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reaction medium was stirred by a Rushton turbine or a self-
suction turbine. A total volume of 40 mL of the desired
mixture of aldehyde (1.5 M in heptane) were placed in the
Notes and references
1 For select reviews, see: (a) J. R. McNesby and C. A. Heller,
Chem. Rev., 1954, 54, 325; (b) L. Sajus and I. Sere De Roch,
ꢀ
reactor. The temperature was set to 25 C and the reactor was
´ ´
then pressurized with reconstituted air (O2 21%wt and N2 79%
wt). The time-course of the gas pressure decrease was measured
with a pressure transducer and recorded on-line using Labview.
The reaction mixture was analysed at the end of each experi-
ment using a Shimadzu 2010 GC-MS system equipped with a
DB-5 column.
in Liquid-Phase Oxidation, ed. C. H. Boamford and C. F. H.
Tipper, Elsevier, Amsterdam, 1980, vol. 16, p. 89; (c)
E. T. Denisov and I. B. Afanas'ev, Oxidation and
antioxidants in organic chemistry and biology, Taylor &
Francis, Boca Raton, 2005.
2 W. Riemenschneider, in Ullmann's Encyclopedia of Industrial
Chemistry, Wiley-VCH, 6th edn, 2003, vol. 6, p. 493.
´
3 L. Vanoye, A. Favre-Reguillon, A. Aloui, R. Philippe and C. de
Oxidation of aldehyde in microreactor5
Bellefon, RSC Adv., 2013, 3, 18931.
4 (a) C. Kohlpaintner, M. Schulte, J. Falbe, P. Lappe and
J. Weber, in Ullmann's Encyclopedia of Industrial Chemistry,
Wiley-VCH, 6th edn, 2003, vol. 2, p. 65; (b) T. Seki,
J.-D. Grunwaldt and A. Baiker, Chem. Commun., 2007, 3562.
5 L. Vanoye, A. Aloui, M. Pablos, R. Philippe, A. Percheron,
A PFA tubing (Upchurch Scientic) (internal diameter of 1000
mm, length 5 m) was used as reactor. Sample were injected via
HPLC sample injector (Rheodyne) using an external PEEK loops
of 1 mL. The organic phase (Harvard pumps PHD 4400) and the
oxygen (Analyt-MTC massow controller) were fed via two
separate lines and brought together using a T-mixer (Inter-
chim). A back pressure of 5 bar was applied using a home made
back pressure regulator controlled with nitrogen ow (Analyt-
MTC massow controller) and micro-metering valve. The
outlet port of the microreactor was connected to a 6-way gas
sampling injection valve (Agilent) for on line analysis by Agilent
6890 GC equipped with FID detector and Red dot FFAP column
(5 m  0.05 mm  0.05 mm). Liquid products were retrieved
from back-pressure regulator and could be further analysed by a
Shimadzu 2010 GC-MS system equipped with a DB-5 column (15
m  0.1 mm  0.1 mm.).
´
A. Favre-Reguillon and C. De Bellefon, Org. Lett., 2013, 15,
5978.
6 (a) J. R. Alvarez-Idaboy and L. Reyes, J. Org. Chem., 2007, 72,
6580; (b) R. D. Bach, J. Org. Chem., 2012, 77, 6801.
7 (a) C. Lehtinen and G. Brunow, Org. Process Res. Dev., 2000, 4,
544; (b) C. Lehtinen, V. Nevalainen and G. Brunow,
Tetrahedron, 2000, 56, 9375; (c) C. Lehtinen, V. Nevalainen
and G. Brunow, Tetrahedron, 2001, 57, 4741.
8 (a) R. L. Hartman, J. P. McMullen and K. F. Jensen, Angew.
Chem., Int. Ed., 2011, 50, 7502; (b) V. Hessel, D. Kralisch,
¨
N. Kockmann, T. Noel and Q. Wang, ChemSusChem, 2013,
6, 746.
The general experimental procedure is as follows. Heptane
was loaded in 50 mL syringes. Heptane (Harvard pump) and
oxygen (Analyt-MTC massow controller) were delivered into
the microreactor via a T-mixer. A portion of a freshly prepared
solution of aldehyde (1.5 M in heptane), catalyst (0 to 100 ppm)
and salt (0 to 5 wt%) is introduced into the sampling loop and
injected into the microreactor. The residence time control was
achieved by varying the ow rate of the organic phase and/or
oxygen. Conversion and selectivity toward the carboxylic acid
were determined on the basis of the normalized peak areas for
aldehyde, carboxylic acid and side products obtained by one-
line GC. By-products were identied and quantied using
post-run analysis of the liquid phase by GC-MS.
9 For recent papers on gas–liquid reactions in
microreactors, see: (a) T. Fukuyama, T. Totoki and
I. Ryu, Green Chem., 2014, 16, 2042; (b) J. Wu,
J. A. Kozak, F. Simeon, T. A. Hatton and T. F. Jamison,
Chem. Sci., 2014, 5, 1227; (c) A. Nagaki, Y. Takahashi and
J.-I. Yoshida, Chem.–Eur. J., 2014, 20, 7931. For select
exemples on oxidation in microreactors, see: (d)
A. Leclerc, M. Alame, D. Schweich, P. Pouteau,
C. Delattre and C. de Bellefon, Lab Chip, 2008, 8, 814; (e)
C. Aellig, D. Scholz and I. Hermans, ChemSusChem,
2012, 5, 1732; (f) M. Hamano, K. D. Nagy and
K. F. Jensen, Chem. Commun., 2012, 48, 2086; (g)
T. P. Petersen, A. Polyzos, M. O'Brien, T. Ulven,
I. R. Baxendale and S. V. Ley, ChemSusChem, 2012, 5,
274; (h) B. Pieber and C. O. Kappe, Green Chem., 2013,
15, 320; (i) S. L. Bourne and S. V. Ley, Adv. Synth. Catal.,
2013, 355, 1905; (j) X. Ye, M. D. Johnson, T. Diao,
M. H. Yates and S. S. Stahl, Green Chem., 2010, 12, 1180–
1186; (k) Z. He and T. F. Jamison, Angew. Chem., Int. Ed.,
2014, 53, 3353; (l) U. Neuenschwander and K. F. Jensen,
Ind. Eng. Chem. Res., 2014, 53, 601.
Conclusions
In conclusion, we were able to demonstrate that aldehyde could
be safely and selectively transformed into the corresponding
carboxylic acid using molecular oxygen in ow. The reaction
conditions were optimized and full conversion with almost full
selectivity toward carboxylic acid was obtained under mild
conditions through the use of synergistic effect of salt and
Mn(II). The usual by-products obtained via the rearrangement of
the Criegee intermediate (i.e. formate) could be nearly
completely eliminated. Finally it was also demonstrated that
microow reactors are interesting tools for high-throughput
screening of experimental conditions in gas–liquid reactions.
10 C. de Bellefon, N. Tanchoux, S. Caravieilhes,
P. Grenouillet and V. Hessel, Angew. Chem., Int. Ed.,
2000, 39, 3442.
57162 | RSC Adv., 2014, 4, 57159–57163
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