Heats of combustion of normal saturated fatty acids and their methyl esters

Abstract

Accurate heats of combustion of the title compounds were measured in an electrically calibrated calorimeter; the liquid samples were burned in Pyrex ampoules; the water content in the samples was titrated by the Karl Fischer method.The increment of the standard enthalpy of combustion, -AHgliq. (-1-AHeliq.) for one C H Z group in the chain proved to be 653.8 kjlmole for both the acids and the methyl esters studied, which is the same value as determined for the liquid paraffins. The following formulae, in which c = the number of carbon chain atoms (c > 5) can be used to calculate the standard enthalpies of combustion (based on the 1951 atomic weights): -AHgliq = 653.8 c -430.2 kj/mole for the acids, accurate to 0.03 -0.04%, -AHgIiq. = 653.8 c + 292.6 k j h o l e for the methyl esters, accurate to 0.02%. The theoretical heat of esterification of a fatty acid with methanol at 25 " C , disregarding heats of solution and dilution, was calculated to be 3.8 f 0.6 kj/mole, which can be compared with the value of 4.2 f 0.3 kj/mole for the theoretical heat of esterification of acetic acid with ethanol at about 20 "C, determined directly by Mme BPretiger-Calvet. Syntheses and purificationThe series of normal saturated fatty acids and their corresponding methyl esters with 5 to 20 carbon chain atoms were synthesized and carefully purified, as described in a previous paper 1.The impurity in the final samples was such (except for the water content, which was accurately determined) that its influence on the heat of combustion was less than 0.01 %. The water content was corrected for. Apparatus and procedureThe original calorimetric equipmentprovided with an isothermal jacketwas described in 1947 2 . Some minor alterations were made in * Full details can be found in the thesis of N. Adriaarise, Vrije Universiteit, Amsterdam (1960), which is available on request. N . Adriaatjse, H. Dekker and J. Coops, Rec. Trav. Chim. 83, 557 (1964).

The standard enthalpies of formation and thermal stability of diacyldiperoxides

“…The enthalpy of formation of diacyldiperoxides (DADPs) in the gaseous state can also be calculated independently using the enthalpies of formation of ( ) [13,14] and di (MDCA) [15] carboxylates. Calculations of the enthalpies of forma tion of the corresponding carboxyl radicals was per formed using the equations…”

Heterogeneous Catalysis in Oleochemistry

“…The superposed saturation of double bonds itself is an exothermic reaction (see Section 14.10.4.4). The reaction enthalpy can also be calculated on the basis of the standard formation enthalpies, which have been determined for fatty acids and their methyl esters by combustion experiments [60,61]. If esters of saturated fatty acids are hydrogenated, the reaction enthalpy amounts to −41 kJ mol −1 [47], whereas for the hydrogenation of fatty esters, whose content of unsaturated components is comparable to palm oil, the reaction enthalpy is about −84 kJ mol −1 .…”

Thermochemical and Ab Initio Studies of Biodiesel Fuel Surrogates: 1,2,3-Propanetriol Triacetate, 1,2-Ethanediol Diacetate, and 1,2-Ethanediol Monoacetate

“…Whereas the adaptation of current diesel engines to fossil fuel has been performed mainly by trial and error over the past 100 years, the determination of thermochemical data for biodiesel and related compounds shall serve to accelerate this optimization process considerably. So far, only the heats of combustion and some other physical data of normal saturated fatty acids and their methyl esters have been determined in the 1960s. , …”

“…So far, only the heats of combustion and some other physical data of normal saturated fatty acids and their methyl esters have been determined in the 1960s. 58,59 In this work, we explore the thermochemistry of 1,2ethanediol monoacetate, 1,2-ethanediol diacetate, and 1,2,3propanetriol triacetate, including the vaporization enthalpies (∆ l g H m ) and the standard enthalpies of formation in the liquid state (∆ f H m °(l)), using experimental methods (combustion calorimetry and vapor pressure measurements). For a validation of the experimental data on these compounds, high-level ab initio calculations of the ∆ f H m °(g) value of these molecules have been performed using the Gaussian 03 program package.…”