of research.7 Typically, gas-liquid contact in flow chemistry
devices involves the mechanical mixing of two phases.8 We
envisaged that a more efficient, controllable, and reliable phase
contact might be realized using a semipermeable membrane which
can have extremely high effective surface areas and selectively
allow gases (but not liquids) to cross from one side to the other.
One commercially available material whose permeability to a range
of gases (including ozone) has been demonstrated is Teflon AF-
2400,9 an amorphous copolymer of tetrafluoroethylene and a
perfluorodimethyldioxolane (shown in Figure 1).
cm) was filled with solutions (1 mM) in various solvents of either
Sudan-red 7B or oil-red O (dyes which are known to be bleached
by ozone)16 and capped at the ends. While an external oxygen
atmosphere had no observable effect on any dye solution, both
dyes were bleached when the sealed tubing was exposed to ozone
at atmospheric pressure, Sudan-red 7B being bleached at a faster
rate than oil-red O. The relative rates of bleaching of Sudan-red
7B in various solvents are shown in Table 1.
Table 1. Relative Rates of Bleaching of 1 mM Sudan-red 7B
entry
solvent
timea (min)
1
2
3
4
5
6
MeOH
MeCN
DCM
CHCl3
EtOAc
EtOH
1.15
1.20
2.30
2.30
2.34
>8
a Time required for complete discoloration.
The rate of bleaching did not differ after repetition of the
test using the same piece of tubing (10 times). All subsequent
(4) (a) McCreary, M. D.; Lewis, D. W.; Wernick, D. L.; Whitesides,
G. M. J. Am. Chem. Soc. 1974, 96, 1038–1054. (b) Rigaudy, J.; Cuong,
N. K.; Albouy, J.-P.; Che´trit, A. Tetrahedron Lett. 1976, 17, 1089–1092.
(c) Pryde, E.; Moore, D.; Cowan, J. J. Am. Oil Chem. Soc. 1968, 45, 888–
894. (d) Murray, R. W.; Hagen, R. J. Org. Chem. 1971, 36, 1098–1102.
(e) Greenwood, F. L.; Durham, L. J. J. Org. Chem. 1969, 34, 3363–3366.
(f) Greenwood, F. L. J. Org. Chem. 1965, 30, 3108–3111. (g) Wojciechows-
ki, B. J.; Chiang, C. Y.; Kuczkowski, R. L. J. Org. Chem. 1990, 55, 1120–
1122. (h) Thompson, Q. E. J. Org. Chem. 1962, 27, 4498–4502. (i) Noller,
D.; Mazurowski, S.; Linden, G.; De Leeuw, F.; Mageli, O. Ind. Eng. Chem.
1964, 56, 18–27. (j) Bailey, P. S.; Bath, S. S.; Dobinson, F.; Garcia-Sharp,
F. J.; Johnson, C. D. J. Org. Chem. 1964, 29, 697–702. (k) Kula, J. Chem.
Health Saf. 1999, 6, 21–22.
Figure 1. (A) Flow ozonolysis apparatus (tubing filled with dye).
(B) Bleaching of Sudan red 7B in flow, tubing coiled for clarity.
(C) Molecular formula of Teflon AF-2400.
(5) (a) Bailey, P. S. Chem. ReV. 1958, 58, 925–1010. (b) Bailey, P. S.
Ozonation in Organic Chemistry; Academic Press: New York, 1982; Vol.
II. (c) Bailey, P. S. Ozonation in Organic Chemistry; Academic Press: New
York, 1978; Vol. I. (d) Van Ornum, S. G.; Champeau, R. M.; Pariza, R.
Chem. ReV. 2006, 106, 2990–3001.
(6) Hammond, C. R. In CRC Handbook of Chemistry and Physics, 90th
ed.; Lide, D. R., Ed.; CRC Press: Boca Raton, FL; pp 4-25.
