available and more
expensive than chlorides. The efficiency of superbasic
systems dipolar nonhydroxyl solvent strong ionic
base in alkylation of hydroperoxide I with bromide
was reported in [1]. The same paper also reported that
the yield of dialkyl peroxides in alkylation of I with
HexCl in HMPA alkali was as low as 20%. However,
improvement of the procedure for isolation of the
reaction products allowed the yield to be increased
to 46 51%.
This well-known reaction [2, 3] under traditional
conditions occurs within several tens of hours, with
the yields of dialkyl peroxides being poor [3]. Further-
more, the process involves two preparative steps:
synthesis of the hydroperoxide salt and alkylation
of ROOM (M = Na, K), with each step requiring
appropriate conditions.
With superbasic media (dipolar nonhydroxyl sol-
vent strong ionic base), it appears feasible to combine
both steps in a one-pot synthesis, with improvement
of the synthesis parameters and shortening of the
reaction time. Further advantages of this procedure as
applied to preparation of dialkyl peroxides are higher
purity of the target products, simplicity of their isola-
tion, and safety of the process as a whole. The syn-
thesis can be schematically described by Eq. (1).
One more advantage of chloroalkanes should be
noted: whereas bromides are partially hydrolyzed [1],
chlorides give virtually no by-products. In particular,
with HexCl no 1-hexanol (hydrolysis product) was
detected. For both HexCl and BnCl, a clear correla-
tion was observed between the consumptions of the
hydroperoxide and chlorinated hydrocarbon.
MOH/HMPA, 298 K
(1)
ROOH + R X
ROOR .
MX, H2O
This work continues our studies of specific features
of alkylation of hydroperoxides with halogenated
hydrocarbons in superbasic media of the above com-
position.
Since hydroperoxides in the superbasic medium
HMPA NaOH take part in alkylation only, the initial
1070-3632/04/7407-1068 2004 MAIK Nauka/Interperiodica

SPECIFIC FEATURES OF ALKYLATION OF ORGANIC HYDROPEROXIDES
1069
Table 1. Alkylation of hydroperoxides in the superbasic medium HMPA NaOH (30 ml of HMPA, 298 K)
Amount, mol
System
no.
v0 103,
Conversion,
b
Composition
, min Yield,
%
1
a
mol l 1 s
%
ROOH
R Cl
NaOH
1
2
3
4
5
6
7
I 1-HexCl NaOH
I 1-HexCl NaOH
II 1-HexCl NaOH
III 1-HexCl NaOH
I BnCl NaOH
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.010
0.015
0.015
0.015
0.010
0.015
0.015
0.10
1.50
0.61
1.50
0.61
0.70
0.07
68 (70)
63 (95)
70 (88)
60 (93)
80 (86)
65 (100)
60 (45)
120
60
120
60
90
60
51
46
45
74
10
5
0.015
0.015
0.015
0.01
0.015
0.015
I BnCl NaOH
II BnCl NaOH
210
9
a
b
Without parentheses, halogenated hydrocarbon; in parentheses, hydroperoxide.
Yield of dialkyl peroxide.
ROOM + H2O,
rate of consumption of hydroperoxides and their salts
(v0) be considered as a kinetic parameter of the
alkylation process. Comparison of the initial rates
allows the hydroperoxides to be ranked in the follow-
ing order with respect to the reactivity: III I > II.
ROOH + MOH
(2)
ROOM + S + HOOR
ROOM + S + H2O
ROOH + OH
ROO HOOR + M+ S, (3)
ROO H2O + M+ S, (4)
ROO + H2O,
ROO + ROOH S, (6)
ROO + HOH S. (7)
(5)
It is quite natural that the kinetic parameters ob-
tained for hydroperoxides III and I are virtually equal,
since compound III can be actually considered as a
substituted cumyl hydroperoxide, behaving similarly
to I in reactions that do not involve the peroxy group.
