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Ind. Eng. Chem. Res. 2009, 48, 10120–10128
Re-investigation and Data Assessment of the Isomerization and 2,2′-Cyclization of Stilbenes and Azobenzenes† Heiko K. Cammenga TU Braunschweig, Institut fu¨r Physikalische Chemie, Hans-Sommer-Strasse 10, D-38106 Braunschweig, Germany
Vladimir N. Emel’yanenko and Sergey P. Verevkin* Institut fu¨r Chemie, Abt. Physikalische Chemie, UniVersita¨t Rostock, Dr.-Lorenz-Weg 1, D-18059 Rostock, Germany
The energetics and kinetics of the thermal and photochemical cis/trans-isomerization of azobenzenes and stilbenes are of fundamental interest to physical organic chemistry, because they may serve as “reference reactions” for the various theoretical and computational methods. The same applies to the 2,2′-cyclization of these compounds to benzo(c)cinnolines and phenanthrenes. Although many investigations have been devoted to this topic, a wide variety of energetic data for these fundamental processes can be found in the literature. This paper presents both a compilation and assessment of all data hitherto published and a consistent data redetermination for these fundamental processes. 1. Introduction
2. Experimental Section
Azo compounds are important dyes, and many stilbenes are used extensively as optical brighteners. Azo compounds and stilbenes exhibit cis/trans-isomerism, which is of fundamental interest in physical organic chemistry. In addition, these processes have found applications among others in actinometry, energy conversion, information storage, and photochemical molecular switching devices. Further, the thermodynamics and kinetics of these clear-cut cis/trans-isomerization reactions together with the standard enthalpies of formation (of the compounds in their gaseous phase) and activation (to the transition state) may serve as “calibration means” or consistency proof for the many computational methods of theoretical organic chemistry. This also applies to the cyclization of the compounds mentioned to benzo[c]cinnolines or phenanthrenes. Many data, experimental and theoretical, on all of these processes have over the years been published in the literature, however, with a broad scatter of results. Thus, it seemed appropriate and necessary to us, as well, to compile and assess the many existing data as to redetermine all the pertinent data with ultimate care using highly purified materials. From kinetic and additional investigations, it became evident that isomerization of azobenzenes occurs via an inversion and that of stilbenes via a rotational mechanism around the central bond in these molecules. Due to the steric hindrance of the H-atoms (or substitutes) in 2,2′-position to the central double bond, the cis-compounds are not planar but become only very nearly so after isomerization to the transisomers. Kinetic studies have demonstrated that the Gibbs energy (but not the enthalpy!) of activation to the transition state is practically constant and independent of the state of aggregation in which the isomerization reaction takes place, which strongly suggests that the mechanism is the same in whatever state of aggregation the reaction takes place.1-3
2.1. Materials. The samples of stilbenes (purchased from Aldrich) having a mass-fraction purity of about 0.99 were purified by repeated distillation in vacuum (for cis-isomer) or fractional sublimation (for trans-isomer). The solid sample of benzo[c]cinnoline (purchased from Aldrich) was purified by zone melting followed by high-vacuum sublimation. Examination of the samples using GC showed no discernible amounts of impurities. The products were analyzed with a HewlettPackard gas chromatograph 5890 Series II equipped with a flame ionization detector and Hewlett-Packard 3390A integrator. Carrier gas (nitrogen) flow of 12.1 cm3 · s-1. Capillary column HP-5 (stationary phase cross-linked 5% PH ME silicone); column length, inside diameter, and film thickness 25 m × 0.32 mm × 0.25 µm. The standard temperature program of the GC was T ) 323 K, followed by a heating rate of 0.167 K · s-1 to T ) 523 K. 2.2. Thermochemical Measurements. Transpiration Method. Vapor pressures, enthalpies of vaporization, ∆gl Hm, g Hm, of stilbenes were deterand enthalpies of sublimation, ∆cr mined by using the method of transference in a saturated stream of nitrogen. The method has been described before4,5 and has proven to give results in agreement with other established techniques for determining vapor pressures and enthalpies of vaporization of pure substances from the temperature dependence of the vapor pressure. About 0.5 g of the sample was mixed with glass beads and placed in a thermostatted U-tube of length 10 cm and diameter 0.5 cm. A preheated nitrogen stream was passed through the U-tube at constant temperature ((0.1 K). The flow rate of the nitrogen stream was measured using a soap bubble flow meter ((0.2-0.3%) and optimized in order to reach the saturation equilibrium of the transporting gas at each temperature under study. We tested our apparatus at different flow rates of the carrier gas in order to check the lower boundary of the flow below which the contribution of the vapor condensed in the trap by diffusion becomes comparable to the transpired one. In our apparatus, the contribution due to diffusion was negligible at a flow rate down to 0.5 dm3 · h-1. The upper limit for our apparatus was at a flow rate of 7.5 dm3 · h-1. Thus, we carried out the experiments in the flow rate interval of
† Paper dedicated to Prof. Dr. Christoph Ru¨chardt (University of Freiburg) on the occasion of his 80th birthday. * To whom correspondence should be addressed. E-mail:
[email protected].
