Combine sugar and water in a 3 litre sauce pan. Stir until sugar is dissolved. Stir in lime and lemonade concentrate. Add Creme de Menthe topping and mix well. Stir well and bring to just below the boiling point [210 degrees F]. DO NOT BOIL. Remove from heat and chill. Add at ratio of 1 part syrup to 5 parts chilled water. Yield: 2 litre .