Tri-liquid system in the synthesis of dialkyl peroxides using tetraalkylammonium salts as phase-transfer catalysts

Article abstract of DOI:10.1016/j.apcata.2010.07.015

A highly effective method to synthesise dialkyl peroxides from alkyl hydroperoxides and alkyl bromides in a liquid-liquid-liquid system using tetraalkylammonium salts as phase-transfer catalysts is reported. This process was conducted in the presence of h

Full text of DOI:10.1016/j.apcata.2010.07.015

Applied Catalysis A: General 385 (2010) 208–213
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Tri-liquid system in the synthesis of dialkyl peroxides using
tetraalkylammonium salts as phase-transfer catalysts
Stefan Baj∗, Agnieszka Siewniak
The Silesian University of Technology, Chair of Chemical Organic Technology and Petrochemistry,
Krzywoustego 4, 44-100 Gliwice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly effective method to synthesise dialkyl peroxides from alkyl hydroperoxides and alkyl bromides
in a liquid–liquid–liquid system using tetraalkylammonium salts as phase-transfer catalysts is reported.
This process was conducted in the presence of highly concentrated aqueous KOH solutions and cyclohex-
ane as an organic solvent. In a liquid–liquid–liquid system, the phase-transfer catalyst forms an insoluble
third-liquid phase between the organic and aqueous phases that enables the catalyst to be recycled
multiple times. Dialkyl peroxides were obtained in high yields and with 100% selectivity.
© 2010 Elsevier B.V. All rights reserved.
Received 23 February 2010
Received in revised form 8 July 2010
Accepted 8 July 2010
Available online 15 July 2010
Keywords:
Dialkyl peroxides
Hydroperoxides
Phase-transfer catalysts
Liquid–liquid–liquid PTC
1. Introduction
soluble phase-transfer catalysts, such as quaternary onium salts
and crown ethers in two-phase L–L and L–S PTC systems [14,15], as
The development of catalytic processes that afford an easy
separation of the reaction mixture, easy removal of the catalyst,
and facile reuse of the catalyst is one of the main aims of chemical
research and the chemical industry today. These characteristics are
reflected in phase-transfer catalysis (PTC). Particularly, PTC meth-
ods conducted in a liquid–liquid–liquid system (L–L–L PTC) have
aroused considerable interest in recent years [1–12]. Compared
to conventional liquid–liquid PTC (L–L PTC), the phase-transfer
catalyst for L–L–L PTC can easily be recovered and recycled because
in this system, the catalyst forms a third-liquid phase between
the organic and aqueous layers. Moreover, reactions conducted
under L–L–L PTC conditions proceed with higher reaction rates and
yields. This system is also competitive with liquid–liquid–solid
systems (L–L–S PTC) because it affords easy catalyst separation
without necessitating immobilisation of the catalyst on a solid
carrier. Therefore, additional costs associated with the use of
expensive immobilised PTC catalysts can be avoided.
well as insoluble PTC catalysts, such as polymer-supported quater-
nary onium salts and polyethylene glycols in a L–L–S PTC system
[16,17]. Further, we have applied triphase L–L–L PTC to the syn-
thesis of dialkyl peroxides using polyethylene glycols and their
derivatives as PTC catalysts [18]. High yields of dialkyl peroxides
were achieved, and because the catalyst formed an insoluble liq-
uid phase, it could be reused several times. Thus, the present study
has focused on the application of quaternary ammonium salts as
phase-transfer catalysts in the synthesis of dialkyl peroxides with
alkyl hydroperoxides and alkyl halides proceeding in a triphase
liquid–liquid–liquid system. Tetraalkylammonium salts are typical
phase-transfer catalysts, and they are most often used in organic
synthesis, as they are relatively inexpensive and commercial avail-
able [19]. However, if they are used in two-phase systems, then
they are dissolved in the reaction mixture and are thus difficult to
separate. The separation of the PTC catalyst requires added process
stages and generates additional costs and waste. This problem can
be avoided by providing the process with a liquid–liquid–liquid sys-
tem where the catalyst, which is a tetraalkylammonium salt, forms
a separated liquid phase.
