What is the product in an esterification of of vanillin with acetic anhydride in
ID: 1056660 • Letter: W
Question
What is the product in an esterification of of vanillin with acetic anhydride in the presence of base? What is the product in the presence of acid? If these products are the same, explain why the base product has a significantly higher melting point (90-91) then the acid product (70-72), and why there is a peak at 10ppm on the hnmr of the acid product, but not on the base product. What is the product in an esterification of of vanillin with acetic anhydride in the presence of base? What is the product in the presence of acid? If these products are the same, explain why the base product has a significantly higher melting point (90-91) then the acid product (70-72), and why there is a peak at 10ppm on the hnmr of the acid product, but not on the base product. What is the product in an esterification of of vanillin with acetic anhydride in the presence of base? What is the product in the presence of acid? If these products are the same, explain why the base product has a significantly higher melting point (90-91) then the acid product (70-72), and why there is a peak at 10ppm on the hnmr of the acid product, but not on the base product.Explanation / Answer
1. Base catalysed reaction:
a) Aromatic aldehydes on reaction with anhydrides undergo perkin condensation in the presence of base to give ferulic acid (4-hydroxy-3-methoxy-cinnamic acid).
b) Vanillin also undergoes base catalysed esterification with anhydrides.
Therefore, acetic anhydride reaction with vanillin in the presence of a base yields 4-acetoxy-3-methoxy-cinnamic acid.
2. Acid catalysed reaction:
The acid catalyed reaction of acetic anhydride with vanillin results only in the esterification of phenolic group at 4th position resulting in acetyl vanillin. The other groups, aldehyde and methoxy at 1 and 3 positions remain undisturbed.
Since the base catalysed reaction involves the conversion of aldehydic group to enoic acid, the aldehyde proton which appears at ~ 10 ppm disappears from 1H NMR spectrum and since the acid catalysed reaction does not disturb the aldehyde group, the proton signal at 10 ppm remains.
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