Heat capacity and enthalpy of fusion of pyrimethanil laurate (C 24 H 37 N 3 O 2 )

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1 J. Chem. Thermodynamics 36 (24) Heat capacity and enthalpy of fusion of pyrimethanil laurate (C 24 H 37 3 O 2 ) Xiao-Hong Sun a, *, Yuan-Fa Liu a, Zhi-Cheng Tan b, You-Ying Di b, Hui-Fang Wang a, Mei-Han Wang b a College of Chemical Engineering, Chemical Research Institute, orthwest University, Xi-an 7169, PR China b Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 11623, PR China Received 5 May 24; accepted 8 June 24 Available online 17 August 24 Abstract Low-temperature heat capacities of pyrimethanil laurate (C 24 H 37 3 O 2 ) were precisely measured with an automated adiabatic calorimeter over the temperature range between T = 78 K and T = 34 K. The sample was observed to melt at ( ±.4) K. The molar enthalpy and entropy of fusion as well as the chemical purity of the compound were determined to be (67244 ± 11) J Æ mol 1, (29.28 ±.2) J Æ mol 1 Æ K 1, (.9943 ±.4) mass fraction, respectively. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was ( ±.6) K. Ó 24 Elsevier Ltd. All rights reserved. Keywords: Pyrimethanil laurate; Heat capacity; Adiabatic calorimetry; DSC 1. Introduction Pyrimidinamine compounds are heterocyclic compounds with novel biological activities [1]. They have been applied to medicine and pesticide synthesis for their important physiological-action [2,3]. Compared with the free pyrimethanil, pyrimethanil salts have a reduced vapour pressure, which increases the persistence of the compounds on the crop and they have increased activities in many aspects. Pyrimethanil laurate (molecular formula: C 24 H 37 3 O 2 ) is an important new compound. It was synthesized by pyrimidinamine and lauric acid. The preliminary biological activities tests * Corresponding author. Tel.: ; fax: address: xhsun888@sohu.com (X.-H. Sun). showed it could be used for controlling many kinds of fungi, such as Pythium solani, Gibberella nicotiancola, Fusarium oxysporium f.sp. uasinfectum and Fusarium oxysporium f.sp. cinerea [4] of plant, fruit, vegetable and foodstuff. So, It can be used for a new high-efficiency fungicide. The application and synthetic methods of the compound have been reported [4], but no reports on the thermodynamic properties of the new substance have been reported. For the application of the compound, the thermodynamic data for the pyrimethanil laurate are urgently required. In the present work, it was synthesized and its structure has been confirmed by IR, 1 H MR and elemental analysis. The low-temperature heat capacity measurements of the compound were carried out with an adiabatic calorimeter. The basic thermodynamic parameters, such as the melting point, molar enthalpy and entropy of melting have been determined /$ - see front matter Ó 24 Elsevier Ltd. All rights reserved. doi:1.116/j.jct

2 896 X.-H. Sun et al. / J. Chem. Thermodynamics 36 (24) Experimental 2.1. Sample preparation and characterization Equipment and reagents Pyrimethanil laurate was made according to the method reported in literature [5], pyrimethanil (purified 3 times, the purity was.998 mole fraction, m.p C [6]), ethanol, lauric acid, were of analytical grade. PE-24 elemental analyzer, BRUKER EQUIOX- 55 IR spectral meter, Varian Inova-4 1 H MR spectrum, Agilent gas chromatograph/hewlett Packard mass spectrometry and SMP3 melting point apparatus were applied to characterize the structure of the compound The scheme of the formation reaction of pyrimethanil laurate in the temperature range of (78 to 364) K to eliminate the heat loss owing to the gas convection, and a small amount of helium gas was introduced through a length of copper capillary at the centre of the upper cover