Experimental and computational thermochemical study of the dichloronitrobenzene isomers

J. Chem. Thermodynamics 41 (2009) 904–910

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Experimental and computational thermochemical study of the dichloronitrobenzene isomers Manuel A.V. Ribeiro da Silva *, Ana I.M.C. Lobo Ferreira, Ana Rita G. Moreno 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 2 March 2009 Accepted 10 March 2009 Available online 20 March 2009 Keywords: Thermochemistry Energy of combustion Enthalpy of sublimation Enthalpy of formation Rotating bomb combustion calorimetry Calvet microcalorimetry Cox scheme Dichloronitrobenzene isomers

a b s t r a c t The standard (p° = 0.1 MPa) molar enthalpies of formation of 2,4-, 2,5-, 3,4- and 3,5-dichloronitrobenzene isomers, in the crystalline state, at T = 298.15 K, were derived from the standard (p° = 0.1 MPa) massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the four isomers, at T = 298.15 K, were obtained by hightemperature Calvet microcalorimetry. 1

Dc U m ðcrÞ=ðkJ  mol 2,4-Dichloronitrobenzene 2,5-Dichloronitrobenzene 3,4-Dichloronitrobenzene 3,5-Dichloronitrobenzene

2792.8 ± 0.9 2793.0 ± 1.8 2774.1 ± 1.2 2769.6 ± 0.9

Þ

Df Hm ðcrÞ=ðkJ  mol 47.4 ± 1.2 47.2 ± 2.0 66.1 ± 1.4 70.6 ± 1.2

1

Þ

Dgcr Hm =ðkJ  mol1 Þ 87.8 ± 1.7 87.4 ± 2.5 85.8 ± 2.5 83.2 ± 1.5

From the determined experimental results, the values of the gaseous standard (p° = 0.1 MPa) molar enthalpies of formation were derived. The gas-phase enthalpies of formation of all the six chloronitrobenzene isomers were also estimated by the Cox scheme and by computational thermochemistry methods and compared with the available experimental values. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction The chlorinated nitroaromatic compounds are characterized by their long life, chemical stability and non-biodegradability and over the years have become a serious environmental issue [1,2]. They are environmental pollutants released from automobile exhausts and industrial areas and shown to be potential mutagens or carcinogens. Toxicity induced by the various chloronitrobenzene isomers in vivo includes hematotoxicity, immunotoxicity, hepatotoxicity, and nephrotoxicity [3,4], and they are also suspected to have genotoxic and carcinogenic potential, being identified as priority pollutants by the Environmental Protection Agency (EPA) [5]. The natural formation of these compounds is rare, with their vast presence in the environment resulting from massive industrial production, which conducted to an extensive research work in the study of means of quick and reliable detection of these substances in aqueous phase and soil [6,7] and on methodologies for their elimination, such as advanced oxidation process or biological degradation process [8–11].

* 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 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2009.03.001

Thermodynamic properties of some chloronitrobenzenes have been studied [12–15]. To the best of our knowledge, however, in what concerns the dichloronitrobenzenes there are only available, experimental results of the vapour pressure, enthalpy of sublimation, and enthalpy of fusion of the 3,4-dichloronitrobenzene, recently reported by Verevkin et al. [16]. In this work, the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous state, at T = 298.15 K, of four dichlorinated nitrobenzenes isomers were experimentally determined, whereas the gas-phase standard molar enthalpies of formation of the other two dichloronitrobenzenes isomers, which were not available, were estimated by means of the empirical methodology developed by Cox and by computational methods. The choice of these molecules is due to the fact that the effects of the introduction of chlorine atoms in benzene rings [15,17–23] as well as the effect of the same substituents into heterocycles [24–30] has been, for some years, one of the research objectives of our Research Group on thermochemical properties. The experimental investigation includes the determination of the standard molar energies of combustion, in oxygen, at T = 298.15 K, of four dichloronitrobenzene isomers, using a rotating bomb combustion calorimeter, from which the values of the standard molar enthalpies of formation, in the condensed phase, were derived. The determination of the

M.A.V. Ribeiro da Silva et al. / J. Chem. Thermodynamics 41 (2009) 904–910

standard molar enthalpies of sublimation, at T = 298.15 K, was performed by Calvet microcalorimetry using the high-temperature vacuum sublimation technique. These experimental values allowed the derivation of the standard molar enthalpies of formation, in the gaseous state, of 2,4-dichloronitrobenzene [CAS 611-06-3], 2,5-dichloronitrobenzene [CAS 89-61-2], 3,4-dichloronitrobenzene [CAS 99-54-7] and 3,5-dichloronitrobenzene [CAS 618-62-2], which were compared with values estimated from the Cox scheme [31] and those obtained by computational thermochemistry.

