Investigation of the interaction of ethyl acetoacetate with nano alumina particle as Lewis acid in acetonitrile solvent

Abstract

The enol form of ethyl acetoacetate (EAA) displays interesting spectroscopic characteristics; this form of ethyl acetylacetate is very important in condensation reaction. In this investigation, we have studied the interactions and the complex formation constants (K_f) with nano alumina (10–20 nm) particle and alumina (mesh 135) compounds as Lewis acids in the acetonitrile solvent using absorption spectroscopy and related calculations. Furthermore, in this study we calculated the thermodynamic parameters of this reaction. The trend of reactivity of the ethyl acetoacetate (EAA) complexes toward the above Lewis acids, based on the solvent as follows: nano alumina compound>alumina compound.

Keywords

complex formation constant / ethyl acetoacetate / nano alumina / alumina / thermodynamic

Introduction

β-diketones are important compounds in chemistry. They are among the most widely used ligands in coordination chemistry [1]. β-diketones are in solutions as keto and enol tautomers. Since the enolic hydrogen is labile, it can be replaced by a metal cation to form a six-member chelate ring. The β-diketonate complexes thus formed have been the topic of hundreds of papers and reviews [1-5], and widely used in a lot of aspects in industry, such as organic electroluminescent technology, luminescent materials, sensors for bioinorganic applications, luminescent labels in bioaffinity assays [1,2], NMR shift reagents [6-8], laser chelates [9,10], extraction agents [11-13], heat stabilizers for polymers, drugs [14,15], chemical and photochemical catalysts [16]. Moreover, they are used in manufacturing supra-conductors [17,18] and gas chromatography [19,20]. A few papers have also appeared in which β-diketones have been shown to act as neutral ligands by establishing a coordinative interaction with the metal cation [21-26].

However, in this paper, we report the thermodynamic studies on the complexes formation constants (K_f) of ethyl acetoacatate with nano alumina particle and alumina compounds as Lewis acids in acetonitrile solvents by Scatchard’s Eq. (1) [27] and the evaluation of the effect of the size of the Lewis acids on K_f of complexes. (Scheme 1)

Experimental

Materials and apparatus

The materials, ethyl acetoacetate (EAA), the solvent and Lewis acids were obtained from Merck, Fluka and Aldrich. All of the scanning UV-Vis spectra were recorded by Cintra 101 spectrophotometer.

Electronic spectra

The electronic spectra of all investigated complexes show an absorption band at 300-200 nm in this solvent in various temperatures. All complexes show an intensive absorption band at 270-220 nm. During the reactions, we could not observe the isobestic point in all solutions. Fig. 1 shows the spectrum of complex EAA with Al₂O₃ (nano) compound as Lewis acids in acetonitrile as solvent at different temperatures. The other spectrum of EAA complex with the Al₂O₃ compound as Lewis acid is similar to Fig. 1. All measurements for the thermodynamic studies were carried out at maximum wavelength (λ_max = 242 nm) (Table 1).

Results and discussion

A solution from each complex with a concentration of about 10^-3 mol/L was prepared. The formation constants and the thermodynamic parameters were measured spectrophotometrically. The complex formation measurements were carried out using the Lewis acids in acetonitrile solvent at various temperatures (Scheme 1). The formation constants of EAA complexes were calculated by Scatchard’s Eq. (1) in which b₀ and a₀ are the initial concentrations of the acceptor (Lewis acid) and the donor (EAA) respectively; D (λ) is the optical density of the solution including the acceptor (Lewis acid) and the donor (EAA). ϵ_AB (λ) is the molar extinction coefficients of the complex. The absorption bond data of EAA concentration at room temperature are reported in Table 1 and the concentration of Lewis acids is constant (3.92 × 10^-4 mol/L). The fixed wavelength (242 nm) and absorption bond of EAA complexes in various systems at room temperature are listed in Table 2. K is the formation constant of the complex formed, and the cell optical path is 1 cm.

