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.
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reaction time
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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