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S. Baj et al. / Applied Catalysis A: General 395 (2011) 49–52
Table 1
2.2.2. Kinetics measurments
The effect of the addition of water (10 cm3) and phase transfer catalyst (TBAB,
1.02 mmol) on the oxidation of cyclohexanone. Reaction conditions: cyclohex-
anone, 1.0 g, 10.2 mmol; 2KHSO5·KHSO4·K2SO4, 6.3 g, 10.2 mmol; dichloromethane,
30 cm3; decane, 0.5 g, 3.5 mmol; temperature, 40 ◦C; 800 rpm.
Cyclohexanone (10.2 mmol), decane (an internal standard,
0.5 g), 2KHSO5·KHSO4·K2SO4 (10.2 mmol), H2O (10 cm3) and an
organic solvent (30 cm3) were introduced into a three-neck round
bottom flask (150 cm3) equipped with a mechanical stirrer and
a condenser. The vessel was placed in a temperature-controlled
oil bath with an accuracy of 1 ◦C, and a phase transfer cata-
lyst (1.02 mmol) was added to the flask. The reaction was stirred
at 40 ◦C for 6 h and was monitored by GC. Samples were taken
from organic layer after 15, 30, 60, 90, 150, 240, 360 min and
analyzed by GC. When the reaction was complete, phases were sep-
arated. When hexane or toluene was used as the organic solvent,
dichloromethane (25 cm3) was added to the post-reaction mixture
to dissolve the product. The organic layer was washed with water
(10 cm3) and 5% aqueous NaOH (3 × 10 cm3) to remove all resid-
ual peroxy compounds and phase transfer catalyst. Next, the crude
mixture was washed with water (2 × 10 cm3), dried over anhydrous
MgSO4 and the solvent was evaporated under vacuum. The crude,
concentrated mixture was analysed by NMR.
O
O
2KHSO5.KHSO4.K2SO4
O
CH2Cl2, 40o
C
Water (cm3)
TBAB – PTC
Conversion of
cyclohexanone
after 6 h (%)
Yield of
-caprolactone
after 6 h (%)
–
+
–
+
–
–
+
+
0
98
0
0
0
0
82
82
of the reactant from one phase to another. This technique allows
for acceleration of the reaction rate and easy separation of reac-
tion mixtures. With phase transfer catalysis, good selectivity for
hydrolytically unstable reagents can be obtained despite the pres-
ence of water in the reaction medium [12,13].
added to the studied reaction systems, which consisted of an
organic phase and inorganic phase (a solid triple salt or a triple salt
and water). As a result, only in the system with water high yields of
-caprolactone were obtained, and by-products were not detected
(Table 1). Thus, to achieve BV oxidation with KHSO5, water and a
phase transfer catalyst are necessary.
An interesting phenomenon was observed when toluene and
hexane were used as the solvent. As shown in Fig. 1, the type of
organic solvent had a significant effect on the oxidation of cyclo-
hexanone. For instance, when hexane was used as the organic
solvent, 100% conversion of cyclohexanone was obtained within
30 min. -Caprolactone is not soluble in hexane and is only par-
tially soluble in toluene; thus, the reaction rate may have increased
due to the formation of a separate layer based on the insoluble
product. Unfortunately, in the aforementioned layer, the desired
product was exposed to the effects of water, and -caprolactone
was hydrolysed, and in hexane only 6-hydroxyhexanoic acid was
2.2.3. Synthesis of -caprolactone
Cyclohexanone (0.102 mol), 2KHSO5·KHSO4·K2SO4 (0.102 mol),
H2O (100 cm3) and CH2Cl2 (300 cm3) were introduced into a three-
neck round bottom flask (750 cm3) equipped with a mechanical
stirrer and a condenser. The vessel was placed in a temperature-
controlled oil bath with an accuracy of 1 ◦C, and TBAB as a phase
transfer catalyst (10.2 mmol) was added to the flask. The reac-
tion was stirred at 40 ◦C for 6 h. When the reaction was complete,
phases were separated. The organic layer was washed with water
(50 cm3) and 5% aqueous NaOH (3 × 50 cm3) to remove all resid-
ual peroxy compounds and TBAB. Next, the crude mixture was
washed with water (2 × 50 cm3), dried over anhydrous MgSO4
and concentrated. The crude product was chromatographed with
hexane/ethyl acetate (v/v 3/1) as the eluent. The solvent was evap-
orated under vacuum and -caprolactone was obtained with 77%.
1H-NMR (300 MHz, CDCl3, TMS): ı = 4.23 (m, 2H); 2.63 (m, 2H); 1.77
(m, 6H); 13C NMR (CDCl3): ı = 175.55; 68.53; 33.75; 28.57; 28.07;
22.23; b.p. 235 ◦C.
3. Results and discussion
The oxidation of the cyclohexanone to -caprolactone was
selected as a model reaction. The synthesis of -caprolactone
is of great importance in the chemical industry. Currently, -
caprolactone is prepared through the oxidation of cyclohexanone
using O2/acetaldehyde (BASF) or peroxyacetic acid (Perstorp).
Potassium peroxomonosulphate, the active compound in the
triple salt (2KHSO5 ·KHSO4·K2SO4), was selected as an alternative
tion. However, because potassium peroxomonosulphate is only
soluble in water, it was essential to find a solvent system to carry
out to the synthesis of -caprolactone.
In our preliminary studies (Table 1), it was found out that the
oxidation process in a two-phase system consisting of organic
phase (cyclohexanone dissolved in dichloromethane) and inor-
ganic solid phase (2KHSO5·KHSO4·K2SO4) conducted at 40 ◦C did
not proceed. -Caprolactone was not detected, and the conversion
of cyclohexanone was not observed. Although high conversions
were obtained after water was added to the reaction mixture, the
synthesis of -caprolactone was not achieved. Rather, the prod-
uct of lactone hydrolysis, 6-hydroxyhexanoic acid, was detected in
the crude mixture. Thus, the results suggested that the BV lactone
product was sensitive to hydrolysis.
Y=0%
100
Y=48%
Y=82%
80
60
40
20
0
0
60
120
180
240
300
360
420
Reaction time [min]
Fig. 1. Variation of the conversion of cyclohexanone with the time on stream dur-
ing the reaction of cyclohexanone with 2KHSO5·KHSO4·K2SO4 in the presence of
different solvents (30 cm3): (
) hexane; ( ) toluene; (
) dichloromethane.
Phase transfer catalysis is a powerful method that allows reac-
tions to be conducted in a two phase system (liquid–liquid or
liquid–solid). The role of the PT catalyst is to facilitate the transfer
Reaction conditions: cyclohexanone, 1.0 g, 10.2 mmol; 2KHSO5·KHSO4·K2SO4,·6.3 g,
10.2 mmol; TBAB, 1.02 mmol; H2O, 10 cm3; decane, 0.5 g, 3.5 mmol; temperature,
40 ◦C; 800 rpm. Y – yield of -caprolactone after 6 h.