I know that an imine can undergo acid hydrolysis to yield a corresponding amide:

enter image description here https://chem.libretexts.org/@api/deki/files/13283/10.jpg?revision=1

But I am looking at a mechanism for acid hydrolysis of a drug where the doubly-bonded N remains, and instead a different R-group (NH3) is cast off.

enter image description here https://imgur.com/zH43bi4

Empirically, this the primary degradant produced after exposure to acid, so I know it's 'correct', but I don't understand why the general imine-to-amide mechanism is not occuring. Does it have something to do with the relative properties of the NH3 and NHSO2NH2 R groups?

  • $\begingroup$ The first example you drew shows the hydrolysis of an imine to a ketone (not an amide). The second example isn’t an imine to start with, it’s an amidine. Basically, in both cases the C=N bond is hydrolysed to C=O, but since the starting materials are different functional groups, the products are different too. $\endgroup$ – PCK Jun 13 '19 at 20:05
  • $\begingroup$ Thanks. I found this regarding amidines: i.stack.imgur.com/jYLC2.jpg. I can't find any general information about relative rates but is it plausible that when you limit the amount of acid exposure, there is a resonance that happens that flips the double bond position and then that become the site of the hydrolysis? $\endgroup$ – Chris Weber Jun 13 '19 at 21:00

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