The present invention relates to an improved process for the preparation of process for the preparation of 7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one (Brexpiprazole) of Formula (II). More particularly the present invention provides a process for synthesis of 7-hydroxyquinolin-2(1H)-one co...