Certain compounds of antimony appear to be toxic, particularly antimony trioxide and antimony potassium tartrate. Selenium forms two oxides&colon; selenium dioxide (SeO) and selenium trioxide (SeO). Sulfur trioxide and sulfates () are related to sulfuric acid (HSO). Portland Cement Type I with Bismuth Trioxide. Remission with arsenic trioxide has been reported. Ruthenium tetroxide (RuO) is highly volatile, as is ruthenium trioxide (RuO). Paris green may be prepared by combining copper(II) acetate and arsenic trioxide. Boron trioxide (or diboron trioxide) is one of the oxides of boron. Its surface consists of cadmium selenide trioxide (CdSeO). Usually the sulfonating agent is sulfur trioxide. The conversion is achieved by treating ethoxylated alcohols with sulfur trioxide. At , copper(II) sulfate decomposes into copper(II) oxide (CuO) and sulfur trioxide (SO). Molybdenum trioxide dissolves slightly in water to give "molybdic acid". Uranium dioxide is produced by reducing uranium trioxide with hydrogen. This reaction is reversible and the formation of the sulfur trioxide is exothermic.