Res. Chem. Intermed.
, Vol. 30, No. 7-8, pp. 763–774 (2004)
Also available online - www.vsppub.com
Sonochemical reactions occurring in organic solvents:
reaction kinetics and reaction site of radical trapping
, HIROSHI NAKAMURA, NORIMICHI TAKENAKA,
HIROSHI BANDOW, YASUAKI MAEDA and YOSHIO NAGATA
Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai,
Osaka 599-8531, Japan
Received 4 March 2004; accepted 3 May 2004
Abstract—The reaction of 1,1-diphenyl-2-picrylhydrazyl (DPPH) with a radical intermediate was
investigated in the sonolysis of several organic solvents. The rate of the DPPH consumption in
the sonolysis of methanol obeyed ﬁrst-order kinetics at low concentrations of DPPH, while the rate
became zero-order as the concentration of DPPH further increased. The radical trapping reactions
of DPPH were found to be considerably slow compared with the formation of hydrogen molecules
in the sonolysis of alcohols and hydrocarbons. These results indicate that H atoms formed in the
solvent sonolysis quickly react to form stable molecules such as hydrogen in the cavitation bubble
and/or at the interface region. The rates of the DPPH consumption were strongly dependent on the
vapor pressure and relative evaporation rate of the solvents. It was proposed that the optimum vapor
pressure exists for an effective formation of radical species.
Keywords: 1,1-Diphenyl-2-picrylhydrazyl; reaction kinetics; radical trapping; sonolysis.
Cavitation phenomena derived from ultrasonic irradiation of a liquid provide
interesting chemical effects due to a locally formed micro-stirring, shock waves
and cavitation bubbles with high temperature and high pressure. Chemical effects
of ultrasound have been actively researched in the ﬁeld of organic syntheses. One
of the most primitive and effective applications of ultrasound is the use of a micro-
stirring effect which can accelerate a large number of chemical reactions. Shock
waves themselves cannot directly excite any atoms and molecules like as photolysis.
However, in the case of a heterogeneous solution including a solid metal reagent,
To whom correspondence should be addressed. E-mail: email@example.com