3448
J . Phys. Chem. 1986, 90, 3448-3452
than the diffusion-controlled rate limit, although there will be considerable Coulombic repulsion between the two negatively charged reactants. Under identical conditions, corrected k,, values of 1.2 X lo8 and 5.4 X lo7 dm3 mol-' s-', respectively, were obtained with ZnTSPP+ (Eox= 0.90 V) and CdTSPP+ (Eox= 0.77 V). Here, the electrostatic forces remain constant, but it seems that k,,, increases with increasing Eox. Consequently, it appears that decay of the radical cations involves electron abstraction from the catalyst particle under such conditions. Earlier work' has shown that interaction between ZnTSPP' and colloidal Ru02.2H20results in oxidation of water to O2on the catalyst surface. MgTSPP and CdTSPP were used in similar experiments. The metalloporphyrin (ca. mol dm-)) in Arpurged, buffered aqueous solution containing Na2S04(0.2 mol drn-)), Na2S208( lo4 mol dm-3), and RuO2.2Hz0( lo4 mol dm-3) was irradiated with green light within the chamber of the MPD. The rate and total yield of evolved O2were monitored as a function of pH for the two systems. With CdTSPP, virtually no O2 was detected during irradiation at pH 9-14 but with MgTSPP small amounts of O2were observed. The maximum rate and yield of O2 formation were found at pH 12, where the thermodynamic driving force for water oxidation is 68 kJ mol-'. Under optimized conditions, the initial quantum efficiency for O2 evolution was 27% f 5% but the total yield of O2formed upon prolonged irradiation was only 5 X lod mol d ~ n - ~These . values compare unfavorably with the optimized values reported earlier' for ZnTSPP. In control experiments, it was found that both CdTSPP and
MgTSPP reacted very efficiently with O2upon illumination. In fact, the reaction between triplet CdTSPP and O2is so efficient that any O2formed in the S2082-/Ru02.2H20photosystem will be consumed immediately. This accounts for the absence of O2 in the photochemical experiments. With MgTSPP, O2evolution and consumption reactions are more balanced and modest yields of O2are observed in the photolyses. However, with ZnTSPP the O2evolution process competes favorably with O2consumption, and this system is much the better one for water oxidation. This is an interesting trend because it parallels the redox potentials of the metalloporphyrin triplet excited states rather than the triplet energies. Thus, from low-temperature photophorescence spectra the triplet energy levels for Zn(II), Cd(II), and Mg(I1) TSPP complexes are 1.57, 1.54, and 1.42 eV, respectively, while the redox potentials of the triplet excited states are -0.67, -0.77, and -0.74 V vs. NHE, respectively. This suggests that the O2consumption reaction involves electron rather than energy transfer. MP*
+ O2
-
MP+ + 02-
(10)
Since superoxide is an important intermediate radical in biological systems, the very high efficiency for O2consumption noted with CdTSPP is worth investigating further. Acknowledgment. We thank Dr. R. E. Huie for the use of his stopped-flow apparatus, P. Ouellette for technical assistance with the stopped-flow, and the SERC GE (Schenectady) and the Offce of Basic Energy Sciences of the U S . Department of Energy for financial support.
GENERAL PHYSICAL CHEMISTRY Studies on the Diamagnetic Susceptibility of Substituted 2,5-Dianllino-3,&di halo-p-benzoquinones R. R. Gupta,* M. Kumar, Rakesh Kumar, and R. K. Gautam Chemistry Department, Rajasthan University, Jaipur-4, India (Received: September 27, 1985; In Final Form: January 17, 1986)
Diamagnetic susceptibilitiesof a number of differently substituted 2,5-dianilino-3,6-dihalo-p-benzoquinones have been reported. Theoretical diamagnetic susceptibilitieshave been calculated to analyze different existing structural environmentsby considering 2,5-dianilino-3,6-dihalo-p-benzoquinones as a combination of three structural units consisting of p-benzoquinone and substituted anilines. The results of empirical diamagnetic susceptibility are excellent, and divergence is not more than 1.5%, since all the structural interactions affecting the molecular diamagnetism have been duly accounted for in the calculations of diamagnetic susceptibilities.
Introduction
In continuation of our previous studies on diamagnetic susceptibility,'V2 it is considered worthwhile to extend diamagnetic (1) Gupta, R.
R.; Kumar, M.; Kumar, R. J . Am. Chem. SOC.1984, 106,
studies to the structurally interesting series of substituted dianilino-p-benzoquinones.*Such studies are of value not only for characterizing their diamagnetic behavior but also for throwing light on the influence of variable environments. Changes (2) Gupta, R. R.; Swaroop, R.;Kurnar, M.; Kishan J . Am. Chem. SOC. 1984, 106, 4378.
1888.
