The Hive > Novel Discourse

Nitrostyrenes to oximes with sodium dithionite

<< < (2/6) > >>

The best route to amines is probably reduction to nitroalkanes with aqueous sodium borohydride/PTC followed by dithionite-reduction to the amine.

I guess the reaction conditions for the nitroalkane --> amine reduction would be similar than the ones above.  Am I right?  It would be great to see how the / / reduction compares to the Zn reduction / ammonium formate of an arylnitropropane. 

It is misterous to see how all those reductions of nitropropenes get stuck in oximes: Pd/C, Pb - DMF, Fe + HCl (where the oxime is converted in a ketone).

Well done, Chappy. This has to be one of the most facile reductions of a nitrostyrene that I have ever seen. Kudos to you. So now what? How about a facile borohydride reduction under alkaline conditions to yield the n-hydroxyamine which may have activity. Note of caution, are you sure about the acetic acid wash of an oxime; could this lower yield and form a ketone?

Strangely enough, says that imines are reduced to the corresponding amine with sodium dithionite, while oximes are hydrolyzed to the corresponding carbonyl compound.

Oh well, at least we can look forward to dithionite being another reducing agent with which we can go from phenyl-2-nitropropenes to pheny-2-propanones.

Dithionite preparations:
Post 429965 (lugh: "Inorganic Syntheses", Chemistry Discourse)

I applied the dithionite procedure twice on p-methoxyphenyl-2-nitropropene (10 mmol), one time using MeOH and a second time utilizing EtOH. In both cases, the end result is an amorph crusty yellow solid; the yellow is very similar to the nitropropene colour. When I screen a solution of the solid in MeOH via GC/MS, I retrieve a major compound with M+ = 193. This, for sure, is not the ketoxime but most probably the unreacted nitropropene. Other compounds in the chromatogram are solvent impurities, and a trace of anisaldehyde (area 0.4% of the chromatogram).
When adding the dithionite to the nitropropene/alcohol suspension, there was no raise in temperature. In case of using EtOH as co-solvent, the reaction mixture has also been slightly heated (ca 35-40°C), but as demonstrated, this did not give the hoped results.

EDIT - Before everybody starts yelling, screaming and panicking: I'm not claiming the method is bogus, only that I have been unable to reproduce the method by applying it on a different substance.

when the proceedure was attempted on 2,5-dimethoxynitrostyrene. Three atempts in all, all in MeOH, using a tech grade of dithionite. These were the observations

1 - In all cases the colour was reduced
2 - In all cases the colour reduction took from 0.5 hours to two hours
3 - temp rose only slightly with a 100mmol rxn but not w/ 25mmol rxns
4-1st attempt (100mmol) using sodium dithionite containing some alkali, rxn remained a mixture throughout, at the end of which( 2hours) a HOAc and H2O insoluble crystal was obtained which yeilded nothing but foul sulfur smell during Al/Hg/HOAc redxn

5- 2nd attempt (25mmol)using dithionite that had been H2O washed to neutrality, temp to 65C was breifly applied everything went into solution, nothing crystalized  - complete failure

6 - 3rd attempt (25mmol)using dithionite that had been H2O washed to neutrality,  resulted in less than 5mmol of what is assumed to be the oxime (i have no physical properties here bees, anyone else?)

this was reduced ok but have yet to take a MP.


[0] Message Index

[#] Next page

[*] Previous page

Go to full version