Langmuir 1988, 4,101-105
101
Electron-Transfer Reactions in Microemulsions. Oxidation of Benzenediols by Hexachloroiridate(IV) Claudio Minero* and Edmondo Pramauro Dipartimento di Chimica Analitica, Universitci di Torino, 10125 Torino, Italy
Ezio Pelizzetti* Istituto di Chimica Fisica Applicata, Universitci di Parma, 43100 Parma, Italy Received March 10,1987. I n Final Form: July 13,1987 The oxidation of benzene-1,2-diols(catechol and 3,5-di-tert-butylcatechol) by hexachloroiridate(1V) has been investigated in SDS/1-butanol/toluene/watermicroemulsion over a wide range of composition. The rate constants exhibit an expected decrease in respect to the aqueous solution at high water content, which is more relevant for the more hydrophobic benzenediol. However, after reaching a minimum, the rate constants show an increase as the water content becomes lower. A three-pseudophase model (water, interphase, and oil), which takes explicitly into account the partitioning of the microemulsion components in the pseudophases, allows us to analyze the experimental results. The hydration of the interphase is crucial in order to explain both kinetic data as well as the upper demixing line of the phase diagram.
Introduction Microemulsions are transparent fluids preparated from oil and water in the presence of a surfactant and a cosurfactant. Many of these systems appear to be a thermodynamically stable single phase and form spontaneously upon mixing.’ The O/W microemulsions have similarities to the normal micelles in water and can be described as a stable collection in an aqueous continuous phase of “oil” microdroplets, which have a usual diameter of 10-60 nm, while W/O microemulsions should be similar to the reverse micelles in apolar solvents. Reactions in organized assemblies have been extensively studied, with particular attention devoted to micellar agg r e g a t e ~ . ~ Nevertheless, -~ processes in microemulsions have been considered and r e v i e ~ e d .The ~ ~ ~submicroscopic aggregates can bring reactants together or keep them apart and can also exert a medium effect. As reaction media, however, the microemulsions can incorporate relatively large amounts of hydrophobic and ionic solutes, and the volume of the dispersed phase can generally be varied over a fairly wide range. In this work, the oxidation of benzenediols by means of hexachloroiridate(1V) has been investigated in water/ 1butanol/SDS/ toluene microemulsions. Additional experiments in the presence of anionic micelles and in water/ 1-butanol mixtures have been carried out in order to gain information about the effect of different media on the reaction rates. Experimental Section Materials. 1,2-Benzenediol (I) and 3,5-di-tert-butyl-l,2benzenediol (11) were supplied by Aldrich and K&K and were recrystallized before use. Sodium hexachloroiridate(1V) was (1) (a) Prince, L. M. Microemulsions, Theory and Practice; Academic: New York, 1974. (b) Overbeek, J. Th. G. Faraday Discuss. Chem. SOC. 1978,65,7. (c) Robb, I. Microemulsions; Elsevier: Amsterdam, 1982. (d) Danielsson, I.; Lindman, B. Colloids Surf. 1981,3, 391. (e) Shah, D. 0. Macro and Microemulsions; ACS Symposium Series 272; American Chemical Society: Washington, D.C., 1985. (2) Fender, J. H. Membrane Mimetic Chemistry; Wiley-Interscience: New York, 1982. (3) Bunton, C. A.; Savelli, G. Adu. Phys. Org. Chem. 1986, 22, 213. (4) Meisel, D.; Pelizzetti, E. Prog. React. Kinet., in press. (5) Mackay, R. A. Adu. Colloid Interface Sci. 1981, 15, 131. (6) (a) Pelizzetti, E.; Pramauro, E.; Minero, C. In Colloids and Surfactants, Fundamentals and Applications; Bami, E., Pelizzetti,E., E&.; SocietB.Chimica Italiana: Rome, 1987; Vol. 77, p 127. (b) OConnor, C. J.; Lomax, T. D.; Ramage, R. E. Adu. Colloid Interface Sci. 1984,20,21.
obtained from Alfa. Sodium dodecyl sulfate (SDS)was purchased from Merck and recrptalliied. Toluene and 1-butanolwere used as received from Carlo Erba. Apparatus and Procedure. The kinetic runs were carried out on a Durrum-Gibson stopped-flow spectrophotometer at the wavelength of maximum absorbance of IrCb2-(487 nm). The two solutionsto be mixed were always of the same compmition,except for the reactants, in order to avoid bubble formation and incomplete mixing because of the different viscosities. Since the microemulsion densities change significantly as a function of the composition,the concentrations of reactants are expressed in molality. The initial concentration of 1rCls2-was 1X m,while that of the benzenediols was chosen in order to work under pseudo-first-order conditions. The reactions were performed at 25.0 i 0.1 O C . Conductivity measurements were obtained on an Amel Model 123 conductimeter with the cell in a water bath thermostated at 25.0 f 0.1 OC.
