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J . Phys. Chem. 1988, 92, 2978-2981
in MeOH than in H 2 0in the case of the small molecule MMeI, and is predicted to be notably smaller in MeOH than in H 2 0in the case of the polymer. The deviations between experimental and calculated values are about 2-3%. The difference between polymer and small molecule predicted by group additivity is not as large as the one found experimentally (in MeOH). Let us consider now the dibenzyl polymer PDBzI. The value of u2 calculated by group additivity (Table 11) can be for the polymer in its rubbery state or in its glassy state. Although PDBzI is in its glassy state a t room temperature, we have used group contributions corresponding to the rubbery state to compare with O2O, since these should be a better representation of the volume properties in solution. The value of u2 thus calculated by using rubbery contributions (Table 11) is practically coincident with the experimental 0 2 measured in dioxane. If glass contributions are
used, then the v2 calculated is higher, but also in good agreement with experiment, when compared with u2 of the solid polymer (Table 11). In summary, the additivity of group contributions gives good description of the data (of special note being the prediction achieved for the relative values in H 2 0 and MeOH using the FC method, adapted here for its application also to polymers).
Acknowledgment. We thank the Ministerio de Educacidn y Ciencia, Spain, for partial financing (CAICYT) under project no. PR84/528, and for a sabbatical fellowship awarded to L.G. as Visiting Professor in U.N.E.D., and the Direccidn de Investigacidn (DIUC), Pontificia Universidad Catdlica de Chile. Registry No. PMMeI, 29691-62-1; MMeI, 113451-48-2; DBzI, 73773-32-7; PDBzI, 58991-68-7.
Sonolytk Decomposition of Poly(vlnylpyrrolidone), Ethanol, and Tetranitromethane in Aqueous Solution M. Gutierrez and A. Henglein* Hahn- Meitner- Institut Berlin, Bereich Strahlenchemie, 1000 Berlin 39, Federal Republic of Germany (Received: September 1, 1987; In Final Form: November 17, 1987)
Aqueous solutions of poly(vinylpyrrolidone), PVP (as nonvolatile solute), ethanol (as volatile and soluble solute), and tetranitromethane, TNM (as volatile and almost insoluble solute), were irradiated under argon with 300-kHz ultrasound at an intensity of 2 W.cm-2. In all three cases, products were observed (such as CH4, C2H4,C2H6,CO, and C 0 2 from PVP and ethanol, and NOz-, NO3-, N2, CO, and C02 from TNM), the formation of which can only be understood in terms of pyrolysis in or close to the cavitation bubbles. More pyrolysis products are formed from PVP than bonds are broken in the main chain by hydrodynamic shear forces in the neighborhood of cavitation bubbles. The decomposition of TNM is one of the fastest sonochemical reactions. The yields were determined at various solute concentrations, and it was concluded from these data that (1) the extent of pyrolysis depends on the rate of dehydration of solute molecules, this rate increasing with their hydrophobicity, and (2) pyrolysis might be supported by free-radical attack.
Introduction The chemical effects of ultrasound in aqueous solution are often similar to these of ionizing radiation. For example, H, and H202 are while H atoms and OH radicals can be traced by spin t r a ~ p i n g . ~However, dissolved substances often experience chemical changes which cannot be understood simply in terms of attack by H or OH radicals. A typical example is the production of hydrogen in aqueous solutions of propanol-2 (