2. Experimental 2.1. Compounds and purity control The isomers 2,4-dichloronitrobenzene [2,4-Cl2NO2Benz], 2,5dichloronitrobenzene [2,5-Cl2NO2Benz], 3,4-dichloronitrobenzene [3,4-Cl2NO2Benz] and 3,5-dichloronitrobenzene [3,5-Cl2NO2Benz], were commercially available from Aldrich Chemical Co., with an assessed mass fraction minimum purity of 0.97, and were purified by repeated sublimations at 0.1 Pa background pressure. The final purity of each isomer 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 temperature of the injector was set at 473 K and the oven temperature was programmed as follows: 323 K (1 min), ramp at 10 K  min1, 423 K (5 min). No impurities greater than 103 in mass fraction could be detected in the samples of the chloronitrobenzene isomers used for the rotating bomb combustion calorimetry and Calvet microcalorimetry measurements. The specific densities used to calculate the true mass from the apparent mass in air, were for 2,4-, 3,4-, and 3,5-dichloronitrobenzene, respectively, 1.69 g  cm3, 1.64 g  cm3 and 1.63 g  cm3, determined from the ratio mass/volume of the pellet, made in vacuum, with an applied pressure of 105 kg  cm2, and were of 1.442 g  cm3 for 2,5-dichloronitrobenzene [32]. The relative atomic masses used in the calculation of all molar quantities throughout this paper were those recommended by the IUPAC Commission in 2005 [33], yielding for the molar mass of the dichloronitrobenzene isomers 192.0005 g  mol1. 2.2. Combustion calorimetry measurements The combustion experiments were performed with an isoperibol rotating bomb calorimeter, already described [34,35], which was originally constructed at the University of Lund, Sweden, according to the design of Professor Stig Sunner [36]. The stainless steel combustion bomb with internal volume of 0.258 dm3 and wall thickness of 1 cm, is a twin valve bomb lined with platinum, with the internal fittings machined from platinum. The bomb is suspended from the lid of the calorimeter can, to which a mass of nearly 5222.5 g of water, previously weighed in a Perspex vessel, is added. A Mettler PM 11-N balance, sensitivity ±101 g, was used to weigh the amount of distilled water added to the calorimeter from a weighed acrylic vessel. Calorimetric temperatures were measured to ±104 K, at time intervals of 10 s, with a quartz crystal thermometer (Hewlett–Packard HP 2804A), interfaced to a PC programmed to compute the adiabatic temperature change. The calorimetric system was calibrated, in the conventional way, without bomb rotation, according to the procedure suggest by Coops et al. [37], by combustion of benzoic acid (NIST Standard Reference Material 39j) having a massic energy of combustion under bomb conditions of (26434 ± 3) J  g1 [38]. Calibration

905

experiments were carried out in oxygen, at a pressure of 3.04 MPa, with 1.00 cm3 of deionised water added to the bomb. The obtained value of the energy equivalent of the calorimeter was e(calor) = (25164.0 ± 2.1) J  K1, (0.0083%), as a mean of seven calibration experiments, where the uncertainty quoted is the standard deviation of the mean. This value was used for the experiments carried out for the 2,4-Cl2NO2Benz, 2,5-Cl2NO2Benz, and 3,4-Cl2NO2Benz. Then, since the equipment was subject to maintenance works, a new calibration constant e(calor) = (25157.4 ± 1.1) J  K1, (0.0044%), was used for the 3,5-Cl2NO2Benz. The uncertainty quoted for the calibration constants is the standard deviation of the mean. For each combustion experiment, the ignition temperature was chosen so that the final temperature would be close to T = 298.15 K. The ignition energy was measured by the change in potential difference on the discharge of a capacitor (1400 lF) across a platinum wire (/ = 0.05 mm, Goodfellow, mass fraction 0.9999). At least 100 temperature readings were taken for the main period and for both the fore and after periods. Data acquisition and control of the calorimeter were performed using the program LABTERMO [39]. The calibration results, as well as the results of the combustion experiments of the studied compounds, were corrected to give the energy equivalents corresponding to the average mass of water added to the calorimeter: 5222.5 g. The accuracy of the calorimeter was checked in our laboratory by measuring the energy of combustion of 4-chlorobenzoic acid [17,18]. Within the precision of the analytical method, no evidence was found for the oxidation of the aqueous solution of As2O3 after the bomb had been charged with oxygen at p = 3.04 MPa and left up to 5 h at room temperature [17,35]. The four isomers of dichloronitrobenzene were burned in pellet form. Since the first experiments of combustion of the 3,4- and 3,5dichloronitrobenzene compounds yielded considerable amounts of carbon soot, the combustion experiments were performed enclosing the pellet of the compounds in sealed polyester bags made from Melinex (0.025 mm thickness) using the technique described by Skinner and Snelson [40]. One of the combustion experiments with 3,5-dichloronitrobenzene was performed enclosing the pellet in a polyethylene bag. The combustion experiments of the dichloronitrobenzenes were carried out in oxygen, at p = 3.04 MPa and in the presence of 30.00 cm3 of aqueous solution of As2O3 (0.09 mol  dm3), insuring that all the free chlorine formed in the combustion experiment was reduced to aqueous hydrochloric acid. For each combustion experiment of the studied compounds, the rotation of the bomb was started when the temperature rise of the main period reached about 0.63 of its total value and then continued throughout the experiment. It has been shown that by adopting this procedure, 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 isothermal jacket [41]. The rotating mechanism allows the simultaneous axial and end-over-end rotation of the bomb, causing the aqueous solution of As2O3 placed in the bomb to wash all internal surfaces of the bomb, yielding a homogeneous final solution. At the end of some experiments a small residue of carbon was found due to incomplete combustion. If the carbon soot formed stays only on the walls of the platinum crucible, and not in the combustion solution or on the walls of the bomb, an energy correction for the carbon soot was done by weighing the crucible before and after calcinations. Otherwise, the experiments were discarded. Corrections for carbon soot formation were based on the standard massic energy of combustion of carbon, Dc u ¼ 33  kJ  g1 [37]. The HNO3 formed from the combustion of the chloronitrobenzene samples and from traces of atmospheric nitrogen remaining

