1. A diurethane of the general formula see diagramm : EP0000030,P50,F6 where Z denotes the radical see diagramm : EP0000030,P50,F7 and Y denotes the radical see diagramm : EP0000030,P50,F8 Z always being different from Y and R**1 and R**2 being identical or different and each denoting hydrogen, alkyl of 1 to 4 carbon atoms, alkoxyalkyl of 2 to 4 carbon atoms, alkoxycarbonylalkyl of 3 to 5 carbon atoms, haloalkyl of 1 to 4 carbon atoms, unsubstituted benzyl, or benzyl substituted by alkyl of 1 to 4 carbon atoms or halogen, R**3 and R**4 being identical or different and each denoting unsubstituted alkyl of 1 to 6 carbon atoms, alkyl of 1 to 4 carbon atoms substituted by halogen, alkoxy of 1 to 2 carbon atoms, halogen-substituted phenyl or unsubstituted phenyl, alkenyl of 2 to 4 carbon atoms, alkynyl of 3 to 4 carbon atoms, unsubstituted or C1 -C4 -alkyl- substituted cycloalkyl of 5 to 8 carbon atoms, bicycloalkyl of 7 to 8 carbon atoms, tricycloalkyl of 10 to 15 carbon atoms, phenyl with a fused ring system, phenyl or mono- or poly-substituted phenyl with the substituents alkyl of 1 to 4 carbon atoms, halogen or alkoxy of 1 to 3 carbon atoms, X denotes hydrogen, alkyl of 1 to 4 carbon atoms, haloalkyl of 1 to 3 carbon atoms, alkoxy of 1 or 2 carbon atoms, halogen, nitro or amino, n denotes one of the integers 1, 2, 3 and 4, and A, B, D and E are identical or different and each denotes oxygen or sulfur (with the proviso that the radicals A, B, D and E are not simultaneously oxygen and one of the radicals always denotes sulfur).