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Benzoquinone Powered Wacker Oxidation of Safrole

Principal Author: Strike

HTML by Rhodium

Strike

With people throwing around remedies and new twists on the Wacker Oxidation, Strike would like to ask those interested to comment on the use of benzoquinone as the oxygen source. There seems to be a great reduction in rxn time and simplicity of equipment.

Experimental

2-Decanone (using p-Benzoquinone)1

Palladium chloride (0.020mol), p-benzoquinone (0.10mol), 1-dodecene [safrole] (0.01mol), and 50mL of DMF were placed in a 250mL roundbottomed flask fitted with a stirrer, condenser, thermometer and dropping funnel, and 1mL of water was added from the dropping funnel. The solution temperature rose to 70°C. After 0.25hr an additional 1mL of water was added and heat was applied to maintain a 70°C temperature. A third milliliter of water was introduced at 0.75hr and a milliliter at 2.5hr. The mixture was cooled and flooded with water after a total reaction time of 3hr and the product was extracted with pentane. The pentane solution was washed several times with water and then dried. Removal of the solvent etc. etc. gave 13.5g 2-decanone (77%)."

Strike knows all of ya'll know that article and then Spiceboy (Strike believes) gave this account below:

Holy Ketone! What a dream...

Dream setup; 100 ml of DMF stirring in a flask equipped w/ a sidearm 34 g of safrole was added in 4 portions of about 8 g each. Mixed intimately. Next, 11g of p-benzoquinone was added. Stir rate was upped. Finally, 7 g of PdCl2 was added. A dry addition funnel was coupled to the flask, and 5ml of H2O was measured into it. Thermometer was attached to side tube. At midnite, one ml of H2O was added, temp went to 70°C. Brisk stir rate. 15 min et and another ml of H2O added. External heat, if needed is used. At 1:00 another ml was added, and temp held at 70°C. At 2:30 the final ml was added, and there should be a trace left, but ok if it ain't... held at 70°C for 30 more minutes, allowed to cool to room temp, flooded w/ chilled H2O, and extracted w/ starting fluid. BOOOOOM! yield; over 70%

So Spiceboy's story checks out ok. She followed the JOC article except she doubled the amounts of PdCl2 and Safrole (the ratio between them the same though), but kept the benzoquinone amount the same (didn't double it). Yet things look good.

In studying for TSII Strike came across another article by Tsuji (The doctor that wrote the wacker article that Strike first used to work out this thing). Anyway, this came much later after his first publication so he should be all-the-more wiser. Here it follows:

Experimental

2-Decanone (using p-Benzoquinone)2

In a 100mL round-bottomed flask fitted with a magnetic stirrer is placed a mixture of palladium(II) chloride (89mg, 0.5mmol), p-benzoquinone (5.94g, 55mmol) and 7:1 dimethylformamide/water (20mL). To the solution, 1-decene [substitute safrole for this compound] (7.0g, 50mmol) is added in 10 min and the mixture is stirred at room temperature for 7h. The solution is poured into cold 3 normal hydrochloric acid (100mL) and extracted with 5 portions of ether. The extracts are combined and washed with three portions of 10% aqueous NaOH solution and a portion of brine, and then dried After removal of the solvent, the residue is distilled to give 2-decanone [MDP2P]; yield 6.1g (78%).

This one looks pretty good too. The reaction time is a little longer but it goes at room temp. But the really interesting thing is that that the extra- polated ratio of PdCl2/safrole is about 22 times less than the other method. It would be around 0.16g PdCl2 for ~16g(~1M) safrole. That's pretty nice.

Strike found this account written on the back of a chewing gum wrapper:

"Don't get me wrong, but you just can't believe everything you see on this site. Take that shit Strike wrote above. Looks ok. But what does Strike know. Anyway, I jotted it down, went to my Lab at the University, applied for a grant, got the money and was about to try a representative run when I fell asleep. Had an interesting dream though. Here's how it went:

"Decided to see if the Tsuji method above would work. Wouldn't try it on an illegal ketone like safrole, but decided to use a ketone called not-safrole.

In a flask was placed the following:

In dropping funnel was 320g not-safrole. Dripped into the solution at room temp (30°C) over 30min time. After addition the solution was dark reddish orange. Almost black. Throughout the addition, and for a few minutes after, the temp stayed at room temp so it was left alone unattended. After 4½ hours the solution had progressed on its own to 48°C. Who knows how hot it got during the 4hrs. Obvious exothermic reaction. After 7 hours solution was back to 30°C.

The reaction mix was flooded with water (3L). The oil fell out of solution to the bottom. It was black in color. The upper aqueous layer was a dark blood red. The upper layer was decanted from the oil. The aq. Layer washed with 2x200mL DCM. The DCM added back to the oil. The oil/DCM was washed twice with clean water. Each time an emulsion formed which eventually separated out after 15min. Vacuum filtering helped a lot (next time am gonna skip the water washes and go straight to distillation).

