Patent GB-603160-A (GB)
Title: Improvements in or relating to cyclic ureas and processes for producing same
IPC: C07D235/26
Filed: 1945-04-10
Abstract: Cyclic ureas of the general formula <FORM:0603160/IV(b)/1> (wherein R1, R2, R3, R4, R5, R6, R7 and R8 may represent hydrogen or alkyl groups and may be the same or different, and n is zero or one, or wherein, when n is zero, R2, R3, R6 and R7 may jointly form, with the carbon atoms to which they are attached, a benzene ring, are manufactured by treating a diamine R1NHCR2R3(CR4R5)nCR6R7NH 8 with carbon dioxide at elevated temperature (preferably 200-300 DEG  C.) and superatmospheric pressure (preferably not exceeding 176 atmospheres, e.g. 30-70 atmospheres).  The process may be carried out in two stages by first reacting the diamine with carbon dioxide at one pressure to form the corresponding carbamate and treating this, with or without additional quantities of the diamine and carbon dioxide, at a different pressure. Either of the reactants may be employed in excess, e.g. of 0.1-5 molecular proportions.  The cyclic urea may be separated from the reaction mixture by selective solvent action (e.g. by the use of butyl alcohol or chloroform), or by distillation (preferably under reduced pressure).  The reaction may be effected as a continuous process by mixing the diamine and carbon dioxide with a recycling fraction from the reaction product, subjecting to moderately elevated temperature and pressure the resulting mixture of recycling composition, diamine, carbon dioxide and carbamate, separating from the crude reaction product the cyclic urea and a recycling composition, and removing water from the latter at some stage in the process.  For this process there may be used apparatus, described in detail with drawings, in which the heating (by means of steam pipes or electrically-heated oil baths) and cooling (by means of water jackets) of various units, and the flow of the reactants, are automatically regulated by electrically-controlled valves and electric heating elements in accordance with the readings of suitably located electrical thermometers, and in which the cyclic urea is finally crystallized on a water-cooled rotating drum. Another advantageous procedure consists in spraying the diamine into the top of a chamber containing carbon dioxide under about 200 atmospheres pressure and withdrawing molten cyclic urea from the bottom of the chamber. Examples describe the preparation of ethyleneurea from ethylenediamine by: (1) the continuous process described above, using between 2 and 3 mols. of diamine per mol. of carbon dioxide and effecting the main reaction at about 235 DEG  C. under about 48 atmospheres pressure; (2) to (4) passing carbon dioxide into a solution of ethylene diamine in ethyl, isopropyl or butyl alcohol, separating the precipitated carbamate and heating it in a continuous or batch autoclave alone or with an excess of diamine or of carbon dioxide.  Reference is also made to the production of tetramethylethyleneurea from tetramethylethylenediamine, methylethyleneurea from 1 : 2-propylenediamine, trimethyleneurea from trimethylenediamine and benzimidazolidone from o-phenylenediamine. The Specification as open to inspection under Sect. 91 comprises also the manufacture of compounds of the general formula given above in which the symbols R1 to R8 may represent aryl-alkyl or aryl groups, and in which the groups represented by these symbols may be substituted or unsaturated.  This subject-matter does not appear in the Specification as accepted.