A rather simple thermochemical experimental technique was applied to determine the enthalpy of formation of Diperoxide of acetone. The study is complemented with theoretical calculations ab initio and by the density functional theory (DFT) procedure
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Keywords: DPAC, heat of formation, DFT calculationUna técnica experimental sencilla y rápida se emplea para determinar la entalpía de formación de acetona diperóxido. El estudio se complementa con cálculos teóricos en ab initio y los niveles de funciones de densidad (DFT).
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Palabras clave: DPAC, calor de formación, cálculo DF

Beatriz Reguera, Mónica

Castro, Eduardo Alberto

Inés Profeta, Mariela

Lidia Jorge, Nelly

Marcelo Romero, Jorge

Natalia Pila, Andrea

English

Nereis. Magazin Iberoamericana Interdisziplinäre Methoden, Modellierung und Simulation

Nereis. Revista Iberoamericana Interdisciplinar de Métodos, Modelización y Simulación4 31-36 Universidad Católica de Valencia “San Vicente Mártir”Valencia (España) ISSN 1888-8550NEREIS 4 [Marzo 2012], 31-36, ISSN: 1888-8550Calorimetric and Computational Study of Enthalpy of Formation of Acetone DiperoxideFecha de recepción y aceptación: 15 de noviembre de 2011, 30 de noviembre de 2011Andrea Natalia Pila†, Mónica Beatriz Reguera‡, Mariela Inés Profeta†, Jorge Marcelo Romero†, Nelly Lidia Jorge†, Eduardo Alberto Castro∞† Laboratorio de Investigaciones en Tecnología del Medio Ambiente, Facultad de Ciencias Exactas y Naturales y Agrimensura, UNNE, Corrientes, 3400, Argentina.‡ UNCAUS, Area de Fisicoquímica, Presidencia Roque Sáenz Peña, 3700, Chaco. Argentina∞ INIFTA, Theoretical Chemistry Division, La Plata, 1900, Buenos Aires. ArgentinaABStRACtA rather simple thermochemical experimental technique was applied to determine the enthalpy of formation of Diperoxide of acetone. The study is complemented with theoretical calculations ab initio and by the density functional theory (DFT) procedure.KEYwoRDS: DPAC, heat of formation, DFT calculation. RESUMENUna técnica experimental sencilla y rápida se emplea para determinar la entalpía de formación de acetona diperóxido. El estudio se complementa con cálculos teóricos en ab initio y los niveles de funciones de densidad (DFT).PALABRAS CLAVE: DPAC, calor de formación, cálculo DFT.INtRoDUCtIoNPeroxides are widely used in several areas of chemistry due to their high reactivity with organic and inorganic substrates [1]. Their specific properties as free radical reaction initiators are widely employed in synthetic chemistry [2], especially in polymerization processes. [3] More recently, tetroxanes have been found to possess impressive antimalarial activity [4]. As a result of an apparent association between the peroxide functional group and antimalarial activity, a substantial effort has been devoted to developing new peroxide antimalarial drugs [4-6]. Unfortunately, several members of this compound class are very unstable; only a small number are easy to manipulate with adequate safety and are available as commercial products.Among these peroxides is a large number of peroxyacids and peroxyesters [7]. Although the importance of these compounds is well known in chemistry, several aspects of their structure and reactivity modelling remain to be precisely defined [8].Ketone and aldehyde diperoxides (1,2,4,5-tetroxanes) contain two peroxy groups in a six membered heterocycle and they are readily formed by acid-catalysed oxidation of carbonyl compounds with hydrogen peroxide. These compounds are also described as carbonyl dimers since they can be generated by dimerization of a carbonyl oxide intermediate derived from ozonolysis of olefins [9-11].In this article, we report on the experimental determination of the enthalpy of formation of diperoxide