10.1021/ie900800q CCC: $40.75 2009 American Chemical Society Published on Web 08/31/2009
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Table 1. Results from Measurements on the Stilbenes Using the Transpiration Method Ta (K)
mb (mg)
V(N2)c (dm3)
gas flow (dm3/h)
pd (Pa)
(pexp - pcalc) (Pa)
g ∆cr Hm or ∆lgHm (kJ · mol-1)
g trans-stilbene ∆cr Hm(298.15 K) ) 101.95 ( 0.41 kJ · mol-1
ln(p/Pa) ) 336.62/R - 112 680.27/(R(T,K)) - (36.0/R) ln((T,K)/298.15) 324.3 328.6 331.1 333.9 336.6 339.3 341.5 344.3 346.5 349.3 351.5 354.5 356.4 359.1 361.3 361.9 364.3 366.2 367.0
0.34 0.37 0.35 0.38 0.34 0.32 0.34 0.53 0.35 0.38 0.37 0.34 0.38 0.42 0.44 0.37 0.38 0.35 0.65
24.9 16.3 11.8 9.13 6.35 4.55 3.73 4.24 2.26 1.91 1.48 1.06 0.988 0.832 0.702 0.572 0.441 0.368 0.624
4.98 4.64 4.64 4.35 4.48 4.48 4.48 4.24 4.24 4.24 4.24 4.24 1.56 1.56 1.56 1.56 1.47 1.47 1.56
0.18 0.31 0.40 0.56 0.73 0.95 1.23 1.71 2.09 2.74 3.38 4.44 5.29 6.83 8.56 8.82 11.74 12.85 14.12
0.00 0.00 0.00 0.01 -0.01 -0.03 0.00 0.07 0.04 0.04 0.01 -0.06 -0.09 -0.11 0.07 -0.16 0.58 -0.39 -0.10
101.01 100.85 100.76 100.66 100.56 100.47 100.39 100.29 100.21 100.11 100.03 99.92 99.85 99.75 99.68 99.65 99.57 99.50 99.47
cis-stilbene ∆lgHm(298.15 K) ) 70.49 ( 0.37 kJ · mol-1 ln(p/Pa) ) 324.34/R - 97 199.85/(R(T,K)) - (89.6/R) ln((T,K)/298.15) 308.3 310.2 313.3 315.4 318.2 320.4 323.2 325.2 328.3 330.2 333.2 335.3 338.3 340.3 343.2
0.84 0.74 0.74 0.94 0.73 0.90 0.75 0.76 0.74 0.78 0.72 0.78 0.77 0.76 0.75
5.60 4.17 3.17 3.28 2.08 2.08 1.42 1.25 0.974 0.864 0.658 0.594 0.486 0.405 0.324
4.80 5.00 5.00 4.80 5.00 4.80 5.00 5.00 1.58 1.62 1.58 1.62 1.62 1.62 1.62
2.05 2.43 3.16 3.91 4.77 5.85 7.16 8.29 10.25 12.25 14.93 17.75 21.56 25.46 31.41
-0.02 -0.01 -0.02 0.11 -0.01 0.14 0.03 -0.05 -0.32 0.05 -0.29 0.03 -0.37 0.25 0.66
69.58 69.41 69.13 68.94 68.69 68.50 68.25 68.07 67.79 67.62 67.35 67.16 66.89 66.71 66.45
Temperature of saturation. b Mass of transferred sample condensed at T ) 243 K. c Volume of nitrogen used to transfer mass m of sample. d Vapor pressure at temperature T calculated from m and the residual vapor pressure at condensation temperature T ) 243 K. a
0.8-3.5 dm3 · h-1 which has ensured that the transporting gas was in saturated equilibrium with the coexisting solid phase in the saturation tube. The amount of material transported was condensed in a cold trap at 243 K. The amount of condensed substance was determined by GC analysis using an external standard (tridecane). The saturated vapor pressure psat i at each temperature T was calculated from the amount of product collected within a definite period of time. Assuming that Dalton’s law of partial pressures was applied to the nitrogen stream saturated with the substance i of interest is valid, values of psat i were calculated: psat i ) miRTa /VMi; V ) VN2 + Vi; (VN2 . Vi)
(1)
where R ) 8.31447 J · K-1 · mol-1; mi is the mass of transported compound, Mi is the molar mass of the compound, and Vi is its volume contribution to the gaseous phase. VN2 is the volume of transporting gas, and Ta is the temperature of the soap bubble meter. The volume of transporting gas VN2 was determined from the flow rate and time measurements. Experimental results are presented in Table 1. 2.3. Thermochemical Measurements. Combustion Calorimetry. An isoperibol bomb calorimeter was used for the measurement of the energies of combustion of cis-stilbene and benzo[c]cinnoline. From a practical point of view, careful
encapsulation of a sample is important in combustion calorimetry of liquids. In the present study, we used commercially available polyethene bulbs (NeoLab, Heidelberg) of 1 cm3 volume as the sample container for liquids in order to reduce the capillary effect and make the encapsulation easier. The liquid specimen was transferred to the polyethene bulbs with a syringe. The narrow neck of the container was compressed with special tweezers and was sealed outside the glovebox by heating with hot air. Then, the loaded container was placed in the bomb and burned in oxygen at a pressure of 3.04 MPa. The solid samples were compressed to pellets of mass ≈300 to 400 mg and were burned in oxygen. Completeness of the combustion of the crystalline sample was ensured by the addition of a weighed amount of oil to the pellet. Results from combustion experiments are given in Tables 2 and 3. The detailed procedure has been described previously.6 The combustion products were examined for carbon monoxide (Dra¨ger tube) and unburned carbon, but none was detected. The energy equivalent of the calorimeter εcalor was determined with a standard reference sample of benzoic acid (sample SRM 39i, N.I.S.T.). From nine experiments, εcalor was measured to be 14807.1 ( 0.85 J · K-1. The correction for nitric acid formation was based on the titration with 0.1 mol · dm-3 NaOH (aq). The atomic weights used were those recommended by the IUPAC Commission.7 The sample masses were reduced to vacuum, taking into consideration their density
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Table 2. Formula, Density G (T ) 293 K), Specific Heat Capacity cp (T ) 298.15 K), and Expansion Coefficient (δV/δT)p of the Materials Used in the Present Study compounds
formula
cis-stilbene benzo[c]cinnoline polythenee oilf cottong
C14H12 C12H8N2 CH1.93 CH1.94 CH1.774O0.887
cpa 10-6(δV/δT)pd F (g · cm-3) (J · K-1 g-1) (dm3 · K-1) 1.011b 1.307c 0.920 0.880 1.500
1.20 1.20 2.53 0.84 1.67
1.0 0.1 0.1 1.0 0.1
a From DSC measurements. b Taken from ref 59. c Measured with a pycnometer. d Estimated. e From 10 combustion experiments: ∆cu° ) -46361.0 ( 4.0 J · g-1. f From 10 combustion experiments: ∆cu° ) -46186.2 ( 3.0 J · g-1. g From 10 combustion experiments: ∆cu° ) -16945.2 ( 4.2 J · g-1.