Results Microemulsion Phase Diagram. Phase maps of the SDS/ 1-butanol/toluene/water microemulsionshave been published.’ Since the addition of electrolytes strongly affects the stability of microemulsions, some of the pseudoternary phase diagrams have been determined. The pseudoternary phase diagram for 1-butanol/SDS (2 w/w) (referred to as S) and water/NaCl 0.09 M/HC1 0.01 M (referred to as C) is reported in Figure 1. Microemulsions of different composition,indicated by full points in Figure 1, were prepared by mixing the appropriate amount of 75% S + 25% C with toluene and then diluting the mixture with C. The microemulsions obtained along a dilution line are characterized by a constant ratio [1-butanol]/ [SDS]/ [toluene]. Varying the proportion of the different constituents makes it possible to obtain O/W or W/O microemulsions. In between the areas of the diagram pertaining to the high percentage of C (X,Z 0.8), which exhibits high electric conductivity, and that at high oil content, which shows low conductivity and the offset of the conductivity at X = 0.15, there is an intermediate area in which a conductivity variation can be observed and that separates the O/W and W/O regions. (7) (a) Roux, A. H.; Roux-Degranges, G.; Grolier, G. P. E.; Vialland,
A. J. Colloid Interface Sci. 1981,84, 250. (b) Sanchez-Rubio, M.; Santos-Vidals, L. M.; Rushforth, D. s.;Puig, J. E. J.Phys. Chem. 1985,89, 411.
0743-7463/88/2404-0101$01.50/00 1988 American Chemical Society
102 Langmuir, Vol. 4, No. 1, 1988
Minero et al.
S line0
3l
5 2
1
I
L
1
Toluene
C
Figure 1. Pseudobinary phase diagram for SDS/1-butanol/ toluene/water microemulsions: S = 1-butanol/SDS = 2 w/w; C = water/0.09 M NaCl + 0.01 M HCl. The demixing line is indicated by a dashed line, while the continuous line is the calculated upper demixing line (see text). The compositions of the homogeneous microemulsions that were used in the kinetic experiments are indicated by full points. They are obtained by a dilution procedure (see text) along the dilution lines numbered from 0 to 5. Each line is characterized by a constant toluene/ 1-butanol/SDSratio (w/w/w): (0) 00.67:0.33; (1)0.1:0.6:0.3; (2) 0.25:0.5:0.25; (3) 0.4:0.4:0.2; (4) 0.55:0.30:0.15; (5) 0.67:0.22:0.11.
0
3
90
6
100
95
1-butanol
% (v;v)
Figure 3. Experimental rate constants in water/0.09 M NaCl 0.01 M HC1/1-butanol mixtures for compounds I ( 0 )and I1 (0). The very poor solubility of 11in water does not allow measurementa at a 1-butanolcontent less than 4%. k, = 8 X lo4M-’ s-l can be estimated by extrapolation to 0% 1-butanol. 6
l/kexil( 5 4 3 2
1
0 0
1
2
3
10‘. cd 0.5
1
15
10’ c d
2
M
Figure 2. Elution volume of compound I1 over a C18 reversedphase HPLC column, plotted according to eq 1against the concentration of micellized SDS. Experimental parameters: V , = 2.06; V , = 1.52. The data allow us to estimate P,, = 1.4 X lo3 and Kmw= 8 X lo2 M-l. Whereas the lower phase-separation limit can be explained by various current theories: the upper limit can be ascribed to the necessity for the surfactant to be located at the water-oil interface and for its polar head to have a minimum area. Since the surfactant is insoluble in oil, in the water-poor region of the phase diagram the failure of the bulk aqueous phase leads to surfactant precipitation: Le., to the demixing of the microemulsion. Binding Constant of I1 with SDS Micelles. For liquid chromatographic determination of the binding constant of 11, a previously derived equation was appliedlO
4
5
M
Figure 4. Experimental rate constants of compound I1 with IrC1:- in the presence of SDS, plotted according to eq 4. tionary phase, the volume of the mobile phase, and the elution volume of a solute, respectively; P,, and P,, are the partition coefficientsbetween the stationary phase and water and between the micellar phase and water, respectively; u is the partial molar volume of the surfactant in the micelle; and Cd is the concentration of the micellized surfactant. From plots according to eq 1,the ratio of slope over intercept gives the values of v(PmW - l), which corresponds to the binding constant Kmw. The data obtained with a reversed-phase C18 HPLC column are plotted in Figure 2. The uncertainty affecting the intercept allows an estimate of the binding constant in the order of 8 X lo2 M-l. Stoichiometry and Kinetics. The oxidation of benzenediols by means of hexachloroiridate(1V) in aqueous“ and micellar systems has been previously investigated in detail. l2 The overall reaction can be represented as
-
HzQ + 21rClG2- Q + ~ I I - C &+~ -2H+ where V,, V,, and V, represent the volume of the sta(8) (a) Talmon, y.; Prager, S. J. Phys. Chem. 1978, 69, 2984. (b) Degennes, P. G.; Taupin, C. J . Phys. Chem. 1982,86, 2294. (9) Roux,P.; Bellocq, A. M.; Leblanc, M. S. Chem. Phys. Lett. 1983, 94, 156. (10)Amstrong, D. W.; Nome, F. A n d . Chem. 1981, 53, 1662.
