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Literature Cited API Research Project No. 44, 1974. Bhinde, M. Ph.D. Dissertation, Unlversity of Delaware, 1979. Breck, D. W. “Zeoilte Molecular Sieves”; Wlley: New York, 1974. Draper, N. R.; Smith, H. “Applied Regression Analysis”; Wiley: New York, 1966. Flock, W.; Kuznekov. J. I.; Hofmnn, J.; Beskov, W. S. Chem. Techno/. 1978, 28, 130. Froment, G. F. AIChE J. 1975, 21, 1041. Froment G. F.; Blschoff, K. 8. “Chemical Reactor Analysis and Design”; Wiley: New York, 1979. Gates, B. C.; Katzer, J. R.; Schuit, G. C. A. “Chemistry of Catalytic Processes”: McGraw-Hill: Englewood Cliffs, NJ, 1979. Hosten, L. H.; Froment, G. F. Ind. Eng. Chem. ProcessDev. 1971, 70, 280. Himmelblau, D. M.; Jones, C. R.; Bischoff, K. 8. Ind. Eng. Chem. fundam. 1887, 6, 541. Klrell. J. R. Adv. Chem. Eng. 1970, 8, 97. Lo, H. S. Ph.D. Dissertation, University of Delaware, 1981. Santacesaria, E.; Morbidelli, M.; Danise, P.; Mercenari, M. Carra, S. Ind. Eng. Chem. Process Des. Dev. 1982, 21, 440.
Steijns, M.; Froment, G. F.; Jacobs, P. A.; Uytterhoeven, J.; Weitkamp, J. ErdiilKohle-Erdges-Petrochem. 1978, 31, 581. Steijns, M.; Froment, G. F.; Jacobs, P. A.; Uytterhoeven, J.; Weitkamp, J. Ind. Eng. Chem. Prod. Res. Dev. 1981. 20,654. Steijns, M.;Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 660. Sinfelt, J. H. A&. Chem. Eng. 1984, 5, 37. Sternes, W. C.; Zabor, R. C. Symposium, Division of Petroleum Chemistry, American Chemical Society, Boston, MA, April 5-10, 1959. Thinh, T. R.; Duran, J. L.; Ramalho, R. S.; Kaiiaguine, S. Hydrocarbon Process. Jan 1971, 98. Vansina, H.; Baltanas, M. A.; Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1983, preceding paper of this issue. Weitkamp, J.; Schuiz, H. J . Catal. 1973, 29, 361. Weitkamp, J.; Jacobs, P. A. Award Symposium on Fundamentals of Catalysis and Thermal Reactions, 181st National Meeting of the American Chemical Society, Atlanta, GA, March 29-April 3, 1981.
Received for review March 7, 1983 Accepted June 20,1983
Catalytic Hydrogenation of Nitrobenzene by Use of a Mixture of Carbon Monoxide and Water Yasuhlro Takemura’ and Klyoshl Onodera College of Education, Akita University, Akita 0 10, Japan
Kojl Ouch1 Faculty of Engineering, Hokkaido University, Sapporo 080, Japan
Catalytic hydrogenation of nitrobenzene was performed by using a mixture of CO and H,O under atmospheric pressure at 300 and 350 O C . Among the various catalysts, alumina-supported iron oxide catalyst shows the highest activity for this reaction. An addition of the optimum quantity of potassium cation brings about a considerable increase in the surface area of the catalyst and its activities for either hydrogenation of nitrobenzene or the water gas shift reaction. The reactions were also carried out on the various-alkali cations-added iron oxide catalyst. A s in the case of potassium-added catalyst, additions of alkali cations bring about an increase in the surface areas of the catalysts and in their activities. At the same concentration of metal cations, the order of the promotion effect observed is Cs > Rb > K > Na > Li. Cesium-added catalyst has a maximum surface area and shows the largest conversion in this series.