0022-3654/86/2090-3448$01.50/0
0 1986 American Chemical Society
Substituted 2,5-Dianilino-3,6-dihalo-p-benzoquinones in chemical substituents cause changes in electronic configuration as well as conformations of the molecules and hence considerably affect their molecular diamagnetism.
The Journal of Physical Chemistry, Vol. 90, No. 15, 1986 3449 TABLE I: Diamagnetic Susceptibility (xM)of Chloraoil, Bromanil, and Substituted Anilines and Their Diamagnetic Susceptibility Contributions contribution
Experimental Section Substituted dianilino-p-benzoquinonesrequired for the diamagnetic studies have been synthesized3v4by the condensation of chloranil/bromanil and substituted anilines. Their diamagnetic susceptibilities have been measured by the Gouy method and are summarized in Tables I and 11.
Results and Discussion
wmpd
(3) Ojha, K. G. Ph.D. Thesis, University of Rajasthan, Jaipur, 1980. (4) Goswami, N. K. Ph.D. Thesis, University of Rajasthan, Jaipur, 1979. ( 5 ) Baudet, J. J . Chim. Phys. 1961, 58, 228. (6) (a) Hameka, H. F. J . Chem. Phys. 1961, 34, 1996. (b) Sullivan, P. S.0.;Hameka, H. F. J . Am. Chem. SOC.1970,92,25, 1821. (c) Stockham, M. E.; Hameka, H. F. J. Am. Chem. SOC.1972,94,4076. (d) Haley, L. V.; Hameka, H. F. J. Am. Chem. SOC.1974, 96, 2020. (7) Gupta, R. R.; Kumar, M. Chem. Phys. Lett. 1983, 100, 297. (8) Gupta, R. R.; Kumar, M.;Ojha, K. G. J . Chem. Phys. 1981,75,4173. Gupta, R. R.; Kumar, M.; Kishan J . Chem. Phys. 1983, 79, 3410. (9) Gupta, R. R.; Kumar, M.; Ojha, K. G. Chem. Phys. Left. 1980, 76, 366. (10) Gupta, R. R.; Kumar, M.; Kishan J. Chem. Phys. 1982, 76, 1173. (1 1) Gupta, R. R.; Kumar, M.; Kalwania, G. S. J. Chem. Phys. 1982, 76, 5182. (12) Mital, R. L.; Gupta, R. R. J . Pure App. Phys. 1970, 8, 179. (13) Pascal, P.; Pacault, A.; Hoarau, J. C.R. Seances Acad. Sei. 1951, 233, 1078. (14) Haberditzl, W. Sitzungsber. Dtsch. Akad. Wiss.Berlin, KI. Chem., Geol. Biol. 1964, 2.
R
of R to X M
chloranil
1 12.60
75.60
bromanil
150.20
94.60
aniline
62.5
59.00
o-bromoaniline
88.12
84.62
o-chloroaniline
79.78
76.28
o-toluidine
74.04
70.54
o-anisidine
78.81
75.31
o-phenetidine
92.47
88.97
a-naphthylamine
92.9
89.4
p-bromoaniline
85.93
82.43
p-chloroaniline
77.62
74.12
p-toluidine
68.48
64.98
p-anisidine
77.48
73.98
p-phenetidine
93.44
89.94
3-bromo-&toluidine
95.5
92.00
2-chloro-o-toluidine
91.83
88.33
3-chloro-o-toluidine
92.07
88.57
4-chloro-o-toluidine
92.50
89.00
In order to analyze different existing structural environments in substituted dianilino-p-benzoquinones,it has become essential to estimate their theoretical diamagnetic susceptibilities and to correlate these with the experimental values. Substituted dianilino-p- benzoquinones have been considered to be comprised of three structural units. One is p-benzoquinone, while the other two consist of substituted anilines. Diamagnetic susceptibilities of substituted dianilino-p-benzoquinonesby incremental systems, based on atomic and bond susceptibility concepts, cannot be calculated, since in this approach the effects caused by the interactions of substituents, which influence the molecular diamagnetism, cannot be accounted for. The wave-mechanical5 approach also cannot be applied to calculate diamagnetic susceptibilities of these molecules, because of the nonavailability of the susceptibility data required for calibrating the wavemechanical calculations. Although the semiempirical approach has been successfully applied to different classes of aliphaticslq2*68as well as organometallics*-” with very promising results, it cannot be applied to these molecules. The different parameters required for the semiempirical calculations of diamagentic susceptibility could not be