Damn it, actually i realized the mixture hasn't been acidified as it was supposed to right after i posted it - damn it, but it was too late
I asked Vitsh about that and expect to get his answer shortly after he wakes up - he lives about 5 hours 'earlier' than me, geographically speaking.
So, if it turns that he indeed made a mistake, here are my thoughts:
1) It is possible that nitroalkene forms only after the hydrolysis stage; however - why then in the analogous preps of
nitroalkohols the reaction time is always from 1 to 3 minutes, strictly measured by clock?? Obviously, it needs to bee stopped at that stage, no?
2) In any case, w/out acidification the product one arrives at is a sodium salt. NitropropEnes also form salts, don't they?
Decomposing that salt is probably the stage where most of the yield goes down, here's a quote from
https://www.thevespiary.org/rhodium/Rhodium/chemistry/nef.html
:
"...Primary and secondary nitro paraffins (nitroalkenes
- a typo here! -) are acidic in nature and form sodium salts. When mineral acid is added to these sodium salts, the nitro paraffins are regenerated. The action is different, however, when the sodium salts are added to an excess of the acid. In the latter case aldehydes or ketones are formed with the evolution of nitrous oxide."
So, to maximize the yield it might bee beneficial to add the acid very slowly, as well as to use a weaker one - like AcOH, which i also have seen in one of the nitroalcohol procedures.
Again, bees, i'm terribly sorry to post misinformation - i'll edit the above post, so it needs not to bee classified as 'misinforming'; but please, take off the 'excellent' rating from it.
Antoncho