New strategies for the synthesis of lactones using peroxymonosulphate salts, ionic liquids and microwave or ultrasound irradiation

Article abstract of DOI:10.1039/c3nj01170d

A new method for the rapid synthesis of lactones via the one-pot oxidation of alcohols with potassium peroxymonosulphate in an ionic liquid was developed. The use of microwave or ultrasonic irradiation increased the reaction rates significantly. Additionally, new peroxymonosulphate ionic liquids were synthesised and used as effective oxidants in the synthesis of lactones. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014.

Full text of DOI:10.1039/c3nj01170d

NJC
View Article Online
View Journal | View Issue
PAPER
New strategies for the synthesis of lactones using
peroxymonosulphate salts, ionic liquids and
microwave or ultrasound irradiation†
Cite this: New J. Chem., 2014,
3
8, 237
a
b
b
Karolina Matuszek, Przemysław Zawadzki, Wojciech Czardybon and
Anna Chrobok*
a
Received (in Porto Alegre, Brazil)
6th September 2013,
Accepted 18th October 2013
2
A new method for the rapid synthesis of lactones via the one-pot oxidation of alcohols with potassium
peroxymonosulphate in an ionic liquid was developed. The use of microwave or ultrasonic irradiation
increased the reaction rates significantly. Additionally, new peroxymonosulphate ionic liquids were
synthesised and used as effective oxidants in the synthesis of lactones.
DOI: 10.1039/c3nj01170d
www.rsc.org/njc
Therefore, in our previous work, alternative methods for the
oxidation of ketones or alcohols were presented. The first
Introduction
In recent years, new safety and environmental requirements have method was based on the use of an alternative solvent, such
led to the design of new reaction systems based on sustainable as an ionic liquid, to dissolve KHSO and eliminate water from the
The second method used phase transfer
5
6,7
chemistry principles. Classical processes are being modified to reaction system.
8
minimise the use and generation of hazardous substances and catalysis to avoid the hydrolysis of lactones. Y. Wei also presented
1
wastes. The use of ionic liquids in organic synthesis provides an interesting approach for the synthesis of aldehydes and
a good alternative to the use of volatile organic solvents. Ionic ketones. Specifically, a new oxidising agent, tetrabutylammonium
liquids possess many interesting properties, including a low peroxymonosulphate ([N4444][HSO ]), was employed in the clean,
5
vapour pressure, the ability to dissolve organic and inorganic selective oxidation of alcohols catalysed by a nitroxyl radical,
substances, thermal and chemical stability, non-flammability and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), in the presence of
9
non-corrosive behaviour. Moreover, they are called ‘‘designer tetrabutylammonium bromide (TBAB) in an ionic liquid. Other
2–4
solvents’’ and can act as both catalysts and solvents.
work has described the oxidation of primary and secondary
Ionic liquids could also potentially be used as oxidants, an alcohols to ketones with KHSO in classical solvents, such as
5
10
application that has not yet been described. One way to synthesise dichloromethane or toluene. According to the literature, the
an ionic-liquid oxidant is to introduce a peroxy group into the solubility of the peroxymonosulphate salts and the use of homo-
À
anion structure, e.g., HSO
5
. Commercial sources of potassium genous conditions are critical for the oxidation of ketones to
s
peroxymonosulphate, e.g., Oxone , are stable oxidising agents lactones, which is in contrast to the oxidation of alcohols to
commonly used in fine chemicals synthesis. The oxidising ketones where homogenous conditions are not required. Thus,
5
peroxymonosulphate salt is easy to handle, non-toxic and alcohols can only be oxidised to ketones with KHSO
relatively inexpensive, and it generates non-polluting by-products.
5
in classical
solvents. The one-pot, tandem oxidation of alcohols directly to
However, peroxymonosulphate salts have poor solubility in esters or lactones has not been well studied. Only a few reports of
5
11–14
organic solvents, making it difficult to apply effectively in this type of oxidation reaction have appeared in the literature.
oxidation reactions. To use KHSO in oxidation reactions, an The one-pot oxidation would be especially useful for e-caprol-
5
aqueous reaction medium must be employed, which can lead actone production. Currently, e-caprolactone is produced from
to the hydrolysis of unstable products, e.g., lactones or esters. cyclohexanol via a two-step process. From a synthetic and
industrial viewpoint, a one-pot procedure would be economically
a
favourable.
