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Experimental and computational study on the molecular energetics of monobromoanisole isomers
J. Chem. Thermodynamics 41 (2009) 499–505
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Experimental and computational study on the molecular energetics of monobromoanisole isomers Manuel A.V. Ribeiro da Silva *, Ana I.M.C. Lobo Ferreira Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal
a r t i c l e
i n f o
Article history: Received 17 October 2008 Accepted 11 November 2008 Available online 25 November 2008 Keywords: Thermochemistry Energy of combustion Enthalpy of vaporization Enthalpy of formation Rotating bomb combustion calorimetry Calvet microcalorimetry Cox scheme Computational thermochemistry Bromoanisole isomers
a b s t r a c t The standard (p° = 0.1 MPa) molar enthalpies of formation in the liquid phase of three isomers of bromoanisole were derived from the standard molar energies of combustion, in oxygen, which yields CO2(g) and HBr 600H2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The determination of the standard molar enthalpies of vaporization of these compounds, at T = 298.15 K, was done by Calvet microcalorimetry using the high-temperature vacuum sublimation technique. Combining the former sets of experimental results, the standard molar enthalpies of formation, in the gas-phase, were derived. The gas-phase enthalpies of formation were also estimated by means of the empirical scheme developed by Cox and by density functional theory calculations performed at the B3LYP/6-31+G(d) level of theory. Dc U m ðlÞ=ðkJ mol 2-Bromoanisole 3-Bromoanisole 4-Bromoanisole
3629.0 ± 1.4 3624.0 ± 1.4 3623.8 ± 1.5
1
Þ
Df Hm ðlÞ=ðkJ mol 101.5 ± 1.7 106.5 ± 1.7 106.7 ± 1.8
1
Þ
Dgl Hm =ðkJ mol1 Þ 61.8 ± 1.3 58.0 ± 1.2 58.3 ± 1.2
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The anisole (methoxybenzene) and its derivatives have received considerable attention mainly in pharmaceutical industries, as well as in new technologies and development of new materials. The bromoanisole (bromomethoxybenzene) isomers are used as starting material of many drugs with high therapeutic potential, such as analgesics [1,2], antidepressant [3], anti-cancer and drugs [4,5]. Recently, it was investigated the complexation of [60]fullerene [6,7] and [70]fullerene [8] with anisole, 3- and 4-bromoanisole, in order to provide novel materials with unusual conducting and magnetic properties. The 3-bromoanisole was used in the synthesis of 9,90 -spirobifluorene-1,10 -diol [9], a backbone molecule with a wide range of applications in molecular electronics, light-emitting materials and enantioselective molecular recognition. Although halogenated anisoles are not produced in large quantities, they have been extensively detected in the environment [10,11], as result of the O-methylation of the respective halogenated phenols. Hence, thermochemical data, more specifically enthalpies of formation in the gaseous state, are important to establish correlations between structure, energetic and reactivity, for a better understanding of the properties of the molecules, which are local units of complicated large biological molecules. As part of our * Corresponding author. Tel.: +351 22 0402 521; fax: +351 22 0402 522. E-mail address: [email protected] (M.A.V. Ribeiro da Silva). 0021-9614/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2008.11.008
interest on the thermochemistry of halogenated benzene derivatives and in view of a better understanding of the energetic effect of the substitution of a bromine atom in the aromatic ring, we have studied, in previous works, the thermochemical properties of bromine substituted benzoic acids [12], naphthalenes [13], anilines [14], pyridines [15] and indolines [16]. In the present paper, we extend our study to the mono bromine substituted anisoles. This paper reports the standard (p° = 0.1 MPa) molar enthalpies of formation, in the liquid phase, at T = 298.15 K, of the title compounds, derived from the standard molar energies of combustion, in oxygen, measured by rotating-bomb combustion calorimetry, and also the respective standard molar enthalpies of vaporization, measured by high temperature Calvet microcalorimetry, at T = 298.15 K. These two sets of values allowed the derivation of the standard molar enthalpies of formation, in the gaseous state, of 2-, 3- and 4-bromoanisole, and were compared with the results estimated by the Cox scheme [17] and those obtained by density functional theory calculations.
2. Experimental details 2.1. Materials and purity control The three liquid isomers of monobromoanisole namely, 2bromoanisole [CAS 578-57-4], 3-bromoanisole [CAS 2398-37-0],
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4-bromoanisole [CAS 104-92-7], with the assessed minimum purity of, respectively, 0.97, 0.98 and 0.99 (mass fraction), were supplied by Sigma–Aldrich Chemical Co and purified by repeated fractional distillations under reduced pressure, having been stored under nitrogen atmosphere. The final purity of all monobromoanisole isomers was checked by gas chromatography, performed on an Agilent 4890D gas chromatograph equipped with an HP-5 column, cross-linked, 5% diphenyl and 95% dimethylpolysiloxane (15 m 0.530 mm i.d. 1.5 lm film thickness), and with nitrogen as carrier gas. The 4-bromobenzoic acid [18] [CAS 586-76-5], BDH Organic Analytical Standard, recommended as test material for combustion calorimetry of bromine compounds [19], was obtained commercially from BDH Chemicals Ltd. and used as supplied. The relative atomic masses used throughout this paper were those recommended by the IUPAC Commission in 2005 [20] yielding the following molar masses: 187.0346 g mol1 for the monobromoanisoles and 201.0182 g mol1 for 4-bromobenzoic acid. The benzoic acid NIST Standard Reference Material, sample 39j [21] and the n-undecane (Aldrich, mass fraction purity > 0.999) were used, respectively, to calibrate the rotating bomb calorimeter and the high-temperature Calvet microcalorimeter. 2.2. Combustion calorimetry measurements The isoperibolic rotating-bomb combustion calorimeter that was formerly used at the National Physical Laboratory, Teddington, UK, was used to measure the massic energies of combustion of the 2-, 3- and 4-bromoanisole and 4-bromobenzoic acid. Both the apparatus and the operating technique have been described [22– 25], so only a brief description of the apparatus will be given here. For the combustion of bromine containing compounds it is recommend the use of tantalum-lined bombs [26]. So, in this work, the combustion experiments were performed with a twin-valve bomb lined with tantalum and with all the internal fittings also made from tantalum, having an internal volume of 0.329 dm3. The calorimetric system was calibrated with benzoic acid (NBS Standard Reference Material 39j), having a massic energy of combustion under standard bomb conditions of (26434 ± 3) J g1 [21]. Ten calibration experiments were made in oxygen, at p = 3.04 MPa, with 1.00 cm3 of deionised water added to the bomb, according to the procedure suggest by Coops et al. [27], leading to the value of the energy equivalent of the calorimeter: e(calor) = (20369.0 ± 2.3) J K1. The quoted uncertainty refers to the standard deviation of the mean. The calibration results, as well as the results of the combustion experiments of all the studied compounds (monobromoanisoles and of 4-bromobenzoic acid), were corrected to give the energy equivalents corresponding to the average mass of water added to the calorimeter: 3969.2 g. A Mettler PC 8000 balance, sensitivity ±101 g, was used to weigh the amount of distilled water added to the calorimeter from a weighed Perspex vessel. Calorimeter temperatures were measured within the bounds of ±104 K, with time intervals of 10 s using a Hewlett–Packard (HP2804A) quartz crystal thermometer interfaced to a PC programmed to collected data and to compute the adiabatic temperature change, by means of a version of the LABTERMO program [28]. At least 100 readings were taken for the main period and 125 for initial and final periods. For all combustions experiments, the ignition temperature was chosen so that the final temperature would be close to T = 298.15 K, and the rotation of the bomb was started when the temperature rise of the main period reached about 0.63 of its total value and was continued throughout the experiment. Employing this procedure, Good et al. [29] have shown that the frictional work due to the rotation of the bomb is automatically accounted in the temperature corrections for the work of water stirring and for the heat exchanged with the surrounding isother-
mal jacket. This jacket consists of a thermostatic bath containing a cavity of exactly the same shape as the calorimeter can, but 1 cm larger in overall dimensions. The water bath temperature was maintained at T = (299.050 ± 0.001) K using a temperature controller (Tronac PTC 41). To check the accuracy of the benzoic acid calibration and the experimental procedure, combustion experiments of 4-bromobenzoic acid, recommended as a test material for the combustion calorimetry of bromine compounds with an atomic ratio of hydrogen to bromine equal to or greater than unity [19], were performed. From six combustions done with 4-bromobenzoic acid in the pellet form, enclosed in polyester bags made from Melinex (0.025 mm thickness) using the technique described by Skinner and Snelson [30], at a pressure p = 3.04 MPa and in the presence of 20.00 cm3 of aqueous solution of As2O3 (0.09 mol dm3), Dc u ¼ ð15260:9 2:2Þ J g1 , where the uncertainty quoted is the overall standard deviation of the mean. Our experimental value is in excellent agreement with the recommended value [19], Dc u ¼ ð15261:0 4:2Þ J g1 , and with the previous value for the enthalpy of formation of 4-bromobenzoic acid obtained in this Laboratory using the same calorimetric system, Df Hm ðcrÞ ¼ 1 [12] (this work: Df Hm ðcrÞ ¼ ð379:5 ð379:6 1:3Þ kJ mol 1 1:6Þ kJ mol ). The values of Dc u refer to the reaction with HBr600H2O(l) as the single bromine-containing product in the final state. At the end of some experiments with 4-bromobenzoic acid a small residue of carbon was found due to incomplete combustion. If the carbon soot formed was found only on the walls of the platinum crucible, and not in the combustion solution or on the walls of the bomb, and if the amount of carbon soot formed was equal or lower than 1 mg, an energy correction was done based on the standard massic energy of combustion of carbon, Dc u ¼ 33 kJ g1 [27]. The liquid samples of bromoanisole isomers were also burnt enclosed in polyester bags made from Melinex (0.025 mm thickness), at a pressure p = 3.04 MPa and in the presence of 15.00 cm3 of an aqueous solution of As2O3 (0.09 mol dm3), in order to reduce all the free bromine produced by the combustion to hydrobromic acid. The extent of the oxidation of As2O3(aq) was determined by titration with a standardized iodine solution. For the calculation of the energetic term DU(As2O3), corresponding to the energy of oxidation of As2O3(aq) to As2O5(aq) in aqueous solution, the procedure described by Hu et al. [31], which uses the enthalpies of oxidation of As2O3(aq) by Br2 [32] and the thermal effects of mixing As2O5(aq) with strong acids [33], was followed. Within the precision of the analytical method, no evidence was found for oxidation of As2O3(aq) within about 5 h at room temperature in the presence of oxygen at p = 3.04 MPa. The nitric acid formed was determined using the Devarda’s alloy 1 method [34], and corrections were based on 59:7 kJ mol [35] for the standard molar energy of formation ðDf U m Þ, in which 0.1 mol dm3 HNO3(aq) is formed from O2(g), N2(g) and H2O(l). The amount of H2PtBr4(aq) formed was determined from the mass loss of the platinum crucible and its supporting ring, which leads to an energy correction based on Df Hm ðH2 PtBr4 ; aqÞ ¼ ð368:2 1 0:1Þ kJ mol [35]. For the cotton thread fuse of empirical formula CH1.686O0.843, Dc u ¼ 16; 240 J g1 [27] and for dry Melinex, Dc u ¼ ð22; 902 5Þ J g1 [30]; these values have been confirmed in our Laboratory. The mass of Melinex used in each experiment was corrected for the mass fraction of water (0.0032) and the mass of carbon dioxide produced from it was calculated using the factor previously reported [30]. The electrical energy for ignition was measured from the change in potential difference on the discharge of a capacitor (1281 lF) across a platinum wire (/ = 0.05 mm, Goodfellow, mass fraction 0.9999). The values of (ou/op)T at T = 298.15 K, were assumed to be 0:2 J g1 MPa1 [36] and 0:12 J g1 MPa1 [12], respectively,
M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505
for the title compounds and for 4-bromobenzoic acid. The specific densities, used to calculate the true mass from apparent mass in air, were q = 1.502 g cm3 [37], q = 1.477 g cm3 [37], q = 1.494 g cm3 [37] and q = 1.894 g cm3 [12], respectively, for 2-, 3- and 4-bromoanisole and 4-bromobenzoic acid. For each compound, DUR and the heat capacities of the bomb contents, ei and ef, were calculated by the procedure given by Bjellerup [38], using the solubility constants and energies of solution of CO2 and O2, as given by Hu et al. [31]. All the necessary weighings for the combustion experiments were made on a Mettler Toledo AE 240 balance, sensitivity of ±105 g, and corrections from apparent mass to true mass were introduced.
