J . Phys. Chem. 1992, 96, 764-767
764
it is concluded that the fast (direct) radical dissociation and the molecular dissociation originate from two different electronic excited states of A" and A' symmetry, respectively. Therefore, it is expected that the molecular and the radical decay proceed on different potential energy surfaces. Using high laser power, the primary SOCl fragments are further photofragmented to SO and C1, indicating the existence of a SOCl electronic transition near MOO0 cm-'. Moreover, a low-lying electronic state of SOCl at -9000 cm-l (26 kcal/mol) was evidenced from the fragment translational energy distribution at 248 and 193 nm. After absorption of a photon at 193 nm more than 80% of the CI2S0molecules undergo three-body dissociation to SO C1+ C1. The rest decays either along the radical or along the minor molecular channel. The anisotropy parameters of all the fragments can be accommodated by an initially excited state of ANsymmetry. Therefore, it is not inconceivable, and hence encouraging for a dynamic study based on a quantum chemical PES calculati0n,3~~~
+
(36) Heller, E. J. Ace. Chem. Res. 1981, 14, 368. (37) Zhang, J.; Imre, D. G. J . Chem. Phys. 1989, 90, 1666. (38) Nonella, M.; Huber, J. R.; Untch, A.; Schinke, R. J . Chem. Phys. 1989, 91, 194.
that competition between the three dissociation pathways takes place on a single PES. In the recently investigated CF212molecule," the three-body dissociation to CF2 + I I was found to be the only active decay at 248 nm, a selectivity which is favored by the low dissociation energies of the two C-I bonds. A theoretical study of Hg12 by Grtibele et al.9 has shown the branching ratio between the three-body reaction and the singlebond rupture to increase with excitation energy. An extension of the experimental photofragmentation work to include various (most desirable continuously adjustable) excitation wavelengths would certainly be informative and in combination with dynamic calculations on a b initio potential energy surfaces would provide a very detailed picture of the competing dissociation modes in thionyl chloride.
+
Acknowledgment. Support of this work by the Schweizerischer Nationalfonds zur Fiirderung der Wissenschaftlichen Forschung and by the Alfred Werner Legat is gratefully acknowledged. (39) Untch, A.; Weide, K.; Schinke, R. Chem. Phys. Lett. 1991,180,265 and references quoted therein.
Photophyslcal Properties of Fullerenes and Fullerene/N,N-Diethylanilhe Charge-Transfer Complexest Y. Wang Central Research and Development, E. I . du Pont de Nemours and Company, P.O. Box 80356, Wilmington, Delaware 19880-0356 (Received: August 8, 1991; In Final Form: September 3, 1991)
Well-resolved fluorescence and phosphorescence spectra of fullerenes in methylcyclohexaneand the determination of important photophysical parameters are reported. The fluorescence quantum yield depends on the excitation wavelength, which indicates the Occurrence of a very rapid photoprocess directly from upper excited states, in competition with internal conversion to the lowest excited state. For C70 the fluorescence quantum yields are 6 X 10" at 370 nm, 1.3 X lo4 at 378 nm, and 2.2 X lo4 at 471 nm. The singlet-triplet energy splitting for C70is 7.0 kcal/mol. For Cm the fluorescence quantum yields at 405 nm and 3.8 X lo4 at 370 nm. The singlet-triplet energy splitting for Cm is 5.5 kcal/mol. In the are 1.9 X presence of N,N-diethylaniline (DEA),charge-transfer complexes between fullerenes and DEA for formed. In the excited state, luminescence from both the singlet and the triplet exciplex of C70 are observed.
The possible existence of the soccer ball-shaped, 60-carbon molecule has long been ~peculated.l-~ The recent success in generating macroscopic quantities of C60and C70 molecules (fullerene~),~ following the earlier observation in beam experiment~:,~has confirmed the existence of this interesting class of molecules and opened the doorway for systematic studies of their properties. Because of their low reduction one expects to find interesting chargetransfer chemistry in both the ground state and the excited states. In this paper, well-resolved fluorescence and phosphorescence spectra of fullerenes and the determination of important photophysical parameters such as quantum yields and singlet-triplet splittings are first reported. The effects of N,Ndiethylaniline, a good electron donor, on the ground-state and excited-state properties of fullerenes are examined. Recently, the luminescence spectrum of Cmsolid film,1° the transient absorption spectrum of Cmin solution," and the phosphorescence spectrum of C70 in polymer film'* have been reported. To the best of my knowledge, fluorescence from the singlet state has not been reported. Also, all of the reported phosphorescence spectra are either incomplete or not well-resolved. 'Contribution No. 5893.
C, and C70 are generated in a modified Denton evaporator according to the published p r o c e d ~ r e s . ~ J JThey ~ are extracted ~
(1) (2) (3) 610. (4) (5)
~~
Jones, D. E. H. New Sci. 1966, 32, 245. Osawa, E. Kagaku 1970, 25, 854. Bochvar, D. A.; Gal'pern, E. G. Dokl. Akad. Nauk USSR 1973,209,
Davidson, R. Theor. Chim. Acta 1981, 58, 193. Kratschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Nature 1990, 347, 354. (6) Rohlfing, E. A,; Cox, D. M.; Kaldor, A. J. Chem. Phys. 1984,81,3322. (7) Kroto, H. W.; Heath, J. R.; OBrien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162. (8) Haufler, R.E.; Conceicao, J.; Chibante, P. F.; Chai, Y.; Byme, N . E.; Flanagan, S.;Haley, M. M.; O'Brien, S. C.; Pan, C.; Xiao, Z.; Billups, W. E.; Ciufolini, M. A.; Hauge, R. H.; Margrave, J. L.; Wilson, L. J.; Curl, R. F.; Smalley, R. E. J . Phys. Chem. 1990, 94, 8634. (9) Allemand, P.-M.; Koch, A.; Wudl, F.; Rubin, Y.; Diederich, F.; Alvarez, M. M.; Anz, S. J.; Whetten, R. L. J . Am. Chem. Soc. 1991, 113, 1050. (10) Reber, C.; Yee,L.; McKiernan, J.; Zink, J. I.; Williams, R. S.; Tong, W. M.; Ohlberg, D. A. A.; Whetten, R. L.; Diederich, F. J. Phys. Chem. 1991, 95, 2127. (1 1) Arbogast, J. W.; Darmanyan, A. P.; Foote, C. S.; Rubin, Y.; Diederich, F. N.; Alvarez, M. M.; Anz, S. J.; Whetten, R. L. J . Phys. Chem. 1991, 95, 11. (12) Wasielewski, M. R.; ONeil, M. P.; Lykke, K. R.; Pellin, M. J.; Gruen, D. M. J . Am. Chem. SOC.1991, 113, 2774.
0022-365419212096-764$03.00/0 0 1992 American Chemical Society
Photophysical Properties of Fullerenes
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Figure 1. Fluorescence (S*),phosphorescence (T"), excitation, and absorption spectra of 4.2 X M C70in methylcyclohexane. The absorption spectrum was taken at room temperature; the others were taken at 77 K. The excitation spectra, monitored at 683 and 828 nm, are identical and agree with the absorption spectrum. The phosphorescence spectra were taken with both the R928 (slit width, 1 mm) and R406 (slit width, 2 mm) photomultiplier tubes and joined together in the 850-nm region.
from the soot with toluene and separated by flash chromatography using neutral alumina as the packing material and 5% toluene/hexane as the e1~ent.l~ Both the X-ray diffraction pattern and the UV-vis spectra agree with the published results. The luminescence spectra were taken with a Spex Fluorolog equipped with either a cooled R928 photomultiplier tube (250-850nm), an R406 tube (700-1000nm), or a cooled Ge detector (850-2500 nm). All spectra are corrected for the photodetector response. The fluorescence quantum yield is determined using quinine sulfate in 1 N sulfuric acid as the standard (quantum yield = 0.546). All spectra are converted to intensity vs wavenumber for integration of the luminescence intensity. The solvents used (methylcyclohexane and N,N-diethylaniline) are purified by passing through a neutral aluminum oxide column. Figure 1 shows the fluorescence, phosphorescence, and excitation spectra of C70 in methylcyclohexane taken at 77 K. The complete phosphorescence spectrum, extending from 775 nm to 1 Mm, is measured with two different detectors and joined together near 850 nm. The excitation spectra of the fluorescence and the phosphorescence agree very well with the absorption spectrum, eliminating the possibility that the luminescences are due to impurities. A similar phosphorescence spectrum has been obtained in toluene/lO% poly(a-methylstyrene).I2 Although the reported phosphorescence spectrum is less resolved and incomplete, the emission wavelengths are in general agreement with those given here. The phosphorescence lifetime has not been measured in the present case. The reported phosphorescence lifetime is 53 ms.I2 The phosphorescence disappears at room temperature, while the fluorescence is still observable. The phosphorescence and fluorescence can be further differentiated by their different quenching behavior by N,N-diethylaniline (to be discussed later). The product of the quantum yield of phosphorescence and the quantum yield of intersystem crossing is determined to be 1.1 X lO-) at 471 nm by integrating the intensity of the phosphorescence at band. At 77 K, the fluorescence quantum yields are 6 X 370 nm, 1.3 X at 378 nm, and 2.2 X lo4 at 471 nm (uncertainty f 10%). These wavelength-dependent quantum yields indicate the existence of upper excited-state photoprocesses. The higher excited states must be able to deactivate directly via some unknown photochemical or photophysical processes. These photoprocesses must be fast enough to compete with the internal conversion process to the lowest excited state. Recently, it has been reported that Ca can abstract hydrogen from solvent upon irradiation by light, and UV light is more effective.14 This (13) Ajie, H.; Alvarez, M. M.; Anz, S.J.; Beck, R. D.; Diederich, F.; Fostiropoulos, K.;Huffman, D. R.; Kratschmer, W.; Rubin, Y.; Schriver, K. E.; Sensharma, D.; Whetten, R. L. J. Phys. Chem. 1990, 94, 8630.
Luminescence, excitation, and absorption ( a k D E A ) spectra M C70 in N,N-diethylaniline. Also plotted is the absorption spectrum (abs-MCH) of 4.2 X 10" M C70 in methylcyclohexane for comparison. The absorption spectra were taken at room temperature, and the others were taken at 77 K. Figure 2. of 4.2 X
observation is consistent with the smaller fluorescence quantum yields in the UV region. However, the efficiency of the photochemical process, if it is present, is not known. Experience has shown that both Cb0 and C70 are reasonably stable to light in hydrocarbon solvents. A series of vibronic peaks can be observed for both the fluorescence (651,658,676,683,694,708,717, and 728 nm) and the phosphorescence bands (775,789, 804,828,843, 850,882, 898,917,and 940 nm). There are at least two or more progressions in the phosphorescence and fluorescence spectra. The first vibronic peak of the fluorescence spectrum at 651 nm is very close to the first observable absorption peak at 648 nm. On the basis of these spectral data, the singlet-triplet energy splitting is determined to be 7.0 f 0.5 kcal/mol or 2458 m i ' , using the first vibronic peaks of the singlet and the triplet. As pointed out before," this small splitting is due to the weak electron-lectron repulsion in a delocalized system. With such a small energy gap and large spin-orbit coupling, one expects a fast intersystem crossing rate. Since fullerenes are good electron acceptors ( E l l 2 = -0.4 vs Ag/Ag+),8*9they should interact with electron donors through charge-transfer interaction. In N,N-diethylaniline ( E l l 2= 0.34 vs Ag/Ag'),I5 the formation of a C7,/N,N-diethylaniline (DEA) charge-transfer complex is demonstrated by the following observations: (1) there is a dramatic increase in the solubility of C70 (also c60) in DEA; (2)the intensity of the lowest symmetry-forbidden absorption band of C70 is enhanced compared to that in methylcyclohexane (Figure 2); and (3) new absorption appears at longer wavelength from 650 to 800 nm (Figure 2). The same effects are also observed for Cw in Nfldiethyhniline, whose lowest absorption band is enhanced by a factor of 5-6. Also, a new charge-transfer band with a peak located at -680 nm can be observed. The change in the absorption spectra cannot be attributed to the general solvent polarity effect since fullerenes have either zero or a very small dipole moment and the dielectric constant of DEA (-6) is also not large. On the basis of the concentration dependence of the absorption spectra, the formation constants of Cso/DEA and C7,/DEA complexes at room temperature are determined to be 0.18 f 0.04 and 0.4 f 0.06, respectively, using the Benesi-Hildebrand equation.16 In pure N,N-diethylaniline, one can calculate from the equilibrium constants that 53 f 6% of c 6 0 and 72 f 4% of C70exist as chargetransfer complexes at room temperature. Additional evidence for the existence of charge-transfer complexes comes from the ESR (14) Taylor, R.; Parsons, J. P.; Avent, A. G.; Rannard, S.P.; Dennis, T. J.; Hare, J. P.; Kroto, H. W.; Walton, D. R. M.Nature 1991, 351, 277. (15) Wawzonek, S.;McIntyre, T. W. J. Electrochem. Soc. 1967, 114, 1025. (16) Connors, K. A. In Binding Constants. The Measurement of Molec-
ular Complex Stability; Wiley: New York, 1987.
