Need help about Mcat synthesis via propio

[MasoN]

Hi guys, I used this Recipe with my friend, but we had some problem with it, We did well until the methylamine step. But in the amination via Methylamine, the solution does not change color like the instructions(it takes some yellow in the first hours then no sensible changing even for 1 day!)
At first trys we just put reflux condensor, but i read some stuff that cork would be better for imprisoning the methylamine, so i tried tht too there was some improvement in the color but not in the final yield,
could it be caused by methylamine high volatility? We maintained temp under 35’ C and dividing methylamine addition 3 to 4 portions for 10 to 12h

Because of this our final product would barely gets to few grams

our scale was 25g propio
And we make our own HBr via PBr and H2SO4

 

[AgamemnonFromTroy]

Hello,
I personally found out that adding all the methylamine solution at once works the best and the fastest, if the reaction mixture color progresses to an opaque, pale yellow colour and stays there for more then 40 minutes the amination should be complete and the reaction should be quenched with distilled water, giving it more time could reduce yields as side reaction products start to form, during this time vigorous stirring should be in place. As for the condenser I find it to be overkill as I've used a vigrux column in the past and couldn't notice any improvements over partially sealing my reaction flask(never fully seal your R.F. as it could lead to a built-up of pressure), a reflux condenser is mandatory if you plan on heating the reaction above 39°c(in the case that DCM is used as a solvent )id advise against heating the Reaction, opting to just let it happen without controlling the temperature.

 

[MasoN]

Are u sure that pale yellow is enough?
So why these experts wait until that red/brown color apear?
And how much was your yield?
Thank you for your response

 

[AgamemnonFromTroy]

The final color depends on the solvent too, for DCM a pale yellow is good but make sure you leave it some time after color stops changing to be sure that there is no unreacted substate as it is very irritating and a pain in the ass to get out afterwards. If it turns reddish then products could have oxidised. My highest yield is above 90%.

 

[MasoN]

Ok dear
We will retest the synthesis soon . My hand is broken now

 

[Acidosis]

Yellow fluorescent is the color

 

[MasoN]

Nice
Still I cant figure why in those tutorials they made up to a dark red despite using DCM as the solvent

 

[MasoN]

@HectorFromTroy could you tell me the story?

 

[AgamemnonFromTroy]

Not sure but it might have something to do with not getting the final product contaminated with bromoketone.

 

[terads]

Hi hector
How we can sure about our propiohenone quality if we don't have any knowledge about which propiohenone is original and make efficient in this reaction

 

[AgamemnonFromTroy]

Melting point analysis, you have to determine it's melting point and compare to known values.

 

[WillD]

How much bromoketone did you get in stage one? Are you sure it gone well?

 

[MasoN]

Well, i didn’t measure the weight of tht, but i guess it had a good process since the color and our expectations
We made Hbr from 20g KBr and 15ml H2SO4 and we had some calculation tht it is enough for our scale
Our problem was the amination step, since the color didnt change like in the videos

 

[MasoN]

These images had taken a couple of hours after adding all the methylamine portions

 

[MasoN]

 

[AgamemnonFromTroy]

How much DCM did you use ?

 

[MasoN]

75ml after the bromination process

 

[AgamemnonFromTroy]

It could also be that because you added the methylamine over time some of the DCM evaporated. I also think that there's too much water in relation to how much DCM is at the bottom. I've attached a picture with how it looks for me after quenching the reaction and transfering it to a sep funnel and washing it for 2 times with distilled water.

 

[MasoN]

i understand your points but They don't seem that effective that make our product shit.
The excessive water i can’t believe it could change any circumstances.

another question i have..
Is your propiophenone colorless or a bit yellow?

 

[AgamemnonFromTroy]

Water in your reaction mixture sure slows everything down try avoiding excess of it.
For my substrate it has a slight tint of yellow both halogenated and un-halogenated.

 

[MasoN]

@HectorFromTroy Hmm. I didnt think of that. Grateful alot for your help
I will share my subsequent production soon