Use and process for the preparation of N-cyclic and N,N'- dicyclic ureas

The use of ureas in which at least one of the two nitrogen atoms of the urea is part of a nonaromatic ring which can be interrupted by an oxygen or sulphur atom as chemical solvent, and a process for the preparation of tri- or tetralkylated ureas or diureas, wherein at least one of the nitrogen atoms of the urea is part of a nonaromatic ring which can be interrupted by an oxygen or sulphur atom, by dialkylation of the -NH2 group of a urea with an alkylene or alkylenearylenealkylene dihalide, disulphonate or dihydrogensulphate in the presence of a solid base and of a phase transfer catalyst.