calculated for these molecules. Therefore, another method, analogous to that reported for polysubstituted benzene,12 has been applied for the empirical estimation of diamagnetic susceptibilities of substituted dianilino-p-benzoquinones. In the present investigation, substituted 2,5-dianilino-p-benzoquinones have been considered to be composed of three structural units: a p-benzoquinone moiety and two substituted anilines which may be the same or different. Diamagnetic susceptiblity contributions of these three structural units have been used in the empirical estimation of diamagnetic susceptibilities of substituted dianilino-p-benzoquinones. The diamagnetic susceptibility contribution of the first unit, Le., thep-benzoquinone moiety, has been calculated by either subtracting the diamagnetic susceptibility contributions of two chlorine atoms [2(18.5 X from that of chloranil or subtracting the diamagnetism of two bromine atoms [2(27.8 X 10-6)]13from the diamagnetic susceptibility of bromanil. The diamagnetic susceptibility contributions of the remaining two units, Le., substituted anilines, have been calculated by subtracting the diamagnetic contribution of a hydrogen atom attached to a nitrogen atom (3.5 X 10”)14 from the diamagnetic susceptibility of substitutd anilines. The diamagnetic susceptibility contributions of these structural units employed in the calculaitons of dia-
106XM
magnetic susceptibilities of substituted dianilino-p-benzoquinones are summarized in Table I. Empirical diamagnetic susceptibilities of substituted 2,5-dianilino-3,6-dihalo-p-benzoquinones calculated by using these contributions are summarized in Table 11. It has been observed from the diamagnetic susceptibility calculations of a number of differently substituted dianilino-pbenzoquinones that their empirical diamagnetic susceptibilities agree excellently with their corresponding experimental values. The deviations between experimental and theoretical results are
3450 The Journal of Physical Chemistry, Vol. 90, No. 15. 1986
Gupta e t ai.
TABLE II: Diamagnetic SwepHBilities of Substituted 2,5-DinniHno-3,6-diho-p-benzoquinones 106Xhi compd
2,5-bis(3- bromo-o-toluidino)-3,6-dichlorobenzoquinone
structure
exptl
calcd
208.07
208.58
225.38
224.89
226.58
226.22
259.30
259.60
225.81
228.16
191.84
193.60
23 1.75
233.34
230.68
232.01
225.93
227.19
224.48
225.03
223.21
223.70
240.48
240.85
240.23
239.52
216.40
215.89
218.81
221.45
217.59
220.12
256.87
253.54
Substituted 2,5-Dianilino-3,6-dihalo-p-benzoquinones
The Journal of Physical Chemistry, Vol. 90, No. 15, 1986 3451
TABLE I1 (continued) 106XM compd
2,5-bis(3-bromo-o-toluidino)-3,6-dibromobenzoquinone
not more than 1.5%. Therefore, such satisfying results in the theoretical deduction of diamagnetic susceptibility can be attributed to the fact that nearly all the structural interactions caused by different substituents that might considerably influence the molecular diamagnetism have been accounted for in these calculations. Hence, it may be concluded that such calculations can also be applied to the other classes of aromatic compounds, by taking into consideration almost all the existing structural interactions affecting molecular diamagnetism. Registry No. C6H5NH2, 62-53-3; 2-BrC6H4NH2, 615-36-1; 2C1C6H4NH2, 95-51-2; 2-CH3C6H4NH2, 95-53-4; 2-MeOC6H4NH2, 90-
04-0;2-EtOC6H4NH2,94-70-2;4-BrC6H4NH2,106-40-1;4-
structure
exptl
calcd
216.07
216.68
253.42
254.40
251.62
252.74
251.48
252.26
251.93
253.60
245.37
245.22
261.42
263.84
278.52
278.60
244.92
247.16
271.08
272.60
276.83
273.40
275.58
272.54
235.32
235.68