The difference between hydroperoxides I and II is
attributable in part to the somewhat higher acidity of I
[2]: pKa 12.6 and 12.8, respectively. It should be
noted that these acidity constants refer to aqueous
solutions. Apparently, in dipolar nonhydroxyl solvents
the difference between the acidities of these hydroper-
oxides will be more significant.
ROO HOOR + S
ROO H2O + S
Since no dialkyl peroxides are formed under the
similar conditions but without alkali, the peroxy anion
can be considered as a key agent in alkylation of hy-
droperoxides with a haloalkane [reaction (8)]:
ROO + R Cl
ROOR + Cl .
(8)
In contrast to HexCl, in alkylation with BnCl the
yields of dialkyl peroxides were low. Furthermore,
large amounts of benzaldehyde and of the alcohol cor-
responding to the hydroperoxide taken were detected.
The low yields of organic peroxides in HMPA
NaOH with BnCl as alkylating agent are due to the
nature of the products formed. In particular, a specific
feature of such dialkyl peroxides is the presence of
labile hydrogen atoms in the -position relative to the
peroxy group. There are indications in the literature
that such peroxides decompose under the action of
nucleophiles to give the corresponding alcohol and
aldehyde [6]. In the system II BnCl HMPA NaOH,
among the reaction products we also detected benzal-
dehyde and tert-butanol. Their accumulation in the
superbasic system suggests realization of this decom-
position pathway in our case also [scheme (9)]:
To account for the different results obtained in
alkylation of hydroperoxides in the chosen superbasic
medium with HexCl and BnCl, let us consider the
sequence of possible transformations (2) (7). The
reaction of a hydroperoxide with an alkali initially
gives a salt, which dissociates under the action of a
solvent (S) and proton-donor components. Formation
of a salt ROOM and its dissociation in the system
hydroperoxide superbase were studied in detail and
were described in [5].
H
H
H
H
H2O
OH
(2)
Ph C ^O O Bu-t
Ph C ^O O Bu-t
Ph C=O + O Bu-t
Ph C=O + t-BuOH.
|
H2O
|
H
OH
^
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 7 2004

1070
LYAVINETS et al.
Table 2. Solvent effect on alkylation of hydroperoxide I with hexyl chloride (amounts of I, HexCl, and NaOH 3 mmol
each; solvent volume 15 ml; 323 K)
1
Solvent
DN
v0 103, moll 1 s
Conversion, %a
, min
Yield, %b
HMPA
DMF
Trimethyl phosphate
Propylene carbonate
38.8
26.6
23.0
15.1
0.71
0.04
0
68
73
2
90
90
120
120
51
42
0
0
0
0
a
b
Hydroperoxide I.
Yield of dialkyl peroxide.
Apparently, the high rate of decomposition of the
To sum up, one more conclusion can be made:
Superbasic media (dipolar nonhydroxyl solvent
strong ionic base) are efficient tools in alkylation of
hydroperoxides with haloalkanes, allowing the use of
chloroalkanes as alkylating agents instead of more
reactive but less available bromoalkanes.
forming peroxide prevents its accumulation in the
superbasic medium. Since decomposition of the per-
oxide is a secondary process, there will be a certain
delay in accumulation of benzaldehyde and tert-butyl
alcohol. Similar transformations occur in the system
with cumene hydroperoxide. Furthermore, the dialkyl
peroxide prepared from I and BnCl decomposes by
reaction (9) more readily, as suggested by comparison
of the amounts of the converted ROOH and formed
ROOBn.
The next step of our study was examination of the
effect of the solvent on alkylation of I with HexCl in
the presence of NaOH. For this purpose, along with
HMPA, we tested dimethylformamide (DMF), tri-
methyl phosphate, and propylene carbonate. The
results are listed in Table 2. It is seen that hydroper-
oxide I is alkylated only in HMPA and DMF. In the
other solvents, no accumulation of dialkyl peroxides
was observed in 2 h.
We believe that the possibility of reaction (9)
should also be taken into account with alkyl peroxides
containing an n-alkyl radical. However, such perox-
ides should decompose much more difficultly, since
the -hydrogen atoms in them are less active. For
example, about 20% of dialkyl peroxide decomposed
in system no. 1, whereas in system no. 2 (with excess
alkali) the fraction of the decomposed peroxide was
considerably higher.
We found that alkylation in HMPA and DMF oc-
curs by similar mechanism. This is indicated, in par-
ticular, by the results of alkylation of I with 1-chloro-
hexane in the binary solvent HMPA DMF (Table 3).
The calculated initial rates of the process in the binary
solvent were determined by Eq. (10):
Our results allow an important conclusion: In syn-
thesis of dialkyl peroxides by alkylation of hydroper-
oxides with halogenated hydrocarbons containing
labile -hydrogen atoms, the alkali should be taken
in an equimolar amount.
logv0(HMPA DMF) = N(HMPA)logv0(HMPA)
+ N(DMF)logv0(DMF),
(10)
where v0(i) are the alkylation rates in individual sol-
vents i and N(i) are the mole fractions of solvents i in
the binary solvent.
Table 3. Experimental and calculated [Eq. (10)] rates of
alkylation of hydroperoxide I
logv0(HMPA DMF)
As seen, the experimental and calculated values of
N(HMPA)
N(DMF)
logv0(DMF HMPA) are very close.
experiment
calculation
The fact that alkylation of the hydroperoxides in
the presence of MOH in HMPA and DMF occurs only
is primarily due, in our opinion, to the specific solvat-
ing properties of these solvents. These solvents are
strong electron pair donors; therefore, they efficiently
solvate cations. However, they do not act as hydrogen
bond donors, since their C H bonds are insufficiently
polar. Specifically these features of solvation with di-
polar nonhydroxyl solvents provide accumulation in
the reaction medium of strong nucleophiles, virtually
1
0
3.158
3.328
3.602
3.810
4.013
4.185
4.328
4.398
3.158
3.332
3.604
3.815
4.013
4.150
4.323
4.398
0.86
0.64
0.47
0.31
0.20
0.06
0
0.14
0.36
0.53
0.69
0.80
0.94
1
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 7 2004

SPECIFIC FEATURES OF ALKYLATION OF ORGANIC HYDROPEROXIDES
1071
nonsolvated peroxy anions. For example, peroxy
anions formed upon addition of a hydroperoxide to a
superbasic medium give complexes with hydroxy com-
pounds (in our case, with nondissociated hydroperox-
ide and water). This significantly decreases their reac-
tivity; we observed such an effect in oxidation of
dimethyl sulfoxide with peroxy anions in a super-
basic medium, when water was added to the reaction
system [7]. At the same time, dipolar nonhydroxyl
solvents also form hydrogen bonds with such hydroxy
compounds. Therefore, the presence of such solvents
shifts the equilibrium toward formation of weakly
solvated peroxy anions. Under such conditions, their
concentration is apparently low. However, their high
nucleophilicity ensures fast alkylation on adding halo-
alkanes. The consumption of haloalkanes shifts the
equilibrium toward accumulation of new weakly sol-
vated peroxy anions and further accumulation of dial-
kyl peroxides at high rates by the ionic mechanism.
ing the haloalkane was considered as the start of the
reaction. The reaction kinetics was monitored by
taking samples at regular intervals and analyzing them
by iodometric titration for the total content of the
hydroperoxide and its salt. As the kinetic criterion we
used the initial rate v0, which was determined by
graphic differentiation of the experimental kinetic
curve of the consumption of the hydroperoxide and its
salt. Experiments showed that v0 is comparable with
the rate of dialkyl peroxide accumulation, which was
determined by HPLC according to [10]; therefore, v0
can be considered as alkylation rate to a full measure.
Also, the reaction progress was monitored by GLC
(consumption of haloalkane, accumulation of transfor-
mation products of reagents and dialkyl peroxides).