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M.A.V. Ribeiro da Silva et al. / J. Chem. Thermodynamics 41 (2009) 904–910

inside the bomb was analyzed by the Devarda’s alloy method [42]; the extent of As2O3(aq) oxidation was determined by titration with a standardized iodine solution [42]. Corrections for the nitric acid formed were based on Df U m (HNO3, aq, 0.1 mol  dm3) = 59.7 kJ  mol1 [43], from 1/2 N2(g), 5/4 O2(g) and 1/2 H2O(l). For the calculation of the energetic term DU(As2O3), corresponding to the energy of oxidation of aqueous As2O3 to As2O5 in solution, the procedure described by Hu et al. [44] using the enthalpies of oxidation of As2O3(aq) by Cl2 [45] and the thermal effects of mixing As2O5(aq) with strong acids [46] was followed. The amount of H2PtCl6(aq) formed was determined from the loss of mass of platinum from the crucible and its supporting parts and the energy correction was based on Df Hm (H2PtCl6, aq) = (676.1 ± 0.1) kJ  mol1 [43]. For the cotton thread fuse, whose empirical formula is CH1.686O0.843, Dc u ¼ 16240 J  g1 [37] was used, and for dry Melinex, Dc u ¼ ð22902  5Þ J  g1 [40]. The values of the standard massic energies of combustion of cotton thread fuse and Melinex have been previously 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 [40]. For polyethylene Dc u ¼ ð46282:4  4:8Þ J  g1 , a value which was determined in our Laboratory. All the necessary weighings for the combustion experiments were made with a precision of ±105 g in a Mettler Toledo AE 245 analytical balance, and corrections from apparent mass to true mass were introduced. An estimated pressure coefficient of massic energy, (ou/op)T = 0.2 J  g1  MPa1, at T = 298.15 K, a typical value for most organic compounds [47], was assumed for all the studied compounds. For each compound, the standard state corrections, DUR, and the heat capacities of the bomb contents, ei and ef, were calculated by the procedure given by Hubbard et al. [48] using the solubility constants and energies of solution of CO2 and O2 as given by Hu et al. [44]. 2.3. Calvet drop microcalorimetry measurements The standard molar enthalpies of sublimation of the four dichloronitrobenzene isomers were measured using the ‘‘vacuum sublimation” drop microcalorimetric method [49,50]. The calibration of the microcalorimeter was done by making use of the reported standard molar enthalpy of sublimation of naphtha1 lene, Dgcr Hm ðT ¼ 298:15 KÞ ¼ ð72:60  0:60Þ kJ  mol [51]. The calibration constants of the calorimeter for each working temperature were k(T = 324.2 K) = (1.0099 ± 0.0036) for the sublimation experiments of 2,4-dichloronitrobenzene, k(T = 339.4 K) = (0.9919 ± 0.0110) for the sublimation experiments of 2,5- and 3,4-dichloronitrobenzene and k(T = 339.9 K) = (1.0107 ± 0.0023) for the sublimation experiments of 3,5-dichloronitrobenzene, being the uncertainties quoted the standard deviations of the means of sets of six independent experiments. Samples of about (4 to 8) mg of crystalline compound, contained in a small thin glass capillary tubes sealed at one end, and a blank capillary with nearly the same mass were simultaneously dropped at room temperature into the hot reaction vessels in the Calvet high-temperature microcalorimeter (Setaram HT 1000) set at a predefined temperature, for the study of the title compounds. An endothermic peak due to the heating of the sample from room temperature to the temperature of the calorimeter was first observed and after the signal returned to the baseline, the sample was removed from the hot zone by vacuum. The thermal corrections for the glass capillary tubes were determined in separate experiments [50] and were minimized in each experiment by dropping glass capillary tubes of near equal mass into both measuring cells. All the necessary weighings for the Calvet experiments