into the cell to improve the heat transfer of the whole sample cell. The sample cell was sealed with the tin solder after the copper capillary was pinched off from the tube end. Two adiabatic shields surrounded the sample cell in turn and a vacuum can was immersed in liquid nitrogen. The two adiabatic shields were made of chromium-plated copper and equipped with manganin heating wires. Two sets of six-junction chromel-contantan (i 55%, Cu 45%) thermocouples were used to measure the temperature differences between the sample cell and the inner adiabatic shield and between the inner and the outer adiabatic shields. The temperatures of the two shields were controlled separately and automatically with two units of auto-adiabatic controller. When the H CH 3 CH EtOH 3 + CH 3 (CH 2 ) 1 COOH H. CH 3 (CH 2 ) 1 COOH CH 3 CH Experimental procedures A solution of pyrimethanil and lauric acid in anhydrous alcohol was stirred for 1 h at room temperature. The precipitate formed was filtered and recrystallized from anhydrous alcohol to yield compound. The final product pyrimethanil laurate was a colorless crystal. Its mass fraction purity was.9957 (GC) Analysis result of pyrimethanil laurate The melting point of the final product was determined to be T = ( to ) K. The results of elemental analysis were: : 1.51 (1.52); C: 72.8 (72.16); H: 9.26 (9.34). 1 H MR (CDCl 3 ) absorption peaks were detected at d =.88 (t, 3 H), 1.29 to 1.32 (m, 18 H), 1.63 to 1.71 (m, 3 H), 2.38 (s, 6 H), 6.46 (s, 1 H), 6.99 to 7.75 (m, 5 H), 8.92 (s, 1 H ) IR (KBr disks) showed characteristic absorption peaks at 3294 (H), 2922 (CH), 2546 ðh þ 2 Þ, 173 (C O), 1628 (Ph) cm Adiabatic calorimetry The heat capacity measurements were made by an adiabatic calorimetric system for small samples over the temperature range between T = (78 and 34) K. The construction of the calorimeter has been described previously [5,6] in detail. It consists of a sample cell, a platinum resistance thermometer, a heater, two (inner and outer) adiabatic shields, two sets of differential thermocouples, a vacuum can and a Dewar vessel. Liquid nitrogen was used as the cooling medium. The evacuated can or chamber was kept within 1 3 Pa vacuum temperature in the sample cell increases due to heating, the thermocouples measure the temperature differences. This signal is used to control the heaters distributed on the walls of the inner and outer shields, respectively. Both shields were heated under the control of the signal and kept at the same temperature as that of the sample cell. In this way, the heat loss caused by the radiation is greatly reduced. The miniature platinum resistance thermometer (IPRT o. 2, produced by Shanghai Institute of Industrial Automatic Meters, 16 mm in length, 1.6 mm in diameter and a nominal resistance of 1 X) was applied to measure the temperature of the sample. The thermometer was calibrated on the basis of ITS- 9 by the Station of Low-temperature Metrology and Measurements, Academia Sinica. The sample was heated using the standard discrete heating method and the temperature of the sample was alternatively measured. The heating duration was 1 min, the equilibrium time of each temperature point is 5 min, and the temperature drift rates of the sample cell measured in an equilibrium period were usually within (1 3 to 1 4 ) K Æ min 1. During the heat-capacity measurements, the temperature difference between the inner adiabatic shield and the sample cell was automatically kept within 1 3 K Æ min 1 in order to obtain a satisfactory adiabatic effect and corresponding equilibrium temperature were corrected for heat loss [7,8]. The mass of the sample loaded in the sample cell amounted to g, which was equivalent to.547 mol based on its molar mass of g Æ mol 1.

