The effects of solvent, acid specificity, acid concentration, added salt, and reaction temperature on the yields of trioxane and formic acid (byproduct) in paraformaldehyde + acid (or acid + salt) + aprotic solvent were investigated. The mechanism that underlies the yield of paraformaldehyde and the selectivity of trioxane was determined. A highly practical and efficient synthesis of trioxane by a salt-mediated and acid catalyzed yield of paraformaldehyde in sulfolane media was developed. The method increased the yield of paraformaldehyde by more than 5 times and decreased the formic acid concentration by 10 times compared to the commercial synthesis of trioxane in an aqueous reaction system (formaldehyde + H2SO4 + H2O).