Chemo-enzymatic Baeyer-Villiger oxidation in the presence of Candida antarctica lipase B and ionic liquids

Article abstract of DOI:10.1039/c4nj01976h

A new method for the chemo-enzymatic Baeyer-Villiger oxidation of cyclic ketones to lactones has been developed. The influence of reaction parameters and the structure of various ionic liquids were studied. Free Candida antarctica lipase B or Novozyme-435 suspended in an ionic liquid was used as the catalytic phase. The reaction was carried out under mild conditions at room temperature using 30% aq. H₂O₂ as the oxidation agent. 1-Butyl-3-methyl bistriflimide was the most effective ionic liquid and increased the reaction rate compared to toluene. Lipase exhibited good stability, and the ionic liquid could be easily reused. Therefore, a general chemo-enzymatic method for the oxidation of cyclohexanones and cyclobutanones to obtain adequate lactones in high yields (79-95%) has been proposed.

Full text of DOI:10.1039/c4nj01976h

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A. Drozdz, K.
Erfurt, R. Bielas and A. Chrobok, New J. Chem., 2014, DOI: 10.1039/C4NJ01976H.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/njc

View Article Online
DOI: 10.1039/C4NJ01976H
Page 1 of 6
New Journal of Chemistry
Dynamic Article Links ►
Journal Name
Cite this: DOI: 10.1039/c0xx00000x
www.rsc.org/xxxxxx
ARTICLE TYPE
Chemo-enzymatic Baeyer-Villiger oxidation in the presence of Candida
Antarctica lipase B and ionic liquids
a
a
a
a
Agnieszka Drożdż, Karol Erfurt, Rafał Bielas and Anna Chrobok*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
A new method for the chemo-enzymatic Baeyer-Villiger oxidation of cyclic ketones to lactones has been
developed. The influence of reaction parameters and the structure of various ionic liquid was studied.
Free Candida Antarctica lipase B or Novozyme-435 suspended in an ionic liquid were used as the
catalytic phase. The reaction was carried out under mild conditions at room temperature using 30% aq.
1
0
2 2
H O as the oxidation agent. 1-Butyl-3-methyl bistriflimide was the most effective ionic liquid and
increased the reaction rate compared to toluene. Lipase exhibited good stability, and the ionic liquid could
be easily reused. Therefore, a general chemo-enzymatic method for the oxidation of cyclohexanones and
cyclobutanones to obtain adequate lactones in high yields (79-95%) has been proposed.
4
5
5
6
6
7
7
5
0
5
0
5
0
5
materials with organosilanes terminated with alkyl groups was
demonstrated.
1
3
Introduction
Only one report demonstrated that the oxidation of ketones by
peracid generated in situ in the reaction system catalysed by
Novozyme-435 could be significantly accelerated due to the
1
2
2
3
3
4
5
0
5
0
5
0
The Baeyer-Villiger reaction is based on the formation of esters
or lactones via the oxidation of ketones with peroxide derivatives,
primarily peracids, catalysed by acids or enzymes. The resulting
esters or lactones are used in the synthesis of antibiotics, steroids,
pheromones and monomers for polymerisation.1-3 The use of
enzymes to perform the chemical transformation of ketones to
lactones can be carried out using Baeyer-Villiger monooxygenases
or Candida Antarctica lipase B. In the first option, the enzyme
catalyses the oxidation of ketones with oxygen and nicotinamide
11
presence of a few hydrogen bond donating ionic liquids. In
addition, Novozyme-435 was dissolved in 1-(3-hydroxypropyl)-3-
methylimidazolium nitrate or 1-butyl-3-methylimidazolium nitrate
forming gel-like homogeneous liquids. When this method was
2 2
used, ketones were oxidised with 50% H O at 50 °C in 5 h to
11
lactones with moderate to excellent yields.
The properties of enzymes and ionic liquids are complex, and
there is no universal method for predicting the appropriate ionic
liquid for a specific bioprocess. The challenge of stabilisation or
destabilisation of enzymes in an ionic liquid environment occurs
in the initial stage. Numerous reports describe the activity and
thermal stability of enzymes in ionic liquids and their application
4
-
adenine dinucleotide phosphate NADPH as a source of electrons.
6
In the second option, the enzyme in used only in one step of the
7
-15
reaction, and therefore, the reaction is called chemo-enzymatic.