of acetone (DPAC) (Figure 1) as well as the theoretical results calculated ab initio by the Hartree-Fock and density functional theory (DFT) methods.NEREIS 4 [Marzo 2012], 31-36, ISSN: 1888-8550Andrea Natalia Pila et al.32EXPERIMENtAL PRoCEDUREMaterialAcetone diperoxide (DPAC) was prepared by dropwise addition of acetone in acetonitrile to a vigorously stirred, cooled (-20 ºC) solution of 69.7% hydrogen peroxide and sulphuric acid (18 M). After stirring for 2 h at -20 ºC, filtration, thorough water washing, and drying, the crude product (71% yield) was purified by recrystallizing from ethyl acetate until a constant melting point was attained (132 – 132.5 ºC [lit., 133-135 and 132-133 ºC]). The product purity was also checked by GC and IR analyses (KC1) 2910 (s), 2850 (s), 1200 (m), 940 (w), 860 (w), 814 (w) and 682 (w) cm-1.Figure 1. Diperoxide of acetone (DPAC)Thermochemical measurementsThe measurement of the heat of combustion of diperoxide of acetone was made in an isoperibol macrocalorimeter fitted with a stirred water bath. The substance was burned in oxygen at p = 25 atm. The current of ignition was determined to be 2 Amp. The heat capacity of the calorimeter (E) was determined with a standard reference sample of benzoic acid (Sample SRM 39i, NIST) for all experiments. E was measured to be (1808.17 ± 1.5) cal/K. The crystalline compounds were pressed into capsules of masses » 10-2 g. The reduction of the data to standard conditions was made through conventional procedures [12]. The atomic weights used were those recommended by the IUPAC Commission [13].Vapour pressures as a function of temperature of DPAC were measured by a mercury manometer using a Bodestein differential equipment and the enthalpy of sublimation was deduced from the temperature dependence of the vapour pressures (Clausius-Clapeyron equation).Theoretical calculations The most important reason for calorimetric studies was to determine the molecular energy of a set of structurally and functionally related molecules in order to establish the corresponding structure-activity relationships and to be able to assess the main electronic features determining chemical reactivity. It is well known that in order to make theoretical calculations of molecular enthalpy of formation it is necessary to find suitable isodesmic chemical reactions to optimize the corresponding molecular structure and to perform the frequency calculations from the optimized equilibrium molecular geometries applying the corresponding theoretical method to obtain the total electronic energy at 298 K. Here we chose the Gaussian 03 package [14] to perform the theoretical calculations ab initio and using Density Functional Theory (DFT). NEREIS 4 [Marzo 2012], 31-36, ISSN: 1888-855033Calorimetric and Computational Study of  Enthalpy of  Formation of Acetone DiperoxideIn order to determine equilibrium molecular geometries, it is necessary to localize the absolute minimum at the potential energy hypersurface. The optimization procedure is complete when the numerical process converges, i.e. when forces are null. Convergence criteria employed in the Gaussian 03 package are: Forces are practically zero. •	The square root of the average forces must be zero. •	The shifting calculation for the next step in the calculation cycle must be small enough. •	The second derivative of the shifting must be zero. •	RESULtS AND DISCUSSIoNExperimental enthalpy of formationResults for a typical combustion experiment on compound DPAC are given in Table 1. The individual values of the standard specific energy of combustion ( 0cU∆ ), enthalpies of combustion (the given standard deviations of the mean include the uncertainties from calibration and the uncertainties from the combustion energies of the auxiliary materials), and enthalpies of combustion and formation