Author Topic: Chromic’s Methylamine.HCl  (Read 5589 times)

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Chromic

  • Guest
IPA
« Reply #20 on: November 07, 2002, 08:16:00 PM »
>recrystallizing methylamine.hcl from isopropyl alcohol gives cleaner results

Sure does, but it takes a lot of IPA to dissolve, say, 250g of MeAm.HCl--even at reflux.

Rhodium

  • Guest
Methylamine Hydrochloride Recrystallization
« Reply #21 on: November 07, 2002, 09:27:00 PM »
When recrystallizing methylamine hydrochloride from methanol, I have found it to be very effective to dissolve the crystals in a minimum amount of boiling methanol, then allowing the solution to slowly cool to room temp, then to 5-10°C in the fridge, and finally to -15-20°C in the freezer before vacuum filtering and then washing the crystals with a very small amount of freezer-cold isopropanol results in very pure, spectacular thin plates (usually up to 1x1 cm) of methylamine hydrochloride. Drying the crystals in a dessiccator over KOH completes the process.

The filtrate gotten after the filtration can be diluted with an equal amount of isopropanol and again cooled in the freezer to give another crop of slightly less pure crystals, maximizing the yield without having to concentrate the alcoholic solution by evaporation or distillation, and without having to introduce any acetone anywhere in the process, which potentially can react with the MeAm.HCl, forming acetone methylimine...

Chromic

  • Guest
Smart idea
« Reply #22 on: November 08, 2002, 04:20:00 AM »
I like your idea of crashing out the methylamine hydrochloride with another solvent after getting the first crop of crystals.

Don't worry about an acetone imine forming, it doesn't happen (or if it does, it's highly reversible). I've found the best way to dry the crystals is to turn the hot plate to low and put the acetone-wet crystals on it until the smell of acetone is gone... then placing in a tightly sealed jar and waiting until you're ready to use them. Don't attempt the clean up on a hot and humid day though... the methylamine will pick up water pretty fast.

Why did you skip the acetone (or DCM or chloroform) wash after recrystallizing? The last run I made, the crystals were beautiful white shards, but I always like washing just to make sure.

P.S. even running this reaction slowly still produces a gas unlike what Terbium has said a number of times. Perhaps this is a difference between the hexamine route and the formaldehyde route he used... or he just didn't notice it?

Rhodium

  • Guest
Chloroform
« Reply #23 on: November 08, 2002, 05:35:00 AM »
The chloroform wash is performed on the crude product before the recrystallization in my scheme (to remove dimethylamine and whatnot). After the methanol recrystallization the crystals are so large that I hardly could believe any contaminants being present. The ice-cold IPA wash of the crystals is just to wash off possibly contaminated methanol from the crystal surface.

terbium

  • Guest
Snowflakes not shards.
« Reply #24 on: November 08, 2002, 06:06:00 AM »
The last run I made, the crystals were beautiful white shards, but I always like washing just to make sure.
Methylamine.HCl crystals should be large plates, as Rhodium mentioned, not shards!


Baseline Does Not Exist.

RoundBottom

  • Guest
term
« Reply #25 on: November 08, 2002, 10:50:00 AM »
is "plates" a technical term?  i would describe them as flat translucent flakes.  kind of shiny, sparkly looking, and "silky" feeling.

SWIM's last MeAm run was a disaster.  vac pump siezed during first suction filtering.  *sigh*  stuff had to sit for 2 weeks while waiting for repair.  final product was very discoloured... not a good enough MeAm during the recrystalization.  SWIM will repeat the recrystalization and hope to rescue it.

SWIM also found that the final acetone wash produced smaller, greyer, less translucent flakes... a la the write up.

Now with 12% more Bottom!
Nymphomania is not a disease, its a goal! (Methadist)

Chromic

  • Guest
Ooops!
« Reply #26 on: November 08, 2002, 04:25:00 PM »
Terb, you and Rhod are right. I looked in the dictionary, for the definition of shards it says pieces of broken pottery (not quite the right word) What I got was very thin plates. After recrystallization they look like pieces of very thin mica, 0.5-1cm in length, <0.5mm in thickness. Kind of like the way snow appears when it's freshly fallen and is very fluffy and has not been packed. I should have just posted a picture.

Boris_Silicunt

  • Guest
This particular synthesis looks simple enough...
« Reply #27 on: August 22, 2003, 02:25:00 AM »
This particular synthesis looks simple enough but I have two small questions.

Could someome answer them please?

If i understand roundbottoms Hexamine& Hcl and some of the other Synthesis i have read it goes like this

-mix X mols of Hexamine and Hcl together
-Reflux for no less than 8 and no more than 24 hours
-distill off the portion up to 107 C(slowly)
-filter out and wash precipitated ammonium chloride
-return combined filtrate and methanol washes to the distillation setup
-distill off all other liquids up to 108 C(slowly)
-filter precipitated methylamine hydrochloride
-wash and recrystallise methylamine chloride

the two points that are not clear in roundbottoms writeup are-

does the thermometer reach into the solution or is the thermometer readings from a standard distillation.(thermometer in the three way adaptor)?

is stirring required? (i have read that stirring is always required when distilling, but roundbottom does not mention it so i figure he left it out as it might interfere with crystal precipitation)
thanks

Rhodium

  • Guest
Methylamine help
« Reply #28 on: August 22, 2003, 03:34:00 AM »
does the thermometer reach into the solution?

Yes, in this case, the 104°C max distillation temp is measured with a thermometer immersed into the liquid in the distillation flask.

is stirring required? (i have read that stirring is always required when distilling, but roundbottom does not mention it

Yes, stirring should always be used even if it isn't mentioned in a writeup - it's rather so that if stirring is not to be used, then that is mentioned explicitly.

Boris_Silicunt

  • Guest
thanks rhodium
« Reply #29 on: August 22, 2003, 04:17:00 AM »
>the 104°C max distillation temp

so roundbottom should not have exceeded 104 celcius when he/she distilled? (roundbottom mentions temps of 107 and 108 celcius)

could this lead to higher yield?

in your opinion, would a higher reflux temperature of 80-85 C and a longer reflux time be more benificial.

thanks

Rhodium

  • Guest
104°C tops
« Reply #30 on: August 22, 2003, 11:07:00 AM »
could this lead to higher yield?

Yes, as the formation of the byproduct dimethylamine is minimized, see these documents:

Organic Syntheses, CV 1, 347

(http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0347)

Methylamine Synthesis FAQ

(https://www.thevespiary.org/rhodium/Rhodium/chemistry/methylamine.html)