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1.
The combustion enthalpy of glyphosate was determined by XRY-1C oxygen-bomb calorimeter at a constant volume. The standard mole combustion enthalpy and the standard mole formation enthalpy have been calculated to be ?1702.19 and ?1478.36 kJ mol?1, respectively. For testing the reliability of instrument, glycine and naphthalene were used as reference materials by comparing the measured values with the literature values, the absolute error and relative error are 2.58 kJ mol?1 and 0.26 % for glycine, respectively, and these of naphthalene are 4.08 kJ mol?1 and 0.08 %, respectively. Moreover, the constant-pressure heat capacities c p of glyphosate were measured by differential scanning calorimetry in the temperature range 303.15–365.15 K, and the relationship between c p and temperature was established. These related studies can provide a thermodynamic basis for their further application.  相似文献   

2.
The combustion enthalpy of diosgenin was determined by oxygen-bomb calorimetry. The standard mole combustion enthalpy and the standard mole formation enthalpy have been calculated to be ?16098.68 and ?528.52 kJ mol?1, respectively. Fusion enthalpy and melting temperature for diosgenin were also measured to be ?34.43 kJ mol?1 and 212.33°C, respectively, according to differential scanning calorimetry (DSC) data. These studies can provide useful thermodynamic data for this compound.  相似文献   

3.
Thermal decomposition of neat TBP, acid-solvates (TBP·1.1HNO3, TBP·2.4HNO3) (prepared by equilibrating neat TBP with 8 and 15.6?M nitric acid) with and without the presence of additives such as uranyl nitrate, sodium nitrate and sodium nitrite, mixtures of neat TBP and nitric acid of different acidities, 1.1?M TBP solutions in diluents such as n-dodecane (n-DD), n-octane and isooctane has been studied using an adiabatic calorimeter. Enthalpy change and the activation energy for the decomposition reaction derived from the calorimetric data wherever possible are reported in this article. Neat TBP was found to be stable up to 255?°C, whereas the acid-solvates TBP·1.1HNO3 and TBP·2.4HNO3 decomposed at 120 and 111?°C, respectively, with a decomposition enthalpy of ?495.8?±?10.9 and ?1115.5?±?8.2?kJ?mol?1 of TBP. Activation energy and pre exponential factor derived from the calorimetric data for the decomposition of these acid-solvates were found be 108.8?±?3.7, 103.5?±?1.4?kJ?mol?1 of TBP and 6.1?×?1010 and 5.6?×?109?S?1, respectively. The thermochemical parameters such as, the onset temperature, enthalpy of decomposition, activation energy and the pre-exponential factor were found to strongly depend on acid-solvate stoichiometry. Heat capacity (C p ), of neat TBP and the acid-solvates (TBP·1.1HNO3 and TBP·2.4HNO3) were measured at constant pressure using heat flux type differential scanning calorimeter (DSC) in the temperature range 32?C67?°C. The values obtained at 32?°C for neat TBP, acid-solvates TBP·1.1HNO3 and TBP·2.4HNO3 are 1.8, 1.76 and 1.63?J?g?1?K?1, respectively. C p of neat TBP, 1.82?J?g?1?K?1, was also measured at 27?°C using ??hot disk?? method and was found to agree well with the values obtained by DSC method.  相似文献   

4.
1,3-Bis(4-aminophenoxy)benzene (TPER) and poly(amic acid) based on TPER and pyromellitic dianhydride (PMDA) were synthesized. After imidization of the poly(amic acid), polyimide based on TPER and PMDA was obtained. The melting process and the specific heat capacity (C p) of TPER were examined by DSC and microcalorimetry, respectively. The melting enthalpy, the melting entropy, and the C p for TPER were obtained. The enthalpy change, the entropy change, and the Gibbs free energy change for TPER were obtained within 283 and 353 K. The thermal decomposition reaction mechanism of the polyimide is classified from the TG–DTG experimental data, and the thermokinetic parameters of the thermal decomposition reaction are E a = 296.87 kJ mol?1and log (A/s?1) = 14.41.  相似文献   

