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Reduction of α,β-unsaturated nitro compounds
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Nancy Nichols
Reduction of α,β-unsaturated nitro compounds
$\ce{NaBH4}$ will only reduce the $\ce{RCH=CHNO2}$ to $\ce{RCH2CHNO2}$. An additional reducing agent, such as $\ce{Zn/HCl}$, can reduce the nitro group to the amine. A catalyst + $\ce{NaBH4}$ could do the whole thing, but you'll have to look at the literature.
Catalytic hydrogenation, using $\ce{Pd/C}$ under moderate conditions (around 5 bar $\ce{H2}$, 30-90 °C), can reduce $\ce{RCH=CHNO2}$ directly to $\ce{RCH2CHNH2}$.
$\ce{NaBH4}$ will only reduce the $\ce{RCH=CHNO2}$ to $\ce{RCH2CHNO2}$. An additional reducing agent, such as $\ce{Zn/HCl}$, can reduce the nitro group to the amine. A catalyst + $\ce{NaBH4}$ could do the whole thing, but you'll have to look at the literature.
Catalytic hydrogenation, using $\ce{Pd/C}$ under moderate conditions (around 5 bar $\ce{H2}$, 30-90 °C), can reduce $\ce{RCH=CHNO2}$ directly to $\ce{RCH2CHNH2}$.
I have done the reduction of RCH=CHNO2 to RCH2CHNO2 using NaBH4 in the presence of column chromatography grade silica gel. It works well. Hydrogenation over Pd/C is poor giving a mixture unless you do it in the presence of ammonia.More
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I'm not aware of a $\ce{NaBH4}$-based reduction of nitroalkenes to saturated amines, such as in:
It is however possible to reduce nitroalkenes to saturated hydroxylamines using $\ce{BH3*THF}$ in the presence of catalytic amounts of $\ce{NaBH4}$. (DOI)
If there's a chance to perform the desired transformation in one step via catalytic hydrogenation at normal pressure: go for it!
The handling of these reactions is nothing to be afraid of.
Typically, I performed hydrogenations in a standard 2- or 3-neck flasks and used ordinary balloons (think childrens' birthday) as gas storage. Advice: Stuff a piece of rubber tube into the inlet of the balloon and secure it with teflon tape.
Either attach this to the glas olive of a valve attached to your flask
or take a plastic syringe, cut off the base, stuff the the plastic cylinder into the rubber tube. Fill the balloon and attach a needle. Hydrogen may now be fed to your reaction mixture through a rubber septum cap.
UPDATE
I still doubt that the intended reduction by $\ce{NaBH4}$ is possible.
There is however another established route from $\alpha,\beta$-unsaturated nitroalkenes to amines which is worth to be mentioned:
Condensation products of aromatic aldehydes and nitroalkenes are reduced by iron in hydrochloric (or acetic) acid to the corresponding arylalkanones.
These ketones can be converted to primary amines by reductive amination in methanol (or ethanol) in the presence of (excess) ammonia and, of course, hydrogen over Raney Nickel or Urushibara Nickel.
In the course of this reaction, the imine intermediate is in situ reduced to the desired primary amine.
The resulting amines are valuable precursors in the synthesis of natural products: Their conversion to imines or amides and subsequent Pictet-Spengler or Bischler-Napieralski cyclisations furnish tetrahydro- and 3,4-dihydroisoquinolines.
I'm not aware of a $\ce{NaBH4}$-based reduction of nitroalkenes to saturated amines, such as in:
It is however possible to reduce nitroalkenes to saturated hydroxylamines using $\ce{BH3*THF}$ in the presence of catalytic amounts of $\ce{NaBH4}$. (DOI)
If there's a chance to perform the desired transformation in one step via catalytic hydrogenation at normal pressure: go for it!
The handling of these reactions is nothing to be afraid of.
Typically, I performed hydrogenations in a standard 2- or 3-neck flasks and used ordinary balloons (think childrens' birthday) as gas storage. Advice: Stuff a piece of rubber tube into the inlet of the balloon and secure it with teflon tape.
Either attach this to the glas olive of a valve attached to your flask
or take a plastic syringe, cut off the base, stuff the the plastic cylinder into the rubber tube. Fill the balloon and attach a needle. Hydrogen may now be fed to your reaction mixture through a rubber septum cap.
UPDATE
I still doubt that the intended reduction by $\ce{NaBH4}$ is possible.
There is however another established route from $\alpha,\beta$-unsaturated nitroalkenes to amines which is worth to be mentioned:
Condensation products of aromatic aldehydes and nitroalkenes are reduced by iron in hydrochloric (or acetic) acid to the corresponding arylalkanones.
These ketones can be converted to primary amines by reductive amination in methanol (or ethanol) in the presence of (excess) ammonia and, of course, hydrogen over Raney Nickel or Urushibara Nickel.
In the course of this reaction, the imine intermediate is in situ reduced to the desired primary amine.
The resulting amines are valuable precursors in the synthesis of natural products: Their conversion to imines or amides and subsequent Pictet-Spengler or Bischler-Napieralski cyclisations furnish tetrahydro- and 3,4-dihydroisoquinolines.
