[justswimmingly]

To start, I’m sorry that I can’t add any images - I’m on mobile and can’t figure out how to add one. Basically, my professor wants us to propose a mechanism for reacting diethyl malonate with HONO to form an oxime (so the oxime is on the alpha carbon and the rest of the molecule is the same). The first mechanism I did was:

1. HONO forms the nitrosonium ion (gets protonated by H3O+)
2. The carbonyl on diethyl malonate tautomerizes to the enol
3. The electrons from that double bond attach to the N in nitrosonium, the carbonyl reforms, and the electrons from the N-O+ triple bond go to the O
4. The nitroso O gets protonated
5. H2O takes the H from the alpha carbon, those electrons form the C=N bond, and the electrons in the N=O bond go to the O.

The problem is, I was just using a generic H3O+ because every mechanism I have seen for the formation of nitrosonium uses a stronger acid to protonate HONO. Specifically, I’ve mostly seen NaNO2 and HCl used. But my professor said we’re not allowed to use anything other than HONO - so no stronger acid, and no water, either. So my questions are:

1. Is this even the right track for this mechanism?
2. Does the nitrosonium ion form when just HONO is present (do acids protonate themselves?)

[Borek]

(do acids protonate themselves?)

That's not the answer to your specific question, but in general - yes, they do. The simplest example (and the one you are aware of, you probably just never thought about it this way) is

H₂O + H₂O H₃O^- + OH^-

but it works very similarly for many other acids. The ion product for acetic acid is 10^-15.6, which is in the same ballpark as ion product for water.