Silesian University of Technology, Faculty of Chemistry, Department of Chemical
Organic Technology and Petrochemistry, ul. Krzywoustego 4, 44-100 Gliwice,
Poland. E-mail: anna.chrobok@polsl.pl; Fax: +48 322371032; Tel: +48 322372917
Selvita S.A., Park Life Science, Bobrzy n´ skiego 14, 30-348 Krak o´ w, Poland.
E-mail: wojciech.czardybon@selvita.com; Fax: +48 122974701;
Tel: +48 122974700
b
Results and discussion
In this work, new strategies for the synthesis of e-caprolactone were
developed. ‘‘Greener’’ chemical syntheses using ionic liquids as
†
Electronic supplementary information (ESI) available: Experimental details and
NMR spectra. See DOI: 10.1039/c3nj01170d
solvents for the KHSO
5
oxidant were performed using ultrasound
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 237--241 | 237

View Article Online
Paper
NJC
s
Table 2 Oxidation of cyclohexanol (1 mmol) with Oxone (4 mmol) in
2
the presence of 5 mol% of the catalyst in [bmim][N(CN) ] (3 ml) at 40 1C
a
[
2
bmim][N(CN) ]
Scheme 1 Ultrasound or microwave-assisted one-pot oxidation of
cyclohexanol.
Reaction Yield of
time e-caprolactone [%]
Mixing procedure
Magnetic stirrer
Catalyst
TEMPO/TBAB 7 h
TMP*HBr 7 h
and microwave irradiation (Scheme 1). The ionic liquids were Ultrasounds irradiation TEMPO/TBAB 5 h
also demonstrated to act as oxidising agents. A new class of
ionic liquids with peroxymonosulphate anions was synthesised
and employed in the model oxidation.
83
63
81
71
53
83
67
81
TMP*HBr
5 h
Microwaves irradiation TEMPO/TBAB 10 min
TEMPO/TBAB 30 min
TMP*HBr
TMP*HBr
10 min
30 min
a
À1
Ultrasound or microwave-assisted synthesis of e-caprolactone
Solubility of KHSO
5
in IL is equal 0.16 [g ml ].
using potassium peroxymonosulphate and ionic liquids
À1
We previously utilised [bmim]BF as a novel medium for the
The solubility of KHSO in the ionic liquid (0.13 g ml for
5
4
7
one-pot, tandem oxidation of cyclohexanol to e-caprolactone [bmim][BF ]) is a key parameter for both steps of the oxidation.
with Oxone in a TEMPO/TBAB catalytic system with magnetic We discovered a more environmentally friendly ionic liquid
4
s
6
stirring (Table 1, magnetic stirring). Because [bmim]BF
4
can based on the dicyanide anion, [bmim][N(CN) ], that could be
2
dissolve both cyclohexanol and KHSO
geneous conditions, the tandem reaction can be performed.
5
, thus resulting in homo- used in this reaction. The solubility of KHSO in this ionic
5
7
liquid was measured as described elsewhere and was also
À1
The inability of dichloromethane and other typical organic found to be high (0.16 g ml ). The results for the oxidation
solvents to dissolve KHSO prevents their use in the tandem of cyclohexanol in [bmim][N(CN) ] are presented in Table 2. In
5
2
oxidation of alcohols.
this case, e-caprolactone was also obtained in high yields in
Microwave reactors and ultrasound baths are new alternative significantly shorter reaction times when ultrasound or micro-
heat sources that generate heat evenly throughout the reactor, wave irradiation was employed. The results also showed that
thus preventing local overheating, which can influence the purity TBAB could be replaced with 2,2,6,6-tetramethylpiperidine
of the reaction product. Furthermore, these methods are very hydrobromide (TMP*HBr).
1
5
efficient, accelerating many organic reactions. The properties of
The successful oxidation of alcohols to lactones demon-
ionic liquids allow them to utilise microwave energy effectively. strated here might lead to a new environmentally friendly
Ionic species, such as ionic liquids, that consist entirely of ions protocol for MW- or ultrasound-assisted reactions in ionic
can absorb microwave energy very efficiently. Another advantage liquids. It should be noted that the reactions performed in a
of ionic liquids is their lack of a measurable vapour pressure, microwave or ultrasound bath are completely homogenous
s
resulting in the low risk of an explosion caused by a rapid with all Oxone inorganic salts and organic reactants dissolved
1
6
increase in the solvent vapour pressure.
during the reaction. Fig. 1 shows the progress of the cyclohexanol
The use of ultrasound or microwave irradiation in the one- oxidation in [bmim][N(CN) ] under ultrasound irradiation in
2
pot, TEMPO-catalysed oxidation of cyclohexanol in [bmim][BF
4
]
terms of the alcohol and intermediate ketone conversions and
reduced the reaction time (Table 1). TBAB acted as the bromide lactone yield over time. When traditional stirring was used for the
ion source and reacted with KHSO to generate hypobromous
5
acid, which is a stronger oxidant, in situ. The nitroxyl radical
1
0
was subsequently oxidised to N-oxoammonium bromide.
