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1 Introduction Urea and thiourea are well known for their propensity to form hydrogen-bonded adducts with other compounds, in particular with organic compounds that are liquids at room temperature – in other words, solvents. Studies by ourselves and others [ 1 – 5 ] have shown that three types of urea adduct are common. First, 1:1 complexes with morpholine and dioxane [ 1 ] involve urea units connected to form chains of rings with graph set C(4)[ R 2 1 ${\rm{R}}_2^1$ (6)], whereby the hydrogen atoms trans to O=C across the N–C bond are hydrogen bond donors to

Synthesis and Structure of Bis-Urea Phenazines Tom Frickea, Anton Dickmansb, Umasish Janab, Manfred Zabelc, Peter G. Jonesd, Ina Dixd, Burkhard König*,a and Rainer Herges*,b a Institut für Organische Chemie, Universität Regensburg, D-93040 Regensburg, Germany. Fax: 499419431717. Tel: 499419434576 E-mail: burkhard.koenig@chemie.uni-regensburg.de b Institut für Organische Chemie, Universität Kiel, D-24098 Kiel, Germany. Fax: 49431-880-1558. E-mail: rherges@oc.uni-kiel.de c Zentrale Analytik der NWF IV, Universität Regensburg, D-93040 Regensburg, Germany. d Institut

References Tengler S.: Niektóre międzycząsteczkowe połączenia mocznika ze związkami nieorganicznymi, Chemik, 1972, 8, 308. Durski Z.: Krystaliczne addukty mocznika ze związkami nieorganicznymi, Wiadomości. Chemiczne , 1971, 25, 829. Whittaker C., Lundstom F., Hendricks S.: Reaction between urea and gypsum, Industrial & Engineering Chemistry, 1933, 11, 1280. Achard P., Schwob Y., Limousin L.: A new route for urea-superphosphate fertilizers, Phosphorus & Potassium, 1994, 191, 27. Patent USA 2074880, 1937. Nagai S., Hara Z.: Studies on gypsum - urea or urea

adapt to changing solvent conditions, hence increasing the solubility. A similar effect was observed when adding urea to aqueous gliadin solutions. The mechanism of urea mediated protein dissolution is still debated. However, molecular dynamics simulations revealed that this occurs predominantly by direct interactions of urea with the protein through van der Waals interactions. These more favorable interactions of urea with the protein, as compared to the urea water interaction, attract urea to the protein surface and further solubilize the protein chain in water [ 19

chemical reactions, especially as a new versatile building block for producing many chemicals [ 5 , 6 ]. Glycerol carbonate can be synthesized by using different reactants, such as glycerol and glycidol [ 7 ]. In recent years, synthesis of glycerol carbonate from glycerol has received much attention. Glycerol can react with carbonyl chloride, carbon monoxide [ 8 ], carbon dioxide [ 9 ], dimethyl carbonate [ 10 , 11 ], diethyl carbonate [ 12 ], cyclic carbonate [ 13 ] and urea to produce glycerol carbonate. The glycerolysis of urea will release ammonia as by-product (as

decomposition of urea is a commercially and scientifically applied process for the precipitation of various transition metal oxides [ 5 ], [ 6 ], [ 7 ]. The urea in solution decomposes via ammonium cyanate to a mixture of ammonia and bicarbonate, according to the following overall reaction [ 7 ]: CO(NH 2 ) 2 + 2 H 2 O + H + → 2  NH 4 + + HCO 3 − . ${\rm{CO(N}}{{\rm{H}}_2}{{\rm{)}}_2} + 2{{\rm{H}}_2}{\rm{O}} + {{\rm{H}}^ + } \to 2{\rm{ NH}}_4^ + + {\rm{HCO}}_3^ - .$ Since the decomposition produces both ammonia and carbonates (if pH is high enough), the metal ions may

. Przemysł Chemiczny, 90, 2128-2135. (in Polish) Borowik, M., Malinowski, P., Biskupski, A., Dawidowicz, M., Schab, S., & Rusek, P. (2012a). Studies on the screw granulation of fertilizers manufactured on the basis of urea and calcium sulphate adduct. Chemik, 66, 535-540. Borowik, M., Malinowski, P., Biskupski, A., Dawidowicz, M., Schab, S., Rusek, P., Igras, J., & K˛esik, K. (2012b). Production technology of nitrogen-sulphur-calcium fertilizers on the base of urea and phosphogypsum. Chemik, 66, 525-534. Borowik, M., Biskupski, A., & Schab, S. (2013a). Prospects and

Abstract

Two basic mechanisms of displacement washing of pulp fibres were investigated. Experiments were carried out in a laboratory washing cell that simulated a single stage of displacement washing. The step-change method has been employed in investigation of alkali lignin profile in outlet stream of washing effluents. The addition of urea to wash water resulted in a decrease of the liquid layer immobilized on the fibre surface. It had a positive effect on the washing efficiency expressed in terms of the void local efficiency.

172 R. Schöllhorn - A. Weiss • Schichteinlagerungsverbindungen des Niob- und Tantaldisulfids Schichteinlagerungsverbindungen des Niobdisulfids und Tantaldisulfids mit Carbonsäureamiden, Harnstoff und Harnstoffderivaten Layer Intercalation Compounds of Niobium Disulfide and Tantalum Disulfide with Amides, Urea and Urea Derivatives R o b e r t S c h ö t . l h o r n und A r m in W e is s Institut für Anorganische Chemie der Universität München (Z. Naturforsch. 28 b» 172-175 [1973]; eingegangen am 25. Januar 1973) Intercalation compounds, niobium disulfide

Volume 6, Issue 1 2011 Article 17 Chemical Product and Process Modeling Modeling of Urea Release from Briquettes Using Semi infinite and Shrinking Core Models Ramananda Bhat M., Manipal University D. V. R. Murthy, National Institute of Technology Karnataka M. B. Saidutta, National Institute of Technology Karnataka Recommended Citation: M., Ramananda Bhat; Murthy, D. V. R.; and Saidutta, M. B. (2011) "Modeling of Urea Release from Briquettes Using Semi infinite and Shrinking Core Models," Chemical Product and Process Modeling: Vol. 6: Iss. 1, Article 17. DOI: 10