Ph control when gassing product

pekebaz3 · Sat Jul 16, 2005 5:59 pm

damn.should the amine turn red when you drop the hcl into it?Did I drop it in too fast?is there anything I can do about this?guess I'll find out later

pekebaz3 · Sun Jul 17, 2005 5:18 am

can no one shed light on this sitution?

The_Dude · Sun Jul 17, 2005 7:02 am

Did you do a proper A/B before adding HCl?

pekebaz3 · Sun Jul 17, 2005 7:17 am

yes.NaOH wash, extract w/ tol., dh20x4,brine,still.droped hcl and shit turned dark red.went through with rxn(even though I should have stopped)and got some orange/off white shards from it.very low yield from freebase weight.tried washing them and got no clarity.thinking of recrysing.anyone know if i should toss this or what?

bio · Working Bee

For the unsubstituted methylamine when nearing the end it will go pink or even red if the pH drops below about 3. This is OK as the impurities stay in the solvent. This of course assumes you weighed amine and not contaminents when calcing the acid amount.

Clean your crystals with Me2CO and reextract the solvent with water or base with ammonia. There is still a lot there somewhere if you got less than your usual yield.

Maybe now you will appreciate the reason distilling is used to purify! You won't go thru all this hassle again if you simply distill! Even w/o an A/B fractionating will give a clear oil pure enough product for any use.

pekebaz3 · Mon Jul 18, 2005 4:12 am

sorry if I was unclear , but I did distill off everything.twice.once for the toluene, then once for the water toluene azeotrop.then I put into acetone and orange "shards" crashed out.so I should extract w/ water then a np and gas as usual?I'm not sure if I"m ready to try the azeotrope again.I wasn't expecting lots of smoke to form when I dropped the hcl in(BIG clouds).plus it took along time to distill all those solvents and I'm still not sure what went wrong, unless I dropped in
too much hcl and or did it too fast.

bio · Working Bee

I meant distill the amine which ensures pure product when properly done.

Did you distill to dryness with vacuum when azeotroping off the water? The PhMe or PhMe2 will be dry when the temp rises to the boiling point then a little more. If some is left in it holds a most of the crud causing the yellowing.

,,,,,,,,,,,, unless I dropped in too much hcl and or did it too fast.............

Probably too much. The pH tells the story, it should be slightly acidic or neutral.
The "smoke" is normal and a temperature rise also. A slow drip is fine. Hell I don't think even boiling from too fast addition would really hurt much if stirred but don't know and ain't going to try it..

It's not that unusual to do the acetone wash 2 or 3x if dirty product. Even dry Me2CO dissolves some hydrochloride and it can be recrystallized from boiling acetone. The water extraction is the last resort.

Live and learn. You'll get it right eventually then hopefully not repeat the same mistakes. Seems I remember bandil saing this method is good for not so clean amine so think about that.