This reaction involves the oxidation of long- or medium-chain
carboxylic acids with hydrogen peroxide in the presence of lipase
to generate in situ peracid, which is used to oxidise ketones to
lactones in the second step. An interesting modification of the
chemo-enzymatic method that utilises ethyl acetate as a solvent
16
in several reactions with considerable success. However, ionic
liquids with very similar structures can exhibit different behaviour
1
7
towards enzymes.
9
and a peracetic acid precursor has been recently proposed. From
Various properties can influence the catalytic performance of
enzymes in ionic liquids including polarity, hydrophobicity,
this point of view, the chemo-enzymatic approach appears to be a
very attractive alternative for avoiding handling of often poorly
stable, hazardous and fairly expensive organic percarboxylic acids,
which are typical oxidants used in the Baeyer-Villiger reaction.
nucleophilicity, hydrogen bonding ability, viscosity, enzyme
18-20
dissolution, and surfactant effect.
In addition, the parameters
that quantify the interactions of the proteins and the aqueous
electrolytes, such as cosmotropicity vs. chaotropicity, have been
proposed for explaining protein behaviour in aqueous ionic liquids.
Unfortunately, the anions of ionic liquids do not always strictly
Although,
chemo-enzymatic
Baeyer-Villiger
reaction
conditions are mild, the required reaction times at room
temperature can be as long as several days. The most often used
enzyme is Candida Antarctica lipase B (CALB) immobilised on
acrylic resin, which is commercially available as Novozyme-435.
In addition, very efficient CALB immobilised as cross-linked
16
follow the Hofmeister series for protein stability. Ionic liquids
can also form so-called organised ‘nano-structures,’ which are
described as hydrogen bonded polymeric supramolecules that have
polar and non-polar regions. The structure of the ionic liquids can
protect the crucial water in the protein from solvophobic
1
2
enzyme aggregates (CLEAs) has also been used. In our previous
study, the high activity of CALB immobilised on siliceous
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

View Article Online
DOI: 10.1039/C4NJ01976H
New Journal of Chemistry
Page 2 of 6
interactions that are necessary to maintain the native protein 50 also used a standard molar excess of acids to ketone (i.e., 2:1). As
structure. Ionic liquids that are enzyme compatible and can
dissolve substrates not soluble in conventional organic solvents are
desired for enzyme-catalysed reactions.
To summarise, the chemo-enzymatic Baeyer-Villiger reaction is
a result of our study, a lower interval of reactive carboxylic acids
(i.e., from pentanoic to nonanoic acids) was observed for native
CALB (Table 1). The reaction does not proceed without lipase
2
1-23
7
5
0
5
catalyst what was also reported by other researchers. Chiral
still under intensive studies to investigate its usefulness in 55 induction was not observed during the reaction. For additional
biotransformations. The major challenges to overcome include
long reaction times, poor stability of lipase in the presence of
studies, octanoic acid was chosen as the peracid precursor.
Table 1 Comparative study of the performance of native CALB and
concentrated H
2
O
2
and the modest yields resulting from this
a
Novozyme-435 for the oxidation of 2-methylcyclohexanone
1
method. Therefore, the current work studies the influence of the
structure of various ionic liquids on the activity of CALB in the
Baeyer-Villiger oxidation of cyclic ketones to lactones. In contrast
to Novozyme-435, the lipase was not attached to a solid support
but used in the free form. Because the operational stability of
native enzymes is rather limited, our intention was to determine if
the presence of ionic liquids influences the stability and activity of
CALB in the Baeyer-Villiger reaction.
a
Entry
Carboxylic acid
Yield of lactone [%]
Native CALB Novozyme-435
1
2
3
4
5
6
7
8
9
Etanoic acid
Propanoic acid
Pentanoic acid
Octanoic acid
16
82
98
98
11
16
81
99
1
b
b
Octanoic acid
0
0
Nonanoic acid
Tetradecanoic acid
Hexadecanoic acid
Octadecanoic acid
97
67
65
60
99
96
99
98
Results and discussion
a
Reaction conditions: native CALB (0.100 g) or Novozyme-435 (0.025
g), toluene (1 ml), 2-methylcyclohexanone (0.5 mmol), acid (1 mmol),
Selection of carboxylic acid structure
60
3
0% aq. H O (1 mmol), 24 h, RT, shaking (250 rpm); yields determined
2 2
2
0
We aimed to develop a clean Baeyer-Villiger process with a
facile catalyst separation and reuse by using hydrogen peroxide
and ionic liquids. As shown in Scheme 1, the applied chemo-
enzymatic method for lactone synthesis involved CALB as the
biocatalyst for peracid formation, 30% aq. H O as the oxidant
2 2
(Scheme 1) and an ionic liquid as the solvent. Commercially
available water solution of CALB was used.
b
by GC; reaction without lipase.