2.3. Calvet drop microcalorimetry The enthalpies of vaporization of the 2-, 3- and 4-bromoanisole were measured using the ‘‘vacuum sublimation drop microcalorimetric method”, described by Skinner et al. [39], for the sublimation of solid compounds, previously tested in our Laboratory for liquid vaporization [40]. Both apparatus and technique have been recently described [41]. In a typical experiment, the sample with a mass in the range 8– 10 mg was placed into a small glass capillary sealed at one end and weighed with a precision of ±106 g on a Mettler CH-8608 analytical balance. The sample and reference capillaries were simultaneously dropped at room temperature into the hot reaction cells of the High-Temperature Calvet Microcalorimeter (Setaram HT 1000), held at T = 329.0 K for 2- and 4-bromoanisole and at T = 328.9 K for 3-bromoansiole. After dropping the capillaries an endothermic peak due to the heating of the sample from room temperature to the temperature of the calorimeter was first observed. When the signal returned to the baseline the sample and reference cells were simultaneously evacuated and the measuring curve corresponding to the vaporization of the compound was acquired. The thermal corrections for the differences in the mass of both glass capillaries were minimized by dropping tubes of nearly equal mass into each of the twin calorimetric cells [41]. The obg;T Hm , have served standard molar enthalpies of vaporization, Dl;298:15K been corrected to T = 298.15 K using the corrective term DT298:15K Hm ðgÞ, which represents the molar enthalpic correction for gaseous phase, calculated by computational thermochemistry. The calorimeter was calibrated with n-undecane, 1 Dgl Hm ð298:15 KÞ ¼ ð56:580 0:566Þ kJ mol [19], using the same experimental procedure as for the compounds. From six independent experiments the calibration constant of the Calvet microcalorimeter was found to be: k(T = 329.0 K) = 1.0104 ± 0.0012, where the quoted uncertainty is the standard deviation of the mean. 2.4. Theoretical calculations The B3LYP exchange-correlation functional [42–44] together with the split-valence polarized 6-31+G(d) basis set [45] were used for the geometry optimization and frequencies calculation of the bromoanisole isomers studied in this work. The scaling factors of 0.9813 and 0.9636 were used for the calculation of the zero-point vibrational energies and for the fundamental vibrational frequencies, respectively [46]. The calculations were performed by means of the Gaussian 03 software package [47]. The above mentioned exchange-correlation functional was chosen since in previous work devoted to the thermochemistry of bromoanilines [14], B3LYP and BP86 with the 6-31+G(d) basis set, yielded identical results and permitted the estimation of accurate gas-phase enthalpies of formation for this class of compounds [48–50].
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3. Results 3.1. Experimental enthalpies of formation Table 1 lists the detailed results for one typical combustion experiment of 4-bromobenzoic acid and of each studied isomer of monobromoanisole, where the symbols have been defined elsewhere [31,38, 51]. The values of the internal energy associated with the isothermal bomb process, DU(IBP), were calculated using the expression (1):
DUðIBPÞ ¼ ðcalorÞcorr DT ad þ ðT i 298:15 KÞei þ ð298:15 K T i DT ad Þf þ DUðignÞ
ð1Þ
where DTad is the calorimeter temperature change corrected for the heat exchange and the work of stirring (adiabatic temperature rise), e(calor)corr. = ecalor + cp(H2O, l) Dm(H2O, l) and Dm(H2O) is the deviation of the mass of water added to the calorimeter from 3969.2 g, the mass assigned to e(calor). The full sets of results for the combustion experiments of 4-bromobenzoic acid and of each isomer of monobromoanisole are given in the Supporting information (Tables S1 to S4). The results of all the combustion experiments of each compound, together with the mean value, hDc u i, and its standard deviation of the mean, are given in table 2. These values of Dc u are referred to the idealized combustion reaction of monobromoanisole, yielding HBr 600H2O(l), accordingly to equation (2)
C7 H7 OBrðcrÞ þ 8O2 ðgÞ þ 597H2 OðlÞ ! 7CO2 ðgÞ þ HBr 600H2 OðlÞ;
ð2Þ
Table 3 lists the derived standard molar energies of combustion, Dc U m ðlÞ, and enthalpies of combustion, Dc Hm ðlÞ, as well as the standard molar enthalpies of formation, Df Hm ðlÞ, for the bromoanisole isomers in the liquid phase at T = 298.15 K. The values of Df Hm ðlÞ were derived from Dc Hm ðlÞ, using the values of the Df Hm of CO2(g), H2O(l) and HBr 600H2O(l), at T = 298.15 K, which are 1 1 [52], ð285:830 0:042Þ kJ mol ð393:51 0:13Þ kJ mol 1 [52] and ð120:294 0:005Þ kJ mol [35,52], respectively. The values of the standard molar enthalpies of vaporization, Dg;T l;298:15K Hm , measured by Calvet microcalorimetry, are given in table 4, where the uncertainties are taken as standard deviations of the mean of five individual results. In accordance with normal thermochemical practice [53,54], the uncertainties assigned to the standard molar enthalpies of combustion, and of vaporization, at T = 298.15 K, are twice the overall standard deviation of the mean and include the uncertainties in calibration and those from the auxiliary quantities used. In table 5 are summarized the values of the standard molar enthalpies of formation, in the gaseous phase, Df Hm ðgÞ, derived from the standard molar enthalpies of formation in the liquid phase, Df Hm ðlÞ, and the standard molar enthalpies of vaporization, Dgl Hm ð298:15 KÞ, all at T = 298.15 K. 3.2. Enthalpies of formation estimated with the Cox scheme The values of Df Hm ðgÞ are compared (table 6) with values estimated using the Cox scheme [17] which assumes that the enthalpy increment for substitution of bromine atom in the different positions of anisole will be the same as for substitution of bromine 1 in benzene with a correction term of 4 kJ mol that was applied for the ortho-pair of substituents. To obtain the estimated values, 1 Df Hm ðgÞ of benzene ð82:6 0:7Þ kJ mol [55], bromobenzene 1 1 [55] and anisole ð67:9 0:8Þ kJ mol ð105:4 4:1Þ kJ mol [55], at T = 298.15 K, were used. Thus, based on the Cox scheme,
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TABLE 1 Typical combustion results at T = 298.15 K (p° = 0.1 MPa), for the 4-bromobenzoic acid and of the monobromoanisole isomers.
