Organic & Biomolecular Chemistry
Paper
yield (593 mg), mp. 92–93 °C. lit.15c mp. 88–89 °C. 1H NMR
(300 MHz, DMSO-d6) δ 8.44 (d, J = 2.75 Hz, 1H), 8.17 + 8.14
(dd, J1 = 2.8 Hz, J2 = 9.2 Hz, 1H), 7.21–7.15 (m, 2H), 7.08–7.03
(m, 2H), 6.92 + 6.89 (ds, 1H), 3.79 (s, 3H).
for Sustainable Chemistry, ed. N. E. Leadbeater, CRC Press,
Boca Raton, 2011.
2 For comprehensive reviews, see: (a) C. O. Kappe and
D. Dallinger, Mol. Diversity, 2009, 13, 71–193; (b) S. Caddick
and R. Fitzmaurice, Tetrahedron, 2009, 65, 3325–3355 and
references cited therein.
Synthesis of adipic acid (5) (Scheme 2)
3 For a survey of commercially available microwave reactors,
see: C. O. Kappe, A. Stadler and D. Dallinger, Microwaves in
Organic and Medicinal Chemistry, Wiley-VCH, Weinheim,
2nd edn, 2012, ch. 3, pp. 41–81.
4 For a discussion and more detailed definition on micro-
wave effects, see: C. O. Kappe, B. Pieber and D. Dallinger,
Angew. Chem., Int. Ed., 2013, 52, 1088–1094 and references
cited therein.
A 10 mL Pyrex microwave vessel was equipped with the vertical
blade stir bar, 10 mg tungstic acid (1 mol%), 1 mL of a 50%
hydrogen peroxide solution, 1 mL of water, and 4 mmol of
cyclohexene (405 μL) to obtain a 4.4 equiv. excess of hydrogen
peroxide. The reaction vessel was sealed with a snap cap con-
taining a PTFE-coated silicone septum and the reaction
mixture was heated for 60 min at 140 °C utilizing a stirring
speed of 1200 rpm (IR temperature control). After cooling to
ambient conditions the reaction mixture was cooled for 2 h at
0 °C to allow precipitation of the desired product. Finally the
adipic acid was filtered and washed with a small amount of
cold 1 N HCl to obtain 351 mg (60% isolated yield) of pure
product, mp. 151 °C (lit.16 mp. 151–152 °C); 1H NMR
(300 MHz, DMSO) δ 12.01 (s, 1H), 2.2 (t, J = 6.0 Hz, 1H),
1.64–1.38 (m, 1H).
5 For
a tutorial review on how to monitor the reac-
tion temperature in single-mode microwave reactors,
see: C. O. Kappe, Chem. Soc. Rev., 2013, 42, 4977–
4990.
6 (a) J. Robinson, S. Kingman, D. Irvine, P. Licence,
A. Smith, G. Dimitrakis, D. Obermayer and C. O. Kappe,
Phys. Chem. Chem. Phys., 2010, 12, 4750–4758;
(b) G. S. J. Sturm, M. D. Verweij, T. van Gerven,
A. I. Stankiewicz and G. D. Stefanidis, Int. J. Heat Mass
Synthesis of ε-polycaprolactone (7) Scheme 3
Transfer,
2012,
55,
3800–3811;
(c)
T.
Durka,
A stock solution consisting of 17.1 g (0.15 mol) ε-caprolactone
and 60.75 mg (0.15 mmol) tin(II)-2-ethylhexanoate was pre-
pared to obtain comparable initiator to monomer ratios. For a
typical reaction 3 mL of the prepared stock solution were filled
in a 10 mL Pyrex vessel that was equipped with a vertical blade
stir bar and closed with a snap cap holding a pierced PTFE-
coated silicone septum to be equipped with an immersion
tube that protects the utilized internal FO probe during the
microwave run. The reaction mixture was heated for 30 min at
180 °C (IR control) using a stirring speed of 600 rpm and sub-
G. D. Stefanidis, T. van Gerven and A. Stankiewicz, Meas.
Sci. Technol., 2010, 21, 045108.
7 D. Obermayer and C. O. Kappe, Org. Biomol. Chem., 2010,
8, 114–121.
8 M. A. Herrero, J. M. Kremsner and C. O. Kappe, J. Org.
Chem., 2008, 73, 36–47.
9 S. Hayden, M. Damm and C. O. Kappe, Macromol. Chem.
Phys., 2013, 214, 423–434.
10 (a) J. D. Moseley, P. Lenden, A. D. Thomson and
J. P. Gilday, Tetrahedron Lett., 2007, 48, 6084–6087;
(b) C. K. Lombard, K. L. Myers, Z. H. Platt and
A. W. Holland, Organometallics, 2009, 28, 3303–3306;
(c) M. Irfan, M. Fuchs, T. N. Glasnov and C. O. Kappe,
Chem.–Eur. J., 2009, 15, 11608–11618; (d) B. Gutmann,
D. Obermayer, B. Reichart, B. Prekodravac, M. Irfan,
J. M. Kremsner and C. O. Kappe, Chem.–Eur. J., 2010, 16,
12182–12194.
1
sequently cooled to 70 °C with compressed air. High H NMR
conversions were obtained for both stir bar designs (93% for
the standard stir bar as well as 94% for the vertical blade stir
bar). The conversion rate was calculated from the relative
1
intensities of the H NMR signals of the ω-methylene protons
(–CH2OC(O)–) in the product (2H, 4.04 ppm) and the
monomer (2H, 4.22 ppm) as previously reported.9
11 See also: M. D. Bowman, N. E. Leadbeater and
T. M. Bernard, Tetrahedron Lett., 2008, 49, 195–198.
12 For a selection of commercial suppliers of rare-earth
noted that most of the magnetic stir bars offered were
either too big to fit inside a 10 mL microwave process
vial or did not allow the insertion of a fiber optic
probe.
Acknowledgements
This work was supported by a grant from the Christian
Doppler Research Society (CDG).
Notes and references
13 Springer Handbook of Condensed Matter and Materials Data,
ed. W. Martienssen and H. Warlimont, Springer, Berlin,
2006, p. 794.
1 For recent books, see: (a) Microwaves in Organic Synthesis,
ed. A. De La Hoz and A. Loupy, Wiley-VCH, Weinheim, 3rd
edn, 2013; (b) C. O. Kappe, A. Stadler and D. Dallinger, 14 (a) Stirring: Theory and Practice, ed. M. Zlokarnik, Wiley-
Microwaves in Organic and Medicinal Chemistry, Wiley-VCH,
Weinheim, 2nd edn, 2012; (c) Microwave Heating as a Tool
VCH, Weinheim, 2007; (b) Rühren, Rührer, Rührbehälterkon-
struktionen: Grundlagen und Anwendungen für
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