Selection of the ionic liquid structure
Because the properties of ionic liquids are primarily determined
by the structure of the anion, various ionic liquids were chosen for
screening studies. Ionic liquids based on 1-butyl-3-
methylimidazolium cation [bmim], both hydrophobic with
6
7
7
5
0
5
2
5
bistriflimide [NTf
hydrophilic ones based on trifluorometanosulphate [OTf],
trifluoroacetate [TFA], biscyanamide [NCN ], tetrafluoroborate
BF ], methylsulphate [MeSO ] and octylsulphate [OcSO ] anions
2 6
] or hexafluorophosphate [PF ] anions or
2
[
4
4
4
were used (Figure 1). Screening oxidation experiments were
performed under mild conditions (24 °C, molar ratio of ketone to
3
metylcyclohexanone and octanoic acid. Yields were determined by
GC after 24 h. For comparison, the results for Novozyme-435 were
also included in the figure.
2 2
0% aq. H O 1:2, with ionic liquid as a solvent) using 2-
Scheme 1 Chemo-enzymatic Baeyer–Villiger oxidation of 2-
methylcyclohexanone
3
3
4
4
0
5
0
5
Only immobilised forms of CALB were used for this process7-
1
5
(e.g., for Novozyme-435 as a catalyst, the best results were
obtained with the long- or medium-chain carboxylic acids). To use
free CALB, preliminary studies focused on the appropriate
selection of a carboxylic acid for this purpose. This part of the
study was carried out at room temperature in toluene, which was
the best organic solvent for this process. A comparison of the
effectiveness of H
2 2
O for converting various carboxylic acids
(from ethanoic to octadecanoic acid) to peracids in the presence of
native lipase or Novozyme-435 followed by the subsequent
oxidation of model ketone 2-methylcyclohexanone to 6-methyl--
caprolactone is shown in Table 1. The comparative study was
performed using 0.100 g of native lipase (CALB) and 0.025 g of
Novozyme-435 for 0.5 mmol of ketone. In both cases, this amount
of lipase was sufficient to carry out the reaction in the region where
the reaction kinetic is controlled by the formation of lactone not by
the formation of peracid in the enzyme-catalysed reaction.
Therefore, a further increase in the amount of enzyme did not
influenced the yield of lactone. In addition, 0.025 g of Novozyme-
Fig. 1 Influence of the anion structure of 1-butyl-3-methylimidazolium
a
80
ionic liquids on the yield of 6-methyl--caprolactone
The influence of hydrophobicity was investigated due to
literature reports on the stability and activity of lipase in ionic
liquids.
liquids, such as based on [NTf
85 activity even after several reuse cycles. In some reports,
1
8-20
It is known that Novozyme-435 in hydrophobic ionic
] or [PF ] anions, can retain its
2
6
1
6
1
1
4
35 per 0.5 mmol of ketone was used in a previous study. We
2
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

View Article Online
DOI: 10.1039/C4NJ01976H
Page 3 of 6
New Journal of Chemistry
Novozyme-435 was dissolved in hydrophilic ionic liquids (e.g., in
[bmim][NTf
2
], which is the most active ionic liquid, and native
triethylmethylammonium methylsulphate [Et
3
MeN][MeSO
4
]) and 60 CALB at 45 °C. As shown in Figure 2, among the different forms
of hydrogen peroxide used (i.e., 30 or 50% aq. H and urea
hydrogen peroxide (UHP)), the most active form is the 30% aq.
. Double molar excess of ketone to H is sufficient to
produce sufficient peracid, and a further increase in the hydrogen
enzymatic Baeyer-Villiger oxidation of 2-methylcyclohexanone 65 peroxide amount does not influence the reaction rate.
maintained its activity and structure.20 However, in others reports,
the activity of lipase in hydrophilic ionic liquids was substantially
2 2
O
1
7,20
5
0
5
0
5
0
5
0
5
0
decreased.