Dialkyl peroxides have mainly been used as initiators of free rad-
ical reactions and as cross-linking agents [13]. In previous papers,
we have shown that phase-transfer catalysis is an effective method
for the synthesis of dialkyl peroxides and peroxyesters, using both
The model reaction of cumyl hydroperoxide with 1-
bromobutane (organic phase) in the presence of an aqueous
solution of inorganic base (aqueous phase) and select quaternary
ammonium salts (Q+X−) as phase-transfer catalysts (a third-liquid
phase) was chosen for this study (Eq. (1)). Based on the obtained
results a reaction mechanism was proposed.
∗
Corresponding author. Tel.: +48 32 2372973; fax: +48 32 2371032.
E-mail address: Stefan.Baj@polsl.pl (S. Baj).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.07.015

S. Baj, A. Siewniak / Applied Catalysis A: General 385 (2010) 208–213
209
(1)
2. Experimental
Product isolation: Upon completion, the reaction mixture was
filtered to remove solid KBr or KCl. The reaction mixture was then
allowed to sit until layers clearly were separated from each other.
Next, the organic phase was washed with water, 5% aqueous NaOH
and again with water, after which it was dried over anhydrous
MgSO4. The organic solvent was recovered by distillation under
reduced pressure.
Amount of the phase-transfer catalyst in a third-liquid phase: The
amount of tetrabutylammonium bromide in a third-liquid phase
was determined by a method described previously [21].
2.1. Chemicals and catalysts
All chemicals and solvents used in this study were com-
mercially available and used without further purification,
unless stated otherwise. Tetrabutylammonium chloride (TBAC)
and tetrabutylammonium bromide (TBAB) were obtained from
Fluka Chemie AG. Benzyltributylammonium chloride (BTBAC),
tetrapropylammonium bromide (TPrAB), tetraethylammonium
bromide (TEAB) and tributylmethylammonium chloride (TBMAC)
were purchased from Merck. Tetrabutylammonium hydrosul-
phate (TBAHSO4), tetrapentylammonium bromide (TPeAB) and
methyltrioctylammonium chloride (Aliquat 336) were obtained
from AlfaAesar. Alkyl halides (purchased from Merck) and cyclo-
hexane were distilled prior to use in kinetic measurements.
The 1-methyl-1-phenylethyl hydroperoxide (cumyl hydroper-
oxide, CHP, 88% pure) was purchased from Aldrich and
purified according to a procedure described in the literature
[20].
3. Results and discussion
3.1. The formation of a third catalyst phase
In the triphase L–L–L PTC system, the organic and aqueous
phases were separated by a middle liquid phase containing the
phase-transfer catalyst. This third-liquid phase appeared when the
catalyst had negligible solubility in both of the other phases. Thus,
reaction conditions that can influence the formation of this third
catalyst phase were determined.
2.2. Experimental procedure
Based on experimental results, it was demonstrated that the
concentration of aqueous solution of KOH affects the formation
of triphase system (Table 1). The middle phase appeared when
the aqueous solutions of KOH had a concentration between 20
and 50 wt.%. When using 60 wt.% KOH, the catalyst remained solid,
whereas in the 10 wt.% KOH solution, it was dissolved. It was also
observed that the third-liquid phase was formed at molar ratios of
CHP to KOH from 1:1 to 1:3. When the molar ratio was 1:4, the
catalyst partially precipitated in the form of a solid phase.
The formation of the third-liquid phase is also dependent on
the type of phase-transfer catalyst used. The majority of previ-
ous work on L–L–L PTC used TBAB as a phase-transfer catalyst.