(2)
where HzQ and Q represent the benzenediol and the corresponding quinone, respectively. (11) (a) Pelizzetti, E.; Mentaati, E.; Baiocchi,C. J.Phys. Chem. 1976, E.:Mentasti, E. 2. Phvs. Chem. (Wiesbaden)
80, 2979. (b) Pelizzetti, 1977, 105,21.
(12) Pelizzetti, E.;Pramauro, E. J.Phys. Chem. 1984,88,990.
Langmuir, Vol. 4, No. 1, 1988 103
Oxidation of Benzenediols by Herachloruiridate(IV)
PSEUDOPHASES
6
oi I
1
1
1
W
E' ?
e
5
r
4 3
.I
0'
2
*. --_-e----__--
'1
0 1 1
I
,
,
.8
I
1
.6
I
I
I
,
,
.2
.4
I 0
XC
Figure 5. Rate constants (m-l 8-l) for compound I in micro-
emulsions as a function of the experimental weight fraction of the aqueous component. The experimental values for different dilution linea are report& (0)line 0; (H) line 4; (A)line 5. Dashes lines are the rate constants calculated according to the threepseudophase model (see text). The dilution lines are indicated by numbers in parentheses. 20
*'
16
E'
X
8 4
0 1
8
6
4
2
0
XC
Figure 6. Rate constants (m-l 8-l) for compound I1 in microemulsions as a function of the experimental weight fraction of
the aqueous component. The experimental values for different line 0; ( 0 )line 1;(A)line 2; ( 0 ) dilution lines are reported (0) line 3; (H) line 4; (A)line 5. Dashed lines are the rate constants calculated according to the three-pseudophasemodel (see text). The dilution lines are indicated by numbers in parentheses. The kinetic data concerning water and water/ 1-butanol mixtures, SDS, and microemulsions as reaction media are reported in Figures 3-6. The reported experimental rate constants are derived from pseudo-first-order treatment and are related to the specific second-order rate constants for the first electron-transfer step by a factor of 2."
Discussion Homogeneous Solution. The specific rate constants observed for I and I1 in aqueous solutions are comparable with kinetic data previously reported" for related systems in analogous experimental conditions. As shown in Figure 3, the effect of the addition of 1butanol to water is to reduce the reaction rates. The influence of the solvent composition on the reaction of I with IrCb2- has been previously investigated with aqueous methanol solutions as reaction media.13 The presently observed pattern is similar to the one reported for that mixture. In terms of the analysis of the solvent effects on reaction rates based on initial- and transition-state solvation changes,14 it can be suggested that the transition (13) Blandamer, M. J.; Burgess, J.; Hamshere, S. J.; Haines, R. I.; McAuley, A,; White,C. Can. J. Chem. 1983, 61, 1361.