(7) (a) Hu¨bner, S.; Bentrup, U.; Budde, U.; Lovis, K.; Dietrich, T.;
Freitag, A.; Ku¨pper, L.; Ja¨hnisch, K. Org. Process Res. DeV. 2009, 13,
2010.
The presence of the perfluorodioxolane units prevents the
polymer from achieving the semicrystalline microstructure
typical of other perfluorinated polymers such as poly(tetrafluo-
roethylene) (PTFE). Instead, a highly microporous, amorphous
structure is obtained which has a low dielectric constant,10 low
refractive index,11 and high gas permeability.12 In addition,
Teflon AF-2400 retains much of the high chemical resistance
of PTFE making it an attractive material for use in chemical
synthesis environments (poly(dimethylsiloxane)/silicone/PDMS
is also permeable to ozone13 but suffers from significant
swelling in a range of common organic solvents).14 As this
material is commercially available in the form of narrow-bore,
thin-walled tubing (providing a high surface-to-volume ratio),
a practical, simple, proof-of-concept apparatus consisting of a
length of membrane tubing that passes through a chamber which
is supplied with a flow of ozone from an ozone generator (Peak
Scientific OZ06) was constructed (Figure 1). For the purposes
of this preliminary investigation Teflon AF-2400 (0.6 mm i.d.,
0.8 mm o.d.) was used, although it is possible to fabricate this
material into tubing and membranes with narrower walls and
higher surface-to-volume ratio.15 In order to ascertain whether
the supplied ozone was permeating this tubing, a short length (3
(8) (a) Csajagi, C.; Borcsek, B.; Niesz, K.; Kovacs, I.; Szekelyhidi, Z.;
Bajko, Z.; Urge, L.; Darvas, F. Org. Lett. 2008, 10, 1589–1592. (b) Jones,
R. V.; Godorhazy, L.; Varga, N.; Szalay, D.; Urge, L.; Darvas, F. J. Comb.
Chem. 2006, 8, 110–116. (c) Fukuyama, T.; Rahman, T.; Kamata, N.; Ryu,
I. Beilstein J. Org. Chem. 2009, 5, No. 34. (d) Rahman, M. T.; Fukuyama,
T.; Kamata, N.; Sato, M.; Ryu, I. Chem. Commun. 2006, 2236–2238. (e)
Miller, P. W.; Jennings, L. E.; deMello, A. J.; Gee, A. D.; Long, N. J.;
Vilar, R. AdV. Synth. Catal. 2009, 351, 3260–3268.
(9) (a) Resnick, P. R.; Buck, W. H. In Fluoropolymers II; HoughamG. G.,
Cassidy, P. E., Johns, K., Davidson, T., Eds.; Kluwer Academic: New York,
1999; pp 25-34. (b) Resnick, P. R. US Patent 3978030, 1976. (c) Nemser,
S. M.; Roman, I. C. US Patent 5051114, 1991. (d) Polyakov, A.; Yampolskii,
Y. Desalination 2006, 200, 20.
(10) (a) DuPont, Teflon AF-2400, product information: (b) Hammoud,
A. N.; Baumann, E. D.; Overton, E.; Myers, I. T.; Suthar, J. L.; Khachen,
W.; Laghari, J. R. Technical Memorandum 1992, 105753, NASA.
(11) Yang, M. K.; French, R. H.; Tokarsky, E. W. J. Micro-Nanolith.
MEMS MOEMS 2008, 7, No. 033010.
(12) Pinnau, I.; Toy, L. G. J. Membr. Sci. 1996, 109, 125–133.
(13) Shanbhag, P. V.; Sirkar, K. K. J. Appl. Polym. Sci. 1998, 69, 1263–
1273.
(14) Lee, J. N.; Park, C.; Whitesides, G. M. Anal. Chem. 2003, 75, 6544–
6554.
(15) Supplied by Biogeneral Inc., 9925 Mesa Rim Rd, San Diego, CA
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