5280
The
synthesis of O-acetyl salicylic acid (aspirin) can be accomplished by the
reaction of salicyclic acid (o-hydroxybenzoic acid) with acetic anhydride. Below is shown a series of thin layer
chromatographic plates from samples of a mixture of salicylic acid (1
equivalent) and acetic anhydride (4 equivalents) which have reacted at room
temperature for the times indicated.
Excess acetic anhydride and acetic acid have been washed out of the
samples prior to TLC analysis.
(a)
Write the equation for the preparation of aspirin showing all chemical structures.
(b)
The Rf
of salicylic acid is 0.53 and the Rf of
aspirin is 0.76 in this solvent. The
data show a problem in the reaction conditions.
State the problem with the reaction conditions, and say what you would
do to correct it.
5281
Draw the structure of the principle organic species present at each
stage indicated below in the preparation of salicylic acid (o-hydroxybenzoic acid).
(a) Starting material, methyl salicylate
(b) Resulting material immediately after adding methyl
salicylate to room temperature aqueous sodium hydroxide
solution
(c) Resulting material in solution after the reflux period
(d) Species which forms when the cooled reaction mixture is
acidified with sulfuric acid