J
Figure 7. Schematic diagram of the three-pseudophase model for the partition of the reagent species. The same scheme should apply to the partition of microemulsion components.
state is more affected by solvent than is the initial state. The extent of the rate variation in going from water to high 1-butanol content is comparable for compounds I and 11, being only slightly more relevant for the more hydrophobic compound 11. Micellar Systems. The electron-transfer reactions of benzenediols in micellar systems have been investigated in detail.12 Since compound I1 was not examined in that report, the present results are analyzed accoding to the two-phase model previously adopted.15 Assuming that the rate of exit and entrance of the solubilizates in and out of the micelle occurs on the microsecond time scale, and that the anionic oxidant will be entirely in the aqueous phase, the observed rate constant can be described by k",K&d + k", (3) kexp = (1 + KBCd) where K Bis the binding constant defined as K,, above; the subscripts m, w, and B represent quantities related to the micellar phase, the aqueous phase, and the benzenendiols; ko are the rate constants for the reaction (eq 2) in the pseudophases; and C d is the surfactant molar concentration. If the contribution of the reactivity at the micellar surface is tentatively neglected, eq 3 is further reduced to (4) Figure 4 shows the experimentally observed rate constant for compound I1 plotted according to eq 4. The intercept is difficult to estimate, but if the value 8 X lo4 M-I s-l is extrapolated from kinetic data in the water/lbutanol mixture and assumed as k",, K B = 9 X lo2 M-' is obtained. This value seems reasonable if the contribution to the binding constant of additional aliphatic carbon atoms is considered. In fact, since the micellar incorporation in the present system is primarily determined by hydrophobic interactions, the free energy change can be expressed as the s u m of two contributions, one arising from the aromatic residue (with its functional or polar group, such as OH) and one from the alkyl substituent where n is the number of aliphatic carbon atoms.12 Based on the series of 4-methyl-, 3-isopropyl-, and 4tert-butylbenzene-l,2-diols, the binding constant for compound I1 with SDS should be on the order of 1 X lo3 M-l. Microemulsion Systems. It can be observed that the variation of the experimental rate constants as a function of the microemulsion composition, reported in Figures 5 (14) (a) Blandamer, M. J.; Burgess, J. Pure Appl. Chem. 1982, 54, 2285; (b) 1983,55,55. ( c ) Burgess, J.; Pelizzetti, E., unpublished results. (15) Berezin, I. V.; Martinek, K.; Yataimirski, Y . A. Russ. Chem. Rev. (Engl. Transl.) 1973, 42, 787.
104 Langmuir, Vol. 4, No. 1, 1988
Minero et al.
and 6, is similar for both compounds; however, at high water fractions inhibition is more pronounced for 11. At lower water content there is an increase in reaction rates dependent on the oil content. In order to analyze the experimental results, a simple microemulsion model, consisting of three distinct pseudophases, without any assumptions about the microstructure, is considered.16 A schematic picture is shown in Figure 7, where the subscripts w, I, and oil or o mean aqueous, interphasal, and oil pseudophases, respectively. In general, if the reagents R are always in equilibrium in f pseudophases, the following kinetic equation holds:
where iz, (M-l s-l) is the second-orderrate constant in the microemulsion, kJ (M-l s-l) are the specific rate constants in each phase, [R] are the local molar concentrations of the reagents, [R,,] are the molar concentrations in the whole microemulsion, and df are the pseudophase volume fractions. Since microemulsions are prepared by weight and it is more convenient to use the scale of molality, because of the change in the specific volume of the microemulsion when the composition is varied, eq 6 is easily transformed into
(7)
of microemulsion components between the pseudophases. By considering the solubilities of microemulsion components, the qualitative composition of each pseudophase can be assumed to be
(C.I~,)W = nW(w)+ nBut(w)
(cjn])I =
+ nBut(I) + nSDS(1) + nTol(I)
nW(I)
(Cjn,)o= nBut(o) + nTol(o)
(10)