? $\ce{BH3}$ is impossible to handle safely in amateur setting, way worse I think than Raney Nickel or even LAH. Perhaps Urushibara nickel will do the job, which is said to be more easy to handle (read non-pyrophoric). For small scale reactions your idea with the balloon might work well indeed. Do you have a link to a somewhat more extensive description of the technique?More
I agree with this, you should not avoid catalytic hydrogenation... Nitro groups are easily reduced, but NaBH4 alone wont make it. Another nice feature of sodium borohydride!More
. In the video, the tube attached to the balloon looks like a commercially available piece, I always chopped something together from material from the lab drawers ;) The balloon technique works nice, but I never did this on a kilogram scale. Btw, Raney Nickel isnt that bad as long as you handle it with care and keep it wet. It really is pyrophoric :DMore
$\ce{NaBH4}$ will only reduce the $\ce{RCH=CHNO2}$ to $\ce{RCH2CHNO2}$. An additional reducing agent, such as $\ce{Zn/HCl}$, can reduce the nitro group to the amine. A catalyst + $\ce{NaBH4}$ could do the whole thing, but you'll have to look at the literature.
Catalytic hydrogenation, using $\ce{Pd/C}$ under moderate conditions (around 5 bar $\ce{H2}$, 30-90 °C), can reduce $\ce{RCH=CHNO2}$ directly to $\ce{RCH2CHNH2}$.
$\ce{NaBH4}$ will only reduce the $\ce{RCH=CHNO2}$ to $\ce{RCH2CHNO2}$. An additional reducing agent, such as $\ce{Zn/HCl}$, can reduce the nitro group to the amine. A catalyst + $\ce{NaBH4}$ could do the whole thing, but you'll have to look at the literature.
Catalytic hydrogenation, using $\ce{Pd/C}$ under moderate conditions (around 5 bar $\ce{H2}$, 30-90 °C), can reduce $\ce{RCH=CHNO2}$ directly to $\ce{RCH2CHNH2}$.
More
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I'm not aware of a $\ce{NaBH4}$-based reduction of nitroalkenes to saturated amines, such as in:
It is however possible to reduce nitroalkenes to saturated hydroxylamines using $\ce{BH3*THF}$ in the presence of catalytic amounts of $\ce{NaBH4}$. (DOI)
If there's a chance to perform the desired transformation in one step via catalytic hydrogenation at normal pressure: go for it!
The handling of these reactions is nothing to be afraid of.
Typically, I performed hydrogenations in a standard 2- or 3-neck flasks and used ordinary balloons (think childrens' birthday) as gas storage. Advice: Stuff a piece of rubber tube into the inlet of the balloon and secure it with teflon tape.
UPDATE
I still doubt that the intended reduction by $\ce{NaBH4}$ is possible.
There is however another established route from $\alpha,\beta$-unsaturated nitroalkenes to amines which is worth to be mentioned:
Condensation products of aromatic aldehydes and nitroalkenes are reduced by iron in hydrochloric (or acetic) acid to the corresponding arylalkanones.
These ketones can be converted to primary amines by reductive amination in methanol (or ethanol) in the presence of (excess) ammonia and, of course, hydrogen over Raney Nickel or Urushibara Nickel.
In the course of this reaction, the imine intermediate is in situ reduced to the desired primary amine.
The resulting amines are valuable precursors in the synthesis of natural products: Their conversion to imines or amides and subsequent Pictet-Spengler or Bischler-Napieralski cyclisations furnish tetrahydro- and 3,4-dihydroisoquinolines.
I'm not aware of a $\ce{NaBH4}$-based reduction of nitroalkenes to saturated amines, such as in:
It is however possible to reduce nitroalkenes to saturated hydroxylamines using $\ce{BH3*THF}$ in the presence of catalytic amounts of $\ce{NaBH4}$. (DOI)
If there's a chance to perform the desired transformation in one step via catalytic hydrogenation at normal pressure: go for it!
The handling of these reactions is nothing to be afraid of.
Typically, I performed hydrogenations in a standard 2- or 3-neck flasks and used ordinary balloons (think childrens' birthday) as gas storage. Advice: Stuff a piece of rubber tube into the inlet of the balloon and secure it with teflon tape.
UPDATE
I still doubt that the intended reduction by $\ce{NaBH4}$ is possible.
There is however another established route from $\alpha,\beta$-unsaturated nitroalkenes to amines which is worth to be mentioned:
Condensation products of aromatic aldehydes and nitroalkenes are reduced by iron in hydrochloric (or acetic) acid to the corresponding arylalkanones.
These ketones can be converted to primary amines by reductive amination in methanol (or ethanol) in the presence of (excess) ammonia and, of course, hydrogen over Raney Nickel or Urushibara Nickel.
In the course of this reaction, the imine intermediate is in situ reduced to the desired primary amine.
The resulting amines are valuable precursors in the synthesis of natural products: Their conversion to imines or amides and subsequent Pictet-Spengler or Bischler-Napieralski cyclisations furnish tetrahydro- and 3,4-dihydroisoquinolines.
More
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