Other symmetrical onium salts (CnH2n+1)4Z+, where n = 2–6, Z = N, P
[22–27] or unsymmetrical benzyltributylammonium or phospho-
nium salt [7,8,10], were only applied in a few studies. In order to
check the influence of the type the catalyst on the formation the
L–L–L PTC in model process, the quaternary ammonium salts with
cations having symmetrical (R4N+) and unsymmetrical (R3N+Rꢀ)
structures were used. The results summarised in Table 2 indicate
that in the case of symmetrical ammonium salts a triphase sys-
tem was observed only for salts with tetrapropyl and tetrabutyl
cations. If TEAB and TPeAB were used, only two liquid phases were
observed. For unsymmetrical quaternary salts different results
The typical experiment was carried out in a two-neck round-
bottom flask (25 cm3) that was placed in an oil bath with a
temperature precision of 1 ◦C. A 50 weight% (wt.%) aqueous solu-
tion of potassium hydroxide (6.0 mmol, 0.673 g), phase-transfer
catalyst as a solid (0.3 mmol), cyclohexane (3 cm3) and CHP
(3 mmol, 0.456 g) were agitated with a magnetic stirrer (mag-
netic stirring bar: 20 mm, ∅ 6 mm; 500 rpm) at 50 ◦C. Then,
1-bromobutane (3 mmol, 0.411 g) diluted in 2 cm3 of cyclohexane
was added. The reaction was agitated for 4 h. At chosen times, the
stirrer was stopped for 60 s to allow adequate separation of the
phases. Then, samples of the organic layer were withdrawn, diluted
with methanol (5 cm3), and analysed by high performance liquid
chromatography (HPLC).
Analysis: HPLC was performed on an Alliance, Waters 2690
liquid chromatography equipped with a Waters PDA detector,
a Waters XBridge C18 (2.1 mm × 30 mm, 2.5 ␮m) and Merck
LiChrospher® Si 100 (250 mm × 2 mm, 5 ␮m) cartridge columns.
Acetonitrile:water 70:30 (v/v) and hexane:2-propanol 99:1 (v/v)
were used as the mobile phases (flow rate 0.25 cm3/min). GC was
performed using PerkinElmer chromatography equipped with a
PerkinElmer Elite-624 column (30 m, 0.53 mm ID) and decane as
the external standard.
Table 1
The effect of the amount, concentration and type of base on the formation of a triphase system.a
Concentration of base (wt.%)
Molar ratio of CHP:base
Molar ratio of catalyst:CHP
Number of phases after reaction
b
60 KOH
50 KOH
40 KOH
30 KOH
20 KOH
10 KOH
50 KOH
50 KOH
40 NaOH
1:2
1:2
1:2
1:2
1:2
1:2
1:3
1:4
1:2
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
–
3
3
3
3
2
3
3c
3
a
CHP, 0.456 g, 3.0 mmol; 1-bromobutane, 0.411 g, 3 mmol; TBAB as PTC catalyst, 0.0967 g, 0.3 mmol; KOH or NaOH, 6 mmol for molar ratio of CHP:base 1:2, 9 mmol for
molar ratio of CHP:base 1:3 and 12 mmol for molar ratio of CHP:base 1:4; cyclohexane, 5 cm3; temperature, 50 ◦C; speed of agitation, 1000 rpm; reaction time, 4 h.
b
Precipitation.
Partial precipitation.
c

210
S. Baj, A. Siewniak / Applied Catalysis A: General 385 (2010) 208–213
Table 2
The effect of the type and amount of phase-transfer catalyst on the formation of a
triphase system.a
Molar ratio of catalyst:CHP
Catalyst
Number of phases after reaction
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:20
1:50
TBAC
TBAB
3
3
3
3
3b
3
2
2
2
3
3
TBAHSO4
TBMAC
BTBAC
TPrAB
TEAB
TPeAB
Aliquat 336
TBAB
Scheme 1. Photograph of the triphase system.
tions per minute)) was the only reaction parameter changed. The
results are shown in Fig. 1. It was observed that once above 100 rpm,
the course of the model reaction was independent of stirring rate.
Interestingly, even in the absence of agitation, a fair yield of prod-
uct was obtained. These results indicate that mass transfer is not
a rate-determining step and that the transport of anions from one
phase to the other occurs quickly.