m(cpd)/g m0 (fuse)/g m00 (Melinex)/g Ti/K Tf/K DTad/K ei/(J K1) ef /(J K1) e(calor)corr./(J K1) Dm(H2O)/g DU(IBP)a/J DU(fuse)/J DU(Melinex)/J DU(HNO3)/J DU(As2O3)/J DU(H2PtBr4)/J DU(ign)/J DUR/J Dcu°/(J g1)
4-Bromobenzoic acid
2-Bromoanisole
3-Bromoanisole
4-Bromoanisole
0.79310 0.00251 0.04128 297.4558 298.1465 0.65687 95.79 94.19 20372.3 0.8 13443.82 40.76 945.35 0.78 324.46 0.06 1.11 26.88 15263.56
0.83724 0.00263 0.03939 297.2827 298.1754 0.85943 75.27 73.93 20374.9 1.4 17574.39 42.71 902.17 3.34 355.03 0.01 1.11 24.67 19404.78
0.72263 0.00253 0.03932 297.3684 298.1508 0.74742 75.14 73.84 20369.4 0.1 15279.60 41.09 900.57 4.18 308.82 0.15 1.10 21.65 19378.02
0.68072 0.00267 0.03936 297.3997 298.1395 0.70689 75.09 73.83 20360.6 2.0 14444.73 43.36 901.49 3.94 285.58 0.06 1.11 20.57 19376.15
m(cpd), m0 (fuse) and m00 (Melinex) are the mass of compound burnt, the mass of fuse (cotton) and the mass of Melinex, respectively, used in each experiment; Ti is the initial temperature rise; Tf is the final temperature rise; DTad is the corrected temperature rise; ei and ef are the energy equivalent of contents in the initial and final states, respectively; e(calor)corr. is the energy equivalent of the calorimeter; Dm(H2O) is the deviation of mass of water added to the calorimeter from 3969.2 g; DU(IBP) is the energy change for the isothermal combustion reaction under actual bomb conditions; DU(fuse) is the energy of combustion of the fuse (cotton); DU(Melinex) is the energy combustion of the Melinex; DU(HNO3) is the energy correction for the nitric acid formation; DU(As2O3) is the energy of oxidation of the aqueous solution of As2O3; DU(H2PtBr4) is the energy correction for the formation of the platinum complex; DU(ign) is the electrical energy for ignition; DUR is the standard state correction; Dc u is the standard massic energy of combustion. a DU(IBP) includes DU(ign).
TABLE 2 Individual values of standard (p° = 0.1 MPa) massic energies of combustion Dc u , of the 4-bromobenzoic acid and of the three bromoanisoles, at T = 298.15 K. 4-Bromobenzoic acid
2-Bromoanisole
3-Bromoanisole
4-Bromoanisole
19404.78 19406.70 19399.45 19403.18 19406.10 19396.02
19378.02 19373.50 19368.58 19379.01 19379.22 19376.85
19378.81 19369.33 19381.06 19378.34 19376.15 19366.95
19402.7 ± 1.7
19375.9 ± 1.7
19375.1 ± 2.3
Dc u =J g 1 15263.40 15265.76 15263.56 15264.59 15253.74 15254.62 hDc u i=ðJ g 1 Þa 15260.9 ± 2.2 a
Mean value and standard deviation of the mean.
the characteristic increment in Df Hm ðgÞ calculated for the introduction of a bromine atom in a benzene ring is 1 ð22:8 4:2Þ kJ mol , and the Df Hm ðgÞ for the different isomers of bromoanisole was estimated.
The values of Df Hm ðgÞ estimated by the Cox scheme, reported in table 6, are in excellent agreement with the experimental ones, dif1 fering from the experimental ones by 1:4—3:4 kJ mol (absolute deviation), with the differences D between experimental and estimated values of Df Hm ðgÞ being smaller than the associated uncertainties. 3.3. Theoretical enthalpies of formation The most stable conformations obtained for all the three bromo-substituted anisoles, taking into account the geometry optimization performed at the B3LYP/6-31+G(d) (Table S5 of the Supplementary Information), were those where the methoxy group is coplanar with the aromatic benzene ring, like anisole itself [56], with the methoxy group in anti orientation with respect to bromine atom for the 2- and 3-bromoanisole. Figure 1 presents selected geometrical parameters for the most stable conformations of the three bromo-substituted anisoles, as well as for anisole and bromobenzene. The ortho, meta or para substitution of a bromine atom in anisole seems to have a small influence on the geometrical parameters of the corresponding bromoanisoles.
TABLE 3 Derived standard molar energies of combustion, Dc U m , standard molar enthalpies of combustion, Dc Hm , and standard molar enthalpies of formation, Df Hm , in the condensed phase, for the bromoanisole isomers at T = 298.15 K, with p° = 0.1 MPa. Compound
Dc U m ðlÞ=ðkJ mol
2-Bromoanisole (l) 3-Bromoanisole (l) 4-Bromoanisole (l)
3629.0 ± 1.4 3624.0 ± 1.4 3623.8 ± 1.5
1
Dc Hm ðlÞ=ðkJ mol
Þ
1
Df Hm ðlÞ=ðkJ mol
Þ
3631.5 ± 1.4 3626.5 ± 1.4 3626.3 ± 1.5
1
Þ
101.5 ± 1.7 106.5 ± 1.7 106.7 ± 1.8
TABLE 4 Standard (p° = 0.1 MPa) molar enthalpies of vaporization, Dgl Hm , at T = 298.15 K determined by microcalorimetry for the monobromoanisole isomers. Compound
Number of experiments
T=K
1 Dg;T H =ðkJ mol Þ l;298:15K m
DT298:15K Hm ðgÞ=ðkJ mol1 Þ
Dgl Hm ð298:15KÞ=ðkJ mol1 Þ
2-Bromoanisole (l) 3-Bromoanisole (l) 4-Bromoanisole (l)
5 5 5
329.0 328.9 329.0
66.2 ± 0.2 62.4 ± 0.2 62.8 ± 0.1
4.4 4.4 4.5
61.8 ± 1.3 58.0 ± 1.2 58.3 ± 1.2
503
M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505 TABLE 5 Standard (po = 0.1 MPa) molar enthalpies of formation, in both condensed and gaseous phase, and standard molar enthalpies of vaporization, at T = 298.15 K. 1
Compound
Df Hm ðlÞ=ðkJ mol
2-Bromoanisole 3-Bromoanisole 4-Bromoanisole
101.5 ± 1.7 106.5 ± 1.7 106.7 ± 1.8
Dgl Hm ð298:15KÞ=ðkJ mol
Þ
61.8 ± 1.3 58.0 ± 1.2 58.3 ± 1.2
TABLE 6 Experimental and estimated (Cox scheme and DFT calculations) gas-phase enthalpies of formation for the isomers of bromoanisoles. Compound
2-Bromoanisole 3-Bromoanisole 4-Bromoanisole a b
Df Hm ðgÞ=ðkJ mol
1
Da/kJ mol1
Þ
Experimental
Cox scheme
DFTb
Cox scheme
DFTb
39.7 ± 2.1 48.5 ± 2.1 48.4 ± 2.2
41.1 ± 4.2 45.1 ± 4.2 45.1 ± 4.2
44.1 50.3 48.2
1.4 ± 4.7 3.4 ± 4.7 3.3 ± 4.7
4.4 1.8 0.2
Difference between the experimental and the estimated values. Calculated at B3LYP/6-31+G(d) level of theory.
However, one can notice a small increase of the C–C–O angle in the ortho isomer due probably to the repulsive interaction with the bromine atom. The angle increases in order to minimize the steric repulsion, but the rigidity of the molecule prohibits larger deformations. The energies of all monobromoanisoles, and those of anisole, benzene and bromobenzene, calculated at the B3LYP/6-31+G(p), and corrected for T = 298.15 K, were used to compute the enthalpy of the homodesmic reaction described by the following equation:
ð3Þ Combining those enthalpies of reaction with the experimental Df Hm ðgÞ of benzene, anisole and bromobenzene given above [55], it was possible to estimate the Df Hm ðgÞ of the bromoanisole isomers. The DFT estimated values for all bromoanisoles are summa-
1
Þ
1
Df Hm ðgÞ=ðkJ mol
Þ
39.7 ± 2.1 48.5 ± 2.1 48.4 ± 2.2
rized in table 6. The values agree well with the experimental ones and the larger deviation occurs for the 2-bromoanisole isomer, where it is predicted a less pronounced steric effect between the two groups in ortho position. However, the ordering of the estimated enthalpies of formation for the three compounds is in agreement with the experimentally determined enthalpies of formation, and the difference between the experimental and calculated results for 2-bromoanisole is acceptable since it lies on the interval of desired accuracy for computational thermochemistry approaches.
4. Discussion From the literature value of the standard molar enthalpies of formation in the gaseous phase of the anisole, ð67:9 0:8Þ 1 kJ mol [55], and of the monobromoanisoles reported in this paper, the enthalpic increments calculated for the introduction of a bromine atom in the ortho, meta and para positions of the anisole 1 ring are, respectively, ð28:2 2:2Þ kJ mol , ð19:4 2:2Þ and 1 ð19:5 2:3Þ kJ mol , as shown in figure 2. From this scheme, it can be seen that the insertion of a bromine atom in ortho position of the anisole ring, induces an additional destabilization effect not observed for that substitution in the meta and para positions. Hence, the 2-bromoanisole is the least stable isomer due to the steric interactions between the two groups, being the 3- and 4-bromoanisole isomers the most stable ones, having similar enthalpic stability. It is also verified that the enthalpic increment of substitution of a bromine atom in the anisole ring is, within the associated uncertainties, similar to the observed for the introduction of a bromine atom in the aromatic ring of the benzene: 1 ð22:8 4:2Þ kJ mol .
FIGURE 1. Optimized most stable configurations for the monobromoanisoles. Selected distances are in Å and angles in degrees.
504
M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505
15.4 ± 2.5
28.2 ± 2.2
Br
Br
NH2
OCH3
−8.8 ± 3.0
Br
Br
20.9 ± 2.5
19.4 ± 2.2
−8.7 ± 3.0
OCH3
7.4 ± 3.4
NH2
−67.9 ± 0.8 [55] 87.1 ± 0.7 [55]
OCH3
0.1 ± 3.0
NH2
OCH3
1.9 ± 3.4
108.0 ± 2.3
−48.5 ± 2.1 Br
5.5 ± 3.3
102.5 ± 2.3
−39.7 ± 2.1
19.5 ± 2.3
− 48.4 ± 2.2
22.8 ± 2.7
Br
NH2
109.9 ± 2.5
FIGURE 2. Enthalpic effect of substitution of a bromine atom in the ortho, meta and para position of the aromatic ring of anisole and aniline, and isomerisation energies (all 1 values are in kJ mol ).