were performed in a Mettler CH-8608 analytical balance with a sensitivity ±106 g. The observed standard molar enthalpies of sublimation,  Dg;T cr;298:15K Hm , at the experimental temperature of the hot reaction vessel, have been corrected to T = 298.15 K using the corrective term DT298:15K Hm ðgÞ, which represents the molar enthalpic correction for the gaseous phase temperature change, calculated by computational thermochemistry. 2.4. Theoretical calculations The enthalpies of formation of the six dichloronitrobenzene isomers were estimated from density functional theory (DFT) or Gaussian-3 based G3MP2B3 computations and the consideration of an appropriate working reaction. In the DFT calculations, the B3LYP exchange-correlation functional [52–54] together with the split-valence polarized 6311++G(d) basis set [55], were used for the geometry optimization and frequencies calculation of all dichloronitrobenzene isomers studied in this work. The scaling factors of 0.9887 and 0.9688 were used for the calculation of the zero-point vibrational energies and for fundamental vibrational frequencies, respectively [56]. The calculations employing the G3MP2B3 composite approach [57] use the B3LYP method and the 6-31G(d) basis set for both the optimization of geometries and calculation of frequencies. Successive introduction of high-order corrections to the B3LYP/631G(d) enthalpy follows the Gaussian-3 philosophy, albeit using a second-order Möller–Plesset perturbation instead of MP4 as in the original G3 method [58]. The calculation of frequencies also permitted us to correct energies for T = 298.15 K, by introduction of the vibrational, translational, rotational and the pV terms. The present computational procedure was chosen since in previous work devoted to the thermochemistry of chloronitroaniline isomers [18,22] permitted the estimation of accurate gas-phase enthalpies of formation. All the calculations were performed by means of the Gaussian 03 software package [59]. The energies of the mono- and dichloronitrobenzene isomers, and those of nitrobenzene, benzene, chlorobenzene, o-dichlorobenzene, m-dichlorobenzene and p-dichlorobenzene, calculated at the B3LYP/6-311++G(d,p) and employing the G3MP2B3 composite approach, corrected for T = 298.15 K, were used to compute the enthalpies of the homodesmic reactions described by the following equations:

ð1Þ

ð2Þ

ð3Þ

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TABLE 2 Individual values of the standard (p° = 0.1 MPa) massic energies of combustion, Dc u , of the four dichloronitrobenzene isomers at T = 298.15 K.

ð4Þ

Combining those enthalpies of reaction with the experimental Df Hm ðgÞ given in the literature [60] for benzene (82.6 ± 0.07) kJ  mol1, nitrobenzene (67.5 ± 0.5) kJ  mol1, chlorobenzene (52.0 ± 1.3) kJ  mol1, o-dichlorobenzene (30.2 ± 1.2) kJ  mol1, m-dichlorobenzene (25.7 ± 2.1) kJ  mol1 and p-dichlorobenzene (22.5 ± 1.5) kJ  mol1, at T = 298.15 K, it was possible to estimate the Df Hm ðgÞ for all the mono- and dichloronitrobenzenes. 3. Results 3.1. Experimental enthalpies of formation Results for one typical combustion experiment of each studied isomer are given in table 1, where Dm(H2O) is the deviation of the mass of water added to the calorimeter from 5222.5 g, the mass assigned to e(calor), DUR is the standard state correction (Washburn correction) derived as recommended in the literature for compounds containing chlorine [44,48], and DU(IBP) is the internal energy associated with the isothermal bomb process, calculated through the following equation:

DUðIBPÞ ¼ eðcalorÞcorr :  DT ad þ ðT i  298:15KÞ  ei þ ð298:15K  T i  DT ad Þ  ef þ DUðignÞ;

ð5Þ

where DTad is the calorimeter temperature change corrected for the heat exchange, work of stirring and frictional work of bomb rotation (adiabatic temperature rise) and e(calor)corr = e(calor) + cp(H2O, l)  Dm(H2O, l). The remaining terms are as previously defined [44,47,48]. Detailed results for each combustion calorimetric experiment performed for each compound are given as Supplementary material (tables S1 to S4).

2,4-Cl2NO2Benz 14545.68 14551.01 14544.34 14547.46 14542.82 14543.18 14545.7 ± 1.3 a

2,5-Cl2NO2Benz

3,4-Cl2NO2Benz

Dc u =ðJ  g1 Þ 14541.64 14447.90 14544.10 14457.42 14562.00 14441.83 14558.37 14445.37 14540.81 14453.48 14534.91 14443.05 hDc u i=ðJ  g1 Þa 14547.0 ± 4.4 14448.2 ± 2.5

3,5-Cl2NO2Benz 14427.89 14425.47 14423.64 14430.00 14419.28 14423.67 14425.0 ± 1.5

Mean value and standard deviation of the mean.

The results of all combustion calorimetric experiments for each compound, together with the mean value and its standard deviation of the mean, are given in table 2. These values of Dc u are referred to the generalized combustion reaction of dichloronitrobenzene isomers, represented by equation (2), yielding HCl  600H2O(l) as the sole chlorine-containing product in the final state

C6 H3 NO2 Cl2 ðcrÞ þ 5:25O2 ðgÞ þ 1199:5H2 OðlÞ ! 6CO2 ðgÞ þ 0:5N2 ðgÞ þ 2HCl  600H2 OðlÞ

ð6Þ

The derived standard molar energies, Dc U m ðcrÞ, and enthalpies, Dc Hm ðcrÞ, of combustion, as well as the standard molar enthalpies of formation, Df Hm ðcrÞ, for the compounds in the crystalline state, at T = 298.15 K, are presented in table 3. The uncertainties assigned to the Dc U m ðcrÞ, correspond, in each case, to twice the overall standard deviation of the mean and include the contributions from the calibration with benzoic acid and from the energy of combustion of Melinex used as combustion auxiliaries [61,62]. The values of Df Hm ðcrÞ were derived from Dc Hm ðcrÞ, using the values of Df Hm of CO2(g), H2O(l) and HCl  600H2O(l), at T = 298.15 K, which are (393.51 ± 0.13) kJ  mol1 [63], –(285.830 ± 0.040) kJ  mol1 [63] and –(166.540 ± 0.005) kJ  mol1 [43,63], respectively.

