Analysis
Experimental
All products were characterized by comparison of their NMR
spectra with authentic samples. 1H NMR and 13C NMR spectra
were recorded at 300 MHz in CDCl3 (Varian Unity Inova plus,
internal TMS). GC analysis was performed using PerkinElmer
chromatograph and decane as the external standard; HPLC
was performed by liquid chromatograph (Alliance, Waters 2690
system) with a 2 ¥ 150 mm column (Nova-Pak Silica, 60A, 4 mm);
the solvent system included hexane/2-propanol (95/5 v/v, flow
rate 0.25 ml/min).
Materials
Ionic liquids: bmimOTf, bmimHSO4 (Merck), ketones and
AlCl3, SnCl4, BF3*OEt2, NaOTf (Acros Organics) were com-
mercial materials; bmimBF4, bmimNTf2 and BTSP12 were
11
prepared according to standard procedures.
Typical procedure for BV oxidation in the presence of Lewis acids
BTSP (1.0 mmol) was added to a solution of ketone (0.5 mmol)
and Lewis acid (1.0 mmol) in ionic liquid (2 ml) and stirred
under the nitrogen atmosphere at room temperature for 5 hours.
The progress of the reaction was monitored by GC. After
this time the post-reaction mixture was extracted with diethyl
ether (6 ¥ 5 ml). The organic layer was washed with 5 ml of
10% of a water solution of NaHCO3, dried over anhydrous
MgSO4, filtered, and concentrated in a vacuum. The yields of
lactones after the purification by column chromatography with
hexane:ethyl acetate (4:1) as an eluent were for d-valerolactone
68–89%; for e-caprolactone 52–90%. The same procedure was
used for the reactions carried out in the presence of Lewis acids
in dichloromethane as solvent.
Conclusions
In summary, we have reported an efficient method for lactones
synthesis that utilizes bis(trimethylsilyl) peroxide as the oxidant
in environmentally attractive ionic liquids. First we proposed
the utilization of bmimNTf2 as the solvent and SnCl4 as a
catalyst. This method yielded results that are comparable to
the literature with dichloromethane as the solvent. Neverless,
substantial benefit is gained from elimination of the classical
solvent for the oxidation process, not only by the minimization
of solvent waste but also by improving work safety.
Our second study is based on the utilization of bmimOTf
as both the solvent and catalyst. This new method seems to
be very attractive, since it gives lactones in high yields. The
simplicity of the methodology, ease of the product isolation,
high yields, mild conditions and possibility of IL recycling could
result in significant progress towards greener processes for the
manufacture of lactones.
Typical procedure for BV oxidation in bmimOTf as the solvent
and catalyst
BTSP (1.0 mmol) was added to a solution of ketone (0.5 mmol)
in bmimOTf (2 ml) and stirred under the nitrogen atmosphere
at room temperature to 40 ◦C for 1 to 24 hours (depending on
the reaction rate). The progress of the reaction was monitored
by GC. After this time, insoluble in bmimOTf by-product,
hexamethylsiloxane, can be isolated by decantation. Next, the
post-reaction mixture was extracted with diethyl ether (6 ¥ 5 ml).
The organic layer was washed with 5 ml of 10% of a water
solution of NaHCO3, dried over anhydrous MgSO4, filtered,
and concentrated in a vacuum. The yields of lactones after
the purification by column chromatography with hexane:ethyl
acetate (4:1) as an eluent were 72–91%.
Notes and references
1 A. Baeyer and V. Villiger, Ber. Dtsch. Chem. Ges., 1899, 32, 3625.
2 G. Krow, Org. React., 1993, 43, 251; M. Renz and B. Meunier,
Eur. J. Org. Chem., 1999, 737.
3 (a) G. Strukul, Angew. Chem., Int. Ed., 1998, 37, 1198; (b) G. Brink,
I. Arends and R. Sheldon, Chem. Rev., 2004, 104, 4105.
4 S. Matsubara, K. Takai and H. Nozaki, Bull. Chem. Soc. Jpn., 1983,
56, 2029.
5 H. Oberhammer and J. E. Boggs, J. Am. Chem. Soc., 1980, 102, 7241.
6 W. Adam and A. Rodriguez, J. Org. Chem., 1979, 44, 4969.
7 M. Suzuki, H. Takada and R. Noyori, J. Org. Chem., 1982, 47, 902.
8 T. Welton, Chem. Rev., 1999, 99, 2071; P. Wasserscheid and K.
Wilhelm, Angew. Chem., Int. Ed., 2000, 39, 3772; H. Olivier-
Bourbigou and L. Magna, J. Mol. Catal. A: Chem., 2002, 182, 419; J.
Dupont, R. F. de Souza and P. A. Z. Suarez, Chem. Rev., 2002, 102,
3667; Ionic Liquids in Synthesis, 2nd Edition; ed. P. Wasserscheid,
T. Welton, Wiley-VCH, Weinheim, 2007; K. Binnemans, Chem. Rev.,
2005, 105, 4148; V. Parvulescu and C. Hardacre, Chem. Rev., 2007,
107, 2615.
Recycling of bmimOTf
For the experiments where bmimOTf was recycled, four times of
the amount of reactants described above, were used. After BV
reaction, bmimOTf was purified for recycling tests by extractions
of post-reaction mixture with diethyl ether (6 ¥ 5 ml). Next,
bmimOTf was concentrated and dried in a vacuum (60 ◦C,
12 h).
9 J. Muzart, Adv. Synth. Catal., 2006, 348, 275.
10 S. Matsugo and I. Saito, Organic peroxides, ed. W. Ando, Wiley-
Interscience, New York, 1992, p. 157.
Stability of BTSP
11 P. Bonhote, A. Dias, N. Papageorgiou, K. Kalyanasundaram, M.
Armand and M. Graetzel, Inorg. Chem., 1996, 35, 1168; H. Shang,
J. Wu, Q. Zhou and L. Wang, J. Chem. Eng. Data, 2006, 51, 1286.
12 W. P. Jackson, Synlett, 1990, 536.
A solution of 0.2 g BTSP in 2 ml IL was stirred for 5 h at room
temperature. After this time the content of BTSP was determined
by iodometric titration.
282 | Green Chem., 2009, 11, 279–282
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The Royal Society of Chemistry 2009
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