Comparable findings were observed for the monobromoaniline isomers [14] (figure 2), for which the enthalpic effect of substitution of a bromine atom in the 3- and 4-position of the aniline ring 1 and ð22:8 4:2Þ kJ is also very similar, ð20:9 2:5Þ kJ mol 1 mol , respectively. For the 2-bromoaniline the enthalpic increment for the introduction in ortho position of a bromine atom 1 was found to be ð15:4 2:5Þ kJ mol , yielding a higher effect of stabilization comparing with the observed in the 2-bromoanisole due to the presence, in the former case, of an intramolecular hydrogen bond between the bromine atom and the hydrogen atoms of the amino group [14]. The values of Df Hm obtained by DFT calculations also give the 2-bromoanisole as the least stable isomer, but sets the 3-bromoanisole slightly more stable than the 4-bromoanisole. The good agreement between experimental and computed values supports the conclusions obtained from the analysis of geometrical parameters, showing that the energetics of these compounds are mainly governed by the presence or absence of destabilizing steric interactions between the bromine atom and the other substituent. The substitution of a bromine atom in the meta or in the para positions do not exert any significant energetic effect on the molecule. For the studied compounds, the Cox scheme [17] revealed to be a good method of estimate yielding values of enthalpies of formation in the gas-phase involving an absolute deviation from the 1 experimental values not larger than 3:4 kJ mol . Acknowledgments Thanks are due to Fundação para a Ciência e Tecnologia (FCT), Lisbon, Portugal and to FEDER for financial support to Centro de Investigação em Química, University of Porto. A.I.M.C.L.F. thanks FCT and the European Social Fund (ESF) under the Community Support Framework (CSF) for the award of the post-doctoral fellowship (SFRH/BPD/27053/2006). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jct.2008.11.008. References [1] J. Zilberman, Org. Process Res. Dev. 7 (2003) 303–305. [2] I.J. Kim, C.M. Dersch, R.B. Rothman, A.E. Jacobsona, K.C. Rice, Bioorg. Med. Chem. 12 (2004) 4543–4550. [3] M. Protiva, Drugs Future 16 (1991) 911–916. [4] C. Pampillón, O. Mendoza, N.J. Sweeney, K. Strohfeldt, M. Tacke, Polyhedron 25 (2006) 2101–2108.
[5] D. Nasipuri, A.K. Mitra, J. Chem. Soc., Perkin Trans. 1 (1973) 285–287. [6] S. Bhattacharya, M. Banerjee, Chem. Phys. Lett. 396 (2004) 377–383. [7] S. Bhattacharya, A.K. Bauri, S. Chattopadhyay, M. Banerjee, J. Phys. Chem. B 109 (2005) 7182–7187. [8] S. Bhattacharya, A.K. Bauri, S. Chattopadhyay, M. Banerjee, Chem. Phys. Lett. 401 (2005) 323–331. [9] X. Cheng, G.-H. Hou, J.-H. Xie, Q.-L. Zhou, Org. Lett. 6 (2004) 2381–2383. [10] U. Führer, K. Ballschmiter, Environ. Sci. Technol. 32 (1998) 2208–2215. [11] C. Flodin, F.B. Whitfield, Phytochemistry 53 (2000) 77–80. [12] M.L.C.C.H. Ferrão, G. Pilcher, J. Chem. Thermodyn. 19 (1987) 543–548. [13] M.A.V. Ribeiro da Silva, M.L.C.C.H. Ferrão, A.J.M. Lopes, J. Chem. Thermodyn. 25 (1993) 229–235. [14] M.A.V. Ribeiro da Silva, A.I.M.C.L. Ferreira, J.R.B. Gomes, Bull. Chem. Soc. Jpn. 79 (2006) 1852–1859. [15] M.A.V. Ribeiro da Silva, M.A.R. Matos, L.M.P.F. Amaral, J. Chem. Thermodyn. 29 (1997) 1545–1551. [16] M.A.V. Ribeiro da Silva, J.I.T.A. Cabral, J. Chem. Thermodyn. 41 (2008) 84–89. [17] J.D. Cox, A Method for Estimating the Enthalpies of Formation of Benzene Derivatives in the Gas State, NPL Report CHEM 83, June 1978. [18] Society for Analytical Chemistry, Analyst 97 (1972) 740–756. [19] R. Sabbah, A. Xu-wu, J.S. Chickos, M.L. Planas Leitão, M.V. Roux, L.A. Torres, Thermochim. Acta 331 (1999) 93–204. [20] M.E. Wieser, Pure Appl. Chem. 78 (2006) 2051–2066. [21] Certificate of Analysis, Standard Reference Material 39j, Benzoic Acid Calorimetric Standard, NIST, Gaithersburg, 1995. [22] J.D. Cox, H.A. Gundry, A. Head, Trans. Faraday Soc. 60 (1964) 653–665. [23] H.A. Gundry, A. Head, J. Chem. Thermodyn. 10 (1978) 195–200. [24] M.D.M.C. Ribeiro da Silva, P. Souza, G. Pilcher, J. Chem. Thermodyn. 21 (1989) 173–178. [25] M.A.V. Ribeiro da Silva, J.M. Gonçalves, G. Pilcher, J. Chem. Thermodyn. 29 (1997) 253–260. [26] A.J. Head, W.D. Good, in: S. Sunner, M. Månsson (Eds.), Combustion Calorimetry, Pergamon, Oxford, 1979 (Chapter 9). [27] J. Coops, R.S. Jessup, K. Van Nes, in: F.D. Rossini (Ed.), Experimental Thermochemistry, vol. 1, Interscience, New York, 1956 (Chapter 3). [28] L.M.N.B.F. Santos, Ph.D. Thesis, University of Porto, 1995. [29] W.D. Good, D.W. Scott, G. Waddington, J. Phys. Chem. 60 (1956) 1080–1089. [30] A. Snelson, H.A. Skinner, Trans. Faraday Soc. 56 (1960) 1776–1783. [31] A.T. Hu, G.C. Sinke, M. Månsson, B. Ringnér, J. Chem. Thermodyn. 4 (1972) 283– 299. [32] L. Bjellerup, Acta Chem. Scand. 11 (1957) 1761–1765. [33] P. Sellers, S. Sunner, I. Wadsö, Acta Chem. Scand. 18 (1964) 202–206. [34] A.I. Vogel, Quantitative Inorganic Analysis, Longmans, London, 1978. [35] The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data, 11(Suppl. 2) (1982). [36] E.W. Washburn, J. Res. Natl. Bur. Stand. (US) 10 (1933) 525–558. [37] Handbook of Fine Chemicals and Laboratory Equipment, Aldrich – España/ Portugal, 2007–2008. [38] L. Bjellerup, in: H.A. Skinner (Ed.), Experimental Thermochemistry, vol. 2, Interscience, New York, 1962 (Chapter 3). [39] F.A. Adedeji, D.L.S. Brown, J.A. Connor, M.L. Leung, M.I. Paz-Andrade, H.A. Skinner, J. Organomet. Chem. 97 (1975) 221–228. [40] M.A.V. Ribeiro da Silva, M.A.R. Matos, L.M.P.F. Amaral, J. Chem. Thermodyn. 27 (1995) 565–574. [41] L.M.N.B.F. Santos, B. Schröder, O.O.P. Fernandes, M.A.V. Ribeiro da Silva, Thermochim. Acta 415 (2004) 15–20. [42] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652. [43] A.D. Becke, Phys. Rev. A 38 (1988) 3098–3100. [44] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789. [45] M.J. Frisch, J.A. Pople, J.S. Binkley, J. Chem. Phys. 80 (1984) 3265–3269. [46] J.P. Merrick, D. Moran, L. Radom, J. Phys. Chem. A 111 (2007) 11683–11700. [47] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,
M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505 J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian03, Revision C.02, Gaussian Inc., Pittsburgh, PA, 2004. [48] M.A.V. Ribeiro da Silva, L.M. Spencer, S. Lima, L.M.P.F. Amaral, A.I.M.C.L. Ferreira, J.R.B. Gomes, J. Chem. Thermodyn. 35 (2003) 1343–1359. [49] J.R.B. Gomes, M.A.V. Ribeiro da Silva, J. Phys. Chem. A 107 (2003) 869–874.
505
[50] M.A.V. Ribeiro da Silva, A.I.M.C.L. Ferreira, J.R.B. Gomes, Chem. Phys. Lett. 422 (2006) 565–570. [51] W.N. Hubbard, D.W. Scott, G. Waddington, in: F.D. Rossini (Ed.), Experimental Thermochemistry, vol. 1, Interscience, New York, 1956 (Chapter 5). [52] J.D. Cox, D.D. Wagman, V.A. Medvedev (Eds.), CODATA Key Values for Thermodynamics, Hemisphere, New York, 1989. [53] F.D. Rossini, in: F.D. Rossini (Ed.), Experimental Thermochemistry, vol. 1, Interscience, New York, 1956 (Chapter 14). [54] G. Olofsson, in: S. Sunner, M. Månsson (Eds.), Combustion Calorimetry, Pergamon, Oxford, 1979 (Chapter 6). [55] J.B. Pedley, Thermochemical Data and Structures of Organic Compounds, Thermodynamics Research Center, College Station, Texas, 1994. [56] M. Onda, A. Toda, S. Mori, I. Yamaguchi, J. Mol. Struct. 144 (1986) 47–51.
