1014
U. Neuenschwander et al. / Ultrasonics Sonochemistry 19 (2012) 1011–1014
tizer for the cavitation-induced radical formation, due to the weak
O–O bond. The present study is a good example of how cavitation
can be of synthetic value. This is complementary to the widely-
used destructive approach, e.g. in the abatement of pollutants in
waste-water treatment.
References
[1] (a) J.H. Bang, K.S. Suslick, J. Am. Chem. Soc. 129 (2007) 2242;
(b) S.-X. Wang, J.-T. Li, W.-Z. Yang, T.-S. Li, Ultrasonics Sonochemistry 9 (2002)
159;
(c) C. Deng, H. Hu, X. Ge, C. Han, D. Zhao, G. Shao, Ultrasonics Sonochemistry
18 (2011) 932.
[2] J. Huang, Y. Liu, Z. Song, Q. Jin, Y. Liu, X. Wang, Ultrasonics Sonochemistry 17
(2010) 521.
[3] H. Xia, Q. Wang, Y. Liao, X. Xu, S.M. Baxter, R.V. Slone, S. Wu, G. Swift, D.G.
Westmoreland, Ultrasonics Sonochemistry 9 (2002) 152.
[4] D.T.C. Yang, C.J. Zhang, P.P. Fu, G.W. Kabalka, Synth. Commun. 27 (1997) 1601.
[5] (a) J.-L. Luche, Ultrasonics Sonochemistry 1 (1994) S111.;
(b) B.S. Bhatkhande, S.D. Samant, Ultrasonics Sonochemistry 5 (1998) 7;
(c) M.-L. Wang, V. Rajendran, Ultrasonics Sonochemistry 14 (2007) 368.
[6] (a) P. Riesz, D. Berdahl, C.L. Christman, Env. Health Persp. 64 (1985) 233;
(b) K.S. Suslick, Sonocatalysis, in: G. Ertl, H. Knözinger, F. Schüth, J. Weitkamp
(Eds.), Handbook of Heterogeneous Catalysis, second ed., Wiley-VCH,
Weinheim, 2008.
Fig. 3. The hot-spot temperature as a function of the hot-spot volume fraction f. The
dashed line indicates the approximate situation for Misik’s hot-spot temperature
[35].
[7] (a) I. Hua, M.R. Hoffmann, Environ. Sci. Technol. 31 (1997) 2237;
(b) T.J. Mason, Adv. Sonochem. 6 (2001) 247;
a
ꢃ ktermð298 KÞ
f ꢃ kinitðThot-spotÞ ¼
¼ 4 ꢁ 10ꢀ11sꢀ1
ðEÞ
2
2
kpropð268 KÞ ꢃ ½RCHOꢄ
Next, by introduction of a TST prefactor of 1015 sꢀ1 and an acti-
vation energy of 40 kcal molꢀ1 for kinit(T) [35], the f-dependency of
Thot-spot can be calculated (Eq. (F) and Fig. 3)
(c) N.M. Mahamuni, Y.G. Adewuyi, Ultrasonics Sonochemistry 17 (2010) 990.
[8] J.-L. Luche, Synthetic Organic Sonochemistry, Plenum Press, New York, 1998.
[9] (a) G.J. Prize, D.J. Norris, P.J. West, Macromolecules 25 (1992) 6447;
(b) M.W.A. Kuijpers, D. van Eck, M.F. Kemmere, J.T.F. Keurentjes, Science 298
(2002) 1969;
(c) G.J. Prize, Ultrasonics Sonochemistry 10 (2003) 277.
[10] E. Nakamura, D. Machii, T. Inubushi, J. Am Chem. Soc. 111 (1989) 6850.
[11] T.P. Caulier, M. Maeck, J. Reisse, J. Org. Chem. 60 (1995) 272.
[12] K.S. Suslick, P.F. Schubert, J.W. Goodale, J. Am. Chem. Soc. 103 (1981) 7342.
[13] K.A. Chervinsky, V.N. Mal’tsev, Ukr. Chim. J. 32 (1966) 69.
[14] E.M. Mokry, V.L. Starchevsky, Adv. Sonochem. 3 (1993) 257.
[15] T.J. Mason, Chem. Soc. Rev. 26 (1997) 443.
Thot-spot
20128
InðfÞ þ 58:48
¼
ðFÞ
K
Using Misik’s experimental value of the hot-spot temperature in
alkanes [36], i.e. 750 K, the estimation of f becomes 10ꢀ14 (see
Fig. 3). Hence, the collapsed hot-spot volume in our 10 mL reactor
[16] L.A. Crum, J.B. Fowlkes, Nature 319 (1986) 52.