Ultrasound irradiation reduced the reaction time for the
e-caprolactone synthesis from 8 h to 5 h and gave a yield of
80%. The microwave reactor led to a significant decrease in the
reaction time for the lactone production to 30 min.
s
Table 1 Oxidation of cyclohexanol (1 mmol) with Oxone (4 mmol) in the
presence of TEMPO/TBAB (5/5 mol%) in [bmim][BF
4
] (3 ml) at 40 1C
a
4
[bmim][BF ]
Reaction
time [h]
Yield of
e-caprolactone [%]
b
Mixing procedure
c
Magnetic stirrer
8
78
Ultrasounds irradiation
Microwaves irradiation
5
0.5
80
85
Fig. 1 Alcohol and ketone conversions and e-caprolactone yield during
the oxidation of cyclohexanol (1 mmol) with Oxone (4 mmol) in the
s
a
À1
7
Solubility of KHSO
5
in IL is equal 0.13 [g ml ], data from literature.
presence of 5 mol% of TEMPO/TBAB in [bmim][N(CN)
under ultrasound irradiation.
2
] (3 ml) at 40 1C
b
c
6
Yield of e-caprolactone was determined by GC. Data from literature.
2
38 | New J. Chem., 2014, 38, 237--241
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
s
Table 3 Oxidation of cyclic alcohols (3 mmol) with Oxone (12 mmol) in Synthesis of peroxymonosulphate ionic liquids (PSILs) and
the presence of TEMPO/TBAB (5/5 mol%) in [bmim][N(CN)
under ultrasound irradiation
2
] (9 ml) at 40 1C
their use in the synthesis of e-caprolactone
To create homogenous conditions in the reactions involving a
peroxymonosulphate oxidation agent, a liquid salt that can act
as both an oxidising agent and a solvent can be used. We
therefore synthesised ionic liquids with a peroxymonosulphate
anion. Only one example of a salt with an organic cation and
Reaction
time [h]
Yield of
lactone [%]
Alcohol
Lactone
5
75
86
peroxymonosulphate anion (tetrabutylammonium peroxymono-
9
sulphate [N4444][HSO ]) has been reported in the literature.
5
Unfortunately, this salt, which is an effective oxidant for oxida-
tive cleavage reactions, is a solid at room temperature.
6
To lower the melting points of the organic salts used in this
work, we treated the following bromides, 1-butyl-3-methyl-
imidazolium [bmim], 1-ethyl-1-methylpyrrolidinium [empy]
and 1-butylpyridinium [bpyr], with sulphuric acid (Scheme 2).
6
6
88
89
s
The produced hydrogen sulphate salts were mixed with Oxone
(molar ratio 1 : 3) in acetone under ultrasound irradiation. The
waste inorganic salts were then filtered out, and the resulting
peroxymonosulphate ionic liquids (PSILs) were concentrated.
The active oxygen content ranged from 6.29% to 6.99%
(Table 4). The resulting salts were liquids at room temperature.
The structures of the new ionic liquids were determined using
H and C NMR. The NMR spectra of the neat ionic liquids
exhibited different proton positions for the peroxymonosulphate
anions than for hydrogen sulphate.
same reaction, the partial insolubility of the inorganic salts
resulted in longer reaction times.
1
13
Finally, to determine its practical potential, other cyclic
alcohols, including cyclobutanol, 1-phenyl-2-propanol, 3-methyl-
cyclohexanol and 4-tert-butylcyclohexanol, were oxidised using the
Additionally, ESI-MS experiments were performed. The peaks
found in positive and negative ESI modes confirmed the
presence of peroxymonosulphate anions and adequate cations
in all PSIL samples. The PSIL decomposition temperatures were
measured using thermogravimetric analysis and were in the
range of 144–344 1C. All detailed data are presented in the ESI.†
Using 1-butyl-3-methylimidazolium peroxymonosulphate as
the oxidant and solvent in the oxidation of cyclohexanol
resulted in the efficient synthesis of e-caprolactone (Table 5).
