Sciencemadness Discussion Board

MeNH2 in methanol

PoissonBoltzmann - 26-4-2012 at 06:09

Hi to all SciMad people.

first post/question here, hope not to much a silly one,
regarding the preparation of MeOH MeNH2 mixture to be used in reduction reactions involving the use of NaBH4.

The "wet" version of the reduction seems to be poor, in terms of results, for the shifting of the equilibrium toward reactants, when water is introduced in the reaction.

So another "dry "version of the reduction require the use of MeNH2 dissolved in methanol.

Underground literature (sorry, but being not academic, apart from abstracts, it is difficult to me to access more serious references),
on that topic is present, and all recipe go through bubbling MeNH2 gas into cold methanol.

Producing MeNH2 gas seems not the most difficult procedure in the world, but it is anyway tricky, and if avoidable for the poor Kitchen (non)Chemist interested in working with very small reactions, just to satisfy his own curiosity, it would be better .

So an alternative would be quite welcome, but I've never noticed (could be simply for my fault) in Und. Lit. any "dry" alternative to that.

Checking solubilities of MeNH2.Cl and NaOH on methanol, I thought on the following procedure:

Dissolve the chloridric salt in the methanol, then add a corresponding molar quantity of dry NaOH, dissolve it directly in the MeOH to liberate the MeNH2 base as a gas, which should then be immediately adsorbed into the chilled alchool.

Nothing really exotic, only the dry version of the other "wet" one.

At the end, the MeOH should contain the MeNH2, some NaCl, and in case small minute quantity of water, which shold not affect too drastically the following reduction.

And that would be much easier than bubbling gas into MeOH... but...

Since it seems to me so easy, but nobody seemed to consider it,
I suspect that or it is so trivial procedure that it is not even worth to be mentioned or discussed, or there should be something wrong in this procedure, which I was not able to understand or know yet.

Any help, please?

PB

GreenD - 26-4-2012 at 06:23

lol NaOH + HCl = ??? H2O!!!! (NaCl)

So this wouldn't be very dry, would it!

You silly goose. This is why they liberate the gas in another chamber, and drive the gas into methanolic solution.

PoissonBoltzmann - 26-4-2012 at 06:57

just erased an additional line in my previous post
let me enter it now

"eventually the MeOH could be dried with MgSO4"

but with the sentence

"At the end, the MeOH should contain the MeNH2, some NaCl, and in case small minute quantity of water, which should not affect too drastically the following reduction."

should have meant that I was aware of the generation of water in the transformation of the salt into the base.

*passive aggressive BS edited* ;)


let me rephrase the question.

not looking for a perfectly "dry" alternative method to the gas bubbling,
would it be the one outlined above a possible way, or just a waste of time?

[Edited on 26-4-2012 by PoissonBoltzmann]

[Edited on 26-4-2012 by PoissonBoltzmann]

GreenD - 26-4-2012 at 07:07

Sorry I couldn't read your mind, or assume that you just forgot about the water and didn't care to write it.

Go for it. Let us know how it goes.

Equimolar amounts of H2O to your methylamine is going to be a bitch to keep "dry" with good yield of the amine.

This really just seems like you don't want to go buy another erlenmeyer or addition funnel.

[Edited on 26-4-2012 by GreenD]

bbartlog - 26-4-2012 at 07:15

Quote:
Underground literature [...] on that topic is present, and all recipe go through bubbling MeNH2 gas into cold methanol.

Present where? Not in your post! I don't care whether it's underground, aboveground or what have you, a link or description would still be nice.
Quote:
Dissolve the chloridric salt in the methanol, then add a corresponding molar quantity of dry NaOH, dissolve it directly in the MeOH to liberate the MeNH2 base as a gas, which should then be immediately adsorbed into the chilled alchool.


Dissolved or maybe absorbed. Adsorption is a surface phenomenon.
Quote:
And that would be much easier than bubbling gas into MeOH...


Bubbling gases into methanol is just not that hard, as far as procedures go.

Anyway, there is a thread of very recent vintage on *just this topic*. Check it out: http://www.sciencemadness.org/talk/viewthread.php?tid=19587

I would also advise you to not respond to tiny slights like 'silly goose' with passive aggressive BS... this is how flame wars get started.

PoissonBoltzmann - 26-4-2012 at 07:53

sorry to be passively aggressive as answer to an active aggression,
for the future I'll silently swallow any free blames and insults.

I apologize also for lack of references:
I was referring in particular to these two:

here they described a very high scale dry reduction with NaBH4, with gas generation

http://www.erowid.org/archive/rhodium/chemistry/redamin.nabh...

here it is described the wet one, claiming reasonably good yield

http://www.erowid.org/archive/rhodium/chemistry/redamin.aque...

which seemed to me more interesting for the small scale aspirant and simply curious chemist.

so the procedure I was asking here, which is a BEGINNER possible idea, was kind of mix between the two procedure, and wondering why it was not considered as a decent alternative (i was wondering in a mild and not arrogant way, since I came here and started post only for the opportunity to understand more on a field which attracts me, the chemistry, but not for being insulted for free...)
Quote:

Dissolved or maybe absorbed. Adsorption is a surface phenomenon.


I think I have not understood that point,
what are you referring to?
would you please clarify it ?

So, I dissolve MeNH2-Cl and NaOH into MeOH, (dissolve is it correct here?)

Then the MeNH2 base should be generated, and adsorbed into the MeOH (adsorbed correct?) .


Thanks for the vintage link, I already read that discussion, but it seemed slightly different to the issue I was asking myself, which is :

would it be possible to simplify as much as possible the reductive amination, using NaBH4 as reducing agent, for example with a procedure similar to the one I have outlined above?

thanks and peace

PB




[Edited on 26-4-2012 by PoissonBoltzmann]

[Edited on 26-4-2012 by PoissonBoltzmann]

Nicodem - 26-4-2012 at 09:04

Quote: Originally posted by PoissonBoltzmann  
Thanks for the vintage link, I already read that discussion, but it seemed slightly different to the issue I was asking myself, which is :

would it be possible to simplify as much as possible the reductive amination, using NaBH4 as reducing agent, for example with a procedure similar to the one I have outlined above?

You read the tread, but you did not find there a simplification to your problem with preparing a methanolic MeNH<sub>2</sub> solution? I'm sorry to say, but either you did not read that thread carefully enough or you simply don't understand what you read. I suggest you to re-read it again and if you still don't find what you look for, re-re-read it...

PoissonBoltzmann - 26-4-2012 at 09:49

ops.. got it... Na2CO3 as base

I was not carefull enough in reading!

my apologies for useless post

PB