J. Phys. Chem. B 2002, 106, 2127-2130
2127
The Enthalpy of Formation and C-H Bond Enthalpy of Hydrofullerene C60H36 Svetlana M. Pimenova, Svetlana V. Melkhanova, and Victor P. Kolesov* Department of Chemistry, Moscow State UniVersity, 119899 Moscow, Russia
Anatolii S. Lobach Institute of Problems of Chemical Physics RAS, ChernogoloVka, Moscow Region, 142432, Russia ReceiVed: June 13, 2001; In Final Form: NoVember 12, 2001
The standard molar enthalpy of combustion of hydrofullerene C60H36 was determined by static bomb calorimetry, ∆cH°m ) -(29769 ( 25) kJ‚mol-1. Using this result and the standard molar enthalpy of sublimation, ∆subH°m ) (175 ( 5) kJ‚mol-1, the values of the standard molar enthalpies of formation of C60H36 in the crystalline and gaseous states were calculated: ∆fH°m(C60H36, cr) ) (1013 ( 26) kJ‚mol-1 and ∆fH°m(C60H36, g) ) (1188 ( 26) kJ‚mol-1. The enthalpy of reaction C60H36(g) ) C60(g) + 36 H(g) was found to be (9196 ( 30) kJ‚mol-1, or (255.4 ( 0.8) kJ‚mol-1 per one C-H bond. The enthalpy of reaction C60F36(g) + 36 H(g) ) C60H36(g) + 36 F(g) was calculated, ∆rH°m ) (1421 ( 203) kJ‚mol-1, or (39.5 ( 5.6) kJ‚mol-1 per one H atom. The enthalpies of bond breaking and of F to H replacement were compared with the analogous values in some other organic compounds.
Introduction In recent years, a very great number of chemical derivatives of fullerene C60 have been obtained.1 Unfortunately, only micro quantities of most of them are accessible; for that reason, thermodynamic data for these compounds are very scarce. In our previous papers we reported on the first determination of ∆fH°m of the fluorofullerenes C60F48 and C60F36 and the C-F bond enthalpies in these molecules.2,3 These results allowed us to determine the tendency of the C-F bond enthalpy decrease with the amount of fluorine atoms attached to the fullerene cage.3 The aim of this work was measuring the enthalpy of combustion of hydrofullerene C60H36 and calculating the enthalpy of formation of this compound and the C-H bond enthalpy. Some estimations of the enthalpies of formation of the most stable isomers of C60H36 by semiempirical methods have been made before (∆fH°m(C60H36, g): from 975 to 1456 kJ‚mol-1;4 from 1066 to 1207 kJ‚mol-1;5 from 944 to 1106 kJ‚mol-1;6 from 1029 to 1175 kJ‚mol-1 7), but no experimental data are available. The experimental determination of the enthalpy of formation would also allow, using the reliable thermodynamic data for C60H36 in combination with those for C60F36, to calculate the enthalpy of F for H replacement in these fullerene derivatives and to compare it with the analogous values in some organic compounds. Experimental Section Hydrofullerene C60H36 was prepared by transfer hydrogenation of C60 (purity 99.5 mass percent purity grade) with 9,10dihydroanthracene (purity 99.0 mass percent, supplied by Lancaster Synthesis Ltd). The mixture of C60 and 9,10dihydroanthracene was heated in a glass ampule at (623.2 ( 0.5) K under reduced pressure during 30 min, as described in * Corresponding author. E-mail:
[email protected]. Fax: 7-(095)-932-8846.
