mill reactor (Fig. 2). In the reactor at 130oC and vacuum, the sodium phe- nolate is reduced to a very dry powder, after which the carbon dioxide is introduced under pressure (700 kPa) and temperature (100oC) to form, first, sodium phenyl carbonate, which isomerizes to sodium salicylate. This can be dissolved out of the mill, and the salicylic acid decolorized by activated carbon and precipitated by addition of sulfuric acid, after which the salicylic acid is purified by sublimation.
To form aspirin, the salicylic acid is refluxed with acetic anhydride in toluene at 88 to 92oC for 20 hours. The reaction mixture is then cooled in aluminum cooling tanks, and the acetylsalicylic acid precipitates as large crystals that are separated by filtration or by centrifugation, washed, and dried.
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