Dried oil/solvent thru sodium sulfate and distilled. With high vacuum at 100-140°C ~35g not-safrole came over. At 166°C came over ~250g ketone. A tiny amount of white precipitate accompanied the the distillate towards the very end of the run.

Hmm, what to do with all this stupid ketone? Could reduce it. Could add a hydrocarbon. Naw! Might as well try an amination. Wow! Amination successful. Have to go now. 70 monkeys working on typewriters just appeared in my living room!"

Boingo

As I was walking through a forest recently, I saw the following words carved (maybe pecked) into a tree.

"In a 1L flat-bottomed flask, equipped with a 1.5" stirbar, added:

Stirred everything vigorously for 15 minutes. Put a claisen adapter on the flask, and on the straight part, put a dropping funnel containing 130 g safrole. (Not sure if the reaction produced pressure, so used the claisen. One could also use a pressurized addition funnel w/out the stopper, if desired.) With vigorous stirring, dripped safrole in over a 1 hour period. Color went from a reddish/greenish/orange to an orangeish-black over this period.

Time Temp
0 min28.5C
30 min29.5C
90 min36.0C
120 min39.5C
150 min39.5C
570 min27.5C

After all safrole was dripped in, I took the following temp readings:

At T = 570, added contents of flask to 1.5L of dH2O and stirred. pH of the solution was 4.5. Using a 1L sep. funnel, began extraction with 2x50 ml aliquots of DCM per portion. There is a tendency for the DCM to form an orangish emulsion that takes quite a while to settle out, but it eventually does. The extracted DCM is dark-reddish to black.

After processing 1L of the solution, I noticed that there were a lot of black solids on the bottom of the container. Added an additional 1 L of dH2O to to the solution, in hopes of dissolving some of the solids (which probably contain most of the oil). After I did this I looked at my Merck, which said that p-benzo. is only slightly soluble in water. duh. Continued extracting the remainder of the liquid in similar fashion until I was left with a black sludge at the bottom of the container. Added DCM to the sludge and proceeded to vacuum filter the sludge from the DCM. Pooled all DCM extracts together and was left w/900 ml of dark black DCM/oil/crap.

(If I had it to do over again, I might have vac filtered the whole mess before I started extracting - rinsing the filter cake w/DCM and saving the DCM.)

Took the dark black oil, and washed it 3 times w/sat. Na2CO3 sol. Lots of grey solids developed in the upper aqueous layer. Washed 3 times w/sat. NaCl sol. More grey solids. Washed 4 times w/ cold dH2O. A filmy red precipitate developed in the aq. layer. This left me with 700 ml of dark black oil that appeared translucent red when a flashlight was shone through the bottom of the flask.

Vacuumed off DCM, + 15-20 ml of additional liquid from 100-170°C. Changed flasks, and collected 99g of yellowish-green ketone from 170-205 deg. Temp began to rise further and brownish liquid started creeping down the condenser. Was left w/120 ml of black, viscous tar in the distilling flask that dissolved easily in acetone. Maybe more washes earlier would have cut down on the tar in the end. Even with mag-stirring there was a lot of bumping during distillation, maybe maybe due to all of the tar and crap in the distilling flask. Total yield of (suspected) ketone = 99g or 76%! Smell/color seemed correct. A portion was tested to see if it formed a bisulfite complex. It did. Now if only this poor woodpecker could aminate successfully!

Thanks to the Bright bee who suggested using p-benzo in 30% molar excess over the safrole."

Getafix

Found this note under my windscreen wiper yesterday:

After dumping your rxn mix in 1.5L 3N HCl and extracting with DCM, wash the DCM with water a couple of times. Then wash with Sodium Bicarbonate twice. After that, wash with 5% NaOH three times. The first wash will cause both phases to be completely black, so separation is really difficult. Not even a torch will help. But some solids form on the interface, so you can stop the separation as soon as you see solids going through the neck.

The second wash will result in a nice emulsion, but with a bit of swirling it will break in about 15 minutes. The DCM layer will now be more red than black. The last wash is quite easy. You will notice that the NaOH layer will contain a lot of tarry shit, but it is water soluble and can be washed away easily. After that, wash with water again, and then with a saturated NaCl soln. By now the DCM should be more red than black and not as viscous.

Dry the DCM and distil of DCM and then add about 50% peanut oil or any other high BP oil. (50% of weight of safrole used) Vacuum distil the mix and you will find the oil coming over will be nice and clear. No red hit coming over, or crystals forming in your condenser. And when the MDP2P has finished coming over, the temp will drop drastically. No orange or black oil coming over, and when you check in your flask there will be nearly no tar. A quick rinse with some toluene will clean it up completely. No struggling with rock hard tar for days. Just wash and dry.

Osmium

Osmium told you weeks ago to remove the hydroquinone with NaOH. Nice to see somebody listened.


References

  1. Tsuji, J. Org. Chem. 29, 241 (1964)
  2. Tsuji, Synthesis, 369 (1984)