JCT 08-373
Contents lists available at ScienceDirect
J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct
Experimental and computational study on the molecular energetics of monobromoanisole isomers Manuel A.V. Ribeiro da Silva *, Ana I.M.C. Lobo Ferreira Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal
a r t i c l e
i n f o
Article history: Received 17 October 2008 Accepted 11 November 2008 Available online 25 November 2008 Keywords: Thermochemistry Energy of combustion Enthalpy of vaporization Enthalpy of formation Rotating bomb combustion calorimetry Calvet microcalorimetry Cox scheme Computational thermochemistry Bromoanisole isomers
a b s t r a c t The standard (p° = 0.1 MPa) molar enthalpies of formation in the liquid phase of three isomers of bromoanisole were derived from the standard molar energies of combustion, in oxygen, which yields CO2(g) and HBr 600H2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The determination of the standard molar enthalpies of vaporization of these compounds, at T = 298.15 K, was done by Calvet microcalorimetry using the high-temperature vacuum sublimation technique. Combining the former sets of experimental results, the standard molar enthalpies of formation, in the gas-phase, were derived. The gas-phase enthalpies of formation were also estimated by means of the empirical scheme developed by Cox and by density functional theory calculations performed at the B3LYP/6-31+G(d) level of theory. Dc U m ðlÞ=ðkJ mol 2-Bromoanisole 3-Bromoanisole 4-Bromoanisole
3629.0 ± 1.4 3624.0 ± 1.4 3623.8 ± 1.5
1
Þ
Df Hm ðlÞ=ðkJ mol 101.5 ± 1.7 106.5 ± 1.7 106.7 ± 1.8
1
Þ
Dgl Hm =ðkJ mol1 Þ 61.8 ± 1.3 58.0 ± 1.2 58.3 ± 1.2
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The anisole (methoxybenzene) and its derivatives have received considerable attention mainly in pharmaceutical industries, as well as in new technologies and development of new materials. The bromoanisole (bromomethoxybenzene) isomers are used as starting material of many drugs with high therapeutic potential, such as analgesics [1,2], antidepressant [3], anti-cancer and drugs [4,5]. Recently, it was investigated the complexation of [60]fullerene [6,7] and [70]fullerene [8] with anisole, 3- and 4-bromoanisole, in order to provide novel materials with unusual conducting and magnetic properties. The 3-bromoanisole was used in the synthesis of 9,90 -spirobifluorene-1,10 -diol [9], a backbone molecule with a wide range of applications in molecular electronics, light-emitting materials and enantioselective molecular recognition. Although halogenated anisoles are not produced in large quantities, they have been extensively detected in the environment [10,11], as result of the O-methylation of the respective halogenated phenols. Hence, thermochemical data, more specifically enthalpies of formation in the gaseous state, are important to establish correlations between structure, energetic and reactivity, for a better understanding of the properties of the molecules, which are local units of complicated large biological molecules. As part of our * Corresponding author. Tel.: +351 22 0402 521; fax: +351 22 0402 522. E-mail address: [email protected] (M.A.V. Ribeiro da Silva). 0021-9614/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2008.11.008
interest on the thermochemistry of halogenated benzene derivatives and in view of a better understanding of the energetic effect of the substitution of a bromine atom in the aromatic ring, we have studied, in previous works, the thermochemical properties of bromine substituted benzoic acids [12], naphthalenes [13], anilines [14], pyridines [15] and indolines [16]. In the present paper, we extend our study to the mono bromine substituted anisoles. This paper reports the standard (p° = 0.1 MPa) molar enthalpies of formation, in the liquid phase, at T = 298.15 K, of the title compounds, derived from the standard molar energies of combustion, in oxygen, measured by rotating-bomb combustion calorimetry, and also the respective standard molar enthalpies of vaporization, measured by high temperature Calvet microcalorimetry, at T = 298.15 K. These two sets of values allowed the derivation of the standard molar enthalpies of formation, in the gaseous state, of 2-, 3- and 4-bromoanisole, and were compared with the results estimated by the Cox scheme [17] and those obtained by density functional theory calculations.
2. Experimental details 2.1. Materials and purity control The three liquid isomers of monobromoanisole namely, 2bromoanisole [CAS 578-57-4], 3-bromoanisole [CAS 2398-37-0],
500
M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505
4-bromoanisole [CAS 104-92-7], with the assessed minimum purity of, respectively, 0.97, 0.98 and 0.99 (mass fraction), were supplied by Sigma–Aldrich Chemical Co and purified by repeated fractional distillations under reduced pressure, having been stored under nitrogen atmosphere. The final purity of all monobromoanisole isomers was checked by gas chromatography, performed on an Agilent 4890D gas chromatograph equipped with an HP-5 column, cross-linked, 5% diphenyl and 95% dimethylpolysiloxane (15 m 0.530 mm i.d. 1.5 lm film thickness), and with nitrogen as carrier gas. The 4-bromobenzoic acid [18] [CAS 586-76-5], BDH Organic Analytical Standard, recommended as test material for combustion calorimetry of bromine compounds [19], was obtained commercially from BDH Chemicals Ltd. and used as supplied. The relative atomic masses used throughout this paper were those recommended by the IUPAC Commission in 2005 [20] yielding the following molar masses: 187.0346 g mol1 for the monobromoanisoles and 201.0182 g mol1 for 4-bromobenzoic acid. The benzoic acid NIST Standard Reference Material, sample 39j [21] and the n-undecane (Aldrich, mass fraction purity > 0.999) were used, respectively, to calibrate the rotating bomb calorimeter and the high-temperature Calvet microcalorimeter. 2.2. Combustion calorimetry measurements The isoperibolic rotating-bomb combustion calorimeter that was formerly used at the National Physical Laboratory, Teddington, UK, was used to measure the massic energies of combustion of the 2-, 3- and 4-bromoanisole and 4-bromobenzoic acid. Both the apparatus and the operating technique have been described [22– 25], so only a brief description of the apparatus will be given here. For the combustion of bromine containing compounds it is recommend the use of tantalum-lined bombs [26]. So, in this work, the combustion experiments were performed with a twin-valve bomb lined with tantalum and with all the internal fittings also made from tantalum, having an internal volume of 0.329 dm3. The calorimetric system was calibrated with benzoic acid (NBS Standard Reference Material 39j), having a massic energy of combustion under standard bomb conditions of (26434 ± 3) J g1 [21]. Ten calibration experiments were made in oxygen, at p = 3.04 MPa, with 1.00 cm3 of deionised water added to the bomb, according to the procedure suggest by Coops et al. [27], leading to the value of the energy equivalent of the calorimeter: e(calor) = (20369.0 ± 2.3) J K1. The quoted uncertainty refers to the standard deviation of the mean. The calibration results, as well as the results of the combustion experiments of all the studied compounds (monobromoanisoles and of 4-bromobenzoic acid), were corrected to give the energy equivalents corresponding to the average mass of water added to the calorimeter: 3969.2 g. A Mettler PC 8000 balance, sensitivity ±101 g, was used to weigh the amount of distilled water added to the calorimeter from a weighed Perspex vessel. Calorimeter temperatures were measured within the bounds of ±104 K, with time intervals of 10 s using a Hewlett–Packard (HP2804A) quartz crystal thermometer interfaced to a PC programmed to collected data and to compute the adiabatic temperature change, by means of a version of the LABTERMO program [28]. At least 100 readings were taken for the main period and 125 for initial and final periods. For all combustions experiments, the ignition temperature was chosen so that the final temperature would be close to T = 298.15 K, and the rotation of the bomb was started when the temperature rise of the main period reached about 0.63 of its total value and was continued throughout the experiment. Employing this procedure, Good et al. [29] have shown that the frictional work due to the rotation of the bomb is automatically accounted in the temperature corrections for the work of water stirring and for the heat exchanged with the surrounding isother-
mal jacket. This jacket consists of a thermostatic bath containing a cavity of exactly the same shape as the calorimeter can, but 1 cm larger in overall dimensions. The water bath temperature was maintained at T = (299.050 ± 0.001) K using a temperature controller (Tronac PTC 41). To check the accuracy of the benzoic acid calibration and the experimental procedure, combustion experiments of 4-bromobenzoic acid, recommended as a test material for the combustion calorimetry of bromine compounds with an atomic ratio of hydrogen to bromine equal to or greater than unity [19], were performed. From six combustions done with 4-bromobenzoic acid in the pellet form, enclosed in polyester bags made from Melinex (0.025 mm thickness) using the technique described by Skinner and Snelson [30], at a pressure p = 3.04 MPa and in the presence of 20.00 cm3 of aqueous solution of As2O3 (0.09 mol dm3), Dc u ¼ ð15260:9 2:2Þ J g1 , where the uncertainty quoted is the overall standard deviation of the mean. Our experimental value is in excellent agreement with the recommended value [19], Dc u ¼ ð15261:0 4:2Þ J g1 , and with the previous value for the enthalpy of formation of 4-bromobenzoic acid obtained in this Laboratory using the same calorimetric system, Df Hm ðcrÞ ¼ 1 [12] (this work: Df Hm ðcrÞ ¼ ð379:5 ð379:6 1:3Þ kJ mol 1 1:6Þ kJ mol ). The values of Dc u refer to the reaction with HBr600H2O(l) as the single bromine-containing product in the final state. At the end of some experiments with 4-bromobenzoic acid a small residue of carbon was found due to incomplete combustion. If the carbon soot formed was found only on the walls of the platinum crucible, and not in the combustion solution or on the walls of the bomb, and if the amount of carbon soot formed was equal or lower than 1 mg, an energy correction was done based on the standard massic energy of combustion of carbon, Dc u ¼ 33 kJ g1 [27]. The liquid samples of bromoanisole isomers were also burnt enclosed in polyester bags made from Melinex (0.025 mm thickness), at a pressure p = 3.04 MPa and in the presence of 15.00 cm3 of an aqueous solution of As2O3 (0.09 mol dm3), in order to reduce all the free bromine produced by the combustion to hydrobromic acid. The extent of the oxidation of As2O3(aq) was determined by titration with a standardized iodine solution. For the calculation of the energetic term DU(As2O3), corresponding to the energy of oxidation of As2O3(aq) to As2O5(aq) in aqueous solution, the procedure described by Hu et al. [31], which uses the enthalpies of oxidation of As2O3(aq) by Br2 [32] and the thermal effects of mixing As2O5(aq) with strong acids [33], was followed. Within the precision of the analytical method, no evidence was found for oxidation of As2O3(aq) within about 5 h at room temperature in the presence of oxygen at p = 3.04 MPa. The nitric acid formed was determined using the Devarda’s alloy 1 method [34], and corrections were based on 59:7 kJ mol [35] for the standard molar energy of formation ðDf U m Þ, in which 0.1 mol dm3 HNO3(aq) is formed from O2(g), N2(g) and H2O(l). The amount of H2PtBr4(aq) formed was determined from the mass loss of the platinum crucible and its supporting ring, which leads to an energy correction based on Df Hm ðH2 PtBr4 ; aqÞ ¼ ð368:2 1 0:1Þ kJ mol [35]. For the cotton thread fuse of empirical formula CH1.686O0.843, Dc u ¼ 16; 240 J g1 [27] and for dry Melinex, Dc u ¼ ð22; 902 5Þ J g1 [30]; these values have been confirmed in our Laboratory. The mass of Melinex used in each experiment was corrected for the mass fraction of water (0.0032) and the mass of carbon dioxide produced from it was calculated using the factor previously reported [30]. The electrical energy for ignition was measured from the change in potential difference on the discharge of a capacitor (1281 lF) across a platinum wire (/ = 0.05 mm, Goodfellow, mass fraction 0.9999). The values of (ou/op)T at T = 298.15 K, were assumed to be 0:2 J g1 MPa1 [36] and 0:12 J g1 MPa1 [12], respectively,
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for the title compounds and for 4-bromobenzoic acid. The specific densities, used to calculate the true mass from apparent mass in air, were q = 1.502 g cm3 [37], q = 1.477 g cm3 [37], q = 1.494 g cm3 [37] and q = 1.894 g cm3 [12], respectively, for 2-, 3- and 4-bromoanisole and 4-bromobenzoic acid. For each compound, DUR and the heat capacities of the bomb contents, ei and ef, were calculated by the procedure given by Bjellerup [38], using the solubility constants and energies of solution of CO2 and O2, as given by Hu et al. [31]. All the necessary weighings for the combustion experiments were made on a Mettler Toledo AE 240 balance, sensitivity of ±105 g, and corrections from apparent mass to true mass were introduced.