values (see Table 2). For converting the energy of the actual bomb process to that of the isothermal process, and reducing to standard states, the conventional procedure8 was applied. 2.4. Computations. Standard ab initio molecular orbital calculations were performed with the Gaussian 03 Rev.04 series of programs.9 Energies were obtained at the G3MP2 level of theory. G3 theory is a procedure for calculating energies of molecules containing atoms of the first and second row of the periodic chart based on ab initio molecular orbital theory. A modification of G3 theory that uses reduced orders of Moller-Plesset perturbation theory is G3MP2 theory.10 This method saves considerable computational time compared to G3 theory with some loss in accuracy but is much more accurate than G2MP2 theory. For all the species included in this study, full geometry optimizations were carried out at the HF/6-31G(d) level. The corresponding harmonic vibrational frequencies were evaluated at the same level of theory to confirm that the optimized structures found correspond to potential energy minima and to evaluate the corresponding zero-point vibrational energies, ZPE, and the thermal corrections at 298.15 K. ZPE values were scaled by the empirical factor 0.9135. All the minima found at the HF/6-31G(d) level were again fully reoptimized at the MP2(FULL)/6-31G(d) level. G3MP2 theory uses geometries from second-order perturbation theory and scaled zero-point energies from Hartree-Fock theory followed by a series of single-point energy calculations at the MP2(Full), QCISD(T), and MP2/GTMP2Large levels of theory (for details, see ref 10). The enthalpy value at T ) 298.15 K of the compounds investigated was evaluated according to standard thermodynamic procedures.11 3. Results and Discussion 3.1. Vapor Pressure, Sublimation, and Vaporization Enthalpies of Stilbenes. Vapor pressures obtained by the transpiration method were fitted using the following equation:4 R ln psat i ) a +
()
T b g + ∆cr Cp ln T T0
(2)
where a and b are adjustable parameters. T0 appearing in eq 2 is an arbitrarily chosen reference temperature, which has been taken as 298.15 K. Consequently, the expression for the sublimation enthalpy at temperature T is derived as follows: g g Hm(T) ) -b + ∆cr CpT ∆cr
(3)
The value of ∆gcrCp, required for the correction of the sublimation enthalpies, has been derived according to a procedure developed by Chickos and Acree,12,13 using the experimental value for -1 · K-1. When isobaric molar heat capacity14 Ccr p ) 235.0 J · mol
the vapor pressures over the liquid sample of cis-stilbene have been treated, eqs 2 and 3 give the expression for the vaporization enthalpy ∆gl Hm at temperature T. Values of the isobaric molar heat capacities Cpl and ∆gl Cp required for the data treatment in this case have been derived according to a procedure developed by Chickos and Acree.13 We have checked our procedure by using measurements of vapor pressures of n-alcohols4 and substituted naphthalenes.15 It turned out that vapor pressures derived from the transpiration method were reliable within 1-3%. In order to assess the uncertainty of the vaporization enthalpy, the experimental data were approximated with the -1 linear equation ln(psat i ) ) f(T ) using the method of leastsquares. The uncertainty in the enthalpy of vaporization was derived from the uncertainty in the slope of the linear correlation. Experimental results and parameters a and b according to eq 2 are listed in Table 1. Although there are several reports of the dependence of vapor pressure with temperature of the stilbenes in the literature,16-24 most authors did not calculate enthalpies of sublimation or vaporization at T ) 298.15 K from their results. Hence, the original experimental results16-24 were treated in this work using eqs 2 and 3, and ∆gl Hm(298.15 K) or g Hm(298.15 K) were calculated for comparison with results ∆cr of this work (see Table 4). Enthalpies of sublimation of transstilbene have been measured by using all possible techniques in the temperature range from 295 to 367 K, and most of the latest available results are remarkably consistent with our new g Hm(298.15 K) ) 102.0 ( 0.4 kJ · mol-1 as shown in result ∆cr Table 4. Vapor pressure measurements on cis-stilbene were performed24 with the quartz-fiber viscosity gauge (only 3 experimental points at 276, 282, and 286 K were measured). These own results were combined by the authors with vapor pressures at various temperatures found in the literature, so that the temperature range was extended to 425 K. The vaporization enthalpy obtained in this way is ∆gl Hm(350.5 K) ) 66.1 ( 1.3 kJ · mol-1. We have adjusted this value to the reference temperature 298.15 K and calculated ∆gl Hm(298.15 K) ) 70.8 ( 1.3 kJ · mol-1 which is in close agreement with our new result (see Table 4). The comprehensive compilation by Stephenson and Malanowski22 also contains vapor-pressure results for cisand trans-stilbene over a wide range of temperature. However, the origin of these data is unclear; methods of measurements are unknown as well as errors of measurements and purities of compounds. Despite of this fact, we treated the results from source22 using eqs 2 and 3 and calculated enthalpies of vaporization/sublimation for the sake of comparison with our own results (see Table 4). However, the agreement or disagreement with our data in each case should be questionable. 3.2. Enthalpies of Formation of cis-Stilbene and Benzo[c]cinnoline. Results of a typical combustion experiment for cisstilbene and benzo[c]cinnoline are summarized in Table 3. The values of the standard specific energies of combustion, ∆cu°, the standard molar enthalpies of combustion, ∆cH°m, and the standard molar enthalpies of formation in the crystalline state ∆fH°m(cr.) were based on the reactions: cis-stilbene
C14H12 + 17O2 ) 14CO2 + 6H2O
benzo[c]cinnoline C12H8N2 + 14O2 ) 12CO2 + 4H2O + N2
(4)
(5)
Values ∆cH°m ) -7401.6 ( 2.8 kJ · mol-1 for cis-stilbene and ∆cH°m ) -6164.9 ( 2.4 kJ · mol-1 for benzo[c]cinnoline have been obtained from the enthalpic balance according to eqs 4 or
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Table 3. Results for Typical Combustion Experiments at T ) 298.15 K (p° ) 0.1 MPa) of cis-Stilbene and benzo[c]cinnoline
a
cis-stilbene b
m(substance)/g m′(cotton)/gb m′′(polythene)/gb m′′(oil)/gb ∆Tc/Kc (εcalor)(-∆Tc)/J (εcont)(-∆Tc)/J ∆Udecomp HNO3/J ∆Ucorr/Jd -m′∆cu′/J -m′′∆cu′′/J ∆cu°(liq)/(J · g-1)
benzo[c]cinnoline
0.358613 0.003291 0.28876
0.354279 0.003352 0.284523
0.339936 0.003827 0.267895
1.90303 -28178.3 -35.16 52.56 10.39 55.77 13387.2 -41012.3
1.87841 -27813.8 -34.65 53.16 10.22 56.80 13190.77 -41034.0
1.78707 -26461.3 -30.65 48.68 13.94 64.85 12419.88 -41021.3
0.10544 0.003402
0.103896 0.003252
0.104722 0.003273
0.369644 1.40204 -20760.1 -25.02 44.79 6.22 57.65 17072.45 -34180.8
0.369228 1.39713 -20687.5 -24.89 44.2 6.17 55.11 17053.24 -34204.2
0.416118 1.54533 -22881.8 -27.94 47.78 6.81 55.46 19218.91 -34193.6
a For the definition of the symbols, see ref 8: Th ) 298.15 K; V(bomb) ) 0.32 dm3; pi(gas) ) 3.04 MPa; mi(H2O) ) 1.00 g. b Masses obtained from apparent masses. c ∆Tc ) Tf - Ti + ∆Tcorr. (εcont)(-∆Tc) ) (εconti)(Ti - 298.15 K) + (εcontf)(298.15 K - Tf + ∆Tcorr.). d ∆Ucorr, the correction to standard states, is the sum of items 81-85, 87-90, 93, and 94 in ref 8. f ε ) 14807.1 J · K-1.
