Sciencemadness Discussion Board

double bond reduction of alpha-methylnitrostyrenes with NaBH4

stoichiometric_steve - 3-3-2006 at 07:56

it was recently discovered that adding NaBH4 to a refluxing mixture of EtOH and nitrostyrene substrate through a soxhlet capsule attached to the lower end of a reflux condensor by means of chemically inert wire provided a method of unattended reduction, using very low molar equivalents of NaBH4 (0.8-1.2), which is apparently due to the use of refluxing solvent which raises solubility and reactivity.

this technique also circumvents the formation of nitronate salts with NaBH4 (which are big insoluble chunks) when adding substrate to a solution of NaBH4.

and the yields are so nice, too!

ziqquratu - 4-3-2006 at 17:25

Could you perhaps provide a reference to this procedure, as I imagine it might prove quite interesting to a number of people!

stoichiometric_steve - 9-3-2006 at 12:02

reference: personal empirical experience. just try it. it works!

enima - 11-3-2006 at 09:45

would you be kind enough to give us an experimental proceedure?

solo - 12-3-2006 at 04:06

Reference Information


Nitrostyrene

nitrostyrene
Status: JMAFF
IUPAC: 4-(2-nitroprop-1-enyl)phenyl thiocyanate
CAS: 4-(2-nitro-1-propenyl)phenyl thiocyanate
Reg. No.: 950-00-5
Formula: C10H8N2O2S
Activity: fungicides (unclassified fungicides)
Notes: There is no ISO common name for this substance; the name “nitrostyrene” is approved by the Japanese Ministry of Agriculture, Forestry and Fisheries.




EXTRACTION APPARATUS, Soxhlet



[Edited on 12-3-2006 by solo]

stoichiometric_steve - 12-3-2006 at 05:06

Quote:
Originally posted by enima
would you be kind enough to give us an experimental proceedure?


of course.

100g 3,4-methylenedioxyphenyl-2-nitropropene are suspended in 500ml EtOH and 5ml dH2O in a 1L RBF, a soxhlet capsule is filled with 1.2eq of NaBH4 and attached with inert wire to the lower loop of a reflux condenser attached to a jointed extension piece. reflux is started and continued until the solution is virtually colourless. GAA or dilute AA is added until fizzing ceases AND a clear solution is obtained.

solo - 12-3-2006 at 07:12

Thank you stoichiometric_steve, for sharing your emperical results using the technique you shared with us,.....often a picture is worth more than one can say.......would it be a great problem to take a snap of the setup and post it.....i for one would be apprecative since I've never used the set up you mention...or maybe I have , I just don't know ............solo

[Edited on 12-3-2006 by solo]

stoichiometric_steve - 21-3-2006 at 15:32

oh it's very very easy to imagine.

take a reflux condenser.
take a soxhlet paper capsule.
take wire and attach the capsule to the wire so you have a U shaped wire, the wire goes at the top of the capsule.
take the 2 open ends of the wire and bend one to form a hook which you can attach to the inner spiral of the reflux condenser so your solvent drips right into the soxhlet capsule.

thats it!

zephler1 - 23-9-2014 at 12:37

And now in scientific language, what exactly does "yields are nice too" correspond to in %? Heating a nitropropene up to 80C doesn't sound like a good idea, isn't this why ice baths are used for the NaBH4 reduction of nitroalkenes to nitroalkanes, or is that only important for the nitroethene to nitroethanes?

Templar - 23-9-2014 at 13:41

Wasn't there something about requiring several molar equivalents of borohydride per nitrostyrene mol so you didnt get dimer formation?

Rabodon - 25-9-2014 at 18:14

Quote: Originally posted by Templar  
Wasn't there something about requiring several molar equivalents of borohydride per nitrostyrene mol so you didnt get dimer formation?


With nitrostyrenes yes, you would get low yields with the procedure from above, but on nitropropenes- and -butenes etc. it shouldn't be such a big issue my chemistry brain says. The alkyl chains are inhibiting dimerisations. That's also why the thread starter said explicit "a-methyl-nitrostyrenes", I guess. But as the alkyl chains doesn't inhibit the dimersations completly, to do it the other way round would be smarter, as the borohydride would be always in massive excess here, which should produce even higher yields and a cleaner reaction.

[Edited on 26-9-2014 by Rabodon]

[Edited on 26-9-2014 by Rabodon]

JefferyH - 25-9-2014 at 22:14

Quote: Originally posted by Rabodon  
Quote: Originally posted by Templar  
Wasn't there something about requiring several molar equivalents of borohydride per nitrostyrene mol so you didnt get dimer formation?


With nitrostyrenes yes, you would get low yields with the procedure from above, but on nitropropenes- and -butenes etc. it shouldn't be such a big issue my chemistry brain says. The alkyl chains are inhibiting dimerisations. That's also why the thread starter said explicit "a-methyl-nitrostyrenes", I guess. But as the alkyl chains doesn't inhibit the dimersations completly, to do it the other way round would be smarter, as the borohydride would be always in massive excess here, which should produce even higher yields and a cleaner reaction.


Do you have a source for that claim? The part about nitrostyrenes and dimerization? I thought I've read a lot about borohydride in these reductions and I have never seen this mentioned.

What has been mentioned frequently is that such large excesses of borohydride are used for these reductions is because borohydride is often used in solvents with which it is extremely reactive, with the most popular being methanol. This also helps to create reactive alcohol-borohydride's. Ethanol works as well but is much less reactive.

Templar - 26-9-2014 at 04:56

I do not.

solo - 26-9-2014 at 05:26

Reference In formation


Selective Reduction of Nitroalkenes with Methanolic Sodium Borohydride: A Facile Route To Nitroalkanes
Rajender S. Varma and George W. Kabalka
Synthetic Communications
15(2), 151-155 (1985)


Abstract
α,β-Unsaturated nitroalkenes are rapidly and selectively reduced at room temperature to nitroalkanes in high yields by sodium borohydride in a tetrahydrofuran-methanol solvent system.

Attachment: Selective Reduction of Nitroalkenes with Methanolic Sodium Borohydride- A Facile Route To Nitroalkanes.pdf (177kB)
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Rabodon - 27-9-2014 at 13:47

My ref is my empirical data ;)
Btw. I've had higher, nearly quanititative yields on similar substrates using normal technical grade 96% EtOH without using any co-solvent. Just dissolve finely powdered(!) NaBH4 in EtOH (solution/suspension it's stable enough when it's cool!) and add substrate in tiny amounts and after each addition wait until color disappears before you add more substrate. At the end of the addition the color doesn't disappear fully anymore. Never let it get warm during that, if I remember well I've kept reaction temperature below 20°C.