Our results indicate that the best ionic liquid for the chemo-
H
2
O
2
2 2
O
was based on the [NTf
maintains the flexibility of lipase in its active conformation. Other
hydrophobic ionic liquid solvents, such as [bmim][PF ], do not
exhibit activity. During the reaction, the water present in the
system most likely liberates HF, which is toxic to the enzyme. All
hydrophilic ionic liquids have a negative impact on this reaction.
The hydrophilic ionic liquids most likely remove essential water
from the lipase, which leads to unfolding of the biomolecule upon
exposure of the inner hydrophobic residues. Therefore, the anion
plays a crucial role in the CALB performance.
Next, the influence of the structure of the cation on the activity
of bistriflimide ionic liquids was studied. Therefore, the ionic
liquids based on dialkylimidazolium, alkylpyridinium,
dialkylpyrrolidinium or trialkylammonium cations were tested. In
a series of dialkylimidazolium bistrifimides, the best results were
obtained for 1-butyl-3-methylimidazolium [bmim] cation when
native CALB was used as the catalyst. When the slightly acidic C2
hydrogen in the [bmim] cation was substituted with a methyl group
2
] anion (Fig. 1), which most likely
Table 2 Influence of the cation structure in bistriflimide ionic liquids
b
Entry
1
Cations of bistriflimide
ionic liquid
Yield of lactone [%]
1
1
2
2
3
3
4
4
5
6
Native CALB Novozyme-435
8
0 (24h)
78 (24h)
2
3
8
9
1 (10h)
9 (18h)
62 (10h)
99 (24h)
68 (10h)
2 (24h)
8
8
8 (24h)
4 (24h)
9
4
5
67 (10h)
8
8
9
1 (18h)
9 (24h)
8 (42h)
8
9
3 (24h)
8 (42h)
70 (24h)
98 (24h)
89 (24h)
6
7
6
3 (24h)
87 (10h)
9
9
(Table 2, enter 5), the reaction time necessary for complete
6 (18h)
9 (24h)
conversion increased from 18 to 42 h. This result may be due to
the hydrogen bonding interactions with CALB, which decreases
the enzyme activity. A slightly different activity for native CALB
compared to Novozyme-435 was observed. In general, native
CALB is slightly more active, and the reaction times are shortened
by several hours. 3-Methyl-1-butylpyridinium bistriflimide (Table
8
9
88 (10h)
96 (18h)
99 (24h)
91 (24h)
67 (24h)
85 (24h)
76 (24h)
76 (24h)
5
3 (24h)
2
2
, entry 8) was as active as [bmim][NTf ] and similar in activity to
1
1
1
0
1
2
trimethylbutylammonium bistrifimide (Table 2, entry 12). 1-Butyl-
1-methylpyrrolidinium bistriflimide exhibited the lowest activity
78 (24h)
(Table 2, entry 11).
8
4 (24h)
Inspired by the work of Arends et al., who described effective
hydrogen bond donating ionic liquids based on [NO
3
] anions
77 (10h)
92 (18h)
98 (24h)
48 (18h)
dissolving Novozyme-435, cations with H-bonding capability
1
0
were also selected for our study. In each case, the activity of the
1
1
3
4
ionic liquids with –OH groups introduced to the cation structure
88 (24h)
15 (24h)
7
2 (24h)
(Table 2, entry 6, 9, 13-15) was lower in the reaction catalysed by
native CALB compared to that of the same ionic liquids without
the –OH groups. This effect is not as dramatic when Novozyme-
435 was used. It is important to note that ionic liquids with two –
OH groups (Table 2, entry 14, 15) were extremely viscous, which
can influence the reaction rate.
66 (24h)
1
5
7
6 (24h)
20 (24h)
The introduction of a –CN group to the [bmim] structure (Table
a
Reaction conditions: native CALB (0.100 g) or Novozyme-435 (0.025
g), ionic liquid (1 ml), 2-methylcyclohexanone (0.5 mmol), octanoic acid
1 mmol), 30% aq. H O (1 mmol), RT, shaking (250 rpm); yield
2 2
2
, entry 7) resulted in maintaining the same activity as that without
the –CN group. For the 3-methyl-1-butylpyridinium ionic liquid,
the presence of a –CN group reduced the activity of the ionic 70 determined by GC.
b
(
liquid. Therefore, the cation structure also plays an important role
in CALB activation.