TABLE 1 Typical combustion results at T = 298.15 K (p° = 0.1 MPa), for the four dichloronitrobenzenes. Experiment

2,4-Cl2NO2Benz

2,5-Cl2NO2Benz

3,4-Cl2NO2Benz

3,5-Cl2NO2Benz

m(cpd)/g m’(fuse)/g m’’(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(H2PtCl6)/J DU(ign)/J DUR/J Dcu°/(J  g1)

1.30136 0.00290 – 297.3497 298.1517 0.78458 135.98 130.62 25168.2 1.0 19851.94 47.10 – 44.30 767.29 2.47 1.30 61.61 14545.68

1.34749 0.00314 – 297.3174 298.1443 0.81202 136.06 130.41 25164.4 0.1 20543.31 50.99 – 32.00 799.33 2.69 1.29 63.58 14541.64

1.07792 0.00206 – 297.3027 297.9707 0.64709 114.86 110.24 25163.6 0.1 16357.06 33.45 – 30.33 674.26 1.88 1.30 43.46 14447.90

1.19747 0.00288 0.07936 297.3649 298.1715 0.78880 135.94 130.69 25147.8 2.3 19942.50 46.77 1817.50 18.57 716.08 2.22 1.29 64.39 14427.89

m(cpd) is the mass of compound burnt in each experiment; m’(fuse) is the mass of fuse (cotton) used in each experiment; m’’(Melinex) is the mass of Melinex used in each experiment; Ti is the initial temperature rise; Tf is the final temperature rise; DTad is the corrected temperature rise; ei is the energy equivalent of the contents in the initial state; ef is the energy equivalent of the contents in the final state; e (calor)corr. is the corrected energy equivalent of the calorimeter for the amount of water used; Dm(H2O) is the deviation of mass of water added to the calorimeter from 5222.5 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 of combustion of Melinex; DU(HNO3) is the energy correction for the nitric acid formation; DU(As2O3) is the energy correction for the oxidation of the aqueous solution of As2O3; DU(H2PtCl6) 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).

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TABLE 3 Derived standard (p° = 0.1 MPa) molar values of the 2,4-, 2,5-, 3,4-, and 3,5-dichloronitrobenzene, in the crystalline phase, at T = 298.15 K. Compound

Dc U m ðcrÞ=ðkJ  mol

2,4-Cl2NO2Benz 2,5-Cl2NO2Benz 3,4-Cl2NO2Benz 3,5-Cl2NO2Benz

2792.8 ± 0.9 2793.0 ± 1.8 2774.1 ± 1.2 2769.6 ± 0.9

1

Dc Hm ðcrÞ=ðkJ  mol

Þ

1

Df Hm ðcrÞ=ðkJ  mol

Þ

2789.7 ± 0.9 2789.9 ± 1.8 2771.0 ± 1.2 2766.5 ± 0.9

1

Þ

1

Þ

47.4 ± 1.2 47.2 ± 2.0 66.1 ± 1.4 70.6 ± 1.2

TABLE 4 Standard (p° = 0.1 MPa) molar enthalpies of sublimation, Dgcr Hm , at T = 298.15 K determined by Calvet microcalorimetry for dichloronitrobenzene isomers. Compound

Number of experiments

T/K

 Dg;T cr;298:15K Hm ðgÞ=ðkJ  mol

2,4-Cl2NO2Benz 2,5-Cl2NO2Benz 3,4-Cl2NO2Benz 3,5-Cl2NO2Benz

5 5 5 5

324.2 339.4 339.4 339.9

91.9 ± 0.3 94.0 ± 0.4 92.1 ± 0.4 89.9 ± 0.2

Table 4 lists the values of the standard molar enthalpies of subg;T Hm , of the four dichloronitrobenzenes measured limation, Dcr;298:15K by Calvet microcalorimetry, where the uncertainties are taken as the standard deviations of the mean of five individual results. The uncertainties quoted for the standard molar enthalpies of sublimation, Dgcr Hm ðT ¼ 298:15 KÞ, at T = 298.15 K, are twice the overall standard deviation of the mean and include the uncertainties in the calibration with naphthalene [61,62]. The experimental value of Dgcr Hm ðT ¼ 298:15 KÞ for the 3,4dichloronitrobenzene, obtained in a previous work by Verevkin et al. [16], who derived the values of Dgcr Hm ðT ¼ 298:15 KÞ from measurements of the vapour pressure dependence with the temperature, using the transpiration method, as being (83.06 ± 0.59) kJ  mol1, is in agreement, within the associated experimental uncertainties, with the result achieved in this work. The combination of the standard molar enthalpies of formation in the crystalline state given in table 3, with the standard molar enthalpies of sublimation, at T = 298.15 K, given in table 4, yield the standard molar enthalpies of formation of the studied dichloronitrobenzenes, in the gaseous state, at T = 298.15 K, which are summarized in table 5. 3.2. Enthalpies of formation estimated with the Cox scheme The experimental values of Df Hm ðgÞ derived for the four isomers of dichloronitrobenzene are compared (table 6) with values estimated using the Cox scheme [31], which assumes that the enthalpic increment for the substitution of two chlorine atoms in different positions of the nitrobenzene ring will be the same as for substitution of two chlorine atoms in benzene with a correction term of 4 kJ  mol1 that was applied whenever the chlorine atom and the –NO2 group are bonded in ortho-position of the aromatic ring and another additional correction of 4 kJ  mol1 for every set of three substituents in three consecutive carbon atoms of the aromatic ring. From the standard molar gas-phase enthalpies of formation given in the literature [60] for benzene, nitrobenzene, o-dichlorobenzene, m-dichlorobenzene and p-dichlorobenzene, at