ref 8. After cooling, anthracene and its derivatives were removed from the product by vacuum sublimation at T ) 393 K during 10 h. The final product was a light yellow powder and was stored under vacuum until the beginning of calorimetric measurements. Three samples of C60H36 were obtained. The composition and the structure of C60H36 were confirmed by mass-spectrometry, IR, UV, and NMR spectroscopies.5,8,9 In particular, the massspectrum of C60H36 was in a good agreement with a calculated isotope spectrum of C60H36 ion and evidenced the absence of hydrides with the number of hydrogen atoms more than 36,9 as well as C60H18.10 The results of elemental analysis of the samples 1, 2, and 3 (in mass percent) are: (Sample 1) C 95.1, H 4.9; (Samples 2 and 3) C 95.0, H 5.0; (calcd) C 95.2, H 4.8. The content of anthracene was determined by UV and fluorescent spectrometric analyses; it was equal to (0.33 ( 0.10) mass percent, (0.11 ( 0.03) mass percent and (0.11 ( 0.01) mass percent for the samples 1, 2 and 3, respectively. The density of hydrofullerene, F ) 1.67 g‚cm-3 and the value (∂u/∂p)T ) -0.00697 J‚g-1‚MPa-1 were assumed to be close to those of C60.11 The molar mass of C60H36, M ) 756.94584 g‚mol-1, was calculated using the IUPAC Table of Standard Atomic Weights.12 The energy of combustion was measured in a static bomb isoperibol macrocalorimeter. The temperature rise was measured with a copper resistance thermometer and a bridge circuit.13 The uncertainty of the temperature measurements was about 5 × 10-5 K. The energy equivalent ε of the calorimeter was determined by combustion of the thermochemical standard benzoic acid (the sample K-1, supplied by the Russian Research Institute of Metrology) and was equal to (54308.0 ( 7.0) J‚Om-1 in the case of the samples 1 and 2, and (54305.4 ( 7.0) J‚Om-1 in the case of the sample 3. The massic combustion energy of benzoic acid was equal to -(26434.0 ( 2.2) J‚g-1 under the certified conditions at T ) 298.15 K. The correction for small deviation from certified conditions was calculated according to Jessup’s formula.14 The uncertainty of the mean ε value (as well
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2128 J. Phys. Chem. B, Vol. 106, No. 9, 2002
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TABLE 1: Combustion Experiments on Hydrofullerene C60H36 at T ) 298.15 K N
m (g)
m′(g)
ε′‚∆Rc (J)
q(aux) (J)
q(HNO3) (J)
q(s) (J)
-∆cu° (J‚g-1)a
m(CO2, expt)/m(CO2, theor)
6.3 6.2 6.3 6.3
39212.8 39294.9 39250.7 39244.5
0.9993 0.9992 0.9986 0.9994
1 2 3 4
0.042471 0.057544 0.045242 0.046430
0.042250 0.057245 0.045007 0.046189
10548.8 10403.2 10524.0 10588.9
8882.1 8143.9 8747.5 8766.3
Sample 1 3.6 3.6 3.6 3.6
5 6 7 8
0.050880 0.053631 0.056456 0.051673
0.050407 0.053132 0.055931 0.051192
10160.6 10511.7 10473.6 10515.9
8166.9 8412.1 8261.1 8494.7
Sample 2 4.8 4.8 5.1 2.4
5.9 6.0 6.0 6.3
39339.7 39312.9 39358.9 39312.1
0.9981 0.9984 0.9981 0.9984
9 10
0.055833 0.035386
10549.9 10348.8
8345.8 8948.6
Sample 3 2.1 1.8
6.5 6.3
39322.3 39340.1
0.9994 0.9996
a ∆cu°, the standard massic energy of combustion of C60H36 corrected for the contents of anthracene; the energy correction for the anthracene impurity in sample 1 was equal to 1.2 J‚g-1, in the samples 2 and 3 was equal to 0.3 J‚g-1 (the correction is given per gram of C60H36).