where the subscripts W, But, SDS, and To1 are the four microemulsion components. Since thermodynamics imposes that the components present in each pseudophase will be in equilibrium, the system (eq 10) with the appropriate mass balances can be solved in terms of mass-transfer constants and activity coefficients of the microemulsion components. But since the chemical system is far from ideality, an approach which takes into account the mutual solubility limits between the components can formally be used. In this way there is a loss of generality, but a detailed discussion of the activity coefficients is avoided and the algebra becomes simpler. The moles of the Components in each pseudophase can be related through proportionality constants a. It is assumed, in other words, that each pseudophase is always saturated with respect to the componentspresent in defect. a coefficients are in fact solvation numbers: nBut(w)
=
alnW(w)
nBut(I)
=
nW(I)
a4nSDS(I)
=
a2nSDS(I) -k a3nBut(I)
nTol(I)
=
a5nSDS(I)
(11)
(9) where k ) = k$ P,? = pw?ywR/YP,SI = (Zjnj)I/(Ejnj)w, So = (~jnj)p/(t;jnj)w, and nj is the number of molecules of any species j present in the pseudophase. In order to solve eq 9, it is necessary to calculate the terms SIand Soand then consider in detail the partitioning
where a1represents the solubility of 1-butanol in water (0.017),17a2 is the hydration number for SDS in the interphase, a3 is the solubility of water in 1-butanol, a4 is related to the alcohol content in the interphase (which is assumed to be proportional to the number of surfactant molecules), and a5represents the average number of toluene molecules per surfactant in the interphase. It is obvious that the present assumptions make the model not valid at the corners of the phase diagram. The multiparametric kinetic equation was solved in two steps by computer simulation using eq 9,10, and 11with the following conditions: 1. Partitioning of Microemulsion Components. Since the solubility of 1-butanol in water is very low, the condition that al = 0 is imposed. azand a3are taken from the literature (a2= 718and a3= 0.9517). a4is obtained from the fit on the upper demixing line by assuming that this one is due to the failure of the aqueous pseudophase. In terms of eq 10 and 11this assumption means that at the composition where the microemulsiondemixes X , will be zero. The loci of points where this happens are the calculated upper demixing line. The best-fitting curve, reported in Figure 1 as a continuous line, is obtained with the following values: a1 = 0, a2= 7,a3 = 0.95, and a4 = 7.5. The value of cy4 suggests that almost all the alcohol is in the interphase. a5is fitted by using the kinetic data, as can be seen below. 2. Partitioning of Reagents. P’,$ is assumed to be constant. The estimated Pa? values for benzenediols should be consistent with the partition data obtained both from kinetic and HPLC measurements for SDS, whereas P & f I r C L 6 ” should be very low, because of the electrostatic interactions. 3. Kinetic Parameters. For purposes of model consistency, the k , values obtained in 1-butanol saturated
(16) (a) Biais, J.; Bothorel, P.; Clin, B.; Lalanne, P. G. J. Colloid Interface Sei. 1981,80, 136. (b) Biais, J.; Odberg, C.; Stenius, P. J. J. Colloid Interface Sei. 1982,86, 350.
(17)Van Nieuwkoop, J.;Snoe, G.J . Colloid Interface Sci. 1986,103, 417. (18)Tokiwa, F.;Ohki, K. J. Phys. Chem. 1967, 71, 1343.
where &p = (kobsd)pE/CoB(tot),(kobsd)@ is the observed pseudo-first-order constant (SI) in the microemulsion, CoB(bt)is the initial molal concentration of the excess reagent, are the local molal concentrations of the species R in the pseudophases f , CR(bt)are the concentrations of reagents in the whole microemulsion, and XF and 6 are the weight fractions and the densities of the pseudophases, respectively. The ratios CR(n/CR(wt)can be evaluated through a suitable equilibrium model of the system. The partition of reagents between the pseudophases can be expressed by means of the partition coefficients for each reagent R in the pseudophases (A = IrCh2-, B = benzenediols): PwIA, PwIB, PwoA, and PwoB. The partition coefficient is here defied in terms of the molar fraction x :
cR,
PwfR = exp where
R R xw Y w
(8)
is the activity coefficient of R in the pseudophase
f. In t i e case considered here of three pseudophases,
substituting eq 8 into eq 7 yields eq 9:
Langmuir, Vol. 4, No. 1, 1988 105
Oxidation of Benzenediols by Hexachloroiridate(IV) Table I. Kinetic Constants (m-l 8-l) and Partition Coefficients Used in the Calculation of the Rate Constants for Reaction 2 in Microemulsions” compd
I I1
k/,
k‘,
p;**
3.9 x 103 6.2 x 103 0.14 6.8 X lo4 6.8 X lo4 0.05
P;? 20 4.8 X 10‘
p;,B 20 5.0 X lo6
“k6, are the experimental rate constants observed in a l-butanol-saturated water/l-butanol mixture.