TBAB
a
CHP, 0.456 g, 3.0 mmol; 1-bromobutane, 0.411 g, 3 mmol; KOH, 50 wt.%, 0,673 g,
cyclohexane, 5 cm3; temperature 50 ◦C; speed of agitation, 1000 rpm; reaction time,
4 h.
b
Precipitation.
were obtained. A third-liquid phase was formed when TBMAC was
used but two-phase system was observed for Aliquat 336, whereas
BTBAC under the reaction conditions precipitated in the form of
a solid phase. These observations suggest that the structure of
the ammonium cation has a significant effect on the formation of
L–L–L PTC and the quaternary ammonium cation should have a
proper hydrophility–lipophility balance [23]. Because of its greater
hydrophilicity, TEAB is soluble in the aqueous phase, whereas
TPeAB and Aliquat 336 are more lipophilic and thus dissolve in
cyclohexane. In the cases of all salts with a tetrabutylammonium
cation, a triphase liquid system was formed, and the anion carried
no influence.
The polarity of the organic solvent is also an important factor
that affects the formation of a third-liquid catalyst phase. To obtain
a triphase system, it was necessary to use non-polar or weakly polar
organic solvents such as cyclohexane or toluene. Relatively more
polar solvents such as chlorobenzene caused the formation of only
two phases, and the catalysts dissolved in chlorobenzene (Table 3).
It was also checked the stability of the triphase system at tem-
peratures between 40 and 70 ◦C and found that it was stable in this
range (Table 3).
3.3. The effect of type and amount of phase-transfer catalyst
Fig. 2 shows the influence of the type of phase-transfer catalysts
on alkylation of CHP. In these experiments quaternary ammonium
salts that formed a third-liquid phase were used. The reactions
were performed in the presence of 50 wt.% KOH and cyclohexane at
50 ◦C. Similar experiment was conducted without a phase-transfer
catalyst. The best yields of peroxide were obtained using tetrabuty-
lammonium salts – (C4H9)4N+X−, irrespective of anion X. A lower
yield of product was obtained with unsymmetrical salt TBMAC. A
comparison of the reaction course with and without phase-transfer
catalyst clearly indicates that the addition of quaternary ammo-
nium salts as phase-transfer catalysts has a pronounced effect on
the reaction course relative to the course of reaction in the absence
of catalyst. TBAB was chosen for all further reactions.
The effect of the amount of phase-transfer catalyst in the range
of 1–10 mol% in reference to the amount of CHP on the reaction
course of alkylation of CHP with 1-bromobutane was investigated.
The reactions were carried out under identical conditions. It was
found that as the amount of catalyst increased from the rate of the
model reaction also increased.
All further experiments were carried out under conditions
where
a third-liquid phase formed, unless stated otherwise
(Scheme 1).
3.2. The effect of agitation speed
The dependence of the reaction course on the rate of agita-
tion was investigated. All of these experiments were carried out
in two-neck round-bottom flasks with identical magnetic stirring
bars (20 mm, ∅ 6 mm) and under the following identical reaction
conditions: 50 ◦C temperature, 50 wt.% KOH, cyclohexane (3 cm3),
TBAB as the phase-transfer catalyst, and using the same amounts
of reagents. The speed of agitation (from 100 to 1000 rpm (rota-
Table 3
The effect of type of organic solvent and temperature on the formation of a triphase
system.a
Organic solvent
Temperature (◦C)
Number of phases after reaction
Cyclohexane
Toluene
Chlorobenzene
Cyclohexane
Cyclohexane
Cyclohexane
50
50
50
40
60
70
3
3
2
3
3
3
Fig. 1. Variation of the yield of peroxide with the time on stream during the reaction
of CHP with 1-bromobutane in the presence of TBAB at different agitation rates:
a
CHP, 0.456 g, 3.0 mmol; 1-bromobutane, 0.411 g, 3 mmol; TBAB as PTC catalyst,
0.0967 g, 0.3 mmol; KOH, 50 wt.%, 0,673 g, 6.0 mmol; organic solvent, 5 cm3; speed
of agitation, 1000 rpm; reaction time, 4 h.