(1)K{b}_{\mathrm{0}}{ϵ}_{AB}(\lambda )-KD(\lambda )=D(\lambda )/a_{\mathrm{0}}

Restrictions:

a_{\mathrm{0}}{b}_{\mathrm{0}}>>C^{\mathrm{2}}AB;a_{\mathrm{0}}>b_{\mathrm{0}};b_{\mathrm{0}}=constant

In Fig. 2 (A and B), we show a plot of D (λ) / a₀ vs. D (λ) for EAA complexes in the acetonitrile solvent at various temperatures. The curves in this figure show that in EAA reactions with two Lewis acids, only 1∶1 complex is formed since all the lines are straight while a mixture of 1∶1 and 1∶2 or only 1∶2 complex in a system would lead to a curve [28]. According to the data reported in Tables 1 and 2 and Scatchard’s Eq. (1), the formation constants of the studied EAA complexes were calculated from the slope of line in the diagram.

The thermodynamic parameters of the studied EAA complexes with two Lewis acids in the various conditions were calculated by use of the well-known, van’tHoff Equation (Eq. (2)):

(2)\ln K=-\mathrm{\Delta }{H}^{\circ }/RT+\mathrm{\Delta }{S}^{\circ }/R

where K is the formation constant, R is the gas constant and T is the temperature in Kelvin scale. The formation constant of the studied EAA complexes were not obtained by the linear plots of lnK vs. 1/T because the range of temperature is not wide. In Fig. 3, we show the scatter data and linear plots for EAA complexes with two Lewis acids at various temperatures and in acetonitrile solvent. The data for the calculations are reported in Tables 3 and 4

We can calculate the values of ∆H° and ∆S° parameters from the slope and the intercept of plot lnK vs. 1/T respectively; Then according to Eq. (3), the values of ∆G° of complex formations were obtained. The thermodynamic parameters are listed in Tables 5 and 6.

(3)\mathrm{\Delta }{G}^{\circ }=\mathrm{\Delta }{H}^{\circ }-T\mathrm{\Delta }{S}^{\circ }

The effect of temperature on the electronic spectra

The formation constants in the same solvent and ligand are dependent on the temperature; however, in the present study, we obtained the data of EAA complexes at various temperatures. The data are reported in Table 7.

According to the data reported in Table 7, it seems that the temperature is very influential for the formation constants of EAA complexes.

Thermodynamic parameters

The value of thermodynamic parameters as ∆H°, ∆G° and ∆S° are dependent on the heat of formation of the complex and the solvent effect [28]. In all EAA complexes with two Lewis acids, it is found that the ∆H° values are positive. This shows that the complex-formation contribution of ∆H° values is more important. The ∆H° value for Al₂O₃ (nano) (10-20 nm) complex as Lewis acid in acetonitrile solvent is more positive than Al₂O₃ (mesh 135) as Lewis acid in the same solvent. This shows that the complex formation for these complexes within acetonitrile is more important because the EAA complexes are very important in the synthesis of organic compounds such as synthesis of 3,4-dihydropyrimidinones [29].

The ∆S° value and its signs are also dependent on the differences in the number of particles of the initial substance and the product complexes, and the liberation of the solvent molecule from EAA complexes. In this work, we do not separate the products, an evolution from the liberation of the solvent molecule from these complexes.

However, according to the data reported in Tables 5 and 6, it is found that the ∆G° values in all EAA complexes are negative.

Conclusion

By considering the formation constants, K_f, and ∆G° of the formation for EAA complexes as the donor and two Lewis acids as the acceptor, we propose the following conclusions:

1) The reactions of EAA with two Lewis acids in the acetonitrile solvent are endothermic. ∆H°>0.

2) The formation constant in two Lewis acids in these complexes changes according to the following trend in acetonitrile solvent: Al₂O₃ (nano) (10-20 nm)>Al₂O₃ (mesh 135).

3) The results of the present work show that the thermodynamic parameters in the ethyl acetoacatate with Al₂O₃ (nano) increase with respect to Al₂O₃, as the homogeneous distribution of the reactants throughout the solution makes a strong case in the increase of these parameters.

4) According to the data obtained for EAA complexes, it seems that the rate of EAA in the organic synthesis is dependent on the thermodynamic parameters.