of the compound DPF are given in Table 2.To derive 0fH∆ (g) from 0fH∆ (c), the following molar enthalpies of formation were used [13]: for H2O(g): -(244.83 ± 0.17) kJ/mol and for CO2(g): -(393.50 ± 0.54) kJ/mol.Table 2 shows the standard molar energy and enthalpy of combustion and formation of diperoxide of acetone, in the crystalline state at T = 298.15 K, and it corresponds to the chemical reaction:C6H12O4(c) + 7O2(g) → 6CO2(g) + 6H2O(g)         (1)The uncertainties of the standard molar energy are four times the final overall standard deviation of the mean and they were estimated as outlined by statistical methods. Vapour pressure was determined at different temperatures and the enthalpy of sublimation was calculated as pointed out before.Table 1. Results from typical combustion experiments at 298.15 K1 2 3 4 5 6 7 8MDPAC/g 0.0311 0.0492 0.0413 0.0487 0.0484 0.0488 0.0495 0.0490mFe/g 0.0025 0.0098 0.0119 0.009 0,0081 0.0130 0.0113 0.0116∆T/K 0.09615 0.15835 0.13440 0.14770 0.15411 0.15789 0.15879 0.15761(mwater+E)∆T/Ja 1445.067 2409.950 1990.478 2211.864 2361.253 1570.532 1750.319 2368.765mFe ∆UFe/Jb 29.085 108.300 138.445 10.471 94.235 138.985 131.464 134.954∆Uc/J/gc 22901.960 23165.751 22915.423 22927.966 23091.932 22900.635 22915.218 22931.164∆Hc/kJ/mol -3376.842 -3415.883 -3378.836 -3380.691 -3404.958 -3376.646 -3378.804 -3381.165a mwater=2700g b DUFe (heat of combustion of iron wire)=1800.00 ± 0.70 cal/g c DUc standard specific heats of combustionThe standard molar enthalpies of formation for both crystalline and gaseous states of DPAC at T = 298.15 K are also given in Table 2. No combustion enthalpy and enthalpy of sublimation have been found in the standard literature for comparison purposes.NEREIS 4 [Marzo 2012], 31-36, ISSN: 1888-8550Andrea Natalia Pila et al.34Table 2. Summary of experimental specific heats of combustion and standard molar thermodynamic function of DPAC at T = 298.15 K. Experiment Nº 0cU∆ (c)a J/mol -∆Hc0 (c)b kJ/mol -∆H f0 (c)c kJ/mol -∆H f0 (g)d kJ/mol1 22901.960 -3376.842 -435.10 -370.402 23165.751 -3415.883 -396.06 -331.363 22915.423 -3378.836 -433.11 -368.414 22927.966 -3380.691 -431.25 -366.555 23091.932 -3404.958 -406.98 -342.286 22900.635 -3376.646 -435.30 -370.607 22915.218 -3378.804 -433.14 -368.448 22931.164 -3381.165 -430.78 -366.08Average value 22968,7561 -3386.728 -425.21 -360.51Standard deviation 1.057055 0.241008 0.241008 0.241008a Standard molar heat of combustionb Standard enthalpy of combustionc Standard enthalpy of formation in crystalline stated Standard enthalpy of formation in gas phase obtained from the sublimation molar enthalpy (∆HS =64.66 kJ/mol)Theoretical Calculation of the enthalpy of formationIn the case of diperoxide of acetone, the suitable isodesmic chemical reaction, is:2 CH3-O-O-CH3 (DMP)(g) + 2 C3H8 (g) ® DPAC (g) + 4 CH4(g)      (2)In order to calculate enthalpy values at 298 K, the difference between the enthalpy at temperature T and 0 K can be evaluated according to standard thermodynamic formula 2. The sum of electronic and enthalpy energies at 298 K calculated ab initio using the Hartree-Fock and Density Functional Theory (DFT) procedures with different basis sets for the studied compounds, are also shown in Table 3.The heats of formation calculated through atomization reaction are given in Table 4. The analysis of theoretical results show that ab initio and DFT procedures yield better results. Besides, the best agreement among experimental data and theoretical predictions happens for the 3-21G** basis set.Table 3. Calculated electronic energy and heat of reaction (in Hartree units)- ( )acorrH+0ε [Hartree]RHF 3-21G** RHF 6-31G** B3LYP 3-21G** B3LYP 6-31G**DPAC -530.393261 -533.276675 -533.624866 -536.434576CH4 -39.945747 -40.151095 -40.271061 -40.477542C3H8 -117.536449 -118.162074 -118.427441 -119.050393CH3OOCH3 -227.520094 -228.748400 -228.895519 -230.091622∆Hrb -0.063188 -0.060110 -0.063204 -0.060718a Sum of electronic and thermal enthalpies calculated using ab initio Hartree-Fock and Density Functional Theory (DFT) techniques with different basis sets levels; b Heat of reaction obtained with ab initio Hartree-Fock and Density Functional Theory (DFT) techniques at different basis sets levels: ( ) ( )∑∑ +−+=∆ tsreaccorrproductscorrr HHH tan00 εεNEREIS 4 [Marzo 2012], 31-36, ISSN: 1888-855035Calorimetric and Computational Study of  Enthalpy of  Formation of Acetone DiperoxideTable 4. Enthalpy of formation of DPAC - ( )af gH 0∆ [kJ mol-1]RHF 3-21G** RHF 6-31G** B3LYP 3-21G** B3LYP 6-31G**-326.58 -318.52 -326.62 -320.10a Standard enthalpy of formation in gas phase calculated ab initio by the Hartree-Fock and Density Functional Theory (DFT) techniques and with different basis sets. CoNCLUSIoNSWe have reported a simple and accurate experimental method to determine the enthalpy of formation of the title compound and we have complemented it with the theoretical calculation of the property under study via ab initio Molecular Orbital methods and DFT procedures. The theoretical value of the enthalpy of formation of diperoxide of acetone, -360.51 kJ mol-1, evaluated by the Hartree-Fock and DFT methods at the 3-21G** basis set level, is in very good agreement with the experimental value, -326.62 kJ mol-1. This methodology, consisting in the experimental determination of the thermochemical property and its complementation with theoretical procedures, represents a prudent way to study similar oxane derivative molecules and further studies along this line are currently under development.LItERAtURE CItEDN. L. JORGE & E. A. CASTRO1. . 2009. Tetroxanes: Structure and Properties. Trends in Organic Chemistry, Vol. 13, 65-74.M. B. SMITH & J. MARCH2. . 2007. March’s advances organic chemistry. Ed. John Wiley & Sons, New Jersey.P. ACUñA & G. MORALES3. . 2011. Síntesis de poliestireno de alto impacto (hips) a partir de diferentes iniciadores multifuncionales: efecto de la estructura y del contenido de oxígeno activo del iniciador. Rev. Iberoam. Polim. Vol. 12(3), pp. 160-168. Y. DONG, K. J. MCCULLOUGH, S. WITTLIN, J. CHOLLET & J. L. VENNERSTROM4. . 2010. The structure and antimalarial activity of dispiro-1,2,4,5-tetraoxanes derived from (+)-dihydrocarvone. Bioorg Med Chem Lett, 20(22), 6359-61.H. 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Chemistry of Heterocyclic Compounds. 45(12), 1455-1459. M. I. PROFETA, J. R. ROMERO, L. A. C. LEIVA, N. L. JORGE, M. E. GóMEz-VARA, E. A. CASTRO10. . 2011. Solvent effect of oxygen in the thermolysis decomposition of the acetone diperoxide. Int. J. Chemoinf. & Chem. Engin. 1(1), 96-102.S. A. I. CAzUT, E. H. RAMíREz MAISULS, M. R. DELFINO, J. M. ROMERO, N. L. JORGE & E. A. CASTRO11. . 2009. Thermal Decomposition of Formaldehyde Diperoxide in Aqueous Solution. Russian Journal of General Chemistry, Vol. 79, No. 10, pp. 2187-2190.NEREIS 4 [Marzo 2012], 31-36, ISSN: 1888-8550Andrea Natalia Pila et al.36W. N. HUBBART, D. W. SCOTT, G. WADDINGTON12. . 1956. In F. D. Rossini, ed. Experimental Thermochemistry; Interscience, New York, 75-127. J. D. COx, D. D. WAGMAN, V. A. MEDVEDEV13. , eds. 1989. CODATA Key Values for Thermodynamics. Hemisphere, New York.Gaussian 03, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Jr Montgomery, 14. T. Vreven, K. 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Calorimetric and Computational Study of Enthalpy of Formation of Acetone Diperoxide

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Calorimetric and Computational Study of Enthalpy of Formation of Acetone Diperoxide

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Nereis. Magazin Iberoamericana Interdisziplinäre Methoden, Modellierung und Simulation