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Kompleksy mocznika z wiązaniami wodorowymi

Polaczek J., Domanowski W.

Wiadomości Chemiczne

2000

[Z] 54, 11-12

971-989

Urea is a commercially available and relatively cheap chemical underestimated in practical use for chemical purposes. One peculiar property of urea is its ability to form hydrogen bonds with many organic and inorganic compounds, where it can play the role of both a proton donor and a proton acceptor. The hydrogen bonds present in urea complexes are revealed by some characteristic points in equilibria curves, especially in the liquidus curves and also in the courses of some physical property curves like viscosity, refractive index or dielectric constant versus composition of a binary mixture. Hydrogen-bonded complexes can be practically applied to purify and to separate organic substances that are able to form hydrogen bonds or to remove contaminants that have such properties. The main advantage of processes based on hydrogen bond formation is that the complexes formed can be easily cleaved e.g. by addition of water or by increasing the temperature whereupon complexant is recycled. The structure and the physical properties of urea complexes with water, hydrogen peroxide, phenol, cresols, dihydroxybenzenes, naphthols and tetrabutylammonium acetate are reviewed. Physical properties of urea single crystals are also mentioned which can be applied in non-linear optics. The literature data on urea behaviour in complexed systems both calculated theoretically and determined experimentally are collected and discussed.