g Table 4. Compilation of Data on the Enthalpies of Sublimation ∆cr Hm and Vaporization ∆lgHm of Stilbenes
compounds
techniquea
temperature range (K)
trans-stilbene(cr)
K TCM C TCM TE, S T N/A K T N/A
329 303-315 298.15 295-318 297.5-364.5 293-338 298-343 298-357 324.3-367.0 419-580
QFG N/A T
276-286 373-428 308.3-343.2
trans-stilbene(l) cis-stilbene(l)
g ∆cr Hm(T) (kJ · mol-1)
90.8 86.5 102.1 100.6 103.8 101.10 ( 0.3 100.2 51.9 68.1
g ∆cr Hm(298 K)b (kJ · mol-1)
ref
91.9 ( 0.8 86.9 ( 0.3 99.2 ( 0.4 102.4 ( 0.6 101.6 ( 0.2 104.4 ( 2.5 100.3 102.1 ( 0.3 102.0 ( 0.4 80.7c 80.0 ( 0.4c,d 50.3 ( 1.0c 75.6c 70.5 ( 0.4c
16 17, 27 18 19 20 21 22 23 this work 22 this work 24 22 this work
Techniques: TCM ) thermal conductivity manometer; T ) transpiration method; K ) mass loss Knudsen effusion method; C ) Calvet calorimetry with Knudsen cell; S ) static method; TE ) torsion-effusion method; QFG ) quartz-fiber viscosity gauge. b Original vapor pressure data available in the literature were treated using eqs 2 and 3 in order to evaluate the enthalpy of sublimation at 298.15 K in the same way as our own results in Table 1. c g l Hm (this table) and ∆cr Hm (Table S1 of the Enthalpy of vaporization. d Enthalpy of vaporization ∆lgHm, calculated as the difference between ∆cr Supporting Information). a
5 and Hess’ law using the molar enthalpies of formation of H2O(l) and CO2(g) as assigned by CODATA.25 The total uncertainty was calculated according to the guidelines presented by Olofsson.26 The uncertainty assigned to ∆fH°m (see Table 5) is twice the overall standard deviation and includes the uncertainties from calibration, from the combustion energies of the auxiliary materials used, and the uncertainties of the enthalpies of formation of the reaction products H2O(l) and CO2(g). Only one previous experimental value of ∆fH°m(l) for cisstilbene has been determined by Coops and Hoijtink28 using combustion calorimetry. Their value ∆fH°m(l) ) 183.5 ( 1.6 kJ · mol-1 is in disagreement, by 6 kJ · mol-1, with the result obtained in this work (see Table 5). We do not have any reasonable explanation for such a disagreement, but we intend to validate our new result with the help of the reaction enthalpy of hydrogenation of cis-stilbene (at 298 K): cis-stilbene + H2 ) 1,2-diphenylethane, ∆rHom(l) ) -107.9 ( 0.8 kJ·mol-1 (6) which was calorimetrically measured in the liquid phase.29 First of all we need to obtain the enthalpy of formation of 1,2diphenylethane in the liquid phase. Using the enthalpy of formation of 1,2-diphenylethane in the crystalline state30 ∆fH°m(cr) ) 51.5 ( 1.3 kJ · mol-1, as well as the enthalpy of l Hm ) 22.7 kJ · mol-1 at 324 K31 (corrected to the fusion of ∆cr l reference temperature ∆cr Hm ) 21.2 at 298 K as described in Table S1 of the Supporting Information), the enthalpy of
formation ∆fH°m(l) ) 72.7 ( 1.3 for 1,2-diphenylethane was derived. This value has been used to derive the value ∆fH°m(l) ) 180.6 ( 1.5 kJ · mol-1 for cis-stilbene (see Table 5) according to the Hess’ law applied to the enthalpic balance of eq 6. This value is in agreement with our new value ∆fH°m(l) ) 177.4 ( 2.4 kJ · mol-1 within the combined boundaries of the experimental uncertainties. In a similar way we have been able to validate the enthalpy of formation of trans-stilbene in the condensed state with the help of the calorimetrically measured enthalpy of hydrogenation of trans-stilbene to 1,2-diphenylethane at 298 K:29 trans-stilbene + H2 ) 1,2-diphenylethane, ∆rHom(l) ) -84.2 ( 1.5 kJ·mol-1 (7) Using the experimental enthalpy of formation ∆fH°m(l) ) 72.7 ( 1.3 kJ · mol-1 for 1,2-diphenylethane derived above, the value ∆fH°m(l) ) 156.9 ( 1.5 kJ · mol-1 for trans-stilbene was calculated according to Hess’ law applied for eq 7. With the l Hm ) 22.0 kJ · mol-1 at 298.15 K for trans-stilbene help of ∆cr (see Table S1, the Supporting Information), its enthalpy of formation ∆fH°m(cr) ) 134.9 ( 1.5 kJ · mol-1 was calculated. The latter value is in close agreement with most of the available direct calorimetric determinations (see Table 5). Hussein and Akasheh37 measured ∆fH°m(cr, 298.15 K) ) 279.4 ( 4.0 kJ · mol-1 for benzo[c]cinnoline using combustion calorimetry. Their result is in disagreement, by 20 kJ · mol-1, with the result obtained in this work. The original paper was not available to us, and we are not able to explain such a
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Table 5. Thermochemical Data at T ) 298.15 K (p° ) 0.1 MPa) for Compounds Studied in This Work (kJ · mol-1)a compounds
∆fH°m
g ∆cr Hm or ∆lgHm
cis-stilbene(l)
183.5 ( 1.6
trans-stilbene(cr)
180.6 ( 1.5 177.4 ( 2.4 [this work] 137.8 ( 2.832
28
∆fH°(g) m
70.5 ( 0.4 (this work)
247.9 ( 2.4
102.0 ( 0.4 (this work)
238.7 ( 3.9
29
phenanthrene(cr)
benzo[c]cinnoline(cr)
cis-azobenzene(cr)
trans-azobenzene(cr)
140.5 ( 1.228 133.0 ( 0.833 134.9 ( 1.529 136.7 ( 3.934 113.035 116.1 ( 1.430 109.8 ( 1.636 110.4 ( 1.058 279.4 ( 4.037 295.1 ( 1.741 299.5 ( 2.8 [this work] 359.0 ( 3.038 362.339 367.2 ( 1.61 317.0 ( 2.038 320.039 308.6 ( 1.93 311.3 ( 3.41 311.4 ( 1.040
89.6 ( 0.8b42
103.0 ( 0.6c1
200.0 ( 1.3
402.5 ( 2.8
chemical results on trans-azobenzene are highly consistent, but the enthalpies of formation of cis-azobenzene spread over 8 kJ · mol-1. In order to check consistency of the enthalpies of formation of cis-azobenzene, we have derived the gaseous enthalpy of formation of cis-azobenzene using the earlier value by Cole and Gilbert39 (see value A in Table 5), as well as we have derived the gaseous enthalpy of formation of cis-azobenzene using the more recent value by Schulze et al.1 (see value B in Table 5). High-level ab initio calculations have been a very helpful procedure to reconcile the available experimental data. Hence, in this work we used first-principles method for calculation of the compounds presented in Figure 1 in order to get theoretical values for isomerization and 2,2′-cyclization of azobenzene and stilbene and to compare these values with the experimental findings. 4. Quantum Chemical Calculations
93.9 ( 0.1d1
452.9 ( 3.0 (A)e 461.1 ( 1.6 (B)f 405.5 ( 1.2
93.6 ( 1.93 94.1 ( 0.740
a Values selected for calculation of the gaseous enthalpy of formation are in bold. b The comprehensive review of the available data is presented in this reference. c The original value 101.7 ( 0.6 kJ · mol-1 referred to the middle of the temperature range studied 320-360 K has been extrapolated to the reference temperature according to the procedure developed by Chickos and Acree.12 d The original value 92.9 ( 0.1 kJ · mol-1 referred to the middle of the temperature range studied 298-357 K has been extrapolated to the reference temperature according to the procedure developed by Chickos and Acree.12 e Calculated using the value ∆fH°m(cr) ) 359.0 ( 3.0 kJ · mol-1 from ref 38. f Calculated using the value ∆fH°m(cr) ) 367.2 ( 1.6 kJ · mol-1 from ref 1.
