DMF/O2 Wacker Oxidation of Safrole

KrZ's Voice:

Let's look at the literature:

  • 3.24g PdCl2
  • 32.40g CuCl2.2H2O
  • 324.36g Safrole
  • 70mL H2O
  • 500mL DMF (DiMethylFormamide)

Placed everything except the Safrole in a 4L reactor, stirred heavily for 4 hours, till all compounds were dissolved. Then added Safrole, and removed atmosphere with vacuum. Pressurized to 35 psi O2.

drop (psi)
Time After Last
Drop (minutes)
15 17
15 18
15 20
15 20
15 29
15 38
~4 30

Total O2 uptake ~94 psi. Repressurized to 35 psi after each drop. Total Reaction Time: 172 Minutes

Added 500 mL 5% HCl to reacted solution. Separated precipitated Ketone/Aldehyde. Extracted the 5% HCl solution with 3x100mL DCM and separated those, and pooled the 3 DCM/ketone extracts with the precipitated Ketone.

Clean up:
Washed pooled extracts 2x with 300mL Saturated Sodium Bicarbonate solution and separated pooled extracts each time. Washed pooled extracts with 400mL distillated H2O and separated H2O. Washed pooled extracts with 400mL Brine Solution (saturated NaCl) and separated again. Dried extracts with 50g dry Na2SO4 for 45 minutes. Filtered to Remove Na2SO4. Vacuum distilled at ~2.0mm Hg to recover 311.22g PiperonylMethylKetone (MDP2P) fraction between 105-114°C. There was an Isosafrole forerun, and a minimal high boiling point and thus polymerized glop after 114°C. Molar yield: 81%

Grouch's Voice:

I just (Old Hive confirmed that the 35psi O2 DMF wacker works fine. I used a Nalgene 20L polypropylene carboy and I drilled a hole in the cap and used a threaded long stem tire valve with a nut and washer and rubber grommet. I also used a 3" stirbar and a Thermoline heavy duty stirrer that's rated to stir up to 132 litres. I pressure tested the carboy to 50psi with scalding hot water and stirring for 5 hours and there was a bulge at the bottom but I'm guessing it could even hold much more psi.

Here's my data:

Inside the carboy I placed the following:

  • 30g PdCl2
  • 165g CuCl (not CuCl2)
  • 669ml water
  • 4600ml DMF

I stirred this thing uncapped for close to 3.5 hours then I added 3kg safrole, then capped it and tightened the cap with a BoaConstrictor strap wrench from Canadian Tire, and pressurized it and purged it 3x with O2, and then I took it up to 36psi and started stirring. I checked the psi every 20 minutes exactly and topped it back up to 36 psi:

Time (min) Pressure Drop (psi)  
0 0  
20 10  
40 11 Getting warm
60 7  
80 12 Getting hot
100 12.5 hot to the touch, but still touchable
120 12  
140 9  
160 8  
180 5  
200 4 Still hot

After the reaction, I dumped it into my 22L sep funnel which is made from a 22L heavy walled SHOTT RoundBottomFlask, and then dumped in 5L of 5% HCl. I allowed this to cool for a few hours. When I returned, I let the crude ketone come out and there was already about 2750ml. I then extracted with 3x1L DCM, the combined extracts and crude ketone was then washed with 2x3L saturated sodium bicarbonate (528g/6L), 1x4L saturated sodium chloride solution (1250g NaCl/4L). Then I dried it with 551g sodium sulfate for 54 minutes, then evaporated the DCM to get 3124g crude ketone then distilled to afford me with 2500g ketone (76% yield!)

The way you shake it is by stoppering it and carefully lifting it out of the 'wooden chair with a 6" hole drilled in it' hacked stand, inverting it and resting the shoulder of it on one knee while taking the stopcock side and shaking/swirling it and venting it. When finished, carefully put back, unplug and let settle. The 22L flask was originally just a plain SHOTT RBF but modified by a glassblower with a joint on the neck and a stopcock at the bottom.

CuCl instead of CuCl2? Reason not really important; you can use a little less and have less Cl- ions around. Solubility may be different in different solvents, but I haven't checked. I like the colors more using the CuCl left over from over two years ago back in the days of the 'balloon on top of the flask, ton of catalyst' Wacker.

Above procedure is pretty much EXACTLY the same as KrZ's post a long time back in a thread called 'o2 is shit' or something like that where people were, for wrong reasons, doubting the procedure. The ONLY change is the CuCl and the scale and equipment used. I copied it almost EXACTLY. The reason for the erroneus pressure decrease at 60min was likely due to me not setting the stir speed as fast as the other times. And NO, I wouldn't have used the word 'confirmed' if the reductive amination failed.

PS: The wooden chair had to have been in your family's home and be a minimum of 43 years old and re-painted a few dozen times by your father, or none, ABSOLUTELY NONE, of the above procedure will work.

Addendum by Grouch: For those who saw the O2/DMF/CuCl/H2O/PdCl2/safrole thing in the 20L carboy, on the second try, right when the reaction was complete, i noticed after i picked up the carboy, a few mls leaked out. There were a lot of little cracks all around the bottom sides of the container so choose a better one.