The exposure of lipase to a high concentration of aqueous
hydrogen peroxide may result in its slow deactivation. There is a
The influence of process parameters on the model reaction
2 2
9% mass of water in the reaction system when 30% aq. H O is
used. The water is produced as a by-product, which is introduced
to the system with native CALB (which is a water solution) and
hydrogen peroxide. When anhydrous UHP is used, the additional
water is most likely not introduced to the reaction system, and the
5
5
Next, we studied the key parameters affecting the reaction
including the influence of the ketone to hydrogen peroxide molar
ratio and the concentration of aq. H O on the rate of 2-
2 2
75
methylcyclohexanone oxidation. The reaction was carried out with
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 3

View Article Online
DOI: 10.1039/C4NJ01976H
New Journal of Chemistry
Page 4 of 6
water that is crucial for maintaining the protein structure is not
achieved.
second phase. The recycling experiments were carried out at room
temperature. For the reactions carried out at higher temperatures
the enzymes were not sufficiently stable to survive the next cycle,
and all of the tests of the recycled enzymes after the reaction
carried out at 45 °C failed. For the recycling of native CALB with
the ionic liquid, the following procedure was used: first, the post
reaction mixture was extracted with toluene to remove the product
40 and unreacted starting material. The residue was concentrated and
used for another reaction cycle. After each catalytic run with
Novozyme-435, the post reaction mixture was dissolved in
dichloromethane, and Novozyme-435 was filtered and washed
with ethyl acetate. The filtrate was concentrated under vacuum and
45 extracted with diethyl ether to remove the product and unreacted
starting material. The combined Novozyme-435 and ionic liquid
phase were used for another run.
35
1
00
80
60
40
20
0
Molar ratio of ketone to hydrogen peroxide:
1:1 30% aq. H
:2 50% aq. H
2
O
2
1:2 30% aq. H
2
O
2
2 2
1:3 30% aq. H O
1
O
1:2 UHP
2
2
0
2
4
6
8
10
12
14
Time [h]
Figure 4 shows the yields of lactone in four consecutive runs
with the application of different catalytic systems (i.e., native
CALB or Novozyme-435 in toluene or [bmim][NTf ]
2
5
Fig. 2 Effect of the molar ratio of ketone to hydrogen peroxide and the
concentration of aq. H on the rate of oxidation of 2-
methylcyclohexanone
O
2 2
50
environment). The most important conclusion is that the enzymes
lost their activity after the first run when the reaction was carried
out in toluene. Better results were obtained with the application of
the ionic liquid for the reaction. However, the recycling of the
catalytic phase based on native CALB with the ionic liquid was not
as efficient as Novozyme-435 with the ionic liquid.
1
00
8
6
4
2
0
0
0
0
0
55
45°C; [bmim][NTf2]
3
2
4
2
5°C; [bmim][NTf2]
4°C; [bmim][NTf2]
5°C; toluene
4°C; toluene
0
2
4
6
8
10
12
14
Time [h]
Fig. 3 Influence of temperature on the rate of oxidation of 2-methyl-
1
0
cyclohexanone
The increase in the reaction temperature from room temperature
to 45 °C resulted in an increase in the reaction rate. In fact, the
Fig. 4 Recycling of the catalytic phase
2 2
oxidation of 2-methylcyclohexanone with 30% aq. H O in ionic
Based on these results, we attempted to recycle of the neat ionic
liquid [bmim][NTf ] (Fig. 5). In six consecutive runs, almost no
2
mass loss of the ionic liquid was observed (95-98% of recovery).
Although the yield of lactone appeared to decrease slightly, it
remained within the error bars of the measurement for all six runs
liquid catalysed by native CALB was complete after 10 h (Fig. 3).
The reaction was much slower in toluene and accelerated with
temperature. The study on the influence of temperature on the
reaction rate indicated that CALB is more active in an ionic liquid
environment at higher temperature compared to toluene.
60
1
2
2
5
0
5
(mean yield = 98%, Fig. 5).
By comparing our results with those obtained with other
methods described in the literature, a substantial decrease in the
reaction times was observed. Using Novozyme-435 and ethyl
acetate as the solvent and a peracid precursor, 72 h was required
for the oxidation of 2-metlylcyclohexanone to 6-methyl--
1
0
caprolactone with 95% yield at room temperature. The best
results were obtained using CLEA immobilised on a silica support
1
3
(
h).