disagreement. Another previous calorimetric result by Mills41 for ∆fH°m(cr, 301.15 K) ) 295.1 ( 1.7 kJ · mol-1 for benzo[c]cinnoline seems to be in acceptable agreement with our new result (see Table 5). However, it should be mentioned that the result by Mills41 measured at 301.15 K will be roughly changed only for 0.8 kJ · mol-1 (within the boundaries of experimental uncertainties) by the recalculation of this result to the reference temperature 298.15 K. 3.3. Experimental Gaseous Enthalpies of Formation for Stilbenes and Azobenzenes. Thermochemical processes depicted in Figure 1 have been of interest in this work. Enthalpies of formation, enthalpies of vaporization, and enthalpies of sublimation of the compounds of interest are collected in Table 5. The following thermodynamic relationships have been used to obtain the gaseous enthalpy of formations:
Ab initio molecular orbital methods on the G3 level for calculation of the enthalpy of formation of stilbenes and azobenzenes studied in this work have not yet been reported in the literature. G3MP2 calculations of the compounds presented in Figure 1 have thus been performed. Results of the electronic energy at 0 K, the molecular structures in the lowest energetic state have been obtained. Results of these data are available in the Supporting Information (Table S2). 4.1. Cis-Trans Isomerization of Stilbenes. Theoretical studies of the cis-trans isomerization of stilbenes have been popular endeavors in the recent years.43-47 Results from forcefield, PM, HF, MP, and density functional theory (DFT) methods are collected in Table 6. As can be seen from this table, enthalpies of isomerization calculated using these simple methods spread from -3 to -20 kJ · mol-1. Our result calculated by the sophisticated G3MP2 method, ∆rH°m(I f II) ) -7.9 kJ · mol-1 (see Table 6) is in very close agreement with the experimental value ∆rH°m(I f II) ) -9.2 ( -4.6 kJ · mol-1 derived in this work from the direct calorimetric results (see Table 6), as well as the G3MP2 result is in acceptable agreement with two other experimental isomerization enthalpies -12.5 kJ · mol-1 (from ref 48) and -13.0 kJ · mol-1 (from ref 49)
∆fH°m(g) ) ∆fH°m(l) + ∆gl Hm or ∆fH°m(g) ) ∆fH°m(cr) + g ∆cr Hm (8) Values of the vaporization enthalpy of cis-stilbene, derived in this work (Table 1), have been used, together with the results from our combustion experiments (Table 3), for further calculation of the gaseous standard enthalpies of formation, ∆fH°m(g) at 298 K. The resulting value of ∆fH°m(g) for benzo[c]cinnoline was calculated from our combustion results and the enthalpy of sublimation for this compound reported by Schulze et al.1 In contrast to stilbenes, there were at least three recent experimental studies of the thermochemistry of azobenzenes. As can be seen in Table 5, the recent experimental thermo-
Figure 1. Isomerization and 2,2′-cyclization of stilbenes and azobenzenes.
Ind. Eng. Chem. Res., Vol. 48, No. 22, 2009
Table 7. Experimental and Calculated Enthalpies of the Isomerization Reaction, ∆rH°m, cis-Azobenzene f trans-Azobenzene (kJ · mol-1)
Table 6. Experimental and Calculated Enthalpies of the Isomerisation Reaction, ∆rH°m, cis-Stilbene f trans-Stilbene (kJ · mol-1) ∆rH°m (I f II)
phase
method
ref
∆rH°m (IV f V)
phase
theory -13.0 -21.0 -8.0 -13.9 -17.1 -3.3 -13.0 -8.0 -21.0 -20.2 -9.6 -12.9 -24.6 -7.9
gas gas gas gas gas
MM3(99) B3LYP/6-31G(d,p) MP2/6-31G(d,p) AM1 PM3 PM5 MM3(99) MP2/6-31G(d,p) B3LYP/6-31G(d,p) HF/6-31G(d,p) UBLYP/6-31G(d) UB3PW91/6-31G(d) B3LYP/cc-pVDZ G3MP2
-9.2 ( 4.6
gas
calorimetry
-12.5 -13.0
gas gas
equilibrium constant equilibrium constant
-5.0 ( 0.4 -9.6 ( 1.3 -12.0 ( 1.3 -19.2 ( 0.4
liquid liquid liquid liquid
-18.7 ( 4.6
liquid
thermal analysis with DSC equilibrium study in cyclohexane equilibrium study in toluene equilibrium study in benzene and tert-butylbenzene calorimetryb
method
ref
theory 43 43 43 44 44 44 44 44 44 45 46 47 this work (Table 8)
-66.3 -68.8 -49.8 -45.8
gas gas gas gas
-47.3 ( 0.4 -47.4 ( 3.2 (A) -55.6 ( 2.0(B)
gas gas gas
-48.9 -49.0 -46.1 -54.3
liq liq liq liq
B3LYP/cc-pVDZ B3LYP/CASSCF B3LYP/CASPT2 G3MP2
47 53 53 this work
experiment (gas) thermal isomerization calorimetrya calorimetrya
2 this work this work
experiment (liquid) ( ( ( (
2.3 5.4 3.2 (A) 1.9 (B)
photomicrocalorimetry photomicrocalorimetry combustion calorimetryb combustion calorimetryb
3 54 this work this work
experiment (solid)
experiment (gas) a
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this work (Table 8) 48 49
experiment (liquid) 50 51 51 52 this work
-48.2 ( 0.3 -45.2 ( 2.4
solid solid
-47.6 ( 3.2 (A) -55.8 ( 1.9 (B)
solid solid
DSC photomicrocalorimetry and solution calorimetry combustion calorimetryc combustion calorimetryc
2 3 this work this work
a Calculated using the gaseous enthalpies of formation of azobenzenes, given in the last column of Table 5. b Calculated using the results from combustion calorimetry given in Table 5 (the enthalpy of formation of azobenzenes in the crystalline state were converted to the l liquid state using the enthalpies of fusion ∆cr Hm as described in Table S1 of the Supporting Information). c Calculated using the enthalpies of formation of azobenzenes, given in the second column of Table 5.
a
Calculated using the gaseous enthalpies of formation of stilbenes, given in the last column of Table 5. b Calculated using the results from combustion calorimetry given in Table 5 (the enthalpy of formation of trans-stilbene in the crystalline state was converted to the liquid state l using the enthalpy of fusion ∆cr Hm as described in Table S1 of the Supporting Information).