2.3. Calvet drop microcalorimetry The enthalpies of vaporization of the 2-, 3- and 4-bromoanisole were measured using the ‘‘vacuum sublimation drop microcalorimetric method”, described by Skinner et al. [39], for the sublimation of solid compounds, previously tested in our Laboratory for liquid vaporization [40]. Both apparatus and technique have been recently described [41]. In a typical experiment, the sample with a mass in the range 8– 10 mg was placed into a small glass capillary sealed at one end and weighed with a precision of ±106 g on a Mettler CH-8608 analytical balance. The sample and reference capillaries were simultaneously dropped at room temperature into the hot reaction cells of the High-Temperature Calvet Microcalorimeter (Setaram HT 1000), held at T = 329.0 K for 2- and 4-bromoanisole and at T = 328.9 K for 3-bromoansiole. After dropping the capillaries an endothermic peak due to the heating of the sample from room temperature to the temperature of the calorimeter was first observed. When the signal returned to the baseline the sample and reference cells were simultaneously evacuated and the measuring curve corresponding to the vaporization of the compound was acquired. The thermal corrections for the differences in the mass of both glass capillaries were minimized by dropping tubes of nearly equal mass into each of the twin calorimetric cells [41]. The obg;T Hm , have served standard molar enthalpies of vaporization, Dl;298:15K been corrected to T = 298.15 K using the corrective term DT298:15K Hm ðgÞ, which represents the molar enthalpic correction for gaseous phase, calculated by computational thermochemistry. The calorimeter was calibrated with n-undecane, 1 Dgl Hm ð298:15 KÞ ¼ ð56:580 0:566Þ kJ mol [19], using the same experimental procedure as for the compounds. From six independent experiments the calibration constant of the Calvet microcalorimeter was found to be: k(T = 329.0 K) = 1.0104 ± 0.0012, where the quoted uncertainty is the standard deviation of the mean. 2.4. Theoretical calculations The B3LYP exchange-correlation functional [42–44] together with the split-valence polarized 6-31+G(d) basis set [45] were used for the geometry optimization and frequencies calculation of the bromoanisole isomers studied in this work. The scaling factors of 0.9813 and 0.9636 were used for the calculation of the zero-point vibrational energies and for the fundamental vibrational frequencies, respectively [46]. The calculations were performed by means of the Gaussian 03 software package [47]. The above mentioned exchange-correlation functional was chosen since in previous work devoted to the thermochemistry of bromoanilines [14], B3LYP and BP86 with the 6-31+G(d) basis set, yielded identical results and permitted the estimation of accurate gas-phase enthalpies of formation for this class of compounds [48–50].
501
3. Results 3.1. Experimental enthalpies of formation Table 1 lists the detailed results for one typical combustion experiment of 4-bromobenzoic acid and of each studied isomer of monobromoanisole, where the symbols have been defined elsewhere [31,38, 51]. The values of the internal energy associated with the isothermal bomb process, DU(IBP), were calculated using the expression (1):
DUðIBPÞ ¼ ðcalorÞcorr DT ad þ ðT i 298:15 KÞei þ ð298:15 K T i DT ad Þf þ DUðignÞ
ð1Þ
where DTad is the calorimeter temperature change corrected for the heat exchange and the work of stirring (adiabatic temperature rise), e(calor)corr. = ecalor + cp(H2O, l) Dm(H2O, l) and Dm(H2O) is the deviation of the mass of water added to the calorimeter from 3969.2 g, the mass assigned to e(calor). The full sets of results for the combustion experiments of 4-bromobenzoic acid and of each isomer of monobromoanisole are given in the Supporting information (Tables S1 to S4). The results of all the combustion experiments of each compound, together with the mean value, hDc u i, and its standard deviation of the mean, are given in table 2. These values of Dc u are referred to the idealized combustion reaction of monobromoanisole, yielding HBr 600H2O(l), accordingly to equation (2)
C7 H7 OBrðcrÞ þ 8O2 ðgÞ þ 597H2 OðlÞ ! 7CO2 ðgÞ þ HBr 600H2 OðlÞ;
ð2Þ
Table 3 lists the derived standard molar energies of combustion, Dc U m ðlÞ, and enthalpies of combustion, Dc Hm ðlÞ, as well as the standard molar enthalpies of formation, Df Hm ðlÞ, for the bromoanisole isomers in the liquid phase at T = 298.15 K. The values of Df Hm ðlÞ were derived from Dc Hm ðlÞ, using the values of the Df Hm of CO2(g), H2O(l) and HBr 600H2O(l), at T = 298.15 K, which are 1 1 [52], ð285:830 0:042Þ kJ mol ð393:51 0:13Þ kJ mol 1 [52] and ð120:294 0:005Þ kJ mol [35,52], respectively. The values of the standard molar enthalpies of vaporization, Dg;T l;298:15K Hm , measured by Calvet microcalorimetry, are given in table 4, where the uncertainties are taken as standard deviations of the mean of five individual results. In accordance with normal thermochemical practice [53,54], the uncertainties assigned to the standard molar enthalpies of combustion, and of vaporization, at T = 298.15 K, are twice the overall standard deviation of the mean and include the uncertainties in calibration and those from the auxiliary quantities used. In table 5 are summarized the values of the standard molar enthalpies of formation, in the gaseous phase, Df Hm ðgÞ, derived from the standard molar enthalpies of formation in the liquid phase, Df Hm ðlÞ, and the standard molar enthalpies of vaporization, Dgl Hm ð298:15 KÞ, all at T = 298.15 K. 3.2. Enthalpies of formation estimated with the Cox scheme The values of Df Hm ðgÞ are compared (table 6) with values estimated using the Cox scheme [17] which assumes that the enthalpy increment for substitution of bromine atom in the different positions of anisole will be the same as for substitution of bromine 1 in benzene with a correction term of 4 kJ mol that was applied for the ortho-pair of substituents. To obtain the estimated values, 1 Df Hm ðgÞ of benzene ð82:6 0:7Þ kJ mol [55], bromobenzene 1 1 [55] and anisole ð67:9 0:8Þ kJ mol ð105:4 4:1Þ kJ mol [55], at T = 298.15 K, were used. Thus, based on the Cox scheme,
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TABLE 1 Typical combustion results at T = 298.15 K (p° = 0.1 MPa), for the 4-bromobenzoic acid and of the monobromoanisole isomers.
