Mechanism of direct nitration at substituted benzaldehyde

ipso nitration followed by re-aromatisation with loss of formic acid ?


http://pubs.acs.org/doi/pdf/10.1021/ar50104a002
http://pubs.acs.org/doi/pdf/10.1021/ed060p937

Without experimental data, it’s not easy to conclude whether formic or CO loss (e.g. formic acid isolation or CO trapping). But if the nitration occurs via the formation of the highly toxic CO, then the reaction procedure is dangerous and appropriate safety measures, must be taken.

I've never seen this transformation before and I am somewhat puzzled as to how this works. Any suggestions would be appreciated (:

The aldehyde proton isn't that acidic, and as such I think via the hydrate and release of formic acid is more likely, especially given the conditions.

I agree. But if nitric oxidation of formic acid occurs, given the reaction conditions?

http://onlinelibrary.wiley.com/doi/10.1002/jhet.5570160741/abstract - perhaps (I don't have access to the full article, sadly)

ipso nitration boosted by o-, p-methoxy- conjugation and followed by rearomatisation with loss of CO?

Quote from:

ipso nitration boosted by o-, p-methoxy- conjugation and followed by rearomatisation with loss of CO?

Could be.  I thought loss of formic acid from the hydrate looked easier (and the nitration should be faster for the hydrate since its no longer deactivated by an EWG), but I guess loss of CO is reasonable, especially since the driving force for rearomatisation is so high... Which do people think looks more plausible?