TABLE 2: Results and Derived Quantities for C60H36 at 298.15 K
a
-∆cU°m(cr) (kJ‚mol-1)
-∆cH°m(cr) (kJ‚mol-1)
∆fH°m(cr) (kJ‚mol-1)
∆subH°m (kJ‚mol-1)a
∆fH°m(g) (kJ‚mol-1)
S°m (J‚K-1‚mol-1)b
∆fG°m(cr) (kJ‚mol-1)
29747 ( 25
29769 ( 25
1013 ( 26
175 ( 5
1188 ( 26
506.8
1665
The standard enthalpy of sublimation was measured in ref 19. b The entropy was determined in ref 18.
as of ∆cu°, see below) was calculated as (ts, where s is a standard deviation of the mean value and t is a Student’s coefficient at the 0.05 significance level. In the final overall uncertainty of ε given above, the uncertainty in the energy of combustion of benzoic acid was also taken into account. Prior to combustion, the samples of hydrofullerene were pressed into pellets and hermetically sealed in Terylene film bags. The bags were kept in a desiccator under argon until the combustion experiments, to prevent C60H36 from any contact with oxygen or moisture. The preliminary tests showed that combustion of the hydrofullerene in a platinum crucible was complete, even without using any auxiliary substances. Nevertheless, in all subsequent combustion experiments hydrofullerene was burned together with a pellet of benzoic acid, which was needed to produce a suitable temperature rise. The bomb, with 1 cm3 of added water, was charged with purified oxygen to a pressure of 3.04 MPa. The initial temperature did not differ from T ) 298.15 K by more than 0.02 K. Provision for ignition was made using a platinum wire heated by the discharge of a capacitor. After each run, the combustion products were analyzed for carbon dioxide by the Rossini method.14 No soot was observed after combustion experiments. Qualitative tests for CO with indicator tubes were negative within the limits of their sensitivity {mole fraction x(CO) < 1 × 10-6}. Results and Discussion The results of the calorimetric experiments are presented in Table 1, where m denotes the sample mass by weighing; m′, the sample mass calculated from the results of CO2 determination; ε′, the energy equivalent of the calorimeter corrected for heat capacity of the final bomb contents; ∆Rc, the increase in the thermometer resistance corrected for heat exchange; q(aux), the sum of combustion energies of auxiliary substances (benzoic acid and Terylene film); q(HNO3), the correction for the energy of formation of aqueous nitric acid from nitrogen, oxygen, and water; q(s), the correction to standard states; ∆cu°, the standard massic energy of combustion of C60H36 corrected for the contents of anthracene; and m(CO2, expt)/m(CO2, theor), the ratio of the mass of CO2 recovered after the experiment to
the mass of CO2 expected on the basis of the mass of the compound. The standard massic energy of combustion of benzoic acid, ∆cu° ) -(26413.7 ( 2.2) J‚g-1 was derived from the certified value given above. The standard massic energy of combustion of Terylene film, ∆cu° ) -(22927.9 ( 6.3) J‚g-1, and the resulting ratio of the mass of carbon dioxide to that of the film, (2.2897 ( 0.0006), were measured previously.15 For the samples 1 and 2, a noticeable deficiency of carbon dioxide in combustion products was detected: recovery of CO2 was (0.9991 ( 0.0006) and (0.9983 ( 0.0003) for the samples 1 and 2, respectively. In both sets, the energy of combustion was calculated using the sample mass calculated from the results of CO2 determination. As for sample 3, there was no deficiency of carbon dioxide in combustion products: recovery of CO2 was about 0.9995. In this set, combustion energy was calculated using mass measurement. The energy correction for the anthracene impurity in sample 1 was equal to 1.3 J‚g-1, in samples 2 and 3 was equal to 0.3 J‚g-1 (the correction is given per gram of C60H36); the combustion energy of anthracene, -39619.2 J‚g-1, was taken from ref 16. As a result, the corrected massic energy of combustion of C60H36 was equal to -(39251 ( 54) J‚g-1, to -(39331 ( 36) J‚g-1, and to -(39331 ( 113) J‚g-1 for samples 1, 2 and 3, respectively. Although there is a noticeable difference in ∆cu° values obtained for three samples, the statistical analysis with the t-criterion showed that these three sets can be considered as one and the same series of experiments. The average value of ∆cu° calculated for this unified series of 10 runs equals to -(39299 ( 33) J‚g-1. The standard molar energy of combustion of C60H36, ∆cU°m, is equal to -(29747 ( 25) kJ‚mol-1. This value corresponds to the reaction