1

Þ

DTcr;298:15K Hm ðgÞ=kJ  mol 4.1 6.6 6.3 6.7

1

Þ

Dgcr Hm ð298:15KÞ=ðkJ  mol 87.8 ± 1.7 87.4 ± 2.5 85.8 ± 2.5 83.2 ± 1.5

T = 298.15 K, it is possible to estimate, applying the Cox scheme, the Df Hm ðgÞ for the different dichloronitrobenzene isomers {equations (2)–(4)}. These values are presented in table 6, together with the estimated values of the gas-phase enthalpies of formation for the monochloronitrobenzene isomers, obtained considering the experimental values Df Hm ðgÞ of benzene [60], nitrobenzene [60] and chlorobenzene [60]. For 2-chloronitrobenzene it is necessary to consider a correction term of 4 kJ  mol1 due to the chlorine atom and the –NO2 group being bonded in ortho-position of the aromatic ring, as suggested by Cox [31]. The values of Df Hm ðgÞ estimated by the Cox scheme, presented in table 6, are in excellent agreement with the experimental ones only in the case of 3,4- and 3,5-dichloronitrobenzene, this is for the chlorine substitutions in the positions meta and para with respect to the NO2 group. However, large deviations are found when the substituent is at an ortho-position, which is the cases of 2,4- and 2,5-dichloronitrobenzene, for which experimental results are available. For these compounds, the experimental results are higher than the estimated ones by the Cox scheme, suggesting an unexpected destabilization of these compounds. This is a result of the interaction between the chlorine atoms in the ortho-positions and the NO2 group, i.e. the proximity of the halogen atom and the nitro group in the aromatic ring introduces a significant steric destabilization effect, which leads to a slight rotation of the nitro group favouring the non-planar arrangement with a less p delocalization with the aromatic ring. This effect has been also observed for 2-chloronitrobenzene [15] and in the case of the chloronitroaniline isomers [19] in which the chlorine atom and nitro group are attached in the aromatic ring in ortho-positions. Supported by the former cases, it has been observed that, for benzene derivatives with these two substituents attached in ortho-position a correction term of 22 kJ  mol1 should be considered in the estimation of Df Hm ðgÞ using the Cox scheme. So, considering this additional correction term, the estimated Df Hm ðgÞ values are (36.6 ± 2.3) kJ  mol1 [D = 3.7 ± 3.1 kJ  mol1] and (33.4 ± 1.7) kJ  mol1 [D = 6.8 ± 3.6 kJ  mol1], respectively, for 2,4- and 2,5dichloronitrobenzene.

TABLE 5 Standard (p° = 0.1 MPa) molar enthalpies of formation, in condensed and gaseous phases, and standard molar enthalpies of sublimation, at T = 298.15 K. Compound

Df Hm ðcrÞ=ðkJ  mol

2,4-Cl2NO2Benz 2,5-Cl2NO2Benz 3,4-Cl2NO2Benz 3,5-Cl2NO2Benz

47.4 ± 1.2 47.2 ± 2.0 66.1 ± 1.4 70.6 ± 1.2

1

Þ

Dgcr Hm ð298:15KÞ=ðkJ  mol1 Þ

Df Hm ðgÞ=ðkJ  mol

87.8 ± 1.7 87.4 ± 2.5 85.8 ± 2.5 83.2 ± 1.5

40.4 ± 2.1 40.2 ± 3.2 19.7 ± 2.9 12.6 ± 1.9

1

Þ

909

M.A.V. Ribeiro da Silva et al. / J. Chem. Thermodynamics 41 (2009) 904–910

TABLE 6 Experimental and estimated (Cox scheme and B3LYP/6-311++G(d,p) and G3MP2B3 calculations) values of gas-phase enthalpies of formation of the dichloronitrobenzene isomers. Compound

Df Hm ðgÞ=ðkJ  mol Experimental

2-ClNO2Benz 3-ClNO2Benz 4-ClNO2Benz 2,3-Cl2NO2Benz 2,4-Cl2NO2Benz 2,5-Cl2NO2Benz 2,6-Cl2NO2Benz 3,4-Cl2NO2Benz 3,5-Cl2NO2Benz

62.2 ± 1.8 [15] 40.1 ± 1.9 [15] 39.7 ± 2.6 [15] – 40.4 ± 2.1 40.2 ± 3.2 – 19.7 ± 2.9 12.6 ± 1.9

1

Da/(kJ  mol1)

