Author Topic: MeAm in MeOH for NaBH4 reductions  (Read 2048 times)

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Elvium

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MeAm in MeOH for NaBH4 reductions
« on: December 06, 2000, 10:38:00 AM »
The goal being to produce an anhydrous solution of MeAm in MeOH via the simplest of means.

1) The standard method of dripping aq. 40% MeAm onto KOH or NaOH and chanelling the gas into ice cold MeOH. Can anyone suggest ideal ratios of MeAm to base?

2) NaOH + MeAmHCl in MeOH. Then add in generous amounts of silica gel, stir and filter. This produces the desired solution but contains water. Would the silica gel remove enough of the water to allow a successful reduction? Does silica gel absorb MeOH as well as water?

3) MeAmHCl + NaOH in MeOH. Then distil off the MeOH / MeAm azeotrope under simple distillation or at the rotovap.. would this work? Or would it be one big mess of an azeotrope containing water?

sunlight

  • Guest
Re: MeAm in MeOH for NaBH4 reductions
« Reply #1 on: December 06, 2000, 03:16:00 PM »
1.- 100 cc of aq 40 % MeAm over 225 cc of NaOH works fine.

Sonson

  • Guest
Re: MeAm in MeOH for NaBH4 reductions
« Reply #2 on: December 06, 2000, 03:40:00 PM »
Why not add one eq of triethylamine to the MeAm-HCl solution and then add the ketone and then reduce?

Elvium

  • Guest
Am Acetate for MDA
« Reply #3 on: December 07, 2000, 03:03:00 AM »
Sunlight; As we have a few tests planned for AA in the Boro reduction to mda, I'm very interested in your experiments. If I read your past posts correctly you got ~70% (which is very high btw) by following Strikes Cn synth and replacing the Cn with Boro. Did you do exchange them in equimolar amounts or change any of the other ratios? Perhaps your yields could be higher if you added in water to allow hydrolysis instead of removing the MeOH directly.

sunlight

  • Guest
Re: Am Acetate for MDA
« Reply #4 on: December 07, 2000, 10:04:00 AM »
I got some 65 % yield in a small test, the first one, with may be 9 gr (don't have the papers here), using TS proportions (ketone : am acetate, and 0.2 NaBH4 : 1 ketone ), next tests with 25 , 50 or 100 grs with LabTop proportions yielded form 20 to 40 % only. As we are not too much interested in that material, we ave not researched more. Anyway, let mix the acetate with the ketone some hours, better with silica gel, then filter, wash the silica gel and go for rdxn.

buchiguy

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Re: MeAm in MeOH for NaBH4 reductions
« Reply #5 on: December 22, 2000, 04:18:00 AM »
I think it's better to do the MeAM Hcl + NaOH(aq) in a separate reaction vessel, run the output gas through a drying tube, then bubble it into -20C anhydrous methanol. Then no need to filter silica gel outta the smelliest solution on earth! Yuck! I puke every time I get a wiff of this stuff. Build a scrubber or neighbour may puke too!

About a 10% increase in volume is about right but maybe confirm with titration just in case any water accidently getting in there throws you off.

IMPORTANT NOTE: When producing MeAM gas, pretty common to get a suck back. You MUST use a PP check valve in-line to prevent backflow.

MeAm gas bubbling takes FOREVER! I'm trying to speed things up with multiple reaction vessels. Reaction vessels should be entirely made of glass because MeAM eats through everything! However, the reduction is a breeze. Just get a buzzer to remind you every 20 min to add more borohydride. Easy to extract with DCM and always a high yield. No need for an acid/base extraction because product is so pure. I distill, then acetone/HCL bubble, then wash filtered product with acetone. Whitest shit on earth!

Elvium

  • Guest
Re: MeAm in MeOH for NaBH4 reductions
« Reply #6 on: December 28, 2000, 06:26:00 PM »
For some reason the MeAm 40% + NaOH reaction is very temp sensitive. Placing the gas generating FB flask on regular hotmat is the solution. The slight elevation in temp is all that is needed.

Cesium had a good suggestion about reacting MeAmHCl with NaMethoxide as no water is produced, but he used a sligght excess of MeAmhcl and reasoned it degraded the boro much quicker resulting in a 65% w/w yeild.

KrZ was speculating on using CaO as a drying agent as its the most sellective. Sounds promissing.

What is this NEt3?

Buchiguy; Key to speeding it up is a gas dispersion tube or something simillarly hacked such as a fish tank bubbler (if you can find one that doesn't dissentegrate instantly) or glass wool.


terbium

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Re: MeAm in MeOH for NaBH4 reductions
« Reply #7 on: December 29, 2000, 07:25:00 AM »

100 cc of aq 40 % MeAm over 225 cc of NaOH works fine


This sounds good. I always used MeAmHCL. As I remember, I would drip a saturated solution of the hydrochloride into a flask of NaOH pellets. In either case, the NaOH dissolving in the water generates plenty of heat to drive off the MeAm gas.


sunlight

  • Guest
Re: MeAm in MeOH for NaBH4 reductions
« Reply #8 on: December 29, 2000, 10:08:00 PM »
There's a curious question while dripping MeNH2 40 % in solid NaOH, the whole rxn is endothermic, so the flask becomes chilled, and the gas that goes out is practically dried, I could not observe difference while passing the gas through solid NaOH to dry it and when I did not.

KrZ

  • Guest
Re: MeAm in MeOH for NaBH4 reductions
« Reply #9 on: January 03, 2001, 09:33:00 AM »
Calcium Oxide does indeed work quite well for this, a very exothermic reaction though.  Simply combine the NaOH and MeAm•HCl in MeOH, cool once the reaction is complete, and slowly add the CaO (25% H2O absorption) to the mix.  Be carefull adding CaO to the solution or you may end up boiling your methylamine out!