Dimethoxymethane , a solvent Dioxolane Methylenedioxy group Metaldehyde Paraldehyde 1,3,5-Trioxane Acetic anhydride Acetic anhydride , or ethanoic anhydride , is the chemical compound with the formula (CH 3 CO) 2 O. Commonly abbreviated Ac 2 O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic