production method | (1) reflux dry p-toluenesulfonic acid with excess acetyl chloride for 3~5h until no hydrogen chloride gas is released. The excess acetyl chloride is evaporated under reduced pressure to obtain the colorless crystalline mixed anhydride product. (2) Mix dry p-toluenesulfonic acid with excess acetic anhydride evenly, heat at 130 ℃ for 30min, and then steam the acetic acid and excess acetic anhydride under reduced pressure at 70 ℃. The residue is the obtained mixed anhydride product. The mixed anhydride of the above two methods contains 6% ~ 10% p-toluenesulfonic acid and 5% ~ 20% p-toluenesulfonic acid anhydride, and can be used without further purification |