02-11-03 05:48
No 406509
../rhodium /2cb.bea
Im sure Ill have a few questions regarding this synth... but for right now I just have one:
Why must the reduction be done under anhydrous conditions and why cant one use denatured EtOH? In other words, whats the problem with MeOH being present. NaBH4 doesnt reduce water or alcohols.
thanks... tis all for now
-HoneySuckle
(Hive Addict)
02-11-03 06:07
No 406521
Reactions fail when there is water present. Denatured alcohol contains other things besides ethanol and methanol which could really screw up a reaction. Denature alcohol also contains a pretty heft amount of water which could really screw things over. Methanol can work but its low boiling point, 65C can really make things go crazy. NaBH4 reduction is really exothermic!
Sink or SWIM
(Hive Bee)
02-11-03 07:02
No 406539
Also, am I correct in saying that the crystalizing of the 2ch freebase is uneccesary? Since you extract the freebase to do the bromination. I planned on doing an alternate bromination with Br2.
-HoneySuckle
(Hive Addict)
02-11-03 11:03
No 406592
It sounds like this one of your first synthesis. Donīt take shortcuts!! Follow the directions of more experienced bees until you get the hang of it.
MeOH reacts too eagerly with sodium borohydride to be of any practical use in this reaction. Beaker said that you can use IPA instead of MeOH. Havenīt you read the whole thing?
Freaky
(Hive Bee)
02-11-03 11:25
No 406595
read this thread : Post 249853 (poix: "Problem with 2C-H beaker's method", Methods Discourse)
use some edda for the condensation instead of Nh4Ac ../rhodium /edda.ht
The modification made by barium Post 315979 (Barium: "A modification of Beakerīs method for 2C-H", Novel Discourse) is an alternative too, as well as his reduction by HCOOK which is simpler and quicker Post 382254 (Barium: "A great CTH method", Novel Discourse).
If you have e,nough 2c-h at end of synth you could distill your freebase in vacuum. Otherwise purify it before the next step, and don't forget your acid/base wash.
(Hive Bee)
02-12-03 00:29
No 406802
didn't the product not turn out to be 2C-H in that third post? Correct me if I'm wrong Post 317843 (Barium: "Bad News!", Novel Discourse)
The working man is a sucker
(Hive Bee)
02-12-03 01:03
No 406821
Reduction of the nitrostyrene to the nitro-alkane work well, its this reduction Post 316285 (Barium: "Another reduction method", Novel Discourse) of the nitroalkane to the amine with hypophosphite that do not work.
But the reduction of the nitroalkane to the amine work great with HCOOK like in Post 382254 (Barium: "A great CTH method", Novel Discourse) , it take less time than the CTH with ammonium formate, it is better.
But Barium is more useful than me for all these reduction question anyway...
... so I will let him answer
(Hive Bee)
02-12-03 07:58
No 406953
Ive never done any illicit syntheses, but I have experience in academic o-chem labs, and Ive run NaBH4 reductions in methanol (I realize thats no sort of experience for kitchen chem, but Im not some raver highschool dropout). I have read the whole thing, and it says anhydrous IPA (and I know 91% IPA is easy to dry), but I was just curious about the urgency about the absense of water.
Ive also read your alternate reduction Barium, and I really like it. It seems a bit easier. Instead of adding the alkene solvated in THF (in a pressure equilized funnel), you add solid nitrostyrene (presumably through the top of the condenser). Was the H2 evolution Beaker talked about not a problem for you somehow? And why replace THF with ethyl acetate? Other than the fact that you like to avoid them. What does the ether (or pseudo ether) do at all? The reaction solvent is EtOH.
I realize I am inexperienced, and I really appreciate all the help. Im just trying to ask as many questions as possible before hand. Sorry for the late response btw.
-HoneySuckle
(Hive Addict)
02-12-03 10:30
No 406984
MeOH is a good solvent for NaBH4 reductions when the substrate is suspended/dissolved in the solvent and the borohydride is added dropwise/portionwise. In this reduction the substrate is added to the suspended borohydride. Do you see the difference?
I donīt add the nitrostyrene through the condenser. I just lift the condenser, add some nitrostyrene and put the condenser back. The gas evolution isnīt a problem unless you add too much nitrostyrene at once. A teaspoon at a time is a good rate for small batches. Both THF and EtOAc is solvents for the nitrostyrene with EtOAc as, in my opinion, a better solvent for most nitrostyrenes. They also aids the reduction by trapping the nitronate of the nitroalkane. Otherwise the nitrostyrene is eager to react with the reduced nitroalkane, in a michael addition, forming dimers. When comparing THF and EtOAc the latter is cheaper, less suspicious, doesnīt form peroxides and has a higher flashpoint (-2°C compared to -17°C for THF). EtOH isnīt just a reaction solvent itīs a reactant here too. NaBHB4 reacts with the lower alcohols forming mono-, di- and trialkyloxyborohydrides which are the actual reducing agents.
NaBH4+ XROH --> Na(OR)xBH + H
In our specific case with EtOH itīs mainly sodium triethoxyborohydride which is formed according to: 2NaBH4+ 6EtOH --> 2Na(OEt)3BH + 3H2(g)
Freaky
(Stranger)
02-12-03 20:56
No 407132
Denatured alcohol contains other things besides ethanol and methanol which could really screw up a reaction. Denature alcohol also contains a pretty heft amount of water which could really screw things over.
Industrial methylated spirit contains EtOH, MeOH, and a significant amount of H2O. Ethanol is also available denatured with just Et2O and no H2O, or with just 5% MeOH/5% IPA and no H2O, etc...