Об использовании синхронного термоанализатора Netzsch 449 Jupiter для определения точки кипения ве-ществ

Abstract

The influence of the mass of water, p-xylene, ethylene glycol, and naphthalene on the measured values of temperature and heat of their transformations has been studied. It has been shown that a synchronous thermal analyzer Netzsch 449F1 Jupiter can be successfully used to determine boiling points of substances. The final temperatures of their evaporation monotonously increase together with an increase in the mass of a substance. It has been shown that with the achievement of a certain mass, the boiling process becomes stationary, accompanied by the formation of a linear front of the boiling peak, close in slope to the slope of the front of the melting peaks of various pure substances. A modified technique of differential scanning calorimetry data processing has been proposed and tested to solve this problem, giving an uncertainty in determining the boiling point of ± 4 °C in the case of water, ethylene glycol, and p-xylene, as well as ±6 °С in the case of naphthalene. The error in determining the boiling heats by the data of a synchronous thermal analyzer is ±5 % in the case of water and naphthalene; however, in the case of ethylene glycol and p-xylene, the error reaches 10 % and 40 %, respectively, which makes this method not quantitative, but only semi-quantitative or qualitative in regard to determination of the transformation heat. Using the example of anthranilic acid and diiodoparaxylene, the method has been tested, and the obtained data on temperatures and heats of transformations for these compounds; notably, the transformation heats were not previously known from the literature. For example, anthranilic acid, according to our data, has a previously undescribed polymorphic transformation at 91 °C with the heat of 28.5 J/g, melting at 145.5 °C with the heat of 150 J/g, and boiling at 230 °C with the heat of 310 J/g. According to our data, diiodoparaxylene melts at 102 °C with the heat of 60 J/g and boils at 310 °C with the heat of 95 J/g.