1,3,5-Trioxane, sometimes also called trioxane or trioxin, is a chemical compound with molecular formula C3H6O3. It is a white solid with a chloroform-like odor. It is a stable cyclic trimer of formaldehyde, and one of the three trioxane isomers; its molecular backbone consists of a six-membered ring with three carbon atoms alternating with three oxygen atoms. Thus, cyclotrimerization of formaldehyde affords 1,3,5-trioxane.