766 The Journal of Physical Chemistry, Vol. 96, No. 2, 1992
Wang
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Figure 3. Effects of the addition of DEA on the fluorescence spectrum of C70in methylcyclohexane at room temperature. With each successive addition of DEA, the fluorescence intensity is quenched (down arrow) and the singlet exciplex emission is enhanced (up arrow). The concentrations of DEA used are 0,0.007,0.016,0.021,0.032,0.053,0.078, and 0.095 M.
experiment, where the Cb0radical anion has been detected after photoexcitation of the Ca/DEA charge-transfer complexes at 77 K.17
The effects of N,N-diethylaniline on the photoluminescence spectrum of C70 are now examined. Room temperature data are presented which show the effects on the singlet fluorescence band, and then the 77 K data are given which show the effects on the triplet phosphorescence band. Figure 3 shows the effects of successive addition of DEA to a C70/methylcyclohexane solution on the room temperature fluorescence spectrum of C70. The fluorescence intensity of the singlet is quenched by the addition of DEA. Concurrently, a new luminescence band is formed at longer wavelength (720 nm). A well-defined isosbestic point can be clearly observed (Figure 2). This is the classical signature of the formation of an exciplex.18 Accordingly, this new luminescence band is attributed to the singlet excited state of C,/DEA charge-transfer complex. At higher DEA concentrations, the peak of the luminescence band moves to longer wavelengths and the intensity decreases. This may be due to a solvent polarity effect and/or the formation of higher order complexes. At 77 K, another rather featureless luminescence band can be observed in the infrared region, replacing the C70 phosphorescence band. It has a peak located a t 828 nm which extends to about 1.2 pm (Figure 2). This luminescence is almost totally quenched at room temperature in deoxygenated solution. Its excitation spectrum is also shown in Figure 2. Note that this excitation spectrum should be compared with the absorption spectrum of the charge-transfer complex which is not available at present. The peak positions in the spectrum are consistent with the room temperature absorption spectrum of C70 in N,N-diethylaniline (Figure 2). In Figure 4 are shown the 77 K luminescence spectra of C70 in a series of mixed DEA/methylcyclohexane solutions. With each successive addition of DEA, there is a gradual loss of the fine structure in the phosphorescence band and an increase in the intensity of the new, red-shifted luminescence band. At 10 vol % DEA concentration, the luminescence spectrum looks basically the same as that in pure DEA. The most likely interpretation is that the luminescence is from the C70 triplet state distorted by charge-transfer interaction with DEA (or a weak triplet exciplexl*). This is supported by the fact that the luminescence spectrum in DEA is similar to, but much less structured than, the C70 phosphorescence spectrum in methylcyclohexane. Several such examples have been reported (17) Krusic, P. J.; Wasserman, E.; Parkinson, B. A,; Malone, B.; Holler, E. R.; Keizer, P. N.; Morton, J. R.; Preston, K. F. J . Am. Chem. SOC.1991, 113, 6274. (18) Weller, A. In Exciplex; Gordon, M., Ware, W. R., Eds.; Academic Press: New York, 1975.
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Figure 4. Luminescence spectra of CT0in a series of mixed DEA/ methylcyclohexane solutions taken at 77 K. The DEA concentrations in volume percent are displayed with each curve. The phosphorescence spectra were taken with the R406 photomultiplier tubes and the fluorescence spectra with the R928 tubes. They are joined together in the 750-nm region. The apparent reduction in the luminescence intensity in 10% DEA solution may be due to the fact that a good quality matrix cannot be formed at high DEA concentrations.