Introduction Appell et al. (1968, 1969, 1976, 1977) studied hydrogenolysis of various organic substances, such as carbohydrates and lignite, using CO plus H20. They used Na2C03 as a catalyst and proposed that Na2C03reacts with H 2 0 to form a basic medium which interacts with CO to give the formate ion: subsequent decomposition of formate ion gives the nascent hydrogen which reduces the organic substances. The process has been named “Costeam”. However, the reaction mechanism of the Costeam process is not fully understood and, hence, a possibility of development of new efficient catalysts still remains. For the purpose of finding a catalyst suitable for the hydrogenation and hydrogenolysis process by the use of CO and H20, we (Takemura et al., 1981) have performed hydrogenolysis of diphenylmethane on the various catalysts. Through this work, alumina-supported molybdenum oxide catalyst was found to be most effective. Furthermore, it seemed that the catalyst available for hydrogenolysis of the C-C bond in the Costeam process is responsible not only for promoting the water gas shift reaction (WGSR) but also for promoting the subsequent hydrogenolysis. Our present work was undertaken to study an
application of the Costeam process to hydrogenation of nitro compounds on the basis of our above mentioned paper. Experimental Section Apparatus, Procedure, a n d Analyses. All reactions were carried out by using a conventional flow system with a fixed bed of catalyst under atmospheric pressure a t 300 and 350 “C. A stainless steel (SUS316) tubular reactor (15.0 mm i.d., 400 mm length) surrounded with an electric heater was used. Nitrobenzene, CO, and H 2 0 were fed at constant feed rates into the evaporator kept at 250 OC and then a mixture of the reactants was led to the catalyst bed. The liquid product was trapped in an ice-water trap and analyzed every 5 min during the course of the reaction. The gaseous product passed through the trap was also collected and analyzed a t the same regular intervals as in the case of the liquid product. The liquid and gaseous product were analyzed respectively by gas chromatography and mass spectroscopy when needed. In a later section, discussions will be presented on the percent conversion of nitrobenzene, aniline yield, and the extent of the WGSR which was calculated from the ratio of CO to COz in the gaseous product on the assumption
0196-4321/83/1222-0539$01.5~/0 0 1983 American Chemical Society
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Table I. Activities of Various Catalysts at 350 "Ca conv of nitrobenzene,b
-
aniline yield,b
cat.
%
%
Fe/Al MOO,( 17)/A1 Co0(20)/A1 W03(15)/A1
99.4 44.0 34.2 18.0
95.1 42.1 34.2 18.0
a Feed rate: nitrobenzene, 1.22 x lo', mol min-'; CO, 4.48 X lo-, mol min-' ; H,O,9.23 X mol min-' ; catalysts charged: 2.5 g. The values from 5 to 1 0 min after runs starting.
that the amount of C 0 2 produced by the WGSR is equivalent to that of CO consumed. Material balance of both the liquid and gaseous substances were usually more than 95%, respectively. Materials. Catalysts used were prepared by the following procedure: 5.06 g of Fe(N03)2.9H20was dissolved in 100 mL of H20. To this solution was added 3 g of granular alumina (20-100 mesh size). The resulting mixture was stirred thoroughly for 72 h and then dried in air a t 120 "C. The catalyst precursor thus prepared was calcined in air at 500 "C for 2 h. The concentration of iron oxide, in the form of Fe203,was 25 w t %. This catalyst is designated by Fe/A1. In addition to this catalyst, two series of catalysts were prepared: (1) potassium carbonate-added Fe/A1, designated by Fe/K(a)/Al, and (2) various-alkali carbonates-added Fe/A1, designated by Fe/Li(P)/Al, Fe/Na(P)/Al, Fe/Rb(P)/Al, and Fe/Cs(P)/ Al, respectively, where a and P in the parentheses denote the number of alkali metal atoms per 100 Fe atoms. The addition of each alkali carbonate to Fe/A1 was performed by the use of impregnation solution of the corresponding alkali carbonate. Steps subsequent to impregnation included drying in air a t 120 "C and calcination a t 500 "C for 2 h. Furthermore, potassium carbonate-added alumina in the absence of iron oxide, designated by K/Al, was prepared by an impregnation solution of K2C03,drying at 120 "C, and calcination at 500 "C for 2 h. Concentration of potassium in K/A1, as in the form of K2C03,was 25 wt % . Otherwise, we prepared alumina-supported molybdenum, tungsten, and cobalt oxide catalysts. Their preparation method was the same as that for Fe/Al. As substances for impregnations, ammonium paramolybdate, ammonium tungstate, and cobalt nitrate were used, respectively. These catalysts are designated by Moo8(17)/Al, Wo3(15)/A, and C00(20)/Al, respectively, where the figures in the parentheses are mole percentage of each metal oxide in the catalyst. The preparation method of alumina used throughout in this work has been described previously (Takemura et al., 1981). The surface areas of the catalysts and their related substances were determined by the BET method using nitrogen at 77 K. Nitrobenzene was high-purity grade commercially available reagent and was purified by single distillation before use. CO of research grade was used without purification.
