text: Many acetylations are achieved using these three reagents:
  *Acetic anhydride. This reagent is common in the laboratory; its use cogenerates acetic acid.
  *Acetyl chloride. This reagent is also common in the laboratory, but its use cogenerates hydrogen chloride, which can be undesirable.
  *Ketene. At one time acetic anhydride was prepared by the reaction of ketene with acetic acid: