Vapour pressure and enthalpy of vaporization of aliphatic dialkyl carbonates
Introduction
Dialkyl carbonates are known as outstanding dipolar aprotic solvents widely utilized in electrochemical applications and extraction processes. Their excellent solvency, high flash and boiling temperatures, low toxicity, and evaporation rates make them attractive choices in many solvent applications. Dialkyl carbonates are biodegradable, non-corrosive, and relatively odourless materials, as well as being readily available from several solvent manufacturers. They are “safe” and environmentally friendly solvent alternatives to traditional products such as methylene chloride, aromatic solvents, and other high volatile and hazardous industrial solvents. In our recent work, we have identified advantages of propylene carbonate in asymmetric hydrogenation [1], and also for palladium-catalyzed substitution reactions [2].
Alkyl carbonates are high boiling liquids. Precise measurement of the vapour pressure of low-volatile compounds at ambient temperature is usually difficult, that is why the most of published data are referred to elevated temperatures close to the boiling point [3]. The transpiration method [4] used in this work provided a capability for the measurement of new vapour pressure data for dialkyl carbonates near ambient temperatures, where the data are especially relevant for the assessment of their fate and behaviour in the environment.
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Materials
The liquid samples of dialkyl carbonates of 0.99 mass-fraction purity were obtained from Aldrich and Fluka and further purified by repetitive distillation in vacuum. Gas chromatography (GC) showed no traceable amounts of impurities in dialkyl carbonate samples after they were purified. The products were analyzed with a Hewlett-Packard gas chromatograph 5890 Series II with a flame ionization detector and Hewlett-Packard 3390A integrator. The dimensions of the capillary column HP-5 (stationary
Vapour pressure and vaporization enthalpies
Vapour pressures of alkyl carbonates measured in this work and enthalpies of vaporization (table 1) were treated with equations (2), (3), respectivelywhere is vapour pressure; a and b are adjustable parameters (table 1); T0 is an arbitrarily chosen reference temperature (T0 is 298.15 K in this work); and is the difference of the molar heat capacities of the gaseous and the liquid phase. Values of (see table 2) were either
Acknowledgements
S.A.K. and V.N.E. acknowledge gratefully a research scholarship from the Research Training Group “New Methods for Sustainability in Catalysis and Technique” of German Science Foundation (DFG).
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- 1
On leave from Institute of Organic Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria.