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                Benzoquinone powered Wacker oxidation of Safrole
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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.

From JOC, 29, p241 (1964):

"2-Decanone Using, p-Benzoquinone. - 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 70C. After 0.25hr an additional 1mL of
water was added and heat was applied to maintain a 70C 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 dh2o was
measured into it. Thermometer was attached to side tube. At midnite, one ml of
h2o was added, temp went to 70c.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 70c.at 2:30 the final ml was added, and there should be a trace left,
but ok if it aint.....held at 70 c for 30 more minutes, allowed to cool to room
temp, flooded w/ chilled h2o, and extracted w/ starting fluid (nod toQ)

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 is his benzoquinone recipe from Synthesis, 369 (1984):

        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.

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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 the following:

DMF = 700mL
Water = 100mL
p-Benzoquinone = 216g (2M)
PdCl2 = 3.6g

In dropping funnel was 320g not-safrole. Dripped into the solution at room temp
(30C) 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 4 1/2 hours the
solution had progressed on its own to 48C. Who knows how hot it got during the
4hrs. Obvious exothermic reaction. After 7 hours solution was back to 30C.

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
100-140C ~35g not-safrole came over. At 166C 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!"

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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:

308 ml DMF
 44 ml dH2O
1.5 g PdCl2
110 g p-benzoquinone

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.

After all safrole was dripped in, took the following temp readings:
(T is time in minutes)

  T  deg C
===========
  0  28.5
 30  29.5
 90  36.0
120  39.5
150  39.5
570  27.5

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. Na(CO3)2 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 deg. 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."

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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.

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Osmium

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

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