(
) 1000; ( ) 700; (
) 500; ( ) 300; (ꢁ) 100; ( ) 0. Reaction conditions:
1-bromobutane, 0.411 g, 3.0 mmol; CHP, 0.456 g, 3.0 mmol; 50 wt.% KOH, 0.673 g,
6.0 mmol; TBAB, 0.0967 g, 0.3 mmol; cyclohexane, 3 cm3; temperature, 50 ◦C.

S. Baj, A. Siewniak / Applied Catalysis A: General 385 (2010) 208–213
211
Fig. 2. Variation of the yield of peroxide with the time on stream during the reac-
tion of CHP with 1-bromobutane in the presence of different phase-transfer catalysts
(0.3 mmol): ( ) TBAB; ( ) TBAC; ( ) TPrAB; ( ) TBAHSO4; (ꢁ) TBMAC; ( ) with-
out catalyst. Reaction conditions: 1-bromobutane, 0.411 g, 3.0 mmol; CHP, 0.456 g,
3.0 mmol; 50 wt.% KOH, 0.673 g, 6.0 mmol; cyclohexane, 3 cm3; temperature, 50 ◦C;
speed of agitation, 500 rpm.
Fig. 4. Variation of the yield of peroxide with the time on stream during the reaction
of CHP with 1-bromobutane in the presence of TBAB at different concentration of
and type of inorganic base, wt.% (6.0 mmol): ( ) 50% KOH; ( ) 40% KOH; (
)
30% KOH; ( ) 40% NaOH. Reaction conditions: 1-bromobutane, 0.411 g, 3.0 mmol;
CHP, 0.456 g, 3.0 mmol; TBAB, 0.0967 g, 0.3 mmol; cyclohexane, 3 cm3; temperature,
50 ◦C; speed of agitation, 500 rpm.
3.4. The effect of concentration, type and amount of inorganic
base
shown in Fig. 5 indicate that the lowest yields of product were
obtained when stoichiometric quantities of KOH and CHP were
used. The use of excess KOH at amounts greater than 1:2 did not
appear to enhance the reaction rate and product yield. This lack
of enhancement could be explained as follows: at a molar ratio
of CHP to KOH of 1:1, the concentration of the aqueous phase
decreases during the reaction to such a level that the ammo-
nium salt could dissolve in the aqueous phase, and thus, the
amount of ammonium salt in a third-liquid phase could be smaller
than at molar ratios of 1:2 to 1:4. However, when a ratio above
1:2 was used, the concentration of the aqueous phase was high
enough to maintain a constant amount of catalyst in a third-liquid
phase.
The influence of the concentration of KOH in aqueous solution in
the range of 20–50 wt.% is depicted in Fig. 4. The reaction rate and
yield of the peroxide increased with increasing concentration of
KOH. The reason for this increase could be that at higher concentra-
tions of KOH, the hydration level of all anions present in the system
tends to decrease, and hence their reactivity increases [28,29]. In
the reaction that used a 40 wt.% solution of KOH, the reaction pro-
ceeded with better product yields than when 40 wt.% NaOH was
used.
In order to examine the influence of amount of KOH on the
course of alkylation of CHP, experiments at various molar ratios
of CHP to KOH: 1:1, 1:2, 1:3 and 1:4 were carried out. The results
Fig. 3. Variation of the yield of peroxide with the time on stream during the reaction
Fig. 5. Variation of the yield of peroxide with the time on stream during the reac-
tion of CHP with 1-bromobutane in the presence of TBAB at different molar ratios
KOH (50 wt.%):CHP: ( ) 4:1; ( ) 3:1; ( ) 2:1; ( ) 1:1. Reaction conditions: 1-
bromobutane, 0.411 g, 3.0 mmol; CHP, 0.456 g, 3.0 mmol; TBAB 0.0967, 0.3 mmol;
cyclohexane, 3 cm3; temperature, 50 ◦C; speed of agitation, 500 rpm.
of CHP with 1-bromobutane in the presence of different amount of TBAB (mol%): (
)
10%; ( ) 5%; ( ) 1%. Reaction conditions: 1-bromobutane, 0.411 g, 3.0 mmol; CHP,
0.456 g, 3.0 mmol; 50% KOH, 0.673 g, 6.0 mmol; cyclohexane, 3 cm3; temperature,
50 ◦C; speed of agitation, 500 rpm.