5.
Heat capacity of crystalline L- and DL-phenylglycines was measured in the temperature range from 6 to 305?K. For L-phenylglycine, no anomalies in the C p (T) dependence were observed. For DL-phenylglycine, however, an anomaly in the temperature range 50?C75?K with a maximum at about 60?K was registered. The enthalpy and the entropy changes corresponding to this anomaly were estimated as 20?J?mol?1 and 0.33?J?K?1 mol?1, respectively. In the temperature range 205?C225?K, an unusually large dispersion of the experimental points and a small change in the slope of the C p (T) curve were noticed. Thermodynamic functions for L- and DL-phenylglycines in the temperature range 0?C305?K were calculated. At 298.15?K, the values of heat capacity, entropy, and enthalpy are equal to 179.1, 195.3?J?K?1 mol?1, and 28590?J?mol?1 for L-phenylglycine and 177.7, 196.3?J?K?1 mol?1 and 28570?J?mol?1 for DL-phenylglycine. For both L- and DL-phenylglycine, the C p (T) at very low temperatures does not follow the Debye law C ?C T 3 . The heat capacity C p (T) is slightly higher for L-phenylglycine, than for the racemic DL-crystal, with the exception of the phase transition region. The difference is smaller than was observed previously for the L-/DL-cysteines, and considerably smaller, than that for L-/DL- serines.  相似文献   

6.
A new ionic compound (3-ATz)+ (NTO)?C was synthesized by the reaction of 3-amino-1,2,4-triazole (3-ATz) with 3-nitro-1,2,4-triazol-5-one (NTO) in ethanol. The single crystals suitable for X-ray diffraction measurement were obtained by crystallization at room temperature. The crystal is monoclinic, space group p 2(1)/c with crystal parameters of a?=?0.6519(2)?nm, b?=?1.9075(7)?nm, c?=?0.6766(2)?nm, ???=?94.236(4)°, R 1?=?0.0305 and wR 2?=?0.0789. The thermal behaviors were studied, and the apparent activation energy and pre-exponential constant of the exothermic decomposition stage were obtained by Kissinger??s method and Ozawa??s method. The self-accelerating decomposition temperature is 505.40?K, and the critical temperature of the thermal explosion is obtained as 524.90?K. The specific heat capacity was determined with Micro-DSC method and the theoretical calculation method, and the standard molar specific heat capacity is 221.31?J?mol?1?K?1 at 298.15?K. The Gibbs free energy of activation, enthalpy of activation, and entropy of activation are 151.55?kJ?mol?1, 214.52?kJ?mol?1 and 122.44?J?mol?1?K?1. The adiabatic time-to-explosion of the compound was estimated to be a certain value between 5.0 and 5.2?s, and the detonation velocity (D) and pressure (P) were also estimated using the nitrogen equivalent equation according to the experimental density.  相似文献   

7.
The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC). The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10°C min-1. The melting peak showed an onset at T on = 144°C (417 K) and a maximum intensity at T max = 152°C (425 K), while the onset of the glass transition signal was at T on = 6°C. The melting enthalpy was found to be ΔmH = 28.9±0.3 kJ mol-1, and the heat capacity jump at the glass transition was ΔC P = 108.1±0.1 J K-1mol-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed the determination of the activation energy at the glass transition temperature (245 kJ mol-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as ΔfHm o(C14H10O5, cr) = - (837.6±3.3) kJ mol-1, by combustion calorimetry. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

8.
This study is aimed at exploring the utility of thermoanalytical methods in the characterization of various polymorphs and solvates of nevirapine. The different forms obtained by recrystallization of nevirapine from various solvents showed morphological differences in SEM. The presence of polymorphic forms is suggested by single sharp melting endotherm different from original sample in DSC and no mass loss in TG, while appearance of desolvation peak in TG indicated the formation of solvates. The higher desolvation temperatures of all the solvates than their respective boiling point indicate tighter binding of solvent. The changes in the crystal lattice were demonstrated by X-ray powder diffraction studies. The enthalpy of fusion rule indicated the existence of monotropy in polymorphic pairs I/O and II/O, while I/II is enantiotropically related. The enthalpy of solution, an indirect measure of the lattice energy of a solid, was well correlated with the crystallinity of all the solid forms obtained. The magnitude of ΔH sol was found to be ?14.26  kJ mol?1 for Form V and ?8.29  kJ mol?1 for Form O, exhibiting maximum ease of molecular release from the lattice in Form V. The transition temperature was found to be higher than the melting of both the forms except for polymorphic pair I/II providing complementary evidence for the existence of monotropy as well as enantiotropy in these polymorphic pairs.  相似文献   

9.
A new complex, diaquadi(1,2,4-triazol-5-one)zinc(II) ion nitrate formulated as {[Zn(TO)2(H2O)2](NO3)2}n (1) (1,2,4-triazole-5-one, abbreviated as: TO) was synthesized and characterized by elemental analysis, X-ray single crystal diffraction, infrared spectrum (IR), differential scanning calorimetry (DSC), thermogravimetric analysis and differential thermogravimetric analysis (TG-DTG). The X-ray structure analysis reveals that the complex is orthorhombic with space group Pbca and unit-cell parameters a=6.9504(2) Å; b=10.6473(3) Å; c=17.8555(5) Å. Based on the result of thermal analysis, the thermal decomposition process of the compound was derived. From measurement of the enthalpy of solution in water in 298.15 K, the standard molar enthalpy of solution of lignand TO and the complex were determined as 15.43±0.18 and 52.64±0.42 kJ mol?1, respectively. In addition, the standard molar enthalpy of formation of TO(aq) was calculated as ?126.97±0.72 kJ mol?1.  相似文献   