5) The aim of this study is to obtain the formation constants of EAA in various conditions that are very important in the investigation of the rate of condensation reaction of EAA in organic reactions.

6)zhon The collective data available for the present work strongly suggest that β-diketones can have different behavior in various conditions.

References

[1] Siedle, A. R., Comprehensive Coordination Chemistry, vol. 2, ed., G. Wilkinson, Pergamon Press, Oxford, 1987, pp. 365-412

[2] Mehrotra, R. C.; Bohra, R.; Gaur, D. P., Metal β-Diketonates and Allied Derivatives, Academic Press, London, 1978

[3] Fackler, J. P. Jr, Prog. Inorg. Chem. 1966, 7, 361-425

[4] Kawaguchi, S., Coord. Chem. Rev. 1986, 70, 51-84.

[5] Garnovskii, A. D., Koord. Khim.1992, 18, 675-680

[6] Hinckley, C. C., J. Am. Chem. Soc.1969, 91, 5160-5162

[7] Wenzel, T. J.; Bettes, T. C.; Sadlowski, J. E.; Sievers, R. E., J. Am. Chem. Soc. 1980, 102, 5903-5904

[8] Wenzel, T. J.; Zaia, J., J. Org. Chem. 1985, 50, 1322-1324

[9] Brecher, C.; Lempicki, A.; Samelson, H., J. Chem. Phys. 1965, 42, 1081-1096

[10] Nugent, L. J.; Bhaumik, M. L.; George, S.; Lee, S. M., J. Chem. Phys. 1964, 41, 1305

[11] Poskanzer, A. M.; Foreman, B. M., J. Inorg. Nucl. Chem. 1961, 16, 323-336

[12] Testa, C., Anal. Chim. Acta1961, 25, 525

[13] Ikehata, A.; Shimizu, T., Bull. Chem. Soc. Jpn.1965, 38, 1385-1388

[14] Anjaneyulu, Y.; Rao, R. P.,Synth. React. Inorg. Metal-Org. Chem.1986, 16, 257-261

[15] Keppler, B. K.; Friesen, C.; Moritz, H. G.; Vongerichten, H.; Vogel, E., Struct. Bonding (Berlin)1991, 78, 97-127

[16] Marciniak, B.; Buono-Core, G. E., J. Photochem. Photobiol. Chem. 1990, 52, 1-25

[17] Hubert-Pfalzgraf, L. G., Appl. Organomet. Chem. 1992, 6, 627-643

[18] Sievers, R. E.; Turnipseed, S. B.; Huang, L.; Lagalante, A. F., Coord. Chem. Rev. 1993, 128, 285-291

[19] Robards, K.; Patsalides, E.; Dilli, S., J. Chromatogr. A1987, 411, 1-41

[20] Komarov, V. A., Zh. Anal. Khim. 1976, 31, 366-375

[21] van Leeuwen, P. W. N. M., Recl. Trav. Chim. Pays Bas1968, 87, 396-402

[22] van Leeuwen, P. W. N. M.; Praat, A. P., Inorg. Chim. Acta1970, 4, 101-104

[23] Allred, A. L.; Thompson, D. W., Inorg. Chem. 1968, 7, 1196-1201

[24] Blanco, C. A.; Hynes, M. J., Can. J. Chem. 1992, 70, 2285-2289

[25] Pearson, R. G.; Anderson, O. P., Inorg. Chem. 1970, 9, 39-46

[26] Fay, D. P.; Nichols, A. R.; Sutin, N., Inorg. Chem. 1971, 10, 2096-2101

[27] Ketelaar, J. A. A.; van de Stolpe, C.; Coulsmith, A.; Dzcubes, W., Rec. Trav. Chim. 1952, 71, 1104-1114

[28] Asadi, M.; Kianfar, A. H.; Hemateenejad, B., J. Chem. Res. 2002, 520-523

[29] Khodaei, M. M.; Khosropour, A. R.; Beygzadeh, M., Synth. Commun. 2004, 34, 1551-1557

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