C60H36(cr) + 69O2(g) ) 60CO2(g) + 18H2O(l)
(1)
The standard molar energy and enthalpy of combustion of C60H36, as well as the standard molar enthalpy and the Gibbs energy of formation values, are listed in Table 2. The values of the enthalpies of formation of CO2(g), H2O(l), and the standard entropy S°m of C(cr, graphite) were taken from ref 17. The standard molar entropy of C60H36 was measured recently by Lebedev et al.18 The enthalpy of sublimation of C60H36 was
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J. Phys. Chem. B, Vol. 106, No. 9, 2002 2129
TABLE 3: Enthalpies of the Gaseous Phase Reactions Per 1 H(g); kJ‚mol-1, at T ) 298.15 K
obtained in ref 19; it was equal to (175 ( 5) kJ‚mol-1 at the temperature 298.15 K. The enthalpy of the reaction
C60H36(g) ) C60(g) + 36H(g)
(2)
was calculated using the enthalpy of formation of C60H36(g) listed in Table 2 and the following values: ∆fH°m(C60, cr) ) (2355 ( 15) kJ‚mol-1,20 ∆subH°m(C60) ) (181 ( 3) kJ‚mol-1,21
and ∆fH°m(H, g) ) (217.998 ( 0.030) kJ‚mol-1.17 The resulting value is ∆rH2 ) (9196 ( 30) kJ‚mol-1, or (255.4 ( 0.8) kJ‚mol-1 per C-H bond. It is interesting to compare this result with the enthalpies of bond breaking in some other organic molecules (see Table 3). The enthalpies of formation used in calculating the C-H bond enthalpies for reactions (3-11) were taken from ref 16. Obviously, the enthalpy of the C-H bond breaking in alkanes and cycloalkanes (reactions 3-8) differs insignificantly. The
2130 J. Phys. Chem. B, Vol. 106, No. 9, 2002 formation of aromatic molecules (reactions 9-11) causes a noticeable decreasing in ∆rH°, due to conjugation effect in benzenoid rings. The enthalpy of the C-H bond breaking in hydrofullerene C60H36 (reaction 2) is close to enthalpies of reactions (9-11). It is known that chemically C60 behaves essentially as an electron-deficient alkene, not as an aromatic hydrocarbon.22 This contrasts with the fact that the C-H mean bond enthalpy in C60H36 is more similar to the C-H mean bond enthalpies defined by reactions (9-11) than to those defined (3-8). Enthalpies of some reactions of F for H replacement are also presented in Table 3. It was shown in ref 24 that fluorofullerene C60F36 consists of two major isomer having structures T and C3, and that these are almost certainly the isomers present in C60H36. The determination of the enthalpy of formation of C60H36 enabled us to calculate the enthalpy of substitution of F by H in C60F36, using the values ∆fH°m(C60F36, g) ) -(5223 ( 201) kJ‚mol-1,3 ∆fH°m(F, g) ) (79.38 ( 0.30) kJ‚mol-1,17 and basing on the assumption that fluorofullerene C60F36 and hydrofullerene C60H36 are isostructural (see Table 3). The enthalpies of analogous reactions calculated for some other compounds are also shown in this table. The comparison of the enthalpies of reactions (12-15) shows that the enthalpy of F to H replacement in going from C60F36 to C60H36 is also closer to analogous replacement in hexafluorobenzene than in other cyclic compounds. Acknowledgment. This research was supported by the Russian Foundation for Basic Research (Grants 00-03-32623 and 00-15-97346) and by MNTP “Fullerenes and Atomic Clusters”. References and Notes (1) The Chemistry of Fullerenes; Taylor, R., Ed.; World Scientific: Singapore, 1995. (2) Papina, T. S.; Kolesov, V. P.; Lukyanova, V. A.; Boltalina, O. V.; Galeva, N. A.; Sidorov, L. N. J. Chem. Thermodyn. 1999, 31, 1321.