Ultrasound irradiation enabled the high-yield (90%) production
of the lactone. Unfortunately, the use of microwave assistance
was not successful for this reaction; the reaction system over-
heated. For comparison, the reaction was also performed using
s
most active reaction system, which consisted of Oxone , TEMPO/
2
TBAB and [bmim][N(CN) ] in an ultrasound bath. As shown in
Table 3, the oxidation reactions proceeded very efficiently; in fact,
the cyclic alcohols were readily oxidised to their corresponding
lactones in high yields (75–89%) under our mild conditions
within relatively short reaction times.
The recyclability of the ionic liquid was tested by oxidising
cyclohexanol in the most active reaction system in three successive
runs. The results showed that the activity of the ionic liquid in
the model reaction was very high but slowly declined for each
successive run (Fig. 2).
[
N4444][HSO ] in dichloromethane, but the reaction was not
5
homogenous, which prevented lactone formation. The use of
bmim][N(CN) ] and ultrasound irradiation for this reaction
[
2
resulted in a high product yield (78%).
The reaction pathway can be described as proposed in
Scheme 3. The initial effect of ionic liquid leads to activation
2
Fig. 2 e-Caprolactone yield and [bmim][N(CN) ] recovery over three
s
cycles of cyclohexanol (3 mmol) oxidation with Oxone (12 mmol) in
the presence of TEMPO/TBAB (5/5 mol%) at 40 1C under ultrasound
irradiation. Reaction time: 5 h.
Scheme 2 General procedure for the synthesis of peroxymonosulphate
ionic liquids.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 237--241 | 239

View Article Online
Paper
NJC
Table 4 PSIL structures and properties
a
b
c
d
Peroxymonosulphate ionic liquid (PSIL)
Active oxygen content [%]
T
5% onset [1C]
T
50% onset [1C]
T
dec [1C]
Calc.: 6.34
Found: 6.29
9
7
9
7
8
0
344
144
350
Calc.: 7.05
Found: 6.99
e
116, 139, 300
Calc.: 6.41
Found: 6.34
e
298
—
125, 337
Calc.: 4.50
Found: 4.45
—
—
a
b
c
d
Determined by iodometric titration.
T
5% onset decomposition of 5% of the sample.
T50% onset decomposition of 50% of the sample.
T
dec
e
decomposition. Multistep decomposition was observed.
Table 5 Oxidation of cyclohexanol (1 mmol) with a peroxymonosulphate salt (6 mmol) in the presence of TEMPO/TBAB (5/5 mol%) at 40 1C
bmim][HSO [N4444][HSO
[
5
]
5
]
Mixing procedure
Reaction time [h]
Yield of e-caprolactone [%]
Reaction time [h]
Yield of e-caprolactone [%]
a
Magnetic stirrer
Ultrasound irradiation
7
5
60
90
8
5
17
b
78
a
b
Dichloromethane as a solvent (0.5 ml). [bmim][N(CN)
2
] as a solvent (0.5 ml).
s
Oxone is a cheap, commercially available oxidant and
easily oxidises several functional groups. Our new approach
expands the range of its applications. Using the new method,
lactones were produced in high yields and with high selectivities.
s
Commonly, application of Oxone in Baeyer–Villiger reaction
requires an aqueous reaction medium, which can lead to the
hydrolysis of lactones causing the formation of by-products. This
drawback can be avoided by applying ionic liquids proposed in
this work. Moreover, peroxymonosulphate ionic liquids do not
contain the ballast of inorganic salts (KHSO and K SO ) against
Scheme 3 Proposed mechanism of the Baeyer–Villiger oxidation of
cyclic ketones with peroxymonosulphate ionic liquids.
4
2
4
s
Oxone , thereby resulting in easier work-up and product
purification. Further applications of PSILs to other MW/ultrasonic
of the carbonyl group. This is followed by a nucleophilic attack irradiation reactions are currently under study.
of the peroxymonosulphate anion on the carbonyl group and a
tetrahedral intermediate (Criege adduct) is formed. The rear-
rangement of the Criege adduct gives the final lactone and
ionic liquid [cation][HSO4].
