PREPARATION DE L'ASPIRINE
(texte anglais ŕ traduire, extrait du Vögel)


RETOUR AU SOMMAIRE


Phenols, unlike amines, cannot be acetylated satisfactorily in aqueous solution: acetylation proceeds readily with acetic anhydride in the presence of a little concentrated sulphuric acid as catalyst. Salicylic acid (o-hydroxy-benzoďc acid)upon acetylation yields acetylsalicylic acid or aspirin:

Place 10g. of dry salicylic acid and 15g. (14mL) of acetic anhydride in a small conical flask, add 5 drops of concentrated sulphuric acid, and rotate the flask in order to secure thorough mixing. Warm on a water bath to about 50-60°C, stirring with the thermometer, for about 15 minutes. Allow the mixture to cool and stir occasionally. Add 150 mL of water, stir well and filter at the pump. Recrystallise the crude acetylsalicylic acid from a mixture of equal volumes of acetic acid and water.
The following is an alternative method of purifying the crude aspirin. Dissolve the solid in about 30 mL of hot alcohol and pour the solution into about 75 mL of warm water: if a solid separates at this point, warm the mixture until solution is complete and then allow the clear solution to cool slowly. Beautiful needle-like crystals will separate. The yield is 13g. The air-dried crude product may also be recrystallised from benzene or from ether-light petroleum(b.p. 40-60°C)
Acetylsalicylic acid decomposes when heated and does not possess a true, clearly-defined m.p. Decomposition points ranging from 128°C to 135°C have been recorded; a value of 129-133°C is obtained on a electric hot plate. Some decomposition may occur if the compound is recrystallised from a solvent of high boilng point or if the boiling period during recrystallisation is unduly prolonged.


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