97% yield after 29 h, RT) or CALB-CLEA (84% yield after 48
1
2
Our method unable the full conversion of 2-
metlylcyclohexanone in 18 h at RT or 10 h at 45 °C.
Recycling study
3
0
The recycling of catalytic phase (i.e., ionic liquid together with
native CALB or with Novozyme-435) was studied. In both cases,
65
Fig. 5 Recycling of the ionic liquid
the enzymes were not dissolved in [bmim][NTf
2
] to form the
4
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

View Article Online
DOI: 10.1039/C4NJ01976H
Page 5 of 6
New Journal of Chemistry
a
Table 3 Oxidation of selected cyclic ketones to lactones
Entry
Ketone
Lactone
Time [h] Yield of lactone in
[
bmim][NTf
2
] [%]
Substrate scope
1
15
0
83
85 (80)
b
1
Finally, the most active reaction system was examined in the
chemo-enzymatic Baeyer-Villiger synthesis of various lactones
from the corresponding ketones to determine its practical potential.
As shown in Table 3, the oxidation processes proceeded very
efficiently at 45 °C. In fact, cyclic ketones were readily oxidised to
their corresponding lactones in high yields (79-96%) under mild
conditions in reasonable reaction times. As model reactants, we
chose strained ketones, such as cyclobutanones that form lactones
in high yields and non-strained ketone cyclohexanones, which are
much more difficult to oxidise. The most reactive of these ketones
was cyclobutanones, which oxidised to -butyrolactone with 98%
yield in 1.5 hour, and cyclohexanone yield 85% -caprolactone
after 15 hours. Cyclobutanone is a very reactive molecule because
its ring strain is very high, and therefore, its very fast oxidation was
expected. The oxidation of 2-adamantanone and norcamphor
yielded their corresponding lactones in high yields. Extremely
unreactive cycloheptanone did not undergo oxidation under these
conditions.
2
0
65 (toluene)
5
0
5
0
5
b
10
2
99 (96)
2
3
4
0
95 (toluene)
1
1
0
5
80
94 (89)
b
1
1
2
2
2
71
88
93
4
6
8
2
4
8
b
99 (95)
45
61
70
5
6
b
1
5
85 (79)
1
1.5
2
86
99 (96)
b
91 (toluene)
2
3
4
91
99 (95)
b
7
93 (toluene)
According to the literature method, the oxidation of
cyclohexanone in 1-(3-hydroxypropyl)-3-methylimidazolium
1
1
nitrate or choline nitrate with 50% H
2
O
2
at 50 °C after 5 h yielded
2
3
4
88
98 (95)
b
45-62% -caprolactone. In our method, an 83% yield of lactone
was produce after 10 h.
8
9
90 (toluene)
Experimental
48
8
Materials
a
Reaction conditions: native CALB (0.4 g), [bmim][NTf
2
] (4 ml), ketone
1
-Methylimidazole,
chlorobutane, 1-chlorohexane, 30% and 50% aq. H
hydrogen peroxide were purchased from Acros Organics. 1-butyl-
-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium
1,2-dimethylimidzole,
3-picoline,
1-
55
(2 mmol), octanoic acid (4 mmol), 30% aq. H (4 mmol), 45 °C,
2 2
O
b
3
3
4
0
5
0
2
O
2
and urea
shaking (250 rpm); yields were determined by GC; isolated yields.
Methods
3
octylsulphate, 1-butyl-3-methylimidazolium methylsulphate, 1-
butyl-3-methylimidazolium triflate, lithium bis(trifluoromethane
General method for Baeyer-Villiger oxidation
4 ml of ionic liquid and 0.1 g of Novozyme-435 or 0.4 g of native
sulphate)imide, 1-methyl-3-octylimidazolium bromide and 1- 60 CALB were introduced into a 25 ml round-bottom flask. Next, the
butyl-1-methylpyrrolidinium bis(trifluoromethanesulphate)imide
were purchased from Merck. Cyclic ketones, carboxylic acids, 1-
butyl-3-methylimidazolium hexafluorophosphate and native
CALB [5, 000 LU/G] were purchased from Sigma Aldrich.