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Figure 5. Fluorescence (S*),excitation, and absorption spectra of 1.1 X 10-4 M Cm in methylcyclohexane as well as the luminescence spectrum
[T*(DEA)] in NJ-diethylaniline. The absorption spectrum was taken at room temperature; the others were taken at 77 K. The excitation spectra, monitored at 686 and 724 nm, are identical and agree with the absorption spectrum. The luminescence spectrum in DEA was taken with the R406 photomultiplier tubes and the fluorescence spectrum with the R928 tubes. previously during the course of studying aromatic triplet exciplexes.18 At room temperature the observed singlet exciplex luminescence comes from excited-state reactions between C70 singlet and DEA, rather than the direct excitation of the ground-state charge-transfer complexes (there is no appreciable ground-state complexation at the DEA concentrations used here). However, a t 77 K ground-state complexation exists and the observed triplet exciplex luminescence comes from the direct excitation of the ground-state C70/DEA charge-transfer complexes. This accounts for the existence of an isosbestic point in the former case but not in the latter. Fluorescence from Ca in methylcyclohexane is shown in Figure 5 . The fluorescence band is much narrower than observed for Cs0fiim,1° with a series of clearly observable vibronic peaks (655, 674, 686, 698, 713, 724, 737, and 760 nm). At 77 K, the at 405 nm and 3.8 X fluorescence quantum yield is 1.9 X lod at 370 nm. Again, the quantum yield depends on the excitation wavelength. There is no significant reduction in the fluorescence quantum yield at room temperature, although the apparent intensity is reduced due to spectral broadening. In methylcyclohexane, the phosphorescence of Ca is essentially not observable. The only hint for its existence is the weak shoulder at 8 12 nm (Figure 5 ) . In DEA, all of the fluorescence peaks disappear. Instead, a new band with two prominent peaks at 823
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J. Phys. Chem. 1992,96, 767-770 and 882 nm is observed. On the basis of similarity to the C70 phosphorescence spectrum, this new band is tentatively assigned to the triplet, distorted by the charge-transfer interaction. The energy of the triplet, -35 kcal/mol, is consistent with the previously obtained values based on the energy-transfer method.' The singlet-triplet splitting is estimated to be 5.5 f 1 kcal/mol. Due to the very low intensity of the c 6 0 triplet exciplex luminescence, a good excitation spectrum has not been obtained. In summary, well-resolved fluorescence spectra of c 6 0 and C70 and the phosphorescence spectrum of C70 have been obtained, and singlet-triplet splittings have been determined. The fluorescence quantum yield depends on the excitation wavelength, which indicates the existence of upper excited-state photoprocesses. In N,N-diethylaniline, charge-transfer complexes with fullerenes are formed. In the excited state, luminescences from both the singlet and triplet exciplex of C7,, are observed. The existence of charge-transfer complexes of fullerenes and their enhanced absorption in the visible and IR region suggest potential utilities as photosensitizers and photoinitiators. Note Added in Proof: The photophysical properties of C70 have been studied recently by Arbogast et al.I9 Some of the results
767
reported here, such as the fluorescence spectrum and triplet energy, are reproduced in that study. The paper also show that both Cm and C,,, are reasonably stable with respect to light irradiation, in contrast to the results of ref 14. In another study by Sension et al.zoon the charge-transfer complex of C,/N,Ndimethylanile (DMA), the formation time of the C60DMA+ion pair was determined to be 1-2 ps and the charge recombination time occurs on a time scale in the range 20-55 ps. Acknowledgment. I acknowledge excellent technical assistance from S. Harvey and useful discussions on the separation of fullerenes with R. McCormick, H. Barth, J. Kirkland, and E. Holler. I thank J. Caspar for use of the fluorometer and P.Krusic for the discussion of the ESR results. I also thank Professors C. S.Foote (UCLA) and R. M. Hochstrasser (University of Pennsylvania) for sending preprints before publication and useful discussions. Registry No. DEA, 91-66-7; CT0,115838-22-7; Cm, 99685-96-8. (19) Arbogast, J. W.; Foote, C. S. Unpublished results (private wmmunication) (2O).Sension, R. J.; Szarka, A. Z.; Smith, G. R.;Hochstrasser, R. M. Unpublished results (private communication).
.
