05-21-03 02:45
No 434416
It seems to me that in the course of a p-benzo MM Wacker, that the Palladium Chloride catalyst is basically broken down by say 2 hours after one starts dropping the Safrole in.
If that is the case, why does one have to continue to heat/stir the reaction for another 6 hours? Isn't that a waste of time, and won't the Ketone produced start breaking down?
Also, AFOAF ran a Wacker with some new PdCl2, and post reaction, the whole bottom half of the flask was covered in a "mirrored" surface, which was metallic Palladium. (Looked like an evacuted silvered Dewar flask)
Has anybody seen this "mirror" effect and does it mean anything? (Normally the Palladium after deposit is black)
(Hive Addict)
05-21-03 03:32
No 434424
yes, i have seen that, but only when the PdCl2 was mixed in the MeOH and left to sit for over 3 months. that media bottle is still partially coated.
Now with 12% more Bottom!
Nymphomania is not a disease, its a goal! (Methadist)
(Hive Bee)
05-23-03 06:00
No 434880
Has anyone tried doing a MM Wacker at say 2X what the recipie calls for?
AFOAF was thinking about doing a "Double Scale" MM Wacker in a 3 Liter flask...
Any thoughts on this? Anyone tried a scale up??
(Hive Bee)
05-28-03 16:49
No 436088
A recent MM Wacker provided for a delightful experience: the best yield ever! Now all I need to figure out is why it went so well.
The methanol was a "new brand", 99.99%.
2.5 grams (instead of 2) PdCl2 were used, also a "new brand", lab grade 99+%.
190 ml of Safrole (freeze fractionated) were used (poured a bit too much)
When dripping in the Safrole, the addition funnel clogged after about 50% of the Safrole was added. Over an hour had elapsed already, so when discovered, the additional Safrole was added over another 45 minutes. The temperature was carefully monitored and never got above 69 C. Total addition time close to 2 hours.
Workup: The 10% HCl was added to the sep funnel first, then the Wacker added. The oil that formed at the bottom was sepped off immediately, before even adding DCM. Then usual 500, 250,200 ml DCM was added to sep etc., and added to Oil.
All fractions prior to Ketone (residual DCM, H2O, Methanol) were dumped during the vacuum distillation. Final distillation yielded 150 ml Ketone.
Now trying to figure what gave the great yield.
As I mentioned in first post, pure Palladium formed a mirror coating in the reaction flask, as opposed to the usual Pd Black colored residue.
Could the excess of PdCl2 or the longer addition time be a factor? Better Methanol? Keeping temp under 70 C.? I also did 2 distilled H2O washes of the DCM AFTER the final NaOH wash.
Any ideas?
(Hive Addict)
05-28-03 19:22
No 436108
possibly the extra catalyst- evidently the stuff sucks up water from the atmosphere, which can offset ratios...?...
shit...I found out it was all just one big manic episode!
(Hive Bee)
05-28-03 19:30
No 436113
It seems to me that in the course of a p-benzo MM Wacker, that the Palladium Chloride catalyst is basically broken down by say 2 hours after one starts dropping the Safrole in.
What evidence leads you to believe that?
(Hive Bee)
05-29-03 04:49
No 436217
Previously, reading between the lines in posts and recipies here, the info seemed to stress that the Safrole should be added within 45 - 60 minutes or so, otherwise the catalytic action of the PdCl2 was "gone". Prior to the latest run, I would tend to agree, in that using the "photography grade" PdCl2 I had, it seemed to precipitate out as Black particles and deposit on the sidewalls of the flask after 2 hours or so. This also showed up as the "gunk" and "frog eggs" crap during the cleanup. I had NONE of that this time, AND as well, I didn't bother filtering the post Wacker solution, as there wasn't any precipitate what so ever - no undissolved p-Benzoquinone, no Pd, nada. Just purple-red liquid. And that Pd mirror on the flask walls.
Also, contrary to the MM recipie, I never really had a decent reflux. Maybe a slight one 1/2 a bulb up an 8 bulb condenser. (69 C. max)
Cooler is better????
(Hive Bee)
05-29-03 15:33
No 436326
Higher temps should lead to more isomerization, but to what extent and what would the difference between a 50 degree run and a 70 is hard to predict.
Reading these posts makes me feel like trying a new supplier for PdCl2. The one I use is the photography type and I always get that black crap at the end. I've never seen the mirror coating youre talking about. Feel like trying!
(Hive Bee)
05-29-03 22:14
No 436401
The PdCl2's catalytic action is not gone after the safrole is added. The catalytic action is gone once all of the benzo is reduced though (which is why an excess is used).
Could the mirror coating be due to non-oxidized Pd precipitating in the metallic form? Whereas if an excess of benzoquinone is used the Pd remains in the cationic form. How much benzo was used?
(Stranger)
05-30-03 08:44
No 436501
thanks yinga you have cleared up a few important points for me about the benzo wacker.
(Hive Bee)
05-30-03 14:38
No 436565
150 grams of p-Benzoquinone were used. I add only what is required so excess p-Benzo & hydroquinone don't end up in the final product. (Also, I didn't have any quinone come over during ketone distillation, whereas a gram or so has shown up in the West condenser during some previous runs) Judging from this reaction, I'd say that 150 grams seems to be ideal.
Not being a chemist: For the Palladium to be deposited in metallic form, something has to "reduce" it (split it off) from the Chloride. One would think that if there was a great excess of Benzo, you'd end up with alot of oxidzed Pd, i.e Black stuff. If there were "just the right amount" of Benzo to react with the Safrole, what happens to the PdCl2? Does it break down to elemental Chlorine & Paladium when reaction is done?