Results and Discussion Table I shows the conversion results of nitrobenzene on the various kinds of catalysts. The order of activity for hydrogenation is Fe/Al >> MoO3(17)/A1> Co0(20)/Al> WO3(15)/A1and this order is consistent with that for the WGSR (Takemura et al., 1981). Therefore, in this work only a series of alumina-supported iron oxide catalysts were examined in detail, aiming a t the development for the catalyst being active and less costly. In Figure 1, percent conversion of nitrobenzene on Fe/Al, potassium cation-added Fe/A1, K/A1, K2C03,and
3
20
10
30
40
TIME(min )
Figure 1. Changes in catalytic activities with time (temperature: 300 "C; feed rates: nitrobenzene, 1.22 X mol min-'; CO, 4.48 X mol min-'; HzO, 9.23 X mol m i d ; catalyst charged: 2.5 9).
1
0 0
20
40
60
NUMBER OF K ATOMS PER 100 Fe ATOMS
Figure 2. Relationship between number of potassium atoms per 100 iron atoms in Fe/K/Al and the catalytic activity at 30 min on stream. (Key of reaction conditions: see Figure 1.)
alumina are plotted as functions of time. After 5 min on stream, percent conversion of nitrobenzene and aniline yield on Fe/Al were 94.0 and 86.4%, respectively. The predominant liquid products besides aniline were azobenzene and azoxybenzene,which are considered to be side products. However, the activity of Fe/A1 rapidly declined with time, and after 35 min, ita percent conversion reached only 5.8%. On the other hand, Fe/K(30)/Al and Fe/K(40)/A1 maintained their high activities during the runs. Fe/K(30)/A1 showed the highest percent conversion of nitrobenzene and aniline yield. Even after 35-40 min on stream, 91.8% aniline yield was obtained. Fe/K(50)/Al exhibited a slight decrease in activity with time. On Fe/Al and potassium-added Fe/Al except Fe/K(30)/Al and Fe/K(40)/Al, at 35 min on stream, the main liquid products were aniline and phenyl isocyanate, existence of which suggests that the reduction of nitrobenzene with CO predominantly takes place due to the lack of hydrogen produced by the WGSR (Hardy et al., 1967). The activity measurement for K2C03,alumina, and K/A1 showed that these substances practically have no catalytic activities for this reaction system. Figure 2 shows the relationship between the number of potassium atoms per 100 iron atoms in Fe/K/Al and the catalytic activity at 30 min on stream. In Table I1 are shown the specific surface areas of the catalysts and their activities. It is found that aniline yield began at 31.6% at Fe/Al, passed across a maximum, 90.7%
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 541
Table 11. Catalysts and Their Activities at 300 "C (Reaction Conditions Were the Same as Those Shown in Table 1.) extent of surface aniline yield,a WGSR,a area, cat. mz/g % % 18.1 Fe/Al 308 31.6 17.9 Fe/K(5)/Al 327 33.0 22.6 Fe/K( 10)/A1 325 46.7 24.5 Fe/K(20)/A1 305 40.9 66.5 Fe/K(30)/Al 430 90.7 60.8 Fe/K(40)/A1 259 86.3 255 77.2 46.8 Fe/K(50)/AI 14.4 Fe/K(67)/A1 161 15.2 136 0.9 0.8 A1203 K2CO 3 K/A1
-
3.4
3.2
6.5 3.1 a The values from 25 to 30 min after runs starting. The values from 5 to 10 min after runs starting. 146
a t Fe/K(30)/Al, and then lowered. The extent of the WGSR also shows the same tendency. Evidence presented in Figure 1 and Table I1 suggests that the addition of potassium cation to Fe/A1 enhances its catalytic activity for the hydrogenation of nitrobenzene and the WGSR. High percent conversion of nitrobenzene was given on the catalysts to which the optimum quantity of potassium cation was added, such as in the case of Fe/K(30)/Al. This is due to the fact that on this catalyst the larger amount of hydrogen available for the hydrogenation of nitrobenzene is generated from the WGSR. As already shown, Fe/K(30)/Al and Fe/K(40)/Al exhibited the long catalytic lives. The crystallographic structures