measured in the gas phase according to the Second Law of thermodynamics from the temperature dependence of equilibrium constants. Following, the available data set of reaction enthalpies has been proven to be consistent for the isomerization of stilbenes in the gas phase. Comparison of the isomerization enthalpies ∆rH°m(I f II) in the liquid phase has also revealed a large spread of values from from -5 to -19 kJ · mol-1. However, the experimental result ∆rH°m(I f II) ) -(18.7 ( 4.6) kJ · mol-1 derived in this study from the direct calorimetric results (see Table 6) is in excellent agreement with the most careful equilibrium study of thermal isomerization of stilbenes in benzene and the tert-butylbenzene solutions:52 ∆rH°m(I f II) ) -19.2 ( -0.4 kJ · mol-1. Thus, our additional experimental and theoretical studies of cis- and trans-stilbenes have helped to establish a consistent set of experimental data in the liquid and in the gaseous phases. 4.2. Cis-Trans Isomerization of Azobenzenes. cis- and trans-Azobenzene can interconvert both photochemically and thermally.2,3,54 Experimental values of the isomerization enthalpy ∆rH°m(IV f V) measured in the gas, the liquid, and the solid phases are remarkably close (within their experimental uncertainties) to the average level of -47 kJ · mol-1 (see Table 7). Independence of the isomerization enthalpy from the aggregate state is quite obvioussboth isomers have hardly distinguishable enthalpies of sublimation (see Table 5) and enthalpies of fusion (see Table S1, of the Supporting Information). Enthalpies of isomerization calculated using the DFT47,53 methods spread from -50 to -69 kJ · mol-1, and these values are significantly more negative than the experimental results. Our result ∆rH°m(IV f V) ) -45.8
Table 8. Comparison of Experimental and Calculated Enthalpies of Reaction in the Gaseous State at T ) 298.15 K (kJ · mol-1) Involving Compounds I-VI from Figure 1 G3MP2
a
reaction
∆rHo
∆rH°mexp(g)a
I f II I f III II f III IV f V IV f VI V f VI
-7.9 -52.5 -44.6 -45.8 -62.4 -16.6
-9.2 ( 4.6 -47.9 ( 2.7 -38.7 ( 4.1 -47.4 ( 3.2 -50.4 ( 4.1 -3.0 ( 3.0
Calculated from selected values ∆fH°m(g) given in Table 5.
kJ · mol-1 (see Tables 7 and 8) calculated using G3MP2 method, is in excellent agreement with the average of the experimental values of -47 kJ · mol-1 mentioned above. Such a remarkable agreement of the experimental and theoretical studies of the azobenzenes isomerization has revealed, that the experimental value1 ∆fH°m(cr) ) 367.2 ( 1.6 kJ · mol-1 for cis-azobenzene (see Table 5) seems to be less consistent with the data set for azobenzenes, than those ∆fH°m(cr) ) 362.3 kJ · mol-1 (see Table 5) measured by Cole and Gilbert,39 and ∆fH°m(cr) ) 359.0 ( 3.0 kJ · mol-1 (see Table 5) measured by Corruccini and Gilbert.38 For this reason, we would suggest the value ∆fH°m(cr) ) 359.0 ( 3.0 kJ · mol-1 (see Table 5) for the further thermochemical calculations involving cis-azobenzene (see Tables 7-9). The enthalpy of isomerization of azobenzene (see Tables 6 and 7) is very much higher than that of stilbene (no matter in what state of aggregation the isomerization takes place), although the two pairs of molecules are very similar. This energetic difference must be attributed to the repulsion energy of the orbitals of the lone electron pairs in azobenzene. 4.3. Cyclization of Stilbene and Azobenzene. Experimental values and theoretical calculations of enthalpies of cyclization
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Table 9. Results of Calculation of the Standard Enthalpy of Formation ∆fH°m(g) in the Gaseous Phase at 298.15 K (kJ · mol-1) for the Molecules Studied in This Work G3MP2 compounds
atomization
bond separation a
cis-stilbene trans-stilbene phenanthrene benzo[c]cinnoline cis-azobenzene
236.4 228.5 188.6 386.6 444.2
247.5 237.4a 210.1b 380.6c 447.3d
trans-azobenzene
398.5
401.6d
experimental 247.9 ( 2.4 238.7 ( 3.9 200.0 ( 1.3 402.5 ( 2.8 452.9 ( 3.0 (A) 461.1 ( 1.6 (B) 405.5 ( 1.2
a
Reactions are given according to numeration in Table S2 of the Supporting Information: I(II) + VIII ) 2VII. b IV + IX ) 2X. c IV + XIV ) 2XIII. d V(VI) + 4XI ) 2XII + 2XV.
of stilbene: ∆rH°m(I f III) as well as of azobenzene: ∆rH°m(IV f VI) are presented in Table 8. The enthalpies of 2,2cyclization of the cis-compounds to the corresponding annullated ring compounds (benzo[c]cinnoline respectively phenanthrene), however, fall very close to each other. This is mainly the gain in resonance energy resulting from the change going from bent, nonplanar molecules to flat, annulated and conjugated ring molecules. 4.4. Theoretical G3MP2 Gaseous Enthalpies of Formation for Stilbenes and Azobenzenes. In standard Gaussian-n theories, theoretical enthalpies of formation are calculated through atomization reactions.55 Raghavachari et al.56 have proposed to use a set of isodesmic reactions or “bond separation reactions” to derive theoretical enthalpies of formation. Isodesmic reactions rely more upon the similarity of bonding environments in the reactants and products which leads to cancellation of systematic errors in the ab initio calculations.57 We have calculated the enthalpies of formation of stilbenes and azobenzenes with the help of both standard atomization reactions and “bond separation” reactions according to the following reactions: for cis- and trans-stilbenes
aniline, styrene, naphthalene, diazine-1,3, quinazoline, methane, ethane, and ethane (see Table S2, of the Supporting Information), enthalpies of formation of all studied molecules have been calculated (see Table 9). It should be mentioned that the composite G3MP2 method used in this work to predict enthalpies of formation of stilbenes, azobenzenes, and parent molecules is a quite time-consuming method. For small molecules such as diazine-1,3, the required job CPU time was 62 min only for the longest step 4 with QCISD(T)/6-31G(d). For middle size molecules such as quinazoline, the required job CPU time was already 96 h (the calculations were performed at the university computational center with the help of a Sun Fire 3800 UltraSparc III 900 MHz using two processors and 1800 MB RAM). But already for trans-stilbene it was only possible to complete our calculations within five weeks even using the resources of the university computational center. As can be seen in Table 9, the ∆fH°m(g) values calculated by G3MP2 using the atomization procedure are generally in comparison to the experiment. However, use of the bond separation reactions to predict enthalpies of formation of stilbenes and azobenzenes is quite successful (see Table 9). In contrast, bond separation reactions applied in this work have failed to predict properly the enthalpies of formation of poly condensed aromatics such as phenanthrene and benzo[c]cinnoline. The disagreement with the experiment of 10 kJ · mol-1 is unacceptably large. At the same time, enthalpies of cyclization involving phenanthrene and benzo[c]cinnoline as the reaction participants have been reproduced with the G3MP2 method quite accurately (see Table 8). Conclusion Thermochemical and ab initio calculations of stilbenes and azo-benzenes have been performed. New results help to resolve the uncertainty in the available thermochemical data on for these compounds. Acknowledgment
for phenanthrene
This work has been supported by Research Training Group 1213 “New Methods for Sustainability in Catalysis and Technique” (DFG). Thanks are due to Dr. I. A. Nesterov for the transpiration experiments with stilbenes.