Experimental section
General procedure for the synthesis of peroxymonosulphate
salts
A solution of 4.2 mmol of a hydrogen sulphate salt ([bmim],
Conclusions
s
[bpyr], [empy]) and 12.6 mmol of Oxone in 10 ml of anhydrous
In summary, we developed a new general method for lactone acetone was placed into a 50 ml two-necked flask. The flask was
synthesis via the one-pot oxidation of alcohols with peroxymono- equipped with a cooler, sealed in a nitrogen atmosphere and
sulphate salts. The addition of ionic liquids to this reaction placed in an ultrasound bath for 2 h. Next, the mixture was
system facilitated the formation of homogenous conditions in filtered to isolate the rest of the inorganic salts. The filtrate was
the reactor, which is essential for this tandem reaction, thereby concentrated under vacuum and dried (10 h, 60 mbar). The
providing a more sustainable approach to lactone synthesis. The resulting peroxymonosulphate salts were pale yellow liquids
synthesis was accelerated by MW/ultrasonic irradiation.
and were obtained in yields between 90–98%.
2
40 | New J. Chem., 2014, 38, 237--241
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
General procedure for lactone synthesis using microwave or
ultrasound irradiation
with diethyl ether, the IL was concentrated, dried under
vacuum (60 1C, 5 h) and reused.
Cyclohexanol (1 mmol), TEMPO (0.05 mmol), TBAB (0.05 mmol),
s
Oxone (4 mmol) and [bmim][N(CN)
2
] or [bmim][BF
4
] (3 ml) Acknowledgements
were placed in a round-bottom flask. The reaction mixture was
stirred for 10 minutes to 10 h depending on the reaction rate in
an oil bath, ultrasound bath or microwave reactor at 40 1C. The
reaction progress was monitored by GC. The post-reaction
mixture was dissolved in CH Cl and filtered to separate the
products from the Oxone inorganic salts. Next, the filtrate
was concentrated. The ionic liquid was then extracted with
diethyl ether (6 Â 5 ml). After purifying the product by column
chromatography with hexane–ethyl acetate (4: 1) as the eluent,
the e-caprolactone yields were 75–80%.
This work was financed by the Ministry of Science and Higher
Education (Grant no. N N209 021739).
2
2
Notes and references
s
1
2
R. A. Sheldon, Green Chem., 2005, 7, 267.
H. Olivier-Bourbigou, L. Magna and D. Morvan, Appl. Catal.,
A, 2010, 373, 1.
3
P. Wasserscheid and T. Welton, Ionic Liquids in Synthesis,
Wiley-VCH, Weinheim, 2007.
4
5
N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123.
H. Hussain, I. R. Green and I. Ahmed, Chem. Rev., 2013,
General procedure for the synthesis of e-caprolactone using
peroxymonosulphate salts
113, 3329.
Cyclohexanol (1 mmol), TEMPO (0.05 mmol), TBAB (0.05 mmol)
and a peroxymonosulphate salt (6 mmol) were placed in a
round-bottom flask. The reaction mixture was stirred in an
oil or ultrasound bath at 40 1C for 5–7 h depending on the
reaction rate. The reaction progress was monitored by GC. After
the reaction was completed, the ionic liquid was extracted with
diethyl ether (6 Â 5 ml). After purifying the product by column
chromatography with hexane–ethyl acetate (4 : 1) as the eluent,
the e-caprolactone yields were 75–85%.
6
7
8
9
A. Chrobok, Synlett, 2011, 391.
A. Chrobok, Tetrahedron, 2010, 66, 6212.
S. Baj, A. Chrobok and A. Siewniak, Appl. Catal., A, 2011, 395, 49.
C. Zhu, L. Ji and Y. Wei, Catal. Commun., 2010, 11, 1017.
1
1
0 C.Bolm,A.S.MagnusandJ.P.Hildebrand,Org. Lett., 2000, 2, 1173.
1 L. Balbinot, U. Schuchardt, C. Vera and J. Sep u´ lveda, Catal.
Commun., 2008, 9, 1878.
12 M. L. Morin-Fox and M. A. Lipton, Tetrahedron Lett., 1992,
33, 5699.
1
3 J. A. Cella, J. P. McGrath, J. A. Kelley, O. El Soukkary and
L. Hilpert, J. Org. Chem., 1977, 42, 2077.
2
Recycling of [bmim][N(CN) ]
The model reaction for the e-caprolactone synthesis using 14 O. Fukuda, S. Sakaguchi and Y. Ishii, Tetrahedron Lett.,
s
Oxone as the oxidant and ultrasound irradiation was chosen
2001, 42, 3479.
for the ionic liquid recycling experiments. After the reaction 15 R. S. Varma, Green Chem. Lett. Rev., 2007, 1, 37.
was completed, the IL was purified for the recycling tests. After 16 S. Toma, R. Sebesta and M. Meciarova, Curr. Org. Chem.,
filtering the post-reaction mixture and extracting the product
2011, 15, 2257.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 237--241 | 241