that is thermodynamically very favorable but extremely slow m the absence of a catalyst such as platinum sponge, V 2O5, or NO. SO3, reacts vigorously with water to form sulfuric acid Industrially, SO3 is absorbed m concentrated H2SO4, to give oleum (page 174), which is then diluted. SO3, is used as such for preparing sulfonated oils and alkyl arenesulfonate detergents. It is also a powerful but generally indiscriminate oxidizing agent.