Þ Cox scheme

40.9 ± 1.6 36.9 ± 1.6 36.9 ± 1.6 23.1 ± 2.3 14.6 ± 2.3 11.4 ± 1.7 22.6 ± 2.3 15.1 ± 2.3 10.6 ± 2.3

Calculated I

II

73.0 44.7 41.2 58.7 52.0 51.2 68.3 26.7 26.8

64.4 42.6 40.7 46.9 42.0 41.4 47.8 22.9 21.3

Cox scheme

Calculated I

II

21.3 ± 2.4 3.2 ± 2.5 2.8 ± 3.1 – 25.87 ± 3.1 28.8 ± 3.6 – 4.6 ± 3.3 2.0 ± 3.0

10.8 4.6 1.5 – 11.6 11.0 – 7.0 14.2

2.2 2.5 1.0 – 1.6 1.2 – 3.2 8.7

I

B3LYP/6-311++G(d,p). G3MP2B3. Difference between the experimental and the estimated values.

II a

3.3. Computed enthalpies of formation The B3LYP/6-311++G(d,p) estimated values for the mono- and dichlorinated isomers of nitrobenzenes are compiled in table 6. The agreement between estimated and experimental results is good for the mono- and disubstituted nitrobenzenes in which the chlorine atom is not attached in ortho-position relatively to the nitro group, with exception of the 3,5-dichloronitrobenzene where the differences between theoretical and experimental results is of 14.2 kJ  mol1. Since the B3LYP estimates are consistently more positive than the experimental results for the chlorinated nitrobenzenes and the differences between theoretical and experimental results are in some cases larger than 10 kJ  mol1, G3MP2B3 calculations have also been carried out. The results presented in table 6 clearly show that the computational estimates performed by the G3MP2B3 composite approach are in good agreement with the experimental results, involving absolute deviations not larger than 8.7 kJ  mol1. The analysis of the G3MP2B3 enthalpies (table 6) shows that for the monochloronitrobenzenes, the 2-chloronitrobenzene is the most unstable isomer, and for the dichloronitrobenzenes there are four compounds that are clearly less stable than the other isomers. In all these cases, those compounds are characterized by the adjacent positioning of the chlorine and nitro substituents; the proximity of these groups introduces a significant steric destabilization which leads to a slight rotation of the nitro group and the loss of a favourable ring–NO2 geometry, with a less p delocalization with the aromatic ring. In 2-chloronitrobenzene the rotation of the nitro group is 33.2°, and for 2,3-, 2,4-, and 2,5-dichloronitrobenzene the rotation of the nitro group is comprehended in the interval that goes from 30.9° to 39.1°, and is of 81.9° for the 2,6dichloronitrobenzene isomer. Also, both theoretical methods point out that the dichloronitrobenzene isomers with the three substituents attached in consecutive carbon atoms are the less stable. The most stable dichloronitrobenzene isomer is the 3,5-dichloronitrobenzene where the three substituents are not bond in adjacent carbon atoms of the aromatic ring. Although both, B3LYP/6311++G(d,p) and G3MP2B3 calculations, shows that this isomer is almost degenerate with 3,4-dichloronitrobenzene. The most stable conformations obtained for all the three monochloronitrobenzenes and six dichloronitrobenzenes (table S6 in Supplementary material), taking into account the geometry optimization performed at the G3MP2B3, are those where the nitro group is coplanar with the aromatic benzene ring, allowing the conjugation of the nitrogen’s lone pair with the p-electron of the benzene ring, for the mono- and dichloronitrobenzene isomers in which the chlorine atoms are not attached in an adjacent position

of the nitro group, i.e. 3- and 4-chloronitrobenzene, and 3,4- and 3,5-dichloronitrobenzene; also for the isomers where a chlorine and the nitro substituents are in adjacent carbon atoms of the aromatic ring, the most stable conformations obtained are those in which the nitro group is not in the plane of the aromatic ring. Hence, the analysis of the geometrical parameters, together with the agreement between experimental and computed values, shows that the energetics of these compounds are mainly governed by the presence of steric repulsions between the chlorine and nitro group, leading to the rotation of the nitro group favouring the non-planar arrangement with a less p delocalization with the aromatic ring. 4. Discussion A combined experimental and computational study has been carried out to investigate the gas-phase thermochemistry of all dichloronitrobenzenes in terms of their standard molar gas-phase enthalpies of formation at T = 298.15 K. The experimental work involved the determination of the energies of combustion of the chloronitrobenzenes available in a high-purity state, i.e., 2,4-, 2,5-, 3,4-, and 3,5-dichloronitrobenzene compounds, by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the four compounds have been determined by Calvet microcalorimetry. From the experimental values, the standard molar enthalpies of formation in the gas phase at, T = 298.15 K, have been derived. The experimental results for these four compounds show that the enthalpy of formation is higher for the isomers in which the chlorine atom is bonded in ortho-position, being 3,5-dichloronitrobenzene the most stable isomer. The Df Hm values have also been estimated by DFT and G3MP2B3 composite method by considering a pertinent working reaction. In the case of the mono and dichloronitrobenzene derivatives with the chlorine atom substituted in meta and/or para position, the estimated values of Df Hm obtained using the B3LYP/6311++G(d,p) calculations are in good agreement with the experimental ones, but large deviations are observed in the cases of chlorine ortho substituted nitrobenzenes. The approach considered best for the class of compounds studied in the present work is the G3MP2B3 composite method. Using this method all computed values are in excellent agreement with the experimental data herewith reported, and the larger deviation of 8.7 kJ  mol1 is observed in the case of the 3,5-dichloronitrobenzene. So, we may conclude that the theoretical estimates for the compounds not studied experimentally can be accepted with confidence. The estimated values of Df Hm obtained by the Cox scheme are good estimates for the isomers in which the chlorine atoms are attached into the aromatic ring in meta and para position, as ob-