3 X.-H. Sun et al. / J. Chem. Thermodynamics 36 (24) The molar heat capacities of a-al 2 O 3 used as the standard substance were measured in the same temperature range as that of the sample measurement in order to verify the reliability of the calorimeter. The sample mass used for the measurements was g, which was equivalent to.161 mol based on its molar mass, M(Al 2 O 3 ) = g Æ mol 1. Deviations of the experimental results from those of the smoothed curve lie within ±.2%, while the inaccuracy is within ±.5%, as compared with those of the former ational Bureau of Standard [9] over the whole experimental temperature range Differential scanning calorimetry A TA 21 Thermal Analysis System coupled with a personal computer loaded with the program for data processing was used for the differential scanning calorimetry (DSC) measurements, the DSC with aluminum sample tray and sapphire reference was operated at a heating rate of 1 K Æ min 1 under nitrogen atmosphere with a flow rate of 4 ml Æ min 1. The mass of the sample used for experiment was mg. 3. Results and discussion 3.1. Heat capacity All heat capacity measurements are listed in table 1 and plotted in figure 1. The structure of the compound is stable; no phase change occurred in the solid phase from T = (78 to 38) K, nor did association or decomposition occur in the liquid phase from T = (323 to 34) K. The experimental values of the heat capacities have been fitted to polynomial equations by the least square fitting. For the solid phase: C p:m =J K 1 mol 1 ¼ 113:8876 þ 1:3694X þ 6: X 2 : ð1þ In which X ={(T/K) 193}/115. The above equation is valid from T = (78 to 38) K, with an uncertainty of ±.3%. For the liquid phase: C p:m =J K 1 mol 1 ¼ 824:717 þ 6:3316X :282X 2 þ :61X 3 : ð2þ In which X ={(T/K) 331.5}/8.5. This equation applies to the range from T = (323 to 34) K, with an uncertainty of ±.25% Melting point, molar enthalpy and entropy of fusion Pre-melting occurred owing to the presence of impurities in the sample. The measurement of the melting point and molar enthalpy of fusion of the sample was TABLE 1 Experimental molar heat capacities of pyrimethanil laurate of molar mass M =399.57gÆ mol 1 where the gas constant R = J Æ mol 1 Æ K 1a T/K C p.m /R T/K C p.m /R a Obtained from [13]. T/K C p.m /R done as follows: first, the temperatures for the start of the pre-melting and for compete melting were determined. Between these two temperatures, the melting

4 898 X.-H. Sun et al. / J. Chem. Thermodynamics 36 (24) T = K T 1 = K C p, m / R C p,m /R 4 2 T/K T / K % 99.43% T / K FIGURE 1. The experimental molar heat-capacities (C p,m /R) of pyrimethanil laurate (C 24 H 37 3 O 2 ) plotted against the temperature (T) / F FIGURE 2. The equilibrium temperature (T) plotted against the reciprocal of the melting fractions (1/F) for pyrimethanil laurate (C 24 H 37 3 O 2 ) during fusion. point was determined by successive approximation through stepwise heating. Then, by heating the sample from a temperature slightly lower than the initial melting temperature to a temperature slightly higher than the final melting temperature, the enthalpy of fusion of the sample was evaluated. The heat used for heating the empty container and the sample was subtracted from the total amount of heat introduced to the sample and container during the whole melting process [8]. The melting temperature, T fus of the sample was calculated from an equation based on the heat capacity measurements in the fusion region, as described in literature [8,1]. The molar enthalpy of fusion, D fus H m, was determined in accordance with the method reported in the literature [8 1]. The molar entropy of fusion, D fus S m, was derived from the molar enthalpy of fusion, using D fus S m = D fus H m /T fus [1,11]. The results of T fus, D fus H m and D fus S m obtained from the heat capacity measurements are listed in table 2. The purity of the sample was determined from the fractional melting in accordance with the method given in the literature [8,1,11] to be higher than.9957 mole fraction (see figure 2) Purity determination of the sample The purity of the sample is evaluated from a set of equilibrium melting temperature (T) and melting fractions (F) corresponding to these temperatures [1,11]. The experimental results obtained from the heat capacity measurements in the fusion region are listed in the table 3. The equilibrium melting temperature (T) versus the reciprocal of the melting fractions (1/ F) is a straight line, as shown in figure 3. Extrapolation of the straight line to 1/F = and 1/F = 1 gives T and T 1 for the experiment, as indicated in table 3. Here, T 1 is the melting temperature of the impure compound obtained form fraction fusion experiment and T is the melting temperature of a theoretically or absolutely pure sample. The melting point (T 1 = K) obtained from the fractional melting agrees well with that (T fus = ±.4 K) obtained from the heat capacity measurements as described from the VanÕt Hoff equation [12]. The purity of the sample (1 ) is.9943 mole fraction, in agreement with the result of gas chromatograph analysis (.9957). TABLE 2 The results of phase transition obtained from three series of repeated experiments of pyrimethanil laurate (M = g Æ mol 1 ) Thermodynamic properties Series 1, x i Series 2, x i Series 3, x i Mean value, x Standard deviation, r a T fus /K D fus H m /(J Æ mol 1 ) 67,247 67,26 67,228 67, D fus S m /(J Æ K 1 Æ mol 1 ) T /K T 1 /K (1 ) qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P r a ¼ n i¼1 ðx i xþ 2 =nðn 1Þ, in which n is experimental number (n = 3); x i, experimental value of each series of repeated measurement; x, mean value.