of Fe/A1 and Fe/K(40)/A1 were examined by means of the usual X-ray diffraction technique. Otherwise, the reducibilities of both the catalysts were studied by measuring the changes in their weight under the reaction atmosphere in the absence of nitrobenzene a t 300 "C. In the case of Fe/A1 before reduction, only the weak and broad diffraction lines of Fe304spinel structure were observed. Fe/K(40)/Al before reduction also showed the Fe304structure. However, its diffraction lines were much weaker in strength and broader than those of Fe/A1. These facts may reveal that an addition of potassium cation prevents the crystallization of iron oxide in the catalyst during calcination. Furthermore, the larger part of the iron oxide in these catalysts seems to be in an amorphous state. The percentages of reduction of iron oxide in Fe/A1 under the reductive atmosphere at 300 "C attained values of 7.0 wt % for 2 h reduction and 13.5 wt % for 12 h reduction, respectively. This indicates that a large part of the iron oxide a t and near the surface was reduced to a considerable extent. Nevertheless, no metallic iron was detected by X-ray diffraction. Therefore, metallic iron may be very fine in size, even if it exists in the catalysts. In the case of Fe/K(40)/Al, the percentages of reduction reached values of 6.6 wt % for 2 h reduction and 12.6 wt % for 12 h reduction, respectively. Also in the reduced Fe/K(40)/Al, no metallic iron was detected by X-ray diffraction. Differential thermal analysis of Fe/K(30)/Al before calcination at 500 "C showed neither endothermic or exothermic peak from 120 to 520 "C except for the peak a t about 180 "C due to desorption of H 2 0 therefrom. Furthermore, the difference of the sample weight between Fe/K(30)/Al before and after calcination at 500 "C for 2 h was only a 2.6% decrease. This indicates that decomposition of potassium carbonate practically does not occur during the calcination. Therefore, it is claimed that the chemical state of the potassium on the catalyst surface is K2C03.
Table III. Conversions of Nitrobenzene on the Various-Alkali Cations-Added Catalysts at 300 "C (Reaction Conditions Were the Same as Those Shown in Table I.) surface aniline extent of yield,a WGSR; area, cat. m'/g % % 4.4 Fe/Li(20)/A1 233 0. I 249 11.8 9.3 Fe/Na(20)/A1 Fe/Al 308 31.6 18.1 24.5 Fe/K( 20)/A1 305 40.9 41.2 Fe/Rb(20)/A1 265 57.3 Fe/Cs(20)/A1 333 81.2 47.4 a The values from 2 5 to 30 min after runs starting. The promoting effect of alkali addition upon the iron oxide catalyst, such as those for F-T and ammonia syntheses, has been known for the past more than half a century (Anderson, 1956). Since then, many researchers have tried to elucidate the nature of this promoting effect. An explanation derived therefrom is that alkali, such as K20,does advantageously modify the chemical nature of the catalyst both for the F-T and ammonia syntheses (Anderson, 1956). Morikawa et al. (1972) and Chesnokova et al. (1970) reported that K 2 0 in Fe-A120,-K20 catalyst facilitates the dissociative adsorption of nitrogen molecule on iron metal in the case of the ammonia synthesis and results in an increase in the rate of ammonia formation. This promoting effect seems to be fundamentally due to the electron-donating ability of alkali (Dry et al., 1969; Ozaki et al., 1971; Aika et al., 1973). As shown in Table 11, the addition of the optimum quantity of potassium cation brought about a considerable increase in catalytic activities for either nitrobenzene conversion or WGSR. This is primarily due to the increase in the surface area (Uemura, 1962). As mentioned above, Fe/A1 rapidly loses its activity with time on stream. This is considered to be mainly due to the deposition of carbonaceous matter which covers active surface of the catalyst