The reaction products were isolated after stirring
for 60 120 min. To do this, 5 ml of distilled water
was added to 15 ml of the reaction mixture, and the
mixture was treated with hexane (5 5 ml). The hex-
ane extract was washed with water (3 5 ml) and
dried for 24 h over anhydrous Na2SO4. Then the sol-
vent and unchanged haloalkane were distilled off in a
vacuum. The dialkyl peroxides obtained were identi-
fied by 1H NMR spectroscopy at the Institute of
Organic Chemistry, National Academy of Sciences of
Ukraine.
At the same time, as seen from Table 2, not all
the dipolar nonhydroxyl solvents favor alkylation
of hydroperoxides with halogenated hydrocarbons.
In particular, in trimethyl phosphate and propylene
carbonate, no dialkyl peroxide is formed. An empiri-
cal semiquantitative characteristic of nucleophilic
properties of solvents is the donor number (DN) [8].
Experimental data show that only dipolar nonhydroxyl
solvents with relatively high DN ensure high reaction
rates. In HMPA, which has one of the highest donor
numbers, alkylation of hydroperoxides occurs consid-
erably faster than in DMF whose electron-donor
power is lower. Furthermore, the yield of dialkyl per-
oxide in HMPA NaOH is also lower than in DMF
NaOH. Similar trends are observed in other nucleo-
philic substitutions, in particular, in alkylation of
alkali metal carboxylates with haloalkanes [9]. At the
same time, no correlation was revealed between the
initial reaction rate and other parameters of the sol-
vents used (dielectric permittivity, polarity, polariza-
bility).
REFERENCES
1. Lyavinets’, O.S., Abram’yuk, I.S., and Chervin-
s’kii, K.O., Ukr. Khim. Zh., 1994, vol. 60, no. 8,
p. 587.
2. Rakhimov, A.I., Khimiya i tekhnologiya organiches-
kikh perekisnykh soedinenii (Chemistry and Techno-
logy of Organic Peroxy Compounds), Moscow:
Khimiya, 1979.
3. Ivanov, K.I. and Blagova, T.A., Zh. Obshch. Khim.,
1952, vol. 22, no. 3, p. 784.
4. Swern, D., Organic Peroxides, New York: Wiley,
1972, vol. 3, p. 1.
5. Lyavinets, A.S., Choban, A.F., Slipchenko, E.K., and
Chervinskii, K.A., Neftekhimiya, 1993, vol. 33, no. 5,
p. 445.
6. Sokolov, P.A. and Aleksandrov, Yu.A., Usp. Khim.,
1978, vol. 47, no. 2, p. 307.
Thus, the decisive factor ensuring high rates of
alkylation of hydroperoxides with halogenated hydro-
carbons and high yields of dialkyl peroxides in the
presence of strong ionic bases is the high nucleophi-
licity of the solvent.
7. Choban, A.F. and Lyavinets’, O.S., Ukr. Khim. Zh.,
1997, vol. 63, no. 2, p. 117.
EXPERIMENTAL
8. Gutmann, V., Coordination Chemistry in Non-Aqueous
Solutions, Wien: Springer, 1968. Translated under the
title Khimiya koordinatsionnykh soedinenii v nevod-
nykh rastvorakh, Moscow: Mir, 1971, p. 202.
9. Lyavinets’, O.S., Ukr. Khim. Zh., 1998, vol. 64, no. 3,
p. 49.
Alkylation of hydroperoxides with halogenated hy-
drocarbons was performed in a temperature-controlled
cell at 298 K. The cell was charged with alkali ground
under argon and with the purified solvent. This mix-
ture was kept at the required temperature for 30 min,
after which the hydroperoxide and, 1 min later, the
purified haloalkane were added. The moment of add-
10. Abramyuk, I.S. and Lyavinets, A.S., Zh. Anal. Khim.,
1994, vol. 49, no. 6, p. 599.
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