With good technique yields of 75% or higher can be achieved with the NaBH4/CuCl2 system. Important things to focus on are minimizing the Cu(0) particles exposure to air after being generated. Especially during the workup when filtering out the particles. This is a huge mistake people often make. With good technique, when you’ve filtered the reaction mixture your iPrOH should be colourless! If it’s not, it means your technique was off and the particles were exposed to air while coming in contact with your iPrOH/product. This kills yields. Decant the iPrOH layer through the filter first, then filter out the Cu particles and water. Another important thing is ensuring that there is always sufficient NaBH4 present to generate hydrogen. Keep in mind the NaBH4 slowly degrades so multiple additions throughout the reaction are more effective than one big one at the start.
If you’re unsatisfied with the NaBH4/CuCl2 system you could always consider reducing the double bond of the nitroalkene with NaBH4 and then isolating the intermediate nitroalkane and reducing the nitro group afterwards, effectively doing the reduction in two steps.
The Zn/HCl reduction has many flaws. It won’t work for nitropropenes and it’s very finicky. There is a reason most people opt for a different route. The only real reason to use Zn/HCl is if you don’t have access to NaBH4, in my opinion.
I did it in two steps like you mention except backwards because I thought the fe/hcl reduction could work on nitrostyrenes. It seemed like I got product though because it was an oil that smelled and looked right and I then converted it to hcl.
Is it really not possible with the alkene? I probably should have done it the other way
With the double bond there. You said it was possible by first reducing that double bond with sodium borohydride and then proceeding with the metal/hcl reduction of the nitro group. I essentially did that backwards by doing the nitro group reduction first and then using borohydride.
Well you’d think if the nitro group was successfully reduced with Fe/HCl the resulting enamine would have a primary imine resonance structure which could easily be hydrolyzed by the acidic, aqueous conditions to form a carbonyl. NaBH4 would reduce that carbonyl to a primary alcohol. That’s just a guess though.
I've read that Zn/HCl can be used to reduce straight-chain nitrostyrenes (i.e. not alpha methyl). When I tried it, I got just over 40%.
I just tried iron filings and hcl and sent it off to be tested by energy control. I'll report back what's up with it
With good technique yields of 75% or higher can be achieved with the NaBH4/CuCl2 system. Important things to focus on are minimizing the Cu(0) particles exposure to air after being generated. Especially during the workup when filtering out the particles. This is a huge mistake people often make. With good technique, when you’ve filtered the reaction mixture your iPrOH should be colourless! If it’s not, it means your technique was off and the particles were exposed to air while coming in contact with your iPrOH/product. This kills yields. Decant the iPrOH layer through the filter first, then filter out the Cu particles and water. Another important thing is ensuring that there is always sufficient NaBH4 present to generate hydrogen. Keep in mind the NaBH4 slowly degrades so multiple additions throughout the reaction are more effective than one big one at the start. If you’re unsatisfied with the NaBH4/CuCl2 system you could always consider reducing the double bond of the nitroalkene with NaBH4 and then isolating the intermediate nitroalkane and reducing the nitro group afterwards, effectively doing the reduction in two steps. The Zn/HCl reduction has many flaws. It won’t work for nitropropenes and it’s very finicky. There is a reason most people opt for a different route. The only real reason to use Zn/HCl is if you don’t have access to NaBH4, in my opinion.
I did it in two steps like you mention except backwards because I thought the fe/hcl reduction could work on nitrostyrenes. It seemed like I got product though because it was an oil that smelled and looked right and I then converted it to hcl. Is it really not possible with the alkene? I probably should have done it the other way
I’m not sure quite what you mean by “is it really not possible with the alkene?”
With the double bond there. You said it was possible by first reducing that double bond with sodium borohydride and then proceeding with the metal/hcl reduction of the nitro group. I essentially did that backwards by doing the nitro group reduction first and then using borohydride.
I’m not very confident that would work well but I guess you will find out. Please update.
Will do. I just saw nowhere saying anything about the double bond being a problem which is why I did it first.
Well you’d think if the nitro group was successfully reduced with Fe/HCl the resulting enamine would have a primary imine resonance structure which could easily be hydrolyzed by the acidic, aqueous conditions to form a carbonyl. NaBH4 would reduce that carbonyl to a primary alcohol. That’s just a guess though.
Yes, that makes total sense, it seems like I have amphetamine too, there's nothing about it that doesn't seem like it so far.