10.
The specific heat, the melting heat and entropy, the vaporization heat of naphtalene disulfide (C10H6S2) and of diphenylene disulfide (C12H8S2) have been determined by differential scanning calorimetry (DSC).Over the temperature range examined the specific heat may be represented as follows:
where T is the temperature in degrees Kelvin, while melting heat, vaporization heat, melting entropy are for naphtalene disulfide: 3.10 kcal mol?1, 6.42 kcal mol?1, 7.87 cal deg? mol?1 and for diphenylene disulfide: 4.62 kcal mol?1, 6.90 kcal mol?1 and 11.87 cal deg?1 mol?1.  相似文献   

11.
Summary The binary systems of C60with α-methyl- and α-chloronaphthalene have been studied by means of differential scanning calorimetry. C60was found to form the molecular complex of the van der Waals type with α-methylnaphthalene which melts incongruently below the boiling point of the solvent at temperature 382.7±3.0 K. The enthalpy of the desolvation reaction is 14.1±0.5 kJ mol-1of C60. The molar ratio of fullerene to solvent in the solvate is 1:1.5. In the system C60-α-chloronaphthalene a two-stage incongruent melting process has been observed at temperatures 314.1±4.6 K and 375.7±7.4 K with the enthalpies 8.1±2.6 kJ mol-1and 11.6±1.0 kJ mol-1, respectively. The composition of the most solvated phase equilibrated with the saturated solution at room temperature and below the first of the incongruent melting transitions was determined as 1:1.5. Based on the results obtained the thermodynamic characteristics of the incongruent melting reactions have been revealed and influence of solvate formation on solubility of C60has been discussed.  相似文献   

12.
The enthalpy of solvation of the gaseous chromate ion, ΔHsolv0(CrO42?) (g) is estimated on the basis of recent lattice energy studies made in this laboratory, and a charge distribution assigned to the ion. On the basis of the assigned charge of ?0.57 proton units to the oxygen atoms of the CrO42? unit, the total lattice potential energies are found to be: Upot(Na2CrO4) = 1836 kJ mol?1; Upot(K2CrO4) = 1717 kJ mol?1; Upot(Rb2CrO4) = 1645 kJ mol?1 and Upot(Cs2CrO4) = 1598 kJ mol?1. The corresponding value for ΔHsolv0(CrO42?) (g) = ?1077 kJ mol?1.  相似文献   

13.
通过小样品精密自动绝热热量计测定了自己合成并提纯的腈菌唑 (C15H17ClN4) 在78 ~ 368K温区的低温摩尔热容。量热实验发现, 该化合物在363 ~ 372 K温区, 有一固-液熔化相变过程, 其熔化温度为 (348.800±0.06)K, 摩尔熔化焓、摩尔熔化熵及化合物的纯度分别为:(30931±11) J•mol-1、(88.47±0.02) J•mol-1•K-1和0.9941(摩尔分数)。用差示扫描量热(DSC) 技术对该物质的固-液熔化过程作了进一步研究,结果与绝热量热法一致。  相似文献   

14.
In an effort to probe the reaction of antibiotic hydrolysis catalyzed by B3 metallo-??-lactamase (M??L), the thermodynamic parameters of penicillin G hydrolysis catalyzed by M??L L1 from Stenotrophomonas maltophilia were determined by microcalorimetric method. The values of activation free energy ??G ?? ?? are 88.26, 89.44, 90.49, and 91.57?kJ?mol?1 at 293.15, 298.15, 303.15, and 308.15?K, respectively, activation enthalpy ??H ?? ?? is 24.02?kJ?mol?1, activation entropy ??S ?? ?? is ?219.2511?J?mol?1?K?1, apparent activation energy E is 26.5183?kJ?mol?1, and the reaction order is 1.0. The thermodynamic parameters reveal that the penicillin G hydrolysis catalyzed by M??L L1 is an exothermic and spontaneous reaction.  相似文献   

