Novel substituted dithiocarbamylurea accelerators of the formula R.sup.1 NHC(O)NHSC(S)NR.sup.2 R.sup.3 wherein R is phenyl or substituted phenyl and R.sup.2 and R.sup.3 are alkyl, aryl or aralkyl or together are alkylene, oxydialkalene or thiodialkylene exhibit unexpectedly improved scorch safety when employed as sulfur cure accelerators. In another aspect, this invention relates to accelerator compositions comprising said accelerators and thiuram or benzothiazole sulfenamide accelerators. In yet another aspect, this invention relates to curable compositions comprising such novel accelerators, sulfur and/or a sulfur donor compound and a sulfur curable rubber.
A compound of the formula R.sup.1 --NHC(O)NHSC(S)NR.sup.2 R.sup.3 wherein R.sup.1 is phenyl; phenyl substituted with halogen, alkyl, NR.sup.4 R.sup.5 wherein R.sup.4 and R.sup.5 are the same or different and are hydrogen or alkyl; alkoxy, alkylthio, methylenedioxy, COOR.sup.6 wherein R.sup.6 is alkyl; or NHCOOR wherein R.sup.7 is alkyl; R.sup.2 and R.sup.3 are the same or different and are alkyl, cycloalkyl or aralkyl, and R.sup.2 plus R.sup.3 are alkylene, oxydialkylene or thiodialkylene.