CIC6H4NH2, 106-47-8; 4-CH3C6H4NH2, 106-49-0; 4-MeOC6H4NH2, 104-94-9; 4-EtOC6H4NH2, 156-43-4; chloranil, 118-75-2; bromanil, 488-48-2; a-naphthylamine,134-32-7; 4-bromo-o-toluidine, 583-75-5; 3-chloro-o-toluidine, 87-60-5; 4-chloro-o-toluidine, 95-69-2; 5-chloro-2methylaniline, 95-79-4;2-(p-anisidino)-5-anilino-3,6-dichlorobenzoquinone,34072-01-0;2-(o-anisidino)-5-(p-anisidino)-3,6-dichlorobenzoquinone, 73187-721 ; 2,5-di(o-anisidino)-3,6-dichlorobenzoquinone, 13437-25-7;2,5-bis(3-bromo-o-toluidinol-3,6-dichlorobenzoquinone, 80910-301; 2,5-bis(o-chloroanilino)-3,6-dichlorobenz~uinone, 676201 1-5; 2,5-dianilino-3,6-dichlorobenzoquinone,5030-67-1 ; 2-(0anisidinol)-5-(p-bromoanilino)-3,6-dichlorobenz~uinone, 73187-69-6; 2-@-anisidino)-5-(p-bromoanilino)-3,6 dichlorobenzcquinone,7318776-5;2-(o-anisidino)-5-(o-chloroanilino)-3,6-dichlorobenzoquinone, 73187-74-3;2-(o-anisidino)-5-(p-chloroanilino)-3,6-dichlorobenzo-
3452
The Journal of Physical Chemistry, Vol. 90, No. 15, 1986
quinone, 73187-70-9; 2-@-anisidino)-5-@-chloroanilino)-3,6-dichlorobenzoquinone, 73187-77-6;2-(o-anisidino)-5-(p-phenetidino)-3,6-dichlorobenzoquinone, 73187-73-2; 2-@-anisidino)-5-@-phenetidino)-3.6dichlorobenzoquinone, 73187-79-8; 2-(o-anisidino)-5-(p-toluidino)-3,6dichlorobenzoquinone,73187-71-0; 2-(o-anisidino)-5-(o-toluidino)-3,6dichlorobenzoquinone, 73187-75-4; 2-@-anisidino)-5-(o-toluidino)-3,6dichlorobenzoquinone, 102505-30-6;2,5-di-(o-phenetidino)-3,6-dichlorobenzoquinone, 80904-36-5; 2,5-di-(o-toluidino)-3,6-dichlorobenzoquinone, 67620-10-4; 2,5-bis(cu-napthylamino)-3,6-dichlorobenzoquinone, 63883-1 1-4;2,5-bis(3-chloro-o-toluidino)-3,6-dichlorobenzo-
Additions and Corrections quinone, 80904-39-8; 2,5-bis(2-chloro-o-toluidino)-3,6-dichlorobenzoquinone, 80904-38-7; 2,5-bis(4-chloro-o-toluidino)-3,6-dichlorobenzoquinone, 80904-40-1; 2,5-di-(o-anisidino)-3,6-dibrornobenzoquinone, 67620-1 5-9;2,5-di-(o-bromoanilino)-3,6-dibrornobenzoquinone, 8090435-4;2,5-bis(3-bromo-o-toluidino)-3,6-dibromobenzoquinone, 8090441-2;2,5-di(o-chloroanilino)-3,6-dibrornobenzoquinone, 67620-13-7; 2,5-bis(4-chloro-o-toluidino)-3,6-dibromobenzoquinone, 102505-31-7; 2,5-bis(cu-napthylamino)-3,6-dibrornobenzoquinone,67620-14-8; 2,5-di(o-phenetidino)-3,6-dibrornobenzoquinone,80904-37-6;2,5-di(otoluidino)-3,6-dibromobenzoquinone,67620-12-6.
ADDITIONS AND CORRECTIONS 1983. Volume 87
Rabindra N. Roy, James J. Gibbons, J. Christopher Peiper, and Kenneth S. Pitzer*: Thermodynamics of the Unsymmetrical Mixed Electrolyte HCI-LaC1,. Page 2368. There are errors in certain columns of Table IV. A corrected table is given; nothing else in the paper is affected. TABLE I V Activity Coefficients and Excess Enthalpies for the System H+-La3+-CI--H20 at Ionic Strength Fraction y of LaCI2' yh(HC1) y*(LaCM HCXIRT Z(mo1 kg-') y =0 y = 0.50 y = 1.0 y =0 y = 0.50 y = 1.0 y =0 y = 0.50 0.733 0.741 0.001 0.902 0.897 0.721 0.001 0.010 0.905 0.662 0.865 0.647 0.671 0.002 0.871 0.002 0.020 0.875 0.562 0.571 0.008 0.815 0.543 0.008 0.825 0.050 0.830 0.488 0.495 0.023 0.775 0.469 0.021 0.100 0.795 0.788 0.409 0.424 0.063 0.054 0.756 0.738 0.427 0.200 0.766 0.709 0.370 0.375 0.368 0.173 0.140 0.755 0.736 0.400 0.699 0.360 0.355 0.339 0.314 0.245 0.765 0.735 0.600 0.320 0.479 0.366 0.743 0.696 0.362 0.346 0.800 0.785 0.370 0.342 0.307 0.666 0.756 0.698 0.502 1 .ooo 0.811 0.867 0.738 0.466 0.365 0.280 1.845 1.404 2.000 1.011 0.433 3.295 0.813 0.652 0.281 2.724 1.039 3.000 1.318 0.916 0.967 0.543 0.298 4.866 1.761 1.275 4.555 4.000 0.708 1.048 1.494 0.326 6.428 1.590 7.004 5.000 2.390
y = 1.0
0.001 0.002 0.007 0.019 0.048 0.120 0.205 0.298 0.398 0.988 1.698 2.515 3.439
"The trace activity coefficients of HCl and LaCI3 are given in columns 4 and 5,respectively. The excess enthalpy is given for a quantity of solution containing 1 .O kg of water.