[17] U.A. Peuker, U. Hoffmann, U. Wietelmann, S. Bandelin, R. Jung, Sonochemistry,
in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim,
2006.
[18] T.G. Leighton, Ultrasonics Sonochemistry 2 (1995) S123.
[19] K.S. Suslick, Science 247 (1990) 1439.
[20] V. Misik, P. Riesz, Ultrasonics Sonochemistry 3 (1996) S173.
[21] (a) G. Franz, R.A. Sheldon, Oxidation, in Ullmann’s Encyclopedia of Industrial
Chemistry, Wiley-VCH, Weinheim, 2005;
is only about 1 l
m3. Note that, albeit the relative volume fraction is
known, the number and size of hot-spots cannot be derived from
the available data. In principle, a high number of hot-spots with ex-
tremely small volumes, down to the nm3 range is possible. Indeed,
when applying a literature value of 1013 hot-spots per cubic meter
[14], the average diameter is calculated to be around 1 nm.
Although this is a microscopic volume, the chain initiation that
happens in these hot-spots does have macroscopic implications,
by enabling chain propagation in the bulk volume.
At a typical experiment with [ROOH] = 0.1 M, an overall rate of
4 ꢁ 10ꢀ5 M sꢀ1 can be observed. Using Eq. (B), a quasi-constant
radical concentration in the bulk of 6 ꢁ 10ꢀ10 M can be calculated.
Thus, the total termination rate equals 4 ꢁ 10-11 M s-1 and the
chain length is approximately 106. This supports our hypothesis
of a chain oxidation process. This chain length is substantial and
in agreement with values established in bromine-assisted sonoiso-
merization of alkenes [11], i.e. 104.
(b) U. Neuenschwander, N. Turrà, C. Aellig, P. Mania, I. Hermans, Chimia 64
(2010) 225.
[22] I. Hermans, P.A. Jacobs, J. Peeters, J. Mol. Cat. A 251 (2006) 221.
[23] (a) I. Hermans, P.A. Jacobs, J. Peeters, Chem. Eur. J. 12 (2006) 4229;
(b) I. Hermans, P.A. Jacobs, J. Peeters, Chem. Eur. J. 13 (2007) 754.
[24] U. Neuenschwander, F. Guignard, I. Hermans, ChemSusChem 3 (2010) 75.
[25] K.-G. Fahlbusch, F.-J. Hammerschmidt, J. Panten, W. Pickenhagen, D.
Schatkowski, Flavors and Fragrances, in Ullmann’s Encyclopedia of Industrial
Chemistry, Wiley-VCH, Weinheim, 2005.
[26] U. Neuenschwander, E. Meier, I. Hermans, ChemSusChem 4 (2011) 1613.
[27] W. Riemenschneider, Carboxylic Acids, in Ullmann’s Encyclopedia of Industrial
Chemistry, Wiley-VCH, Weinheim, 2012.
[28] (a) G.E. Zaikov, J.A. Howard, K.U. Ingold, Can. J. Chem. 47 (1969) 3017;
(b) J.R. McNesby, C.A. Heller, Chem. Rev. 54 (1954) 325.
[29] C. Kohlpaintner, M. Schulte, J. Falbe, P. Lappe, J. Weber, Aldehydes, in
Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012.
[30] D.G. Truhlar, B.C. Garrett, J. Phys. Chem. 100 (1996) 12771.
[31] N.N. Mahamuni, A.B. Pandit, Ultrasonics Sonochemistry 13 (2006) 165.
[32] H. Fiege, Cresols and Xylenols, in Ullmann’s Encyclopedia of Industrial
Chemistry, Wiley-VCH, Weinheim, 2012.
4. Conclusions
In this contribution, we characterize radical-chain oxidations
that are initiated by ultrasonic cavitation. Working at room tem-
perature, the substrate valeric aldehyde was successfully oxidized
with oxygen to valeric acid. A dialkyl peroxide was used as sensi-
[33] U. Neuenschwander, I. Hermans, J. Catal. 287 (2012) 1.
[34] G.H. Williams, Advances in Free Radical Chemistry, Elek, London, 1972.
[35] H. Klenk, P.H. Götz, R. Siegmeier, W. Mayr, Peroxy Compounds, Organic, in
Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012.
[36] V. Misik, P. Riesz, Ultrasonics Sonochemistry 3 (1996) 25.