| 摘要 |
<p>Acetyl salicylic acid is prepared by heating a mixture of salicylic acid and excess acetic anhydride in a closed vessel to a temperature of 85 DEG C. to 95 DEG C., reducing the pressure in the vessel to from 160 to 180 mm of mercury absolute and thereafter distilling the mixture to substantial dryness while gradually reducing the pressure to from 80 to 110 mm, the mixture being agitated and maintained at an elevated temperature throughout the distillation. An inert distillable diluent, preferably acetic acid, may also be present, and the complete removal of vapours may be effected by reducing the pressure in the reaction vessel to about 30 mm and maintaining this reduced pressure for about 3 hours while the mixture is maintained at an elevated temperature. The product remaining in the reaction vessel is stated to be substantially pure needle-like crystals of acetyl salicylic acid. A detailed example is given.</p> |