m(cpd)/g m0 (fuse)/g m00 (Melinex)/g Ti/K Tf/K DTad/K ei/(J K1) ef /(J K1) e(calor)corr./(J K1) Dm(H2O)/g DU(IBP)a/J DU(fuse)/J DU(Melinex)/J DU(HNO3)/J DU(As2O3)/J DU(H2PtBr4)/J DU(ign)/J DUR/J Dcu°/(J g1)
4-Bromobenzoic acid
2-Bromoanisole
3-Bromoanisole
4-Bromoanisole
0.79310 0.00251 0.04128 297.4558 298.1465 0.65687 95.79 94.19 20372.3 0.8 13443.82 40.76 945.35 0.78 324.46 0.06 1.11 26.88 15263.56
0.83724 0.00263 0.03939 297.2827 298.1754 0.85943 75.27 73.93 20374.9 1.4 17574.39 42.71 902.17 3.34 355.03 0.01 1.11 24.67 19404.78
0.72263 0.00253 0.03932 297.3684 298.1508 0.74742 75.14 73.84 20369.4 0.1 15279.60 41.09 900.57 4.18 308.82 0.15 1.10 21.65 19378.02
0.68072 0.00267 0.03936 297.3997 298.1395 0.70689 75.09 73.83 20360.6 2.0 14444.73 43.36 901.49 3.94 285.58 0.06 1.11 20.57 19376.15
m(cpd), m0 (fuse) and m00 (Melinex) are the mass of compound burnt, the mass of fuse (cotton) and the mass of Melinex, respectively, used in each experiment; Ti is the initial temperature rise; Tf is the final temperature rise; DTad is the corrected temperature rise; ei and ef are the energy equivalent of contents in the initial and final states, respectively; e(calor)corr. is the energy equivalent of the calorimeter; Dm(H2O) is the deviation of mass of water added to the calorimeter from 3969.2 g; DU(IBP) is the energy change for the isothermal combustion reaction under actual bomb conditions; DU(fuse) is the energy of combustion of the fuse (cotton); DU(Melinex) is the energy combustion of the Melinex; DU(HNO3) is the energy correction for the nitric acid formation; DU(As2O3) is the energy of oxidation of the aqueous solution of As2O3; DU(H2PtBr4) is the energy correction for the formation of the platinum complex; DU(ign) is the electrical energy for ignition; DUR is the standard state correction; Dc u is the standard massic energy of combustion. a DU(IBP) includes DU(ign).
TABLE 2 Individual values of standard (p° = 0.1 MPa) massic energies of combustion Dc u , of the 4-bromobenzoic acid and of the three bromoanisoles, at T = 298.15 K. 4-Bromobenzoic acid
2-Bromoanisole
3-Bromoanisole
4-Bromoanisole
19404.78 19406.70 19399.45 19403.18 19406.10 19396.02
19378.02 19373.50 19368.58 19379.01 19379.22 19376.85
19378.81 19369.33 19381.06 19378.34 19376.15 19366.95
19402.7 ± 1.7
19375.9 ± 1.7
19375.1 ± 2.3
Dc u =J g 1 15263.40 15265.76 15263.56 15264.59 15253.74 15254.62 hDc u i=ðJ g 1 Þa 15260.9 ± 2.2 a
Mean value and standard deviation of the mean.
the characteristic increment in Df Hm ðgÞ calculated for the introduction of a bromine atom in a benzene ring is 1 ð22:8 4:2Þ kJ mol , and the Df Hm ðgÞ for the different isomers of bromoanisole was estimated.
The values of Df Hm ðgÞ estimated by the Cox scheme, reported in table 6, are in excellent agreement with the experimental ones, dif1 fering from the experimental ones by 1:4—3:4 kJ mol (absolute deviation), with the differences D between experimental and estimated values of Df Hm ðgÞ being smaller than the associated uncertainties. 3.3. Theoretical enthalpies of formation The most stable conformations obtained for all the three bromo-substituted anisoles, taking into account the geometry optimization performed at the B3LYP/6-31+G(d) (Table S5 of the Supplementary Information), were those where the methoxy group is coplanar with the aromatic benzene ring, like anisole itself [56], with the methoxy group in anti orientation with respect to bromine atom for the 2- and 3-bromoanisole. Figure 1 presents selected geometrical parameters for the most stable conformations of the three bromo-substituted anisoles, as well as for anisole and bromobenzene. The ortho, meta or para substitution of a bromine atom in anisole seems to have a small influence on the geometrical parameters of the corresponding bromoanisoles.
TABLE 3 Derived standard molar energies of combustion, Dc U m , standard molar enthalpies of combustion, Dc Hm , and standard molar enthalpies of formation, Df Hm , in the condensed phase, for the bromoanisole isomers at T = 298.15 K, with p° = 0.1 MPa. Compound
Dc U m ðlÞ=ðkJ mol
2-Bromoanisole (l) 3-Bromoanisole (l) 4-Bromoanisole (l)
3629.0 ± 1.4 3624.0 ± 1.4 3623.8 ± 1.5
1
Dc Hm ðlÞ=ðkJ mol
Þ
1
Df Hm ðlÞ=ðkJ mol
Þ
3631.5 ± 1.4 3626.5 ± 1.4 3626.3 ± 1.5
1
Þ
101.5 ± 1.7 106.5 ± 1.7 106.7 ± 1.8
TABLE 4 Standard (p° = 0.1 MPa) molar enthalpies of vaporization, Dgl Hm , at T = 298.15 K determined by microcalorimetry for the monobromoanisole isomers. Compound
Number of experiments
T=K
1 Dg;T H =ðkJ mol Þ l;298:15K m
DT298:15K Hm ðgÞ=ðkJ mol1 Þ
Dgl Hm ð298:15KÞ=ðkJ mol1 Þ
2-Bromoanisole (l) 3-Bromoanisole (l) 4-Bromoanisole (l)
5 5 5
329.0 328.9 329.0
66.2 ± 0.2 62.4 ± 0.2 62.8 ± 0.1
4.4 4.4 4.5
61.8 ± 1.3 58.0 ± 1.2 58.3 ± 1.2
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M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505 TABLE 5 Standard (po = 0.1 MPa) molar enthalpies of formation, in both condensed and gaseous phase, and standard molar enthalpies of vaporization, at T = 298.15 K. 1
Compound
Df Hm ðlÞ=ðkJ mol
2-Bromoanisole 3-Bromoanisole 4-Bromoanisole
101.5 ± 1.7 106.5 ± 1.7 106.7 ± 1.8
Dgl Hm ð298:15KÞ=ðkJ mol
Þ
61.8 ± 1.3 58.0 ± 1.2 58.3 ± 1.2
TABLE 6 Experimental and estimated (Cox scheme and DFT calculations) gas-phase enthalpies of formation for the isomers of bromoanisoles. Compound
2-Bromoanisole 3-Bromoanisole 4-Bromoanisole a b
Df Hm ðgÞ=ðkJ mol
1
Da/kJ mol1
Þ
Experimental
Cox scheme
DFTb
Cox scheme
DFTb
39.7 ± 2.1 48.5 ± 2.1 48.4 ± 2.2
41.1 ± 4.2 45.1 ± 4.2 45.1 ± 4.2
44.1 50.3 48.2
1.4 ± 4.7 3.4 ± 4.7 3.3 ± 4.7
4.4 1.8 0.2
Difference between the experimental and the estimated values. Calculated at B3LYP/6-31+G(d) level of theory.
However, one can notice a small increase of the C–C–O angle in the ortho isomer due probably to the repulsive interaction with the bromine atom. The angle increases in order to minimize the steric repulsion, but the rigidity of the molecule prohibits larger deformations. The energies of all monobromoanisoles, and those of anisole, benzene and bromobenzene, calculated at the B3LYP/6-31+G(p), and corrected for T = 298.15 K, were used to compute the enthalpy of the homodesmic reaction described by the following equation:
ð3Þ Combining those enthalpies of reaction with the experimental Df Hm ðgÞ of benzene, anisole and bromobenzene given above [55], it was possible to estimate the Df Hm ðgÞ of the bromoanisole isomers. The DFT estimated values for all bromoanisoles are summa-
1
Þ
1
Df Hm ðgÞ=ðkJ mol
Þ
39.7 ± 2.1 48.5 ± 2.1 48.4 ± 2.2
rized in table 6. The values agree well with the experimental ones and the larger deviation occurs for the 2-bromoanisole isomer, where it is predicted a less pronounced steric effect between the two groups in ortho position. However, the ordering of the estimated enthalpies of formation for the three compounds is in agreement with the experimentally determined enthalpies of formation, and the difference between the experimental and calculated results for 2-bromoanisole is acceptable since it lies on the interval of desired accuracy for computational thermochemistry approaches.
4. Discussion From the literature value of the standard molar enthalpies of formation in the gaseous phase of the anisole, ð67:9 0:8Þ 1 kJ mol [55], and of the monobromoanisoles reported in this paper, the enthalpic increments calculated for the introduction of a bromine atom in the ortho, meta and para positions of the anisole 1 ring are, respectively, ð28:2 2:2Þ kJ mol , ð19:4 2:2Þ and 1 ð19:5 2:3Þ kJ mol , as shown in figure 2. From this scheme, it can be seen that the insertion of a bromine atom in ortho position of the anisole ring, induces an additional destabilization effect not observed for that substitution in the meta and para positions. Hence, the 2-bromoanisole is the least stable isomer due to the steric interactions between the two groups, being the 3- and 4-bromoanisole isomers the most stable ones, having similar enthalpic stability. It is also verified that the enthalpic increment of substitution of a bromine atom in the anisole ring is, within the associated uncertainties, similar to the observed for the introduction of a bromine atom in the aromatic ring of the benzene: 1 ð22:8 4:2Þ kJ mol .
FIGURE 1. Optimized most stable configurations for the monobromoanisoles. Selected distances are in Å and angles in degrees.
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15.4 ± 2.5
28.2 ± 2.2
Br
Br
NH2
OCH3
−8.8 ± 3.0
Br
Br
20.9 ± 2.5
19.4 ± 2.2
−8.7 ± 3.0
OCH3
7.4 ± 3.4
NH2
−67.9 ± 0.8 [55] 87.1 ± 0.7 [55]
OCH3
0.1 ± 3.0
NH2
OCH3
1.9 ± 3.4
108.0 ± 2.3
−48.5 ± 2.1 Br
5.5 ± 3.3
102.5 ± 2.3
−39.7 ± 2.1
19.5 ± 2.3
− 48.4 ± 2.2
22.8 ± 2.7
Br
NH2
109.9 ± 2.5
FIGURE 2. Enthalpic effect of substitution of a bromine atom in the ortho, meta and para position of the aromatic ring of anisole and aniline, and isomerisation energies (all 1 values are in kJ mol ).
