Abstract: A process for the preparation of pure melamine, in which liquid, ammonia-containing melamine is rapidly depressurized from an ammonia partial pressure p1 between 400 and 50 bar to an ammonia partial pressure p2 between 200 bar and atmospheric pressure, where p1 is always greater than p2, at a temperature which is 0 to 60° C. higher than the melamine solidification point dependent oil the particular prevailing ammonia partial pressure, higher pressures permitting a greater temperature interval from the melamine solidification point than lower pressures, by which means pure melamine separates out in solid form, whereupon, in any sequence, the product is further depressurized if appropriate to atmospheric pressure, cooled to room temperature and the pure melamine is isolated.

Abstract: A process for the preparation of pure melamine, in which liquid, ammonia-containing melamine is rapidly depressurized from an ammonia partial pressure p1 between 400 and 50 bar to an ammonia partial pressure p2 between 200 bar and atmospheric pressure, where p1 is always greater than p2, at a temperature which is 0 to 60° C. higher than the melamine solidification point dependent on the particular prevailing ammonia partial pressure, higher pressures permitting a greater temperature interval from the melamine solidification point than lower pressures, by which means pure melamine separates out in solid form, whereupon, in any sequence, the product is further depressurized if appropriate to atmospheric pressure, cooled to room temperature and the pure melamine is isolated.

Abstract: Process for the production of highly pure melamine in which an aftertreatment of the melamine is carried out, comprising the stepsa) separating off the NH.sub.3 /CO.sub.2 gas mixture from the liquid melamine, if appropriateb) reducing the CO.sub.2 dissolved in the liquid melamine by introducing gaseous ammoniac) allowing the liquid melamine to remain for a mean residence time of 0 to 8 hours at a temperature between 430.degree. C. and the melting point of melamine and an ammonia partial pressure of 50 to 400 bar andd) slow, controlled cooling by lowering the temperature from the temperature present in a), b) respectively c) to 330.degree. to 270.degree. C. at a cooling rate of up to 150.degree. C.

Abstract: Process for the preparation of asymmetrically substituted ureas, carbamates, thiocarbamates or substituted isocyanates by reaction of an adduct of isocyanic acid and a tertiary amine with a primary and secondary amine, an alcohol, a thiol or a compound having one or two non-cumulated olefinic double bonds, and a process for the preparation of N-mono- or N,N-disubstituted ureas by reaction of ammonium isocyanates with a primary or secondary amine in a diluent.

Abstract: A process for the dissolution of chemical compounds by use of ureas in which at least one of the urea's two nitrogen atoms is part of a non-aromatic ring which can be broken by an oxygen or sulphur atom as a chemical solvent, and a method of producing tri- or tetraalkylated ureas or bis ureas wherein at least one of the urea's nitrogen atoms is part of a non-aromatic ring which can be broken by an oxygen or sulphur atom by means of dialkylating the --NH.sub.2 group of a urea with an alkene or alkene arylene alkene dihalogenide, disulphonate or dihydrogen sulphonate in the presence of a solid base and a phase-transfer catalyst.

Abstract: A process for the preparation of isocyanic acid, characterized in that N,N-disubstituted ureas are decomposed at elevated temperature to a secondary amine of lower volatility and to isocyanic acid, which is drawn off at the top.

Abstract: Process for the removal of isocyanic acid from a gaseous mixture of isocyanic acid and ammonia by introducing a tertiary amine or ether at 250.degree. to 600.degree. C. The gaseous reaction mixture is passed into an inert diluent and cooled, to condense an adduct of isocyanic acid and tertiary amine or ether, and the ammonia being removed as a gas.

Abstract: Process for the preparation of asymmetrically substituted ureas, carbamates, thiocarbamates or substituted isocyanates by reaction of an adduct of isocyanic acid and a tertiary amine with a primary and secondary amine, an alcohol, a thiol or a compound having one or two non-cumulated olefinic double bonds.

Abstract: Process for the removal of isocyanic acid from a gaseous mixture of isocyanic acid and ammonia by introducing a tertiary amine or ether at 250.degree. to 600.degree. C. The gaseous reaction mixture is passed into an inert diluent and cooled, to condense an adduct of isocyanic acid and tertiary amine or ether, and the ammonia being removed as a gas.

Abstract: Process for the preparation of asymmetrically substituted ureas by reaction of a gaseous mixture of isocyanic acid and ammonia having a temperature of 260.degree. to 600.degree. C. with a primary or secondary amine.