solution are used in the fits. k $ is a fitting parameter that satisfies the condition kBut IkI Ik, where kBut is the specific rate in the water-saturated 1-butanol solution. In eq 9, the term depending on k 6 was neglected and k i are considered constant. On the basis of the above mentioned assumptions, the partition and kinetic parameters to be evaluated are PaIB, P’w~A, and k’p The obtained fitting curves are shown in Figures 5 and 6 as dashed lines and were calculated by using the values reported in Table I. The value cy5 = 1 is also obtained. As expected, a t high Xc the fitting curves are more strongly dependent on the PaIAvalue, whereas other parameters are more important in the region at low PaIB and k modify the shape of the increasing calculated rate, whereas different values of Pa: and a5change the relative distance between the rate curves of the considered dilution lines. For comparison purposes, it must be remembered that the partition coefficients reported in Table I are defined in eq 8 and are related to the usual binding constant KhR (M-l) by P’,? = 55.5(KhR + u ) , where u is the molar volume of the pseudophase f . It is evident that, whereas a two-pseudophase model fails in the interpretatioon of the experimental results over the entire range of microemulsion composition, the threepseudophase approach predicts quite well the kinetic behavior of the oxidation reactions of inorganic compounds by means of inorganic ions. It is noteworthy also that the dilution line 0 (the SDS/1-butanol system, without oil) is described by the same equation. Then, it can be suggested that the solvation of the interphase is crucial. Dielectric relaxation measurements support this concl~sion.’~In particular, in the present treatment the hydration of the interphase allows us to explain together with the kinetic data the upper demixing line. The a values also give information on the composition of the interphase region (i.e., a5= 1has the meaning that one molecule of toluene is present for each surfactant molecule). Concerning the kinetic plots of Figures 5 and 6, it can be observed that for compound I (quite hydrophilic) the microemulsion composition has a mild effect and at low XCthe rate is higher than in aqueous media. Whereas the observed decrease at high X c is due to the partitioning of I between water and micelles or interphase (being the reaction progress mainly in the aqueous pseudophase), the increase a t low X c is due to the decrease of the available
x,.
(19) Epstein, B. R.; Fosker, K. R.; Mackay, R. A. J. Colloid Interface Sci. 1983, 95, 218.
aqueous pseudophase (with the corresponding increase of the term k a / X , in eq 9). Compound 11, which is strongly hydrophobic, shows qualitatively the same behavior. After the expected strong inhibition a t high Xc,a rise in the rate constants is observed at low Xc. In this case the reaction progresses essentially in the interphase, together with a contribution in the aqueous pseudophase. This last term becomes relevant at low Xc (then at corresponding much lower values of X,). It has to be mentioned that, although the qualitative behavior is predicted by eq 9-11, for compound I1 some discrepancies between the calculated and experimental rate constants in X c range 0.5-0.95 are observed. The calculated parameters from the fits are quite reasonable; in fact, for both compounds It’I values are comparable to the rate constants observed in l-butanol-saturated solution, as can be assumed to be the case of the interphase. The partition coefficient PaI*is comparable in both experiments and is quite low, as expected on electrostatic repulsion basis; PLIBand are consistent when compared with the previously reported partition coefficients in SDS micelles. Conclusions The compounds I and I1 were chosen because of their suitability and importance in mimicking natural processes, where the system benzenediols/quinones plays an important tole.20 Compound I exhibits a poor tendency to be partitioned in the aggregate structure, thus ensuring that the reaction with an oxidant with opposite charge in respect to that of the ionic surfactant takes place in the water phase. Compound I1 is virtually soluble only in the oil phase, thus ensuring that the same reaction occurs mainly in the interphase region. While the well-known two-pseudophasemodel correctly predicts the reactivity in micellar systems, for microemulsion systems the proposed three-pseudophase model, which explicitely includes the interphase hydration, is needed. Quite good prediction of observed rates for a hydrophobic and a hydrophilic substrate is encouraging. Since microemulsions exhibit relevant capability in solubilizing strongly hydrophobic molecules, it should be possible to carry out the oxidation of sparingly soluble organic compounds by means of strong ionic oxidants. Since these processes could be relevant in degradation or organic pollutants, work is in progress on this topic. Acknowledgment. We are grateful to CNFt, MPI, and European Research Standardization Group of the U.S. Army under Contract DAJA 45-85-C-0023 for support of this work. Registry No. I, 120-80-9; 11,1020-31-1; IV, 16941-25-6 SDS, 151-21-3; CsHbCH3, 108-88-3; HO(CH&,CH,, 71-36-3; HzO, 7732-18-5. (20) (a) Trumpower, B. L. Function of Quinones in Energy Conserving Systems; Academic: New York, 1982. (b) Witt, H. T. In Bioenergetics of Photosynthesis; Govindjee, Ed.; Academic: New York, 1975.