Comparable findings were observed for the monobromoaniline isomers [14] (figure 2), for which the enthalpic effect of substitution of a bromine atom in the 3- and 4-position of the aniline ring 1 and ð22:8 4:2Þ kJ is also very similar, ð20:9 2:5Þ kJ mol 1 mol , respectively. For the 2-bromoaniline the enthalpic increment for the introduction in ortho position of a bromine atom 1 was found to be ð15:4 2:5Þ kJ mol , yielding a higher effect of stabilization comparing with the observed in the 2-bromoanisole due to the presence, in the former case, of an intramolecular hydrogen bond between the bromine atom and the hydrogen atoms of the amino group [14]. The values of Df Hm obtained by DFT calculations also give the 2-bromoanisole as the least stable isomer, but sets the 3-bromoanisole slightly more stable than the 4-bromoanisole. The good agreement between experimental and computed values supports the conclusions obtained from the analysis of geometrical parameters, showing that the energetics of these compounds are mainly governed by the presence or absence of destabilizing steric interactions between the bromine atom and the other substituent. The substitution of a bromine atom in the meta or in the para positions do not exert any significant energetic effect on the molecule. For the studied compounds, the Cox scheme [17] revealed to be a good method of estimate yielding values of enthalpies of formation in the gas-phase involving an absolute deviation from the 1 experimental values not larger than 3:4 kJ mol . Acknowledgments Thanks are due to Fundação para a Ciência e Tecnologia (FCT), Lisbon, Portugal and to FEDER for financial support to Centro de Investigação em Química, University of Porto. A.I.M.C.L.F. thanks FCT and the European Social Fund (ESF) under the Community Support Framework (CSF) for the award of the post-doctoral fellowship (SFRH/BPD/27053/2006). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jct.2008.11.008. References [1] J. Zilberman, Org. Process Res. Dev. 7 (2003) 303–305. [2] I.J. Kim, C.M. Dersch, R.B. Rothman, A.E. Jacobsona, K.C. Rice, Bioorg. Med. Chem. 12 (2004) 4543–4550. [3] M. Protiva, Drugs Future 16 (1991) 911–916. [4] C. Pampillón, O. Mendoza, N.J. Sweeney, K. Strohfeldt, M. Tacke, Polyhedron 25 (2006) 2101–2108.
[5] D. Nasipuri, A.K. Mitra, J. Chem. Soc., Perkin Trans. 1 (1973) 285–287. [6] S. Bhattacharya, M. Banerjee, Chem. Phys. Lett. 396 (2004) 377–383. [7] S. Bhattacharya, A.K. Bauri, S. Chattopadhyay, M. Banerjee, J. Phys. Chem. B 109 (2005) 7182–7187. [8] S. Bhattacharya, A.K. Bauri, S. Chattopadhyay, M. Banerjee, Chem. Phys. Lett. 401 (2005) 323–331. [9] X. Cheng, G.-H. Hou, J.-H. Xie, Q.-L. Zhou, Org. Lett. 6 (2004) 2381–2383. [10] U. Führer, K. Ballschmiter, Environ. Sci. Technol. 32 (1998) 2208–2215. [11] C. Flodin, F.B. Whitfield, Phytochemistry 53 (2000) 77–80. [12] M.L.C.C.H. Ferrão, G. Pilcher, J. Chem. Thermodyn. 19 (1987) 543–548. [13] M.A.V. Ribeiro da Silva, M.L.C.C.H. Ferrão, A.J.M. Lopes, J. Chem. Thermodyn. 25 (1993) 229–235. [14] M.A.V. Ribeiro da Silva, A.I.M.C.L. Ferreira, J.R.B. Gomes, Bull. Chem. Soc. Jpn. 79 (2006) 1852–1859. [15] M.A.V. Ribeiro da Silva, M.A.R. Matos, L.M.P.F. Amaral, J. Chem. Thermodyn. 29 (1997) 1545–1551. [16] M.A.V. Ribeiro da Silva, J.I.T.A. Cabral, J. Chem. Thermodyn. 41 (2008) 84–89. [17] J.D. Cox, A Method for Estimating the Enthalpies of Formation of Benzene Derivatives in the Gas State, NPL Report CHEM 83, June 1978. [18] Society for Analytical Chemistry, Analyst 97 (1972) 740–756. [19] R. Sabbah, A. Xu-wu, J.S. Chickos, M.L. Planas Leitão, M.V. Roux, L.A. Torres, Thermochim. Acta 331 (1999) 93–204. [20] M.E. Wieser, Pure Appl. Chem. 78 (2006) 2051–2066. [21] Certificate of Analysis, Standard Reference Material 39j, Benzoic Acid Calorimetric Standard, NIST, Gaithersburg, 1995. [22] J.D. Cox, H.A. Gundry, A. Head, Trans. Faraday Soc. 60 (1964) 653–665. [23] H.A. Gundry, A. Head, J. Chem. Thermodyn. 10 (1978) 195–200. [24] M.D.M.C. Ribeiro da Silva, P. Souza, G. Pilcher, J. Chem. Thermodyn. 21 (1989) 173–178. [25] M.A.V. Ribeiro da Silva, J.M. Gonçalves, G. Pilcher, J. Chem. Thermodyn. 29 (1997) 253–260. [26] A.J. Head, W.D. Good, in: S. Sunner, M. Månsson (Eds.), Combustion Calorimetry, Pergamon, Oxford, 1979 (Chapter 9). [27] J. Coops, R.S. Jessup, K. Van Nes, in: F.D. Rossini (Ed.), Experimental Thermochemistry, vol. 1, Interscience, New York, 1956 (Chapter 3). [28] L.M.N.B.F. Santos, Ph.D. Thesis, University of Porto, 1995. [29] W.D. Good, D.W. Scott, G. Waddington, J. Phys. Chem. 60 (1956) 1080–1089. [30] A. Snelson, H.A. Skinner, Trans. Faraday Soc. 56 (1960) 1776–1783. [31] A.T. Hu, G.C. Sinke, M. Månsson, B. Ringnér, J. Chem. Thermodyn. 4 (1972) 283– 299. [32] L. Bjellerup, Acta Chem. Scand. 11 (1957) 1761–1765. [33] P. Sellers, S. Sunner, I. Wadsö, Acta Chem. Scand. 18 (1964) 202–206. [34] A.I. Vogel, Quantitative Inorganic Analysis, Longmans, London, 1978. [35] The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data, 11(Suppl. 2) (1982). [36] E.W. Washburn, J. Res. Natl. Bur. Stand. (US) 10 (1933) 525–558. [37] Handbook of Fine Chemicals and Laboratory Equipment, Aldrich – España/ Portugal, 2007–2008. [38] L. Bjellerup, in: H.A. Skinner (Ed.), Experimental Thermochemistry, vol. 2, Interscience, New York, 1962 (Chapter 3). [39] F.A. Adedeji, D.L.S. Brown, J.A. Connor, M.L. Leung, M.I. Paz-Andrade, H.A. Skinner, J. Organomet. Chem. 97 (1975) 221–228. [40] M.A.V. Ribeiro da Silva, M.A.R. Matos, L.M.P.F. Amaral, J. Chem. Thermodyn. 27 (1995) 565–574. [41] L.M.N.B.F. Santos, B. Schröder, O.O.P. Fernandes, M.A.V. Ribeiro da Silva, Thermochim. Acta 415 (2004) 15–20. [42] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652. [43] A.D. Becke, Phys. Rev. A 38 (1988) 3098–3100. [44] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789. [45] M.J. Frisch, J.A. Pople, J.S. Binkley, J. Chem. Phys. 80 (1984) 3265–3269. [46] J.P. Merrick, D. Moran, L. Radom, J. Phys. Chem. A 111 (2007) 11683–11700. [47] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,
M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira / J. Chem. Thermodynamics 41 (2009) 499–505 J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian03, Revision C.02, Gaussian Inc., Pittsburgh, PA, 2004. [48] M.A.V. Ribeiro da Silva, L.M. Spencer, S. Lima, L.M.P.F. Amaral, A.I.M.C.L. Ferreira, J.R.B. Gomes, J. Chem. Thermodyn. 35 (2003) 1343–1359. [49] J.R.B. Gomes, M.A.V. Ribeiro da Silva, J. Phys. Chem. A 107 (2003) 869–874.
505
[50] M.A.V. Ribeiro da Silva, A.I.M.C.L. Ferreira, J.R.B. Gomes, Chem. Phys. Lett. 422 (2006) 565–570. [51] W.N. Hubbard, D.W. Scott, G. Waddington, in: F.D. Rossini (Ed.), Experimental Thermochemistry, vol. 1, Interscience, New York, 1956 (Chapter 5). [52] J.D. Cox, D.D. Wagman, V.A. Medvedev (Eds.), CODATA Key Values for Thermodynamics, Hemisphere, New York, 1989. [53] F.D. Rossini, in: F.D. Rossini (Ed.), Experimental Thermochemistry, vol. 1, Interscience, New York, 1956 (Chapter 14). [54] G. Olofsson, in: S. Sunner, M. Månsson (Eds.), Combustion Calorimetry, Pergamon, Oxford, 1979 (Chapter 6). [55] J.B. Pedley, Thermochemical Data and Structures of Organic Compounds, Thermodynamics Research Center, College Station, Texas, 1994. [56] M. Onda, A. Toda, S. Mori, I. Yamaguchi, J. Mol. Struct. 144 (1986) 47–51.
JCT 08-373