What is 1,4-dioxane? 1,4-Dioxane is a synthetic industrial chemical that is completely miscible in water (EPA 2006). Synonyms include dioxane, dioxan, p-dioxane, diethylene dioxide, diethylene oxide, diethylene ether and glycol ethylene ether (EPA 2006; Mohr 2001). 1,4-Dioxane is unstable at elevated temperatures and pressures and