ketone (2 mmol) and carboxylic acid (4 mmol) were added, and
the contents of the flask were shaken. 30% aqueous H (1 mmol)
2
O
2
was added in one portion. The flask was sealed with a septum and
o
mixed in a thermostat shaker (0.5 C) with orbital stirring at 250
Novozyme-35 was donated by Novozymes. Quarterisation 65 rpm at 24 °C, 35 °C or 45 °C for 1.5-24 h depending of the reaction
2
4
reactions of 1-methylimidazole or 1,2-dimethylimidzole, 3-
rate. Periodically, 20 μl of the samples diluted with 1.5 ml of
dichloromethane were collected during the reaction to monitor the
progress of the reaction utilising GC. When the reaction with
native CALB was completed, the post reaction mixture was
extracted with toluene (6x2 ml) to remove the product and
unreacted starting material. The extract was washed with 5 ml of a
2
5
26
27
picoline, and aliphatic amines, metathesis reaction, and
1
4
synthesis of 3-substituted cyclobutanones were performed
according to literature methods.
70
4
5
Instrumentation
1H NMR and 13C NMR spectra of the lactones were recorded at
3 4
10% NaHCO solution in water, dried over anhydrous MgSO and
3
00 MHz in CDCl
3
(Varian Unity Inova plus spectrometer with a
concentrated under vacuum. The post reaction mixtures with
Novozyme-435 were dissolved in dichloromethane (5 ml), and
TMS internal standard). All of the lactones were characterised by
comparing their NMR spectra with those of standard samples. GC 75 Novozyme-435 was filtered. The filtrate was concentrated under
5
0
analysis was performed using a Perkin Elmer Clarus 500
chromatograph SUPELCOWAX 10 column (30 m×0.2
vacuum and extracted with toluene (6x2 ml) to extract the product
and unreacted starting material. The extract was washed with 5 ml
TM
mm×0.2μm) with n-decane as an external standard.
3 4
of a 10% NaHCO solution in water, dried over anhydrous MgSO
and concentrated under vacuum. The yields of the lactones after
purification by column chromatography when necessary (with
80
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

View Article Online
DOI: 10.1039/C4NJ01976H
New Journal of Chemistry
Page 6 of 6
hexane:ethyl acetate ratio of 4:1 as an eluent) were in the range of
9-96%.
Recycling of catalytic phase or ionic liquid
9
1
M. Y. Rios, E. Salazar and H. F. Olivo, J. Mol. Catal. B, 2008, 54, 61.
M. Y. Rios, E. Salazar and H. F. Olivo, Green Chem., 2007, 9, 459.
0
7
6
6
0
5
11 A. J. Kotlewska, F. van Rantwijk, R. A. Sheldon and I. W. C. E.
Arends, Green Chem., 2011, 13, 2154.
G. Chavez, R. Hatti-Kaul, R. A. Sheldon and G. Mamo, J. Mol. Catal.
B, 2013, 89, 67.
After reaction completion for the recycling of native CALB with
the ionic liquid the following procedure was used: First, the post
reaction mixture was extracted with toluene (6x2 ml) to remove
the product and unreacted starting material. The residue was
concentrated and used for another reaction cycle. After each
catalytic run with Novozyme-435, the post reaction mixture was
dissolved in dichloromethane (5 ml), and the Novozyme-435 was
filtered and washed with ethyl acetate (3x5 ml). The filtrate was
concentrated under vacuum and extracted with toluene (6x2 ml) to
remove the product and unreacted starting material. The combined
Novozyme-435 and ionic liquid phase were used for another run.
1
2
5
13 A. Drożdż, A. Chrobok, S. Baj, K. Szymańska, J. Mrowiec-Białoń and
A. B. Jarzębski, Appl. Catal. A, 2013, 467, 163.
1
4
D. González-Martínez, M. Rodríguez-Mata, D. Méndez-Sánchez, V.
Gotor and V. Gotor-Fernández, J. Mol. Catal. B: Enzym., 2014, DOI:
1
0.1016/j.molcatb.2014.09.002
1
0
15 G. Chavez, J.-A. Rasmussen, M. Janssen, G. Mamo, R. Hatti-Kaul and
70
R. A. Sheldon, Top. Catal., 2014, 57, 349.
1
1
6
7
A. Kumar and P. Venkatesu, Int. J. Biol. Macromol., 2014, 63, 244.
R. A. Sheldon, R. M. Lau, M. J. Sorgedrager, F. van Rantwijk and K.
R. Seddon, Green Chem., 2002, 4, 147.
1
8
J.-Q. Lai, Z. Li, Y.-H. Lu and Z. Yang, Green Chem., 2011, 13, 1860.