for benzo[c]cinnoline
Supporting Information Available: Auxiliary experimental l Hm, and enthalpies of data on enthalpies of fusion, ∆cr formation, ∆fH°m(l) of the compounds under study (Table S1) and total energies at 0 K and enthalpies at 298 K of the molecules studied in this work (Table S2). This material is available free of charge via the Internet at http://pubs.acs.org. Literature Cited
for cis- and trans-azobenzenes Using enthalpies of reactions,
calculated by the G3MP2 method, together with the wellestablished enthalpies of formation, ∆fH°m(g), for benzene,
(1) Schulze, F. W.; Petrick, H. J.; Cammenga, H. K. Thermodynamic properties of the structural analogues benzo[c]cinnoline, trans-azobenzene, and cis-azobenzene. Z. Phys. Chem. (Neue Folge) 1977, 107, 1– 19. (2) Wolf, E.; Cammenga, H. K. Thermodynamic and kinetic investigation of the thermal isomerization of cis-azobenzene. Z. Phys. Chem. (Neue Folge) 1977, 107, 21–38. (3) Dias, A. R.; da Piedade, M. E.; Martinho Simoes, J. A.; Simoni, J. A.; Teixeira, C.; Diogo, H. P.; Meng-Yen, Y.; Pilcher, G. Enthalpies of formation of cis-azobenzene and trans-azobenzene. J. Chem. Thermodyn. 1992, 24, 439–447. (4) Kulikov, D.; Verevkin, S. P.; Heintz, A. Enthalpies of vaporization of a series of linear aliphatic alcohols. Experimental measurements and application of the ERAS-model for their prediction. Fluid Phase Equilib. 2001, 192, 187–202.
Ind. Eng. Chem. Res., Vol. 48, No. 22, 2009 (5) Verevkin S. P. Pure Component Phase Changes Liquid and Gas. In Experimental Thermodynamics: Measurement of the thermodynamic properties of multiple phases; Weir, R. D., De Loos, Th. W., Ed.; Elsevier: New York, 2005; Vol. 7, Chapter 1, pp 6-30. (6) Verevkin, S. P.; Schick, C. Substituent effects on the benzene ring. Determination of the intra-molecular interactions of substituents in tert-alkyl substituted catechols from thermochemical measurements. J. Chem. Eng. Data 2000, 45, 946–952. (7) Atomic weights of the elements. Review 2000. Pure Appl. Chem. 2003, 75, 683-800. (8) Hubbard, W. N.; Scott, D. W.; Waddington, G. Experimental Thermochemistry; Rossini, F. D., Ed.; Interscience: New York, 1956; pp 75-127. (9) Frisch, M. J.; et al. Gaussian 03; revision B.04, Gaussian, Inc.: Pittsburgh, PA, 2003. (10) Curtiss, L. A.; Redfern, P. C.; Raghavachari, K.; Rassolov, V.; Pople, J. A. Gaussian-3 theory using reduced Møller-Plesset order. J. Chem. Phys. 1999, 110, 4703–4709. (11) McQuarrie, D. A. Statistical Mechanics; Harper & Row: New York, 1976. (12) Chickos, J. S.; Acree, W. E., Jr. Enthalpies of Sublimation of Organic and Organo-metallic Compounds, 1910-2001. J. Phys. Chem. Ref. Data 2002, 31, 537–698. (13) Chickos, J. S.; Acree, W. E., Jr. Enthalpies of Vaporization of Organic and Organometallic Compounds, 1880-2002. J. Phys. Chem. Ref. Data 2003, 32, 519–878. (14) Van Miltenburg, J. C.; Bouwstra, J. A. Thermodynamic properties of trans-azobenzene and trans-stilbene. J. Chem. Thermodyn. 1984, 16, 61–65. (15) Verevkin, S. P. Vapor pressures and enthalpies of vaporization of a series of 1- and 2-halogenated naphthalenes. J. Chem. Thermodyn. 2003, 35, 1237–1251. ¨ ber Sublimationswa¨rmen. Z. Phys. (16) Wolf, K. L.; Weghofer, H. U Chem. B 1938, 39, 194–208. (17) Engelsman, J. J. An Application of a Thermistor Manometer for the Determination of Heats of Sublimation of Slightly Volatile Compounds. Ph.D. Thesis, Vrije Universiteit, Amsterdam, The Netherlands, 1955. (18) Morawetz, E. Enthalpies of vaporization for a number of aromatic compounds. J. Chem. Thermdyn. 1972, 4, 455–60. (19) De Kruif, C. G.; Oonk, H. A. J. The determination of enthalpies of sublimation by means of thermal conductivity manometers. Chem. Ing. Technol. 1973, 45, 455–461. (20) van Erken, P. J.; Jacobs, M. H. G.; Offringa, J. C. A.; de Kruif, C. G. Vapour-pressure measurements on trans-diphenylethene and naphthalene using a spinning-rotor friction gauge. J. Chem. Thermodyn. 1983, 15, 409–417. (21) Kratt, G.; Beckhaus, H.-D.; Bernlo¨hr, W.; Ru¨chardt, C. Thermolabile Kohlenwasserstoffe XVII. Verbrennungsenthalpie und Bildungsenthalpie von zehn sym.Tetraalkyl-1,2-Diarylethanen. Thermochim. Acta 1983, 62, 279–294. (22) Stephenson, R. M.; Malanowski, S. Handbook of the Thermodynamics of Organic Compounds; Elsevier: New York, 1987. (23) Cammenga, H. K.; Petrick, H. J.; Schulze, F. W. Sublimation kinetics of organic molecular crystals. J. Cryst. Growth 1981, 55, 351– 362. (24) Brackman, D. S.; Plesch, P.H. Some physical properties of cisstilbene. J. Chem. Soc 1952, 218, 8–2221. (25) CODATA Key Values for Thermodynamics; Cox, J. D., Wagman, D. D., Medvedev, V. A., Eds.; Hemisphere: New York, 1989. (26) Olofsson, G. Combustion calorimetry; Sunner, S., Mansson, M., Eds.; Pergamon: New York, 1979, Chapter 6. (27) Eliel, E. L.; Engelsman, J. J. The heats of combustion of gaseous cyclotetradecane and trans-stilbene - a tale of long-standing confusion. J. Chem. Educ. 1996, 73, 903–905. (28) Coops, J.; Hoijtink, G. J. Thermochemical investigations on arylethenes. I. Heats of combustion of phenylethenes. Rec. TraV. Chim. Pays-Bas. 1950, 69, 358–367. (29) Williams, R. B. Heats of catalytic hydrogenation in solution. I. Apparatus, technique, and the heats of hydrogenation of certain pairs of stereoisomers. J. Am. Chem. Soc. 1942, 64, 1395–1404. (30) Coleman, D. J.; Pilcher, G. Heats of combustion of biphenyl, bibenzyl, naphthalene, anthracene, and phenanthrene. Trans. Faraday Soc. 1966, 62, 821–827. (31) Messerly, J. F.; Finke, H. L.; Good, W. D.; Gammon, B. E. Condensed-phase heat capacities and derived thermodynamic properties for 1,4-dimethylbenzene, 1,2-diphenylethane, and 2,3-dimethylnaphthalene. J. Chem. Thermodyn. 1988, 20, 485–501.