Letters (3) Papina, T. S.; Kolesov, V. P.; Lukyanova, V. A.; Boltalina, O. V.; Lukonin, A. Yu.; Sidorov, L. N. J. Phys. Chem. B 2000, 104, 5403. (4) Bakowies, D.; Thiel, W. Chem. Phys. Lett. 1992, 193, 236. (5) Okotrub, A. V.; Bulusheva, L. G.; Asanov, I. P.; Lobach, A. S.; Shulga, Yu. M. J. Phys. Chem. A 1999, 103, 716. (6) Buhl, M.; Thiel, W.; Schneider, U. J. Am. Chem. Soc, 1995, 117, 4623. (7) Popov, A. A.; Senyavin, V. M.; Granovsky, A. A.; Lobach, A. S. The 199th Meeting of the Electrochemical Society, Washington. Meeting Abstracts, 2001. Abs. No. 713. (8) Lobach, A. S.; Perov, A. A.; Rebrov, A. I.; Roshchupkina, O. S.; Tkacheva, V. A.; Stepanov, A. N. IzV. Akad. Nauk, Ser. Khim. 1997, 46(4), 671-677. (Russ. Chem. Bull. 1997, 46, 641). (9) Lobach, A. S.; Shul’ga, Yu. M.; Roshchupkina, O. S.; Rebrov, A. I.; Perov, A. A.; Morozov, Yu. G.; Spector, V. N.; Ovchinnikov, A. A. Full. Sci. Technol. 1998, 6, 375. (10) Vasil’ev, Yu.; Wallis, D.; Nu¨chter, M.; Ondruschka, B.; Lobach, A.; Drewello, T. J. Chem. Soc., Chem. Commun. 2000, 1233-1234. (11) Diogo, H. P.; Minas da Piedade, M. E.; Dennis, T. J. S.; Hare, J. P.; Kroto, H. W.; Taylor, R.; Walton, D. R. M. J. Chem. Soc., Faraday Trans. 1993, 89, 3541-3544. (12) IUPAC Commission on Atomic Weights and Isotopic Abundances. Pure Appl. Chem. 1996, 68, 2339. (13) Skuratov, S. M., Goroshko, N. N. Izmer. Tekh. 1964, 2, 6. (14) Experimental Thermochemistry; Rossini, F. D., Editor; Wiley Interscience: New York, 1956. (15) Papina, T. S., Kolesov, V. P. Zh. Fiz. Khim. 1985, 59, 2169. (16) Pedley, J. B.; Naylor, R. D.; Kirby, S. R. Thermochemical Data of Organic Compounds, 2nd ed.; Chapman and Hall: London, 1986. (17) Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Recommended Key Values for Thermodynamics; Hemisphere: New York, 1989. (18) Lebedev, B. V.; Bykova, T. A.; Lobach, A. S. J. Therm. Anal. 2000, 62, 257. (19) Dorozhko, P. A.; Lobach, A. S.; Popov, A. A.; Senyavin, V. M.; Korobov, M. V. Chem. Phys. Lett. 2001, 336, 36. (20) Kolesov, V. P.; Pimenova, S. M.; Pavlovich, V. K.; Tamm, N. B.; Kurskaya, A. A. J. Chem. Thermodyn. 1996, 28, 1121. (21) Piacente, V.; Gigli, G.; Scordala, P.; Giustini, A.; Ferro, D. J. Phys. Chem. 1995, 99, 14052. (22) Fullerenes: chemistry, physics, and technology; Kadish, K. M.; Rodney, S. R., Eds.; John Wiley & Sons: New York, 2000; Chapter 3. (23) Zhogina, E. V.; Papina, T. S.; Kolesov, V. P.; Mel’nichenko, B. A.; Zapol’skaya, M. A.; Prokudin, I. P. Zh. Fiz. Khim. 1987, 61, 2890. (24) Boltalina, O. V.; Buhl, M.; Khong, A.; Saunders, M.; Street, J. M.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1999, 1475.