7
8
8
9
5
0
5
0
19 S. H. Ha, S. H. Lee, D. T. Dang, M. S. Kwon, W.-J. Chang, Y.J. Yu,
I. S. Byun and Y.-M. Koo, Korean J. Chem. Eng., 2008, 25, 291.
1
5
Conclusions
2
2
0
1
R. M. Lau, M.J. Sorgedrager, G. Carrea, F. van Rantwijk, F. Secundo
and R. A. Sheldon, Green Chem., 2004, 6, 483.
H. J. Zhao, Chem. Technol. Biotechnol., 2010, 85, 891.
In summary, we demonstrated the potential of ionic liquids as a
lipase carrier and considered the Baeyer-Villiger reaction as an
exemplary enzyme catalysed reaction of major importance. Since
the early 2000s, ionic liquids are proposed as solvent replacements
for biocatalytic applications due to their low vapour pressure and
ability to stabilise protein structures. The proposed
environmentally benign chemo-enzymatic Baeyer-Villiger process
avoids the use of a relatively unstable peracid, which in the
proposed method is generated in situ in the reaction system during
the enzymatic stage, and the rate of its synthesis, which affects the
rate of the Baeyer-Villiger process, can be effectively controlled
by the applied biocatalysts.
The catalytic activity of the lipases (i.e., native CALB or
Novozyme-435) is highly dependent on the characteristics of the
ionic liquids. The best results were obtained for 1-butyl-3-
methylimidazolum bistrifimide, which is a hydrophobic ionic
liquid that was efficiently recycled several times. The new method
allows for reduction of reaction times compared to the use of
classical solvents in this reaction. The presented method is an
example of a green biotransformation process in promising
nonaqueous media.
22 M. Sureshkumar and C. K. J. Lee, J. Mol. Catal. B: Enzym., 2009, 60,
1
.
2
3
M. Moniruzzaman, N. Kamiyaa and M. Goto, Org. Biomol. Chem.,
2010, 8, 2887.
2
2
3
3
0
5
0
5
24 K. Baba, H. Ono, E. Itoh and S. Itoch, Chem. Eur. J., 2006, 12, 5328.
25 D. Zhao, Z. Fei and T. J. Geldbach, J. Am. Chem. Soc., 2004, 126,
1
5876.
C. Roche, M. Pucheault, M. Vaultier and A. Commeron, Tetrahedron,
010, 66, 8325.
2
6
2
27 C. Yao and J. L. Anderson, Anal. Bioanal. Chem. 2009, 395, 1491.
Acknowledgements
This work was financed by the Polish National Science Centre
(Grant no. UMO-2013/09/N/ST8/02059).
4
0
Notes and references
a
Silesian University of Technology, Faculty of Chemistry, Department of
Chemical Organic Technology and Petrochemistry, ul. Krzywoustego 4,
4
4-100 Gliwice, Poland. Fax: 48 322371032; Tel: 48 322372917;
e-mail: anna.chrobok@polsl.pl
4
5
5
5
0
5
1
2
3
M. Renz and B. Meunier, Eur. J. Org. Chem., 1999, 737.
G. Brink, I. Arends and R. Sheldon, Chem. Rev., 2004, 104, 4105.
A. Corma, L. T. Nemeth, M. Renz and S. Valencia, Nature, 2001, 412,
4
23.
4
D. E. T. Pazmino, H. M. Dudek and M. W. Fraaije, Curr. Opin. Chem.
Biol., 2010, 14, 138.
V. Alphand and R. Wohlgemuth, Curr. Org. Chem., 2010, 14, 1928.
M. M. Kayser, Tetrahedron, 2009, 65, 947.
S. C. Lemoult, P. F. Richardson and S. M. Roberts, J.Chem. Soc.
Perkin Trans., 1995, 1, 89.
5
6
7
8
B. K. Pchelka, M. Gelo-Pujic and E. Guibé-Jampel, J. Chem. Soc.
Perkin Trans., 1998, 1, 2625.
6
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]