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served in a previous study concerned with the thermochemistry of the monochloronitrobenzenes [15]. So, for 3,4- and 3,5-dichloronitrobenzene, the estimations based on the Cox scheme are in very good agreement with the experimental values, cf. table 6. The differences, D, between the experimental and estimated values are, respectively (4.6 ± 3.3) kJ  mol1 and (2.0 ± 3.0) kJ  mol1, which are within the usually accepted limit of 10 kJ  mol1 for agreement between experimental and estimated values by the Cox scheme [31]. In the cases where the chlorine atom is bonded in ortho-position with respect to the NO2 group, i.e. 2,4- and 2,5-dichloronitrobenzene, larger differences, D, are observed. Hence, supported on the former studies devoted to the monochloronitrobenzenes [15] and chloronitroanilines [19], in which it was observed that for benzene derivatives with these two substituents attached in ortho-position a correction term of 22 kJ  mol1 should be considered, the estimated values of Df Hm ðgÞ for 2,3-, 2,4-, 2,5-, and 2,6-dichloronitrobenzene are, respectively, (45.1 ± 2.3) kJ  mol1, (36.6 ± 2.3) kJ  mol1, (33.4 ± 1.7) kJ  mol1 and (44.6 ± 2.3) kJ  mol1, yielding better estimations as compared with the available experimental values. 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.R.G.M and A.I.M.C.L.F. thank FCT and the European Social Fund (ESF) under the Community Support Framework (CSF) for the award of the research grants with references SRFH/BD/23024/2005 and SFRH/ BPD/27053/2006, respectively. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jct.2009.03.001. References [1] M.H. Priya, G. Madras, J. Phothochem. Photobiol. A: Chem. 178 (2006) 1–7. [2] M. MacLeod, D. Mackay, Chemosphere 38 (1999) 1777–1796. [3] S.K. Hong, D.K. Anestis, J.G. Ball, M.A. Valentovic, G.O. Rankin, Toxicol. Lett. 129 (2002) 133–141. [4] Q. Li, M. Minami, T. Hanaoka, Y. Yamamura, Toxicology 137 (1999) 35–45. [5] http://www.epa.gov/chemrtk/pubs/summaries/chlrnbnz/c14392rt.pdf (accessed 04.08). [6] X. Li, J. Chen, L. Du, J. Chromatogr. A 1140 (2007) 21–28. [7] H. Li, J. Kang, L. Ding, F. Lü, Y. Fang, J. Photochem. Photobiol. A: Chem. 197 (2008) 226–231. [8] J. Shen, Z. Chen, Z. Xu, X. Li, B. Xu, F. Qi, J. Hazard. Mater. 152 (2008) 1325– 1331. [9] J. Wu, C. Jiang, B. Wang, Y. Ma, Z. Liu, S. Liu, Appl. Environ. Microbiol. 72 (2006) 1759–1765. [10] N.J. Karrer, G. Ryhiner, E. Heinzle, Water Res. 31 (1997) 1013–1020. [11] P.R. Brookes, A.G. Livingston, Water Res. 28 (1994) 1347–1354. [12] R.M. Stephenson, S. Malanowski, Handbook of the Thermodynamics of Organic Compounds, Elsevier, New York, 1987. [13] T.N. Masalitinova, T.P. Oleinikova, V.L. Ryadnenko, N.N. Kiseleva, N.D. Lebedeva, J. Appl. Chem. USSR 54 (1981) 1551–1554. [14] S. Putcha, R.V. Ivaturi, R. Machiraju, J. Chem. Eng. Data 29 (1984) 135–136. [15] M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira, A.R.G. Moreno, J. Chem. Thermodyn. 41 (2009) 109–114. [16] S.P. Verevkin, C. Schick, Fluid Phase Equilib. 211 (2003) 161–177. [17] M.A.V. Ribeiro da Silva, M.L.C.C.H. Ferrão, F. Jiye, J. Chem. Thermodyn. 26 (1994) 839–846. [18] 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. [19] M.A.V. Ribeiro da Silva, J.R.B. Gomes, A.I.M.C.L. Ferreira, J. Phys. Chem. B 109 (2005) 13356–13362. [20] M.A.V. Ribeiro da Silva, A.I.M.C. Lobo Ferreira, L.M. Spencer, S. Lima, S.M.M. Sousa, J. Chem. Thermodyn. 40 (2007) 137–145. [21] V.M.F. Morais, M.S. Miranda, M.A.R. Matos, J. Chem. Eng. Data 52 (2007) 627– 634.

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JCT 09-66