212
S. Baj, A. Siewniak / Applied Catalysis A: General 385 (2010) 208–213
Table 4
Yields of dialkyl peroxides obtained by reaction of CHP with the corresponding alkyl
bromide.a
Dialkyl peroxide
Yieldb (%); selectivity (%)
93 (100)
92 (100)
67 (100)
94 (fresh catalyst) (100)
94 (recycle 1) (100)
93 (recycle 2) (100)
Fig. 6. Variation of the yield of peroxide with the time on stream during the
reaction of CHP with 1-bromobutane in the presence of TBAB at different sol-
vents (3 cm3): ( ) cyclohexane; ( ) toluene. Reaction conditions: 1-bromobutane,
0.411 g, 3.0 mmol; CHP, 0.456 g, 3.0 mmol; 50 wt.% KOH, 0.673 g, 6.0 mmol; TBAB
0.0967 g, 0.3 mmol; temperature, 50 ◦C; speed of agitation, 500 rpm.
58 (100)
79 (100)
81 (100)
3.5. The effect of an organic solvent
The effects of an organic solvent on the model reaction were
investigated using cyclohexane and toluene under conditions
where the triphase system was formed (Fig. 6). Using cyclohex-
ane as the solvent resulted in a higher yield of product than this
when toluene was used. Furthermore, cyclohexane can be easily
removed from the reaction mixture, then purified and reused.
a
Alkyl bromide, 3.0 mmol; CHP, 0.456 g, 3.0 mmol; 50% KOH, 0.673 g, 6.0 mmol;
TBAB, 0.0967 g, 0.3 mmol; cyclohexane, 3 cm3; temperature, 50 ◦C; speed of agita-
tion, 500 rpm; reaction time, 5 h.
b
Based on the determination of isolated products.
3.6. The effect of temperature
70 ◦C. HPLC analysis indicated that peroxy reagents were stable
under reaction conditions (50 wt.% KOH, 40–70 ◦C). The selectivity
of CHP was 100%.
To examine the effect of the temperature on the course of reac-
tion between CHP and 1-bromobutane, experiments were carried
out at 40, 50, 60 and 70 ◦C (Fig. 7). It was observed that the reaction
rate increased with increasing temperature. Peroxy compounds
are thermally unstable, thus reaction temperatures did not exceed
3.7. Synthesis of dialkyl peroxides
CHP was used in reactions with a variety of alkyl bromides to
prepare dialkyl peroxides under a triphase system. High yields of
the corresponding peroxides were obtained (Table 4). In the case of
butyl 1-methyl-phenylethyl peroxide, the catalyst was also recov-
ered and reused in the next process. It is known that quaternary
onium salts can undergo decomposition in the presence of bases
or at high temperatures. Tributylamine, which is the product of
Hofmann degradation under the reaction conditions used, was not
observed in the reaction products.
3.8. The comparison of two-phase and triphase liquid systems
and the reaction mechanism
In the case of TBAB, where an aqueous solution of KOH and cyclo-
hexane (as an organic solvent) is used, the triphase liquid system
was formed in broad range of KOH concentration, molar ratio of
CHP:KOH and amount of TBAB (Tables 1 and 2) and the course of
the reaction strongly depended on these factors (Figs. 3–5). Thus,
in order to compare the model reaction courses carried out in two-
phase and triphase liquid systems different phase-transfer catalysts
were used. TBAB was chosen for the L–L–L PTC system, whereas Ali-
quat 336 and TPeAB were used in the L–L PTC. The other reaction
conditions remained the same. The results indicate that yields of
dialkyl peroxide were lower in the L–L PTC system than in the L–L–L
PTC system (Fig. 8). Higher activity of the triphase system is proba-
Fig. 7. Variation of the yield of peroxide with the time on stream during the reaction
of CHP with 1-bromobutane in the presence of TBAB at different temperatures: (
)
70 ◦C; ( ) 60 ◦C; ( ) 50 ◦C; ( ) 40 ◦C. Reaction conditions: 1-bromobutane, 0.411 g,
3.0 mmol; CHP, 0.456 g, 3.0 mmol; 50 wt.% KOH, 0.673 g, 6.0 mmol; TBAB 0.0967 g,
0.3 mmol; cyclohexane, 3 cm3; speed of agitation, 500 rpm.

