Thermochemical Study of 1-Methylhydantoin

Using static bomb combustion calorimetry, the combustion energy of 1-methylhydantoin was obtained, from which the standard molar enthalpy of formation of the crystalline phase at T = 298.15 K of the compound studied was calculated. Through thermogravimetry, mass loss rates were measured as a function of temperature, from which the enthalpy of vaporization was calculated. Additionally, some properties of fusion were determined by differential scanning calorimetry, such as enthalpy and temperature. Adding the enthalpy of fusion to the enthalpy of vaporization, the enthalpy of sublimation of the compound was obtained at T = 298.15 K. By combining the enthalpy of formation of the compound in crystalline phase with its enthalpy of sublimation, the respective standard molar enthalpy of formation in the gas phase was calculated. On the other hand, the results obtained in the present work were compared with those of other derivatives of hydantoin, with which the effect of the change of some substituents in the base heterocyclic ring was evaluated.

Experimental and Theoretical Investigation on the Thermochemistry of 3-Methyl-2-benzoxazolinone and 6-Nitro-2-benzoxazolinone

The determination of the reliable thermodynamic properties of 2-benzoxazolinone derivatives is the main goal of this work. Some correlations are established between the energetic properties determined and the structural characteristics of the title compounds, and the reactivity of this class of compounds is also evaluated. Static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry were used to determine, respectively, the standard molar enthalpies of formation in the solid state and the standard molar enthalpies of sublimation, both at T = 298.15 K. Using the results obtained for each compound, the respective gas-phase standard molar enthalpy of formation was derived. High-level quantum chemical calculations were performed to estimate the same property and the results evidence good accordance. Moreover, the gas-phase relative thermodynamic stability of 2-benzoxazolinone derivatives was also evaluated using the respective gas-phase standard molar Gibbs energy of formation. In addition, the relationship between the energetic and structural characteristics of the benzoxazolinones is presented, evidencing the enthalpic increments associated with the presence of a methyl and a nitro groups in the molecule, and this effect is compared with similar ones in other structurally related compounds.

Thermodynamics Properties of 1,1-Carbonyldiimidazole (CDI) and 4-Imidazole Acrylic Acid, Obtained by DSC and Combustion Calorimetry

In this work, thermodynamic properties of 1,1-carbonyldiimidazole (CDI) and 4-imidazole acrylic are reported. The melting temperature, the enthalpy of fusion and the heat capacity of the compounds were determined by differential scanning calorimetry. The standard molar energy of combustion of both compounds were determined by static-bomb combustion calorimetry and the standard molar enthalpy of formation in the crystalline phase, at T = 298.15 K, was derived and evaluated for the two imidazole derivatives studied. The energetic influence of the acrylic group on the imidazole ring in each of the properties obtained is analyzed and compared with the existing results in the literature. Resumen. Se presentan las propiedades termodinámicas del 1,1-carbonildiimidazol (CDI) y el 4-imidazol acrílico. La temperatura de fusión, la entalpía de fusión y la capacidad calorífica de los compuestos se determinaron mediante calorimetría diferencial de barrido. La energía molar estándar de la combustión de ambos compuestos se determinó mediante calorimetría de combustión en bomba estática y la entalpía de formación en fase cristalina, a T= 298.15, fue derivada y evaluada para los dos compuestos derivados del imidazol. La influencia energética del grupo acrílico sobre el anillo de imidazol en cada una de las propiedades obtenidas se analiza y compara con los resultados existentes en la literatura.

Determination for Enthalpies of Combustion of High-Carbon Fatty Alcohols by Static Bomb Calorimetry

The standard molar enthalpies of combustion, (298.15K), of high-carbon faaty alochols (tetradecanol, hexadecanol, stearyl alcohol) were obtained by a precise thermal isolation oxygen bomb calorimeter. The values obtained are, respectively, –(9126.39) kJ•mol-1, –(10446.15) kJ•mol-1, and –(11780.49) kJ•mol-1 for tetradecanol, hexadecanol, and stearyl alcohol. It was found that their standand molar enthlpies of combustion increase when the carbon number increases in the substances. There were also good agreement between the experimental and literature results for tetradecanol and tetradecanol. And the standard molar enthalpies of combustion of stearyl alcohol provided necessary thermodynamics basic data. Therefore, these data are available for the exploiting new synthesis method, engineering design and industry production on high-carbon alochols.