15.
This paper studies the effect of molecular mass on the melting temperature, enthalpy and entropy of hydroxy-terminated poly(ethylene oxide) (PEO). It aims to correlate the thermal behaviour of PEO polymers and their variation of molecular mass (MW). Samples ranging from 1500 to 200,000 isothermally treated at 373 K during 10 min, were investigated using DSC and Hot Stage Microscopy (HSM). On the basis of DSC and HSM results, melting temperatures were determined, and melting enthalpies and entropies were calculated. Considering the melting temperatures, it was found that the maximum or critical value of MW was found around 4000, and then these remain almost constant. This behaviour was interpreted assuming that lower MW fractions (MW<4000) crystallize in the form of extended chains and higher MW fractions (MW>4000), as folded chains. The melting enthalpies showed a scattering effect at least up to MW 35,000. It was difficult to obtain any relationship between melting enthalpies in J g–1 and MW. These variations seem to be of statistical nature. Corrected enthalpy data on a molar basis (kJ mol–1) exhibited a linear relationship with MW. Considering the solid—liquid equilibrium, the melting entropies (in kJ mol–1) were calculated. These values were more negative as compared with molar enthalpy increases. It was explained because the changes in melting temperatures are much smaller than those observed in the enthalpy values. Linear relationship between enthalpies andentropies as a function of MW was deduced.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

16.
The low-temperature heat capacity C p,m of erythritol (C4H10O4, CAS 149-32-6) was precisely measured in the temperature range from 80 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=390.254 K from the experimental C p-T curve. The molar enthalpy and entropy of this transition were determined to be 37.92±0.19 kJ mol−1 and 97.17±0.49 J K−1 mol−1, respectively. The thermodynamic functions [H T-H 298.15] and [S T-S 298.15], were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined: Δc H m0(C4H10O4, cr)= −2102.90±1.56 kJ mol−1 and Δf H m0(C4H10O4, cr)= − 900.29±0.84 kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.  相似文献   

17.
N-Benzoyl-3,3-dinitroazetidine (BDNAZ) has been synthesized and characterized by elemental analysis, FT-IR spectroscopy, 1H NMR and X-ray single crystal diffraction technique. BDNAZ crystallizes in the monoclinic space group P21/c. Its thermal behavior was studied under a non-isothermal condition by DSC and TG/DTG methods, the value of E a and A of the exothermic decomposition reaction of BDNAZ are 143.19 kJ mol?1 and 1014.34 s?1, respectively. The specific heat capacity of BDNAZ was determined with a continuous C p mode of micro-calorimeter and theoretical calculation. The adiabatic time-to-explosion was evaluated as 109.9?C124.4 s.  相似文献   

18.
The thermal stability and kinetics of isothermal decomposition of diosgenin were studied by thermogravimetry (TG) and Differential Scanning Calorimeter (DSC). The activation energy of the thermal decomposition process was determined from the analysis of TG curves by the methods of Flynn-Wall-Ozawa, Doyle, ?atava-?esták and Kissinger, respectively. The mechanism of thermal decomposition was determined to be Avrami-Erofeev equation (n = 1/3, n is the reaction order) with integral form G(α) = [?ln(1 ? α)]1/3 (α = 0.10–0.80). E a and logA [s?1] were determined to be 44.10 kJ mol?1 and 3.12, respectively. Moreover, the thermodynamics properties of ΔH , ΔS , and ΔG of this reaction were 38.18 kJ mol?1, ?199.76 J mol?1 K?1, and 164.36 kJ mol?1 in the stage of thermal decomposition.  相似文献   

19.
The heat capacities (C p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T m), the molar enthalpy (Δfus H m0), and the molar entropy (Δfus S m0) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol−1 and 51.676 J K−1 mol−1, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H T-H 298.15 and S T-S 298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU c(C6H8N2,cr)= −3500.15±1.51 kJ mol−1 and Δc H m0 (C6H8N2,cr)= −3502.64±1.51 kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δr H m0 (C6H8N2,cr)= −1.74±0.57 kJ mol−1.  相似文献   

20.
The heat capacities of 2-benzoylpyridine were measured with an automated adiabatic calorimeter over the temperature range from 80 to 340 K. The melting point, molar enthalpy, ΔfusHm, and entropy, ΔfusSm, of fusion of this compound were determined to be 316.49±0.04 K, 20.91±0.03 kJ mol–1 and 66.07±0.05 J mol–1 K–1, respectively. The purity of the compound was calculated to be 99.60 mol% by using the fractional melting technique. The thermodynamic functions (HTH298.15) and (STS298.15) were calculated based on the heat capacity measurements in the temperature range of 80–340 K with an interval of 5 K. The thermal properties of the compound were further investigated by differential scanning calorimetry (DSC). From the DSC curve, the temperature corresponding to the maximum evaporation rate, the molar enthalpy and entropy of evaporation were determined to be 556.3±0.1 K, 51.3±0.2 kJ mol–1 and 92.2±0.4 J K–1 mol–1, respectively, under the experimental conditions.  相似文献   

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