Standard molar enthalpies of formation of 1- and 2-cyanonaphthalene

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Abstract

The standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline state, of the 1- and 2-cyanonaphthalene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. Vapor pressure measurements at different temperatures, using the Knudsen mass loss effusion technique, enabled the determination of the enthalpy, entropy, and Gibbs energy of sublimation, at T = 298.15 K, for both isomers. The standard molar enthalpies of sublimation, at T = 298.15 K, for 1- and 2-cyanonaphthalene, were also measured by high-temperature Calvet microcalorimetry.

Empty Cell-ΔcUm(cr)/(kJ·mol-1)ΔfHm(cr)/(kJ·mol-1)ΔcrgHm(cr)/(kJ·mol-1)
1-Cyanonaphthalene5514.4 ± 1.6188.5 ± 2.288.6 ± 0.5
2-Cyanonaphthalene5510.5 ± 1.7184.6 ± 2.292.1 ± 0.1
Combining these two experimental values, the gas-phase standard molar enthalpies, at T = 298.15 K, were derived and compared with those estimated by employing two different methodologies: one based on the Cox scheme and the other one based on G3MP2B3 calculations. The calculated values show a good agreement with the experimental values obtained in this work.

Highlights

Enthalpies of formation of 1- and 2-cyanonaphthalene were measured by combustion calorimetry. ► Vapor pressures of crystalline 1- and 2-cyanonaphthalene obtained by Knudsen effusion mass loss technique. ► Enthalpies, entropies and Gibbs functions of sublimation at T = 298.15 K were calculated.

Introduction

The study of the thermochemistry of naphthalene derivatives has been among the interests of the Molecular Energetics Research Group of the University of Porto, aiming to study the influence of the polar and steric effects of the substituents on the thermodynamic stability of the molecules. Following our studies on hydroxy- and dihydroxynaphthalenes [1], bromonaphthalenes [2], nitronaphthalenes [3], and diaminonaphthalene [4], this work deals with the thermochemical study of the 1- and 2-cyanonaphthalene, whose structural formulae are depicted in figure 1.

Naphthalene and its derivatives are biologically, pharmaceutically and industrially useful compounds, with technological applications in a large number of industrial process and have specially attracted the attention of organic chemists for many years due to their occurrence in synthetic and natural products possessing valuable biological activities. Naphthalenes are used as topical and systemic anti-inflammatory drugs [5], [6], [7], anti-psoriatic agents [5], and to treat cardiovascular diseases [8], [9]. Compounds with the nitrile functional group are also very important in many fields of chemistry and biochemistry. The 1-cyanonaphthalene is used in the synthesis of chiral derivatives of Butenafine and Terbinafine; well established antimicotic agents used among others in the treatment of dermatocytes invading skin and nails, with antifungal activity [10], [11]. The 3-cyano-1-naphthalenecarboxylic acid is an intermediate required for the manufacture of tachykinin receptor antagonists; such as ZD60211, under investigation for treatment of depression, asthma, urinary incontinence, and other disease conditions [12].

To the best of our knowledge the literature reports only thermochemical data concerning the enthalpies of combustion, T = 298.15 K, of these two compounds, a work performed by Lemoult and Jungfleisch [13], in 1909, by static bomb combustion calorimetry.

The present study provides results on the standard molar energy of combustion, standard molar enthalpy of sublimation, and standard molar enthalpy of formation in both crystalline and gaseous states, at T = 298.15 K, for the two title compounds. The standard (p° = 0.1 MPa) molar enthalpies of formation of the two isomers, in the crystalline state, at T = 298.15 K, were derived from the standard massic energies of combustion, measured by static bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the vapor pressures as a function of temperature of the two crystalline compounds. From the vapor pressure dependence of the temperature, and by application of the Clausius–Clapeyron equation, the standard molar enthalpies of sublimation, at the mean temperature of the experimental temperature range, were derived. Standard molar enthalpies, entropies, and Gibbs energies of sublimation, at the temperature of 298.15 K, were calculated using estimated values of the heat capacity differences between the gas and the crystal phases of each compound. The standard molar enthalpies of sublimation, at T = 298.15 K, were also measured by high-temperature Calvet microcalorimetry.

The values of the standard molar enthalpies of formation, in the crystalline phase, and of the standard molar enthalpies of sublimation obtained by Knudsen effusion, were combined to derive the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of the 1- and 2-cyanonaphthalenes. These experimental values are compared with estimates based on high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level, and with the ones estimated by the Cox scheme [14].

Section snippets

Materials and purity control

Samples of 1-cyanonaphthalene, [CAS 86-53-3] and 2-cyanonaphthalene, [CAS 613-46-7] were supplied by Aldrich Chemical Co. with an assessed mass fraction minimum purity of 0.98 and 0.97, respectively, and purified in this laboratory. The 1-cyanonaphthalene was purified by successive vacuum sublimation at 0.1 Pa background pressure, firstly at T  306 K, being the temperature of the cold finger T  261 K, and then at T  312 K. The 2-cyanonaphthalene was purified firstly by sublimation at 0.1 Pa background

Computational details

In the present work, the enthalpies of all species considered were obtained using the G3(MP2)//B3LYP method, which is based on standard ab initio molecular calculations and empirically based corrections. Full details and the theoretical basis of the method can be found in Baboul et al. [29]. This approach uses the B3LYP method and the 6-31G(d) basis set for geometry optimization and calculation of the vibrational frequencies to compute thermal corrections for T = 298.15 K by introduction of the

Experimental enthalpies of formation

Detailed results for each combustion experiment performed for 1- and 2-cyanonaphthalene are given, respectively, in TABLE 1, TABLE 2, where Δm(H2O) is the deviation of the mass of water added to the calorimeter and the mass assigned to ε(calor): 3119.6 g, ΔUΣ is the energy correction to the standard state and the remaining terms are as previously described [22], [23]. The internal energy for the isothermal bomb process, ΔU(IBP), was calculated through equation (4):ΔU(IBP)=-{ε(calor)+cp(H2O,l)·Δm(

Discussion

The experimental values of the standard molar enthalpies of formation, in gaseous state, for the two compounds studied were derived from the values of the standard molar enthalpies of combustion obtained by static bomb combustion calorimetry, and from the standard molar enthalpies of sublimation derived from the values of vapor pressures at different temperatures measured by the Knudsen effusion technique.

For the 2-cyanonaphthalene, a slightly higher value of standard molar enthalpy of

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 research grant with reference SFRH/BPD/27053/2006.

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