Temperature Dependence of the Rate Constants for Oxidation of Organic Compounds by Peroxyl Radicals in Aqueous Alcohol Solutions Z. B. Alfassi,' R. E. Hie,* M. Kumar? and P.Neb* Chemical Kinetics and Thermodynamics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received: August 14, 1991; In Final Form: September 27, 1991) Rate constants for reactions of chlorinated methylperoxyl radicals with chlorpromazine (2-chloro- 10-[3-(dimethylamino) acid), and ascorbate in aqueous alcohol propyl]phenothiazine), trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75 O C . The rate constants varied between lo6 and lo9 M-'s-', the calculated Arrhenius activation energies ranged from 1 to 30 kJ mol-', and the preexponential factors also varied considerably, with log A ranging from 7 to 14. In general, room temperature rate constants increase with an increase in the number of chlorine atoms on the radical (increasing its electron affinity and thus the driving force for the reaction) and with an increase in the solvent polarity. The Arrhenius preexponential factor and the activation energy both increased as the proportion of water in the solvent mixture increased; i.e., the increase in rate constant with solvent polarity is a result of two compensating effects. Electron transfer from the organic reductants to the chlorinated methylperoxyl radicals is suggested to take place via an inner-sphere mechanism involving a transient adduct of the peroxyl radical to the reductant.
Introduction Absolute rate constants have been measured for a large number of reactions of peroxyl radicals in aqueous and organic ~olvents,~ with most of the measurements carried out only at room temperature and only in one solvent. Measurements at varying temperatures were limited mostly to the reactions of tert-alkylperoxyl radicals in organic solvents: These reactions are relatively slow, with very low A factors and low to moderate activation (1) Visiting Professor from Ben-Gurion University of the Negev, Beer Sheva, Israel. (2) Visiting scientist from Bhabha Atomic Research Centre, Bombay, India. (3) Neta, P.; Huie, R. E.; Ross,A. B. J . Phys. Chem. Ref.Data 1990, 19, 413. (4) (a) Howard, J. A.; Furimsky, E. J. Orgartomet. Chem. 1972,46, C45. (b) Furimsky, E.; Howard, J. A. J . Am. Chem. SOC.1973, 95, 369. (c) Howard, J. A.; Furimsky, E. Can. J . Chem. 1973,51,3738. (d) Howard, J. A.; Ohkatsu, Y.; Chenier, J. H. B.; Ingold, K. U. Can. J. Chem. 1973, 51, 1543. (e) Chenier, J. H. B.; Furimsky, E.; Howard, J. A. Can. J. Chem. 1974, 52,3682. ( f ) Chenier, J. H. B.; Howard, J. A. Can. J. Chem. 1975,53,623. (g) Howard, J. A.; Tong,S. B. Can. J . Chem. 1980,58, 1962. (h) Howard, J. A.; Tait, J. C.; Yamada, T.; Chenier, J. H. B. Can. J. Chem. 1981,59, 2184. (i) Tavadyan, L. A.; Mardoyan, V. A.; Nalbandyan, A. B. Dokl. Akad. Nauk SSSR 1981,259, 1143 (translated Dokl. Phys. Chem. 1981,259, 737). Q) Bennett, J. E.; Brunton, G.; Forrester, A. R.;Fullerton, J. D. J . Chem. SOC., Perkin Trans. 2 1983, 1477.
energies. For example, the reactions of tert-butylperoxyl radicals with phenols and anilines take place with rate constants generally much less than lo4 M-' s-' a t room temperature with log A = 3-7 and E, between 1 and 20 kJ mol-'. The reaction of methylperoxyl radical with N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) in water is much faster (k = 4.3 X lo7 M-'s-I at room temperature) and has a much higher preexponential factor (log A = 12.1).5 The effect of this higher preexponential factor is partly offset by a higher activation energy (27 kJ mol-'). The mechanisms of the two types of reactions have been suggested to be different; whereas tert-butylperoxyl was suggested to react with phenols and anilines in organic solvents via hydrogen abstraction
+
-
+
ROO' ArOH ROOH ArO' (1) the reaction of methylperoxyl with TMPD in water was suggested to involve electron transfer. ROO'
+ TMPD
ROO-
+ TMPD"
(2)
It appears, however, from solvent and temperature effects, that both reactions take place via an intermediate complex of the (5) Neta, P.; Huie, R.E.; Maruthamuthu, P.; Steenken, S. J . P h p . Chem. 1989, 93, 7654.
0022-3654/92/2096-767$03.00/0 0 1992 American Chemical Society