Experimental Study of Nanoadditives for Biofuel Combustion Improvement

An experimental investigation of the combustion behavior of nano-aluminum (n-Al) and nano-aluminum oxide (n-Al2O3) particles, stably suspended in biofuel (ethanol) as a secondary energy carrier was conducted. The heat of combustion (HoC) was studied using a modified static bomb calorimeter system. Combustion element composition and surface morphology were evaluated using a SEM/EDS system. N-Al and n-Al2O3 particles of 50 nm and 36 nm diameters, respectively, were utilized in this investigation. Combustion experiments were performed with volume fractions of 1%, 3%, 5%, 7%, and 10% for n-Al, and 0.5%, 1%, 3%, and 5% for n-Al2O3. The results indicate that the amount of heat released from ethanol combustion increases almost linearly with n-Al concentration. N-Al volume fractions of 1% and 3% did not show enhancement in the average volumetric heat of combustion, but higher volume fractions of 5%, 7%, and 10% increased the volumetric heat of combustion by 5.82%, 8.65%, and 15.31%, respectively. N-Al2O3 and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the HoC in the tests. A combustion model that utilized Chemical Equilibrium with Applications (CEA) was conducted as well and was shown to be in good agreement with the experimental results.

Isoperibol Reaction-Solution Calorimetry

The determination of enthalpies of reaction in solution, using isoperibol reaction-solution calorimetry, is often the easiest and most accurate method of determining enthalpies of formation of compounds that cannot be studied by combustion calorimetry. The technique was pioneered by Thomsen who, between 1882 and 1886, performed thermochemical measurements involving the solution of various substances in liquids (e.g., diluted acids). Many types of isoperibol reaction-solution calorimeters have been developed since then. The designs vary according to the nature of the reactions of interest. One of the most widely used consists of a vessel, such as the one shown in figure 8.1, immersed in a thermostatic water bath. The sample is sealed inside a thin-walled glass ampule A, fixed to an ampule breaking system B in the calorimeter head C. The calorimeter head also supports the temperature sensor D, the stirrer E, and an electrical resistance F, used for calibration of the apparatus. The Dewar vessel G, containing the solution to be reacted with the sample, is adjusted to C. The assembled calorimetric vessel is transferred to the thermostatic bath, and from then on, the experimental procedure closely follows that already described in section 7.1 for isoperibol static-bomb combustion calorimetry. The reaction is initiated at the end of the fore period by pushing down the plunger H and breaking the ampule against a pin situated at the bottom of the ampule breaking system B. As a result of the calorimetric experiment, a temperature-time curve such as the one in figure 7.2 is obtained. Note that figure 7.2 is typical of an exothermic process. In the case of an endothermic process, a decrease of the temperature of the calorimetric system is observed during the reaction period. The experiments are usually carried out at atmospheric pressure and the initial goal is the determination of the enthalpy change associated with the calorimetric process under isothermal conditions, ΔHICP, usually at the reference temperature of 298.15 K. This involves the determination of the corresponding adiabatic temperature change, ΔTad, from the temperature-time curve just mentioned, by using one of the methods discussed in section 7.1; the determination of the energy equivalent of the calorimeter in a separate experiment.

Combustion Calorimetry

Calorimetric studies of combustion reactions in oxygen and fluorine atmospheres have been a major source of enthalpy of formation data, particularly for organic and inorganic compounds. As referred to in the previous chapter, in bomb combustion calorimetry the reaction proceeds inside a pressure vessel—the bomb—at constant volume, and in this case the derived quantity is ΔcUo. In flame calorimetry the reaction occurs in a combustion chamber, which is in communication with the atmosphere, and the measurements lead to ΔcHo. The methods of combustion calorimetry will be described in the following paragraphs. “Conventional” combustion calorimeters operate on a “macro” scale, that is, they require samples of 0.5–1.0 g per experiment. Unfortunately, many interesting compounds are available only in much smaller amounts. In the case of oxygen combustion calorimetry, however, several combustion microcaloriemeters that only demand 2–50 mg samples have been developed in recent years. The achievements and trends in this area through 1999 have been reviewed, and interested readers are directed to these publications. Since then, a few new apparatus have been reported. Nevertheless, it should be pointed out that the general principles and techniques used to study compounds at the micro scale are not greatly different from those used in macro combustion calorimetry. Static-bomb combustion calorimetry is particularly suited to obtaining enthalpies of combustion and formation of solid and liquid compounds containing only the elements C, H, O, and N. The origins of the method can be traced back to the work of Berthelot in the late nineteenth century. Most static-bomb calorimeters used are of the isoperibol type, such as the one in figure 7.1. Here, the bomb A is a pressure vessel of ∽300 cm3 internal volume. Combustion bombs are usually made of stainless steel and frequently have an internal platinum lining to prevent corrosion. In a typical high-precision experiment, the platinum ignition wire B connects the two electrodes C, which are affixed to the bomb head. A cotton thread fuse D (other materials such as polyethene are also used), of known energy of combustion, is weighed to a precision of±10−5−10−6 g and tied to the platinum wire.