Which rows of the table correctly describe the reactions of the aqueous acids with amines and amides?
A. Rows 2 and 3
B. Rows 1 and 3
C. None of the rows
D. All of the rows
E. Rows 1 and 2
I cannot seem to understand why the answer is E. Both nitrous and ethanoic acid are weak acids. Amide is a weak base. Both acids react with amine because amine is a strong base, that makes sense. But why ethanoic acid doesn’t react with amides while nitrous acid does?
As NH2 is a poor leaving group and the amides RCONH2 are stabilized through a resonance, they generally are not reactive in a sense of hydrolysis, hence necessitating harsh conditions and strong acids. The reaction starts with protonation of the carbonyl oxygen and it’s followed by attack of water on the carbonyl carbon
The ethanoic acid is weak (pKa ~ 5) and would not be suited for rapid hydrolysis as pKa of protonated amide is around -1, meaning that it requires a much stronger acid to effect the proton transfer.
However, amides do rapidly react with weak nitrous acid HNO2 to produce RCOOH (carboxylic acid), nitrogen gas N2 and water. But, by a very different mechanism that is likely to involve a nitrosonium cation NO+ from HONO that attacks the nitrogen of the amide group.