Low yield after MM wacker, what was wrong???

[methlab]

Cause I am in learning stage, I did a HALF BATCH MethylMan wacker as followed:
Methanol + PdCl2 prestired for 6 hours. Added labgrade 1,4-Benzoquinone and stired for 2 hours until nearly dissolved. Added tap water and dripped in Safrole  over 60 minutes. Let stir under reflux (80-85 C) for 8 hours. Made the acidwater as read in MM recipe. Dripped filtered (nearly nothing in filter, except PdCl2) post-wacker solution into acidwater, oil fell out to the bottom. Collected the oil (about 100ml), washed waterlayer with 100ml, 50ml, 50ml DCM to get the rest out of it. Combined oil and DCM washes. Put in freezer overnight. Next day the solution was frozen, but turned back into liquid after a few seconds in handwarm waterbath (this should not happen, why was it frozen?). Did the Bicarb and the NaOH washes, excluded NaCl wash, cause i had only jodized tablesalt. Distilled the 300ml oil/DCM. First without vacuum the DCM was coming off at 40 C, then another liquid under vacuum came over (25 C on my distilling thermometer ), about 50ml. Changed flask and continued distillation. No Safrole came over, but when Ketone temp was reached, just about 20g yellowish MDP2P was collected. Temp decreased, but there was still about 200ml left in the distilling flask. Stopped distilling, but the dark liquid turned immediatly into stonehard black tar, which was very hard to remove. What was wrong ? Anyone an idea ? Thanx and greetings…
please help me

[wolfx]

I agree with you, the DCM + ketone mix should NOT become solid even after stored in the freezer for a long time.

I think you had some MeOH coming under vacuum at 25 C. The first fraction might be ketone, or maybe ketone forerun, which I think is MDP1P.

Looks like you had some sort of problem with your Wacker.

BTW, just plain, OTC IPA 70 % is great in cleaning up glassware and containers after the Wacker.

Sorry I could not help more.

Good luck,

W.

[methlab]

used vaseline like Brightstar says. this worked well during safrole distillation. Go t avery good vacuum, the Safrole came over at 96-101 C. Maybe Vaseline is not working very good under higher temperatures. There is no labshop in my city, that's why i used Vaseline. But i will drive to the next labshop (120km distance) and get some. Will compare the results and tell you. Thanx  

[Kinetic]

If your reaction was successful, then this gives a clue as to the flask tar:

Did the Bicarb and the NaOH washes, excluded NaCl wash, cause i had only jodized tablesalt.

Was your final wash was with a basic aqueous solution? You must perform a final wash with water or brine, preferably followed by drying the DCM solution over magnesium sulfate, unless you want to perform an

aldol

(http://themerckindex.chemfinder.com/TheMerckIndex/NameReactions/ONR4.htm) reaction in your distillation flask again. Aldol reactions can be catalysed either by heat or base (or acid), forming dimers which often condense to polymers. These polymers are best known here as black tar shit.

If I were you I'd use the table salt to prepare you brine for the final wash before drying and distilling. I've never experienced any problems washing various ketones (generally propiophenones) with brine solutions made from tap water and table salt, but then again I've never worked with MDP2P.

For more information on both intentional and unintentional aldol condensations see

Post 336996

(Rhodium: "Base-catalyzed polymerization of P2P", Chemistry Discourse), and further down in the same thread,

Post 337161

(goiterjoe: "NaOH will turn MDP2P into crap", Chemistry Discourse).