An organic compound which is basic and soluble in an organic solvent, does not have a problem in preparation or handling and exhibits catalytic activity as a basic compound, i.e., a phosphine sulfide represented by formula (1), and a manufacturing process therefor, i.e., manufacturing a phosphine sulfide represented by formula (1), by reacting one molecule of thiophosphoryl chloride with three molecules of a phosphorane represented by formula (2). The phosphine sulfide can be used in a process for effectively manufacturing a poly(alkylene oxide) by polymerizing an alkylene oxide in the presence of the phosphine sulfide or of the phosphine sulfide and an active hydrogen compound selected from water and organic compounds having a partial structure of --OH or --NH--; and 2) a process for manufacturing a 1,2-dioxyethane derivative from an epoxy compound, i.e, manufacturing a 1,2-dioxyethane derivative by reacting an epoxy compound with a carboxylate, carboxylic anhydride, carbonate or phenol compound, respectively, in the presence of the phosphine sulfide.