S. Baj, A. Siewniak / Applied Catalysis A: General 385 (2010) 208–213
213
(4) The product (dialkyl peroxide) is transferred to the organic
phase.
4. Conclusion
In summary, a simple and useful method of synthesis of dialkyl
peroxides from alkyl hydroperoxides and alkyl bromides using
quaternary onium salts as phase-transfer catalysts under triphase
liquid–liquid–liquid conditions was developed. In a previous paper
we have revealed that polyethylene glycols and their derivatives
could be also used as PTC catalysts in this system [18]. The studies
demonstrate that the formation of triphase system depends on the
concentration and amount of base in aqueous phase, the polarity of
organic solvents and type of PTC catalyst. In the case of polyethy-
lene glycols tri-liquid system have appeared for more concentrated
solutions of inorganic base and at a higher molar ratio of KOH to
CHP than in the case of the quaternary salts. The results of these
studies clearly indicate that higher reaction rates can be achieved
in the L–L–L system than in the conventional L–L PTC. This is due
to the formation of third-liquid catalyst rich phase where the main
reaction occurs. The course of the reaction stronger depended on
the molar ratio of CHP to KOH and the structure of phase-transfer
catalyst when polyethylene glycols were used.
Both these methods use reagents, such as cyclohexane and qua-
ternary ammonium salts or polyethylene glycols that are relatively
inexpensive and readily available in high purity on a commercial
scale. Moreover, separation and recovery of the phase-transfer cat-
alyst from the reaction mixture can easily be performed because
the catalyst forms an insoluble liquid phase. Thus, these methods
are of practical value for the synthesis of mixed dialkyl perox-
ides.
Fig. 8. The comparison of the model reaction course carried out in: ( ) L–L–L PTC
with TBAB; ( ) L–L PTC with Aliquat 336. Reaction conditions: 1-bromobutane,
0.411 g, 3.0 mmol; CHP, 0.456 g, 3.0 mmol; 50 wt.% KOH, 0.673 g, 6.0 mmol; phase-
transfer catalyst, 0.3 mmol; cyclohexane, 3 cm3; temperature, 50 ◦C; speed of
agitation, 500 rpm.
bly due to the high concentration of reagents and the phase-transfer
catalyst in the third-liquid phase [1,4,6,10–12]. There is about 89%
of TBAB remaining in a third-liquid phase when 50% KOH at molar
ratio of KOH to CHP of 2:1 and cyclohexane as the organic solvent
were used.
The reaction of alkylation between alkyl hydroperoxide and
alkyl halide under liquid–liquid–liquid conditions using tetraalky-
lammonium salts may involve the following steps (see Scheme 1 in
[18]):
Acknowledgement
This work was co-financing by the Ministry of Science and
Higher Education (Grant No. N N209 149236).
(1) The formation of a potassium salt of cumyl hydroperoxide
(PhC(CH3)2OO−K+) occurs at the interface between an inor-
ganic phase and a third phase (Eq. (2)).
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Q+Br− + PhC(CH3)2OO−K+ → Q+PhC(CH3)2OO− + K+Br− (3)
The peroxy anion in this ion pair is in a highly reactive
form due to low interactions with bulky quaternary ammonium
cation and reduced water levels for hydration in the presence
of highly concentrated aqueous KOH solutions.
(3) In the next step, one can assume that the transfer of 1-
bromobutane from the organic phase to boundary between the
organic phase and a third-liquid phase or into a third-liquid
phase occurs; there, 1-bromobutane subsequently undergoes
the desired reaction:
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Q+PhC(CH3)2OO− + C4H9Br → PhC(CH3)2OOC4H9 + Q+Br−
(4)