and crystallizes gradually with the lapse of time. However, on the potassium cation-added catalyst, WGSR serves to maintain a carbon-free surface of the catalyst. As a result, the lifetime of the catalyst is elongated. We detected methane for each run, but its amount was so small that we were not able to discuss the extent of carbonaceous matter formed on the basis of the amount of methane detected. Royen and Erhard (1953) studied the WGSR at 200 " C under atmospheric pressure on potassium carbonate impregnated on charcoal, and they postulated that the WGSR proceeds according to K2C03 + 2CO + H20 2HCOOK + C02 -+
2HCOOK
+ H2O -,K&03 + C 0 2 + 2H2
Furthermore, they postulated that these reactions also take place on the alkali-promoted iron catalysts. Recently, the WGSR has been examined on the potassium cation-impregnated alumina catalyst (Krupay and Amenomiya, 1981;Amenomiya and Pleizer, 1982). They concluded that formate ion formed on potassium cations is an intermediate product of the WGSR surface formate is equilibrated with the reactants and the rate of WGSR is proportional to the concentration of formate: subsequent decomposition of the formate gives hydrogen. In Table I11 are presented the reaction results of nitrobenzene conversion on the various-alkali cations-added catalysts. As in the case of Fe/K/Al, addition of alkali cations brought about an increase in the surface areas of the catalysts and in their activities. Fe/Cs/Al has a
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Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 542-548
maximum surface area and shows the largest conversion in this series. The order of the promotion effect (Cs > Rb > K > Na > Li) observed in this study has been the reverse tendency against the order in ionization potential of these cations (Lee et al., 1963). This means that the electrondonating character of alkali plays an important role in promoting effect as reported by Dry et al. (1969), Ozaki et al. (1971), and Aika et al. (1973). On the other hand, the evidence shown in Table I11 may be explained by the hard and soft acids and bases concept. Even though NO2is a "border line base", nitrobenzene would interacts with "hard acids". The degree of interaction between nitrobenzene and hard acid may be inversely proportional to the hardness of acid. The order of hardness of alkali cations is Li > Na > K > Rb > Cs which is in reverse order for the promoting effect found in this work. Therefore, it is considered that the catalystshaving high activity, such as Fe/Cs/Al and Fe/Rb/Al, strongly interact with nitrobenzene due to the hard acid character of these cations (Ho, 1977). As mentioned above, through our previous work (Takemura et al., 1981), it seemed that the catalyst, available for hydrogenolysis of C-C bond with Costeam process, is responsible not only for promoting the WGSR but also for promoting the subsequent hydrogenolysis, and aluminasupported molybdenum oxide catalyst was found to be most effective. However, in the present work, aluminasupported iron oxide catalyst showed much higher activity for reduction of nitrobenzene than that of alumina-supported molybdenum oxide catalyst. Therefore, it is considered that the catalyst effective for the reduction of nitro compound with Costeam process is responsible only for promoting the WGSR. This may be due to the high re-
activity of nitro compounds toward hydrogen. Acknowledgment
The authors express their gratitude to Dr. A. Nakamura, Akita University, for helpful discussions and advice. Registry No. Fe, 7439-88-5; Moo3, 1313-27-5;COO, 1307-96-6; W03, 1314-35-8;CO, 630-08-0;A1203,1344-28-1;KzCO3, 584-08-7; Li', 17341-24-1;Na+,17341-25-2;K+, 24203-36-9;Rb+, 22537-38-8; CS', 18459-37-5;H,O, 7732-18-5;nitrobenzene,98-95-3;aniline, 62-53-3. L i t e r a t u r e Cited Aika, K.; Yamaguchi, J.; Ozaki, A. Chem. Lett. 1973, 161. Amenomiya, Y.; Pleizier, G. J. Catal. 1982, 7 6 , 345. Anderson. R. B. "Catalysis", Emmett, P. H., Ed.; Reinhold: New York, 1956; pp 29-256. Appell, H. R.; Wender, I. Am. Chem. Soc., Div. FuelChem., Prepr. 1968,
