Action of amines on 1-benzoyl -2-thiobiuret and its 5-phenyl derivative

Recently, it has been reported that l-benzoyl-2-thiobiuret [la] [yellow] which exists in the thione form [thio-lactam] cylices to 6-phenyi-1,2,3,4-[or 2,3,4,6-] tetrahydrothioxo- l,3,5-thiazine-2-one [II] on being treated with 4 N aqueous sodium hydroxide, whereas its phenyl derivative [Ib] gives on similar treatment 5-phenyl-2-thiobiuret [III]