10127
(32) Richardson, J. W.; Parks, G. S. Thermal data on organic compounds. XIX. Modern combustion data for some non-volatile compounds containing carbon, hydrogen and oxygen. J. Am. Chem. Soc. 1939, 61, 3543–3546. (33) Lobanov, G. A.; Karmanova, L. P. Enthalpy of formation of some organic substances. IzV. Vyssh. Uchebdn. ZaVed. 1971, 14, 865– 867. (34) Marantz, S.; Armstrong, G. T. Heats of combustion of transstilbene and trans-2,2′,4′,6,6′-hexanitrostilbene (HNS) (Correction). J. Chem. Eng. Data 1968, 13, 455. (35) Bender, P.; Farber, J. The heats of combustion of anthracene transannular peroxide and dianthracene. J. Am. Chem. Soc. 1952, 74, 1450–1452. (36) Steele, W. V.; Chirico, R. D.; Nguyen, A.; Hossenlopp, I. A.; Smith, N. K. Determination of ideal-gas enthalpies of formation for key compounds. Am. Inst. Chem. Eng. Symp. Ser. 1990, 138–154. (37) Hussein, A.; Akasheh, T. S. Heat of combustion of heterocyclic compounds Part II. Dirasat 1985, 12, 65–72. (38) Corruccini, R. J.; Gilbert, E. C. The heat of combustion of cisand trans-azobenzene. J. Am. Chem. Soc. 1939, 61, 2925–2927. (39) Cole, L. G.; Gilbert, E. C. The heats of combustion of some nitrogen compounds and the apparent energy of the N-N bond. J. Am. Chem. Soc. 1951, 73, 5423–5427. (40) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A.; Smith, N. K. Thermodynamic properties and ideal-gas enthalpies of formation for butyl vinyl ether, 1,2-dimethoxyethane, methyl glycolate, bicyclo[2.2.1]hept-2-ene, 5-vinylbicyclo[2.2.1]hept-2-ene, trans-azobenzene, butyl acrylate, di-tert-butyl ether, and hexane-1,6-diol. J. Chem. Eng. Data 1996, 41, 1285–1302. (41) Mills, G. D. A Thermochemical Study of 7,8-Benzoquinoline; 5,6benzoquinoline, 3,4-Benzoquinoline, 1,10-Phenanthroline, Benzo(c)cinnoline, and Phthalazine; University of Southern Mississippi;. Diss. Abstr. Int. B 1972, 33, 1485. (42) Rojas, A.; Orozco, E. Measurement of the enthalpies of vaporization and sublimation of solid aromatic hydrocarbons by differential scanning calorimetry. Thermochim. Acta 2003, 405, 93–107. (43) Claes, L.; Kwasniewski, S.; Deleuze, M. S.; Francois, J.-P. Comparative study of the molecular structure of stilbene using molecular mechanics, Hartree-Fock and density functional theories. THEOCHEM 2001, 549, 63–67. (44) Vendrame, R.; Coluci, V. R.; Galva˜o, D. S. Comparative parametric method 5 (PM5) study of trans-stilbene. THEOCHEM 2004, 686, 103–108. (45) Quenneville, J.; Martinez, T. Ab initio Study of Cis-Trans Photoisomerization in Stilbene and Ethylene. J. Phys. Chem. A 2003, 107, 829–837. (46) Brink, M.; Mo¨llerstedt, H.; Ottosson, C. H. Characteristics of the Electronic Structures of Diabatically and Adiabatically Z/EIsomerizing of Olefins in the T1 State. J. Phys. Chem. A 2001, 105, 4071– 4083. (47) Chen, P. C.; Chieh, Y. C. Azobenzene and stilbene: a computational study. THEOCHEM 2003, 624, 191–200. (48) Taylor, T. W. J.; Murray, A. R. Isomeric change in certain stilbenes. J. Chem. Soc. 1938, 2078–2086. (49) Kistiakowsky, G.; Smith, W. R. Kinetics of Thermal Cis-Trans Isomerization. III. J. Am. Chem. Soc. 1934, 56, 638–642. (50) Bastianelli, C.; Caia, V.; Cum, G.; Gallo, R.; Mancini, V. Thermal isomerization of photochemically synthesized (Z)-9-styrylacridines. An unusually high enthalpy of Z-E conversion for stilbene-like compounds. J. Chem. Soc. Perkin Trans. 2 1991, 679–683. (51) Fischer, G.; Muszkat, K. A.; Fischer, E. Thermodynamic equilibrium between cis- and trans-isomers in stilbene and some derivatives. J. Chem. Soc. B 1968, 1156–1158. (52) Saltiel, J.; Ganapathy, S.; Werking, C. The ∆H for thermal transstilbene/cis-stilbene isomerization. Do S0 and T1 potential energy curves cross? J. Phys. Chem. 1987, 91, 2755–2758. (53) Cembran, A.; Bernardi, F.; Garavelli, M.; Gagliardi, L.; Orlandi, G. On the mechanism of the cis-trans isomerization in the lowest electronic states of azobenzene: S0, S1, and T1, J. Am. Chem. Soc. 2004, 126, 3234–3243. (54) Adamson, A. W.; Vogler, A.; Kunkely, H.; Wachter, R. Photocalorimetry. Enthalpies of photolysis of trans-azobenzene, ferrioxalate and cobaltioxalate ions, chromium hexacarbonyl, dirhenium dicarbonyl. J. Am. Chem. Soc. 1978, 100, 1298–1300. (55) Curtiss, L. A.; Redfern, P. C.; Raghavachari, K.; Rassolov, V.; Pople, J. A. Gaussian-3 (G3) theory for molecules containing first and second row atoms. J. Chem. Phys. 1998, 109, 7764–7776. (56) Raghavachari, K.; Stefanov, B. B.; Curtiss, L. A. Accurate thermochemistry of molecules: Gaussian-2 theory. J. Chem. Phys. 1997, 106, 6764–6767.
10128
Ind. Eng. Chem. Res., Vol. 48, No. 22, 2009
(57) Notario, R.; Castan˜o, O.; Abboud, J.-L. M.; Gomperts, R.; Frutos, L. M.; Palmeiro, R. Organic Thermochemistry at High ab Initio Levels. 2. Meeting the Challenge: Standard Heats of Formation of Gaseous Norbornane, 2-Norbornene, 2,5-Norbornadiene, Cubane, and Adamantane at the G2 Level. J. Org. Chem. 1999, 64, 9011–9014. (58) Nagano, Y. Standard enthalpies of formation of phenanthrene and naphthacene. J. Chem. Thermodyn. 2002, 34, 377–383.
(59) Beilsteins Handbuch der Organischen Chemie, IV Supplement, Vol. 5, p 2155.
ReceiVed for reView May 16, 2009 ReVised manuscript receiVed August 4, 2009 Accepted August 17, 2009 IE900800Q