12(3),220. Appell, H. R.; Wender, I.; Miller, R. D. Chem. Ind. (London) 1969, 1703. Appell, H. R.; Wender, I.; Miller, R. D. Am. Chem. Soc., Div. Fuel Chem ., Prepr. 1969, 13(4),39. Appell, H. R.; Pantages, P. "Thermal Uses and Properties of Carbohydrates and Lignins"; Academic Press: San Francisco, 1976;p 127. Appell, H. R.; Moroni, E. C.; Miller, R. D. Energy Source 1977, 3(2), 163. Chesnokova, R. V.; Gorbunov, A. I.; Lachinov. S. S.; Maravskaya, G. K. Kinet. Katal. 1970, l l , 1486. Dry, M. E.; Shingles, T.; Boshoff, L. J.; Oosthuijzen, G. J. J . Catal. 1969, 75, 190
Hardy: W. B.; Bennett, R. P. Tetrahedron Len. 1967, (ll),961. Ho, T-L. "Hard and Soft Acids and Bases Principles in Organic Chemistry"; Academic Press: New York, 1977;pp 5-6. Krupay, B. W.; Amenomiya, Y. J. Catal. 1981, 7 6 , 345. Lee, E. H.; Holmes, L. H. J. Phys. Chem. 1963. 6 7 , 947. Morikawa, Y.; Ozaki, A. Nippon Kagaku Kaishi 1972, (6),1023. Ozaki, A,; Aika, K.; Hori, H. Bull. Chem. SOC.Jpn. 1971, 44, 3216. Royen, P.; Erhard, F. Erdoel Kohle 1953, 6 , 195. Takemura, Y.; Itoh, H.; Ouchi, K. Ind. Eng. Chem. Fundam. 1981, 20,94. Umemura, S. Shokubai 1962, 4 , 223.
Received f o r review March 31, 1983 Accepted August 9, 1983
Methanol to Ethanol by Homologation: Kinetic Approach Patrick 6. Franqolsse and Fernand C . Thyrion' Institut de G n i e Chimique, Universit6 Catholique de Louvain, Voie Minckelers, 1, 6-1348 Louvain-la-Neuve, Belgium
A kinetic study is reported for the homologation of methanol to give ethanol. Cobalt carbonyl and iodine or cobalt iodide were used as catalyst systems with tri-n-butylphosphine as ligand. The reaction was investigated in 1,Mioxane in a batch unit at (CO H2)pressures between 3 and 15 MPa, with HJCO ratios in the range of 0.33 to 3. The temperature was varied over the range of 150 to 210 OC. The reaction rate was found to be first order with respect to methanol and cobalt concentrations and CO partial pressure. A rate expression is derived. A reaction mechanism is proposed in which the rate-determiningstep is suggested to be the reaction of methanol with a CO-rich cobalt complex existing in low concentration with regard to cobalt used.
+
Introduction
The cobalt-catalyzed homologation of methanol to ethanol has been the subject of many recent papers and patents (Bahrmann and Cornils, 1980, 1982; Ball and Stewart, 1981; Barlow, 1981; Cornils et al., 1982a,b; Deluzarche et al., 1978, 1979; Doyle, 1981a,b,c; Dumas et al., 1980; Fiato, 1980, 1981a,b; Gane and Stewart, 1979a,b, 1980a,b; Gauthier-Lafaye and Perron, 1981; Isogai et al., 1980, 1982; Koermer and Slinkard, 1978; Pretzer and Kobylinski, 1980; Pretzer et al., 1979, 1980a,b,c; Slinkard and Baylis, 1979; Sugi et al., 1981; Taylor, 1978; Walker, 1981). However, very few authors have dealt with systematic kinetic measurements.
The purpose of this paper is to investigate the influence of the main reaction parameters, to derive reaction orders, rate constants, and activation energy, and to postulate a mechanism for the methanol homologation. Though the overall equation is quite simple
catalyst
CH30H + CO + 2H2 C2H,0H + H 2 0 (1) the mechanism of this reaction appears to be much more complex (Slocum, 1980). This is particularly true if iodides are used as promoters and phosphines as ligands to stabilize the cobalt catalytic species (Berty et al., 1956; Mizoroki and Nakayama, 1964; Slaugh, 1976; Pretzer and Kobylinski, 1980; Bahrmann and Cornils, 1982). 1983 American Chemical Society