5 X.-H. Sun et al. / J. Chem. Thermodynamics 36 (24) TABLE 3 Experimental results of melting fractions (F) and equilibrium temperature (T) of pyrimethanil laurate (C 24 H 37 3 O 2 ) T/K F 1/F Series Series Series F = q/(d fus H m n), in which q is the amount of the heat introduced to melt the sample for the melting fraction F and n is the mole number of the sample DSC analysis It can be seen from the DSC curve (figure 3) that there is a melting endothermic peak in the temperature range from (3 to 45) K. It begins from K and ends at K. This peak is in agreement with that of the experimental molar heat-capacity curve. The melting point and the molar enthalpy of fusion were determined from DSC to be K and kj Æ mol 1, respectively. These values are in agreement with the results obtained from heat-capacity measurements. This further verifies the reliability of the thermodynamic data of the melting process of the substance over the temperature range from T = (321 to 335) K. Acknowledgements The authors gratefully acknowledge The ational ature Science Foundation of China and The ature Science Foundation of of Shannxi Province, China for Endo Heat Flow / W.g Financial support to this work under SFC Grant o and SFSP Grant o. 21H11, respectively. References [1] P.-Z. Zhang, J. Wu, Y.-Q. Gong, J. Appl. Chem. 17 (5) (2) [2] B. Li, B.-D. Lin, J. Synth. Chem. 2 (1996) [3] X.-G. Luo, R.-X. Zhuo, Chem. J. Chin. Univ. 17 (9) (1996) [4] X.H. Sun, H.F. Wang, Y.F. Liu, B.Chen, P.-J.J, J.W. Yang, J. Org. Chem. 24 (5) (24) [5] H.F. Wang, X.H. Sun, Y.F. Liu, B. Chen, J.W. Yang, Huaxue Tongbao 67 (24) W33. [6] C.-L. Liu, Handbook of Foreign Pesticides, Add. Eds. Pesticide Industry Information Center, Beijing, 2 p. 18. [7] Z.C. Tan, G.Y. Sun, Yi Sun, J. Therm. Anal. 45 (1995) [8] Z.C. Tan, J.C. Ye, A.X. Yin, S.L. Chen, W.B. Chin. Sci. Bull. 32 (1987) [9] D.A. Ditmars, S.S. Chang, G. Bernstein, E.D. West, J. Res. atl. Bur. Stand. 87 (1982) [1] S.H. Meng, P. Liang, Z.C. Tang, Y.J. Song, L. Li, L. Wang, Thermochim. Acta 342 (1999) [11] Y.Y. Di, Z.C. Tan, X.M. Wu, S.H. Meng, S.S. Qu, Thermochim. Acta 356 (2) [12] Z.Y. Zhang, M. Frenkel, K.. Marsh, R.C. Wilhoit, Landolt Bornstein, Thermodynamic Properties of Organic Compounds and their Mixtures, Group IV, Subvolume A, vol. 8, Springer, Berlin, 1995, pp.7 9. [13] J.M. Peter,.T. Barry, J. Phys. Chem. Ref. Data 28 (6) (1999) JCT 4/11 C 24 H 37 3 O 2 T m = 322.5K H m = 67.24KJmol Temperature/ K FIGURE 3. The DSC curve of pyrimethanil laurate (C 24 H 37 3 O 2 ) with heat flow plotted against the temperature.