dormouse (Member)
04-23-00 05:43
No 108770
      Wacker oxidation using cheap inorganic reagents? -rev drone  Bookmark   


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Author  Topic:   Wacker oxidation using cheap inorganic reagents? 
rev drone
Member   posted 08-01-99 03:27 AM          
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Now alkyl nitrites have been used by many bees quite successfully as oxidizing reagents in the Wacker oxidation of safrole, but what about other, even simpler nitrite-containing species? For that matter, what about reducable inorganics in general?
Rather than using a nitrite ester, what about a nitrite salt? Sodium, potassium, or ammonium nitrite all have seemingl the same reducing potential as thier esterified counterpart, or do they?

So would this work, or is there some wierd orbital overlap (or lack of wierd overlap) that would keep this reeaction from proceeding? There are examples galore of nitrite species present without adverse affects on palladium-catalyzed oxidations, but is the electron withdrawing presence of an alkyl group attached to the nitrite really needed to get it to do what we want?

Likewise, what about sulfur-based oxidizing reagents, like something as simple as sulfate salts? Unfortunately, my CRC handbook isn't nearby, but it seems that the redox potentials for many of these compounds are within reason for them to be looked at as potential oxidizing reagents with the Wacker.

The beauty of these methods is that they could combine affordability that pressurized O2 offers, with the convenience of a homogeneous system that more expensive reagets such as benzoquinone have. Theoretically, by judicious use of PTC's, any solubility issues could be taken care of.

So what do people think?

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-the good reverend drone


 
ymir
Member   posted 08-01-99 11:02 AM          
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Interesting, was looking at a book on oxidations while locating those other references. Didn't copy the reference, but it was mentioned that mercury salts could promote a Wacker type oxidation of a terminal olefin. Probably is more in the local library as well. Will get back after locating the track.
 
hellman
Member   posted 08-02-99 01:04 AM          
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I guess as long as the sodium doesn't interfere with the olefin, which it probably wouldn't,.
Imagine that, using sodium nitrite, and the final ketone is completely turned into the addition product, you know IT JUST MIGHT WORK,
Maybee it's a job for that guy in the black tights.

'the curtains dissolve, as the last remnents of sanity has been lazily scraped from the cold wooden stage floor, as the crowed settles into it's seats.
Into the bowl, the masked man places 100ml of his olefinic com-par-dree, along with 120 g of sodium's favourite nitrite, and 300ml IPA just for good measure, the parsleys this time was purposly left out, but not so for the unlucky black pepper of pipperonis.
It boiled like a pot on the stove for three hours, the masked man checked the pot once every five minutes, to find that, mistakingly he was watching the wrong pot.
All was well though,.
Off he then took the saucepot lid, to let this now quiet muther fucker, evap to dryness, upon which he was left with 44g of a white oily chicken fat looking substance, which was washed with toluene, not just to clean it, but as to ensure freshness,
Which eventually gave the quite happy Black tight scoundrel 35g of pure extacy,.

He believed it was extacy, as he had a predisposition to psyco-somatic symptoms,

hell, for a days work, he was more than pissed


hellman


Cherrie Baby
Member   posted 08-02-99 02:26 PM          
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Not so easy. I think that it would have to be done with a Pd complex which was soluble in the organic layer. Extracting the oxidising source into the organic layer is easy. But you have to find a suitable method of getting Pd to stay in the organic layer rather than the aqueous.
Otherwise you could try a reverse-PTC. Extracting safrole into the aqueous layer.


 
ymir
Member   posted 08-02-99 05:10 PM          
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Unfortunately, the reference is one well known to the Hive, the problemetical mercuric acetate oxidation method. One piece of perhaps useful information that turned up was two mechanisms for the oxidations of a terminal olefin to a ketone: Removal of hydride ion resulting in an allylic free radical or oxidation at the double bond leading to a ketol derivative, which dehydrates to the ketone. How the man in black got a bisulfite addition product from boiling a terminal olefin in sodium nitrite/IPA is some what unclear. Did the man in black isolate an organic layer, and then treat that with sodium bisulfite, or was distillation required, etc., etc.?
 
rev drone
Member   posted 08-02-99 08:02 PM          
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Cherrie Baby,
Actually, it is that easy; for PdCl2, the solibility partitiion greatly favors DCM over H2O. For more solvent choices, look under some of the more recent titles covering precious metal recovery: this is increasingly the choice of industry.

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-the good reverend drone


 
Osmium
Member   posted 08-03-99 11:56 AM          
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I disagree with the ox. potential of the inorganic nitrites. I don't think that it will be high enough in aq. solution. To be of any value, it must be quite acidic, a condition which is not too favorable with the Wacker (could be wrong on this one, but I don't think so).
 
rev drone
Member   posted 08-05-99 06:17 PM          
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Os,
This is exactly what I wanted to discuss. To be honest, I can't say with certainty that it would work, but that's why I started this thread. I'd be very interested in hearing why EXACTLY you feel that nitrites wouldn't work without low pH's. Do you have any good information sources backing you on this?

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-the good reverend drone


 
Osmium
Member   posted 08-06-99 04:50 AM          
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No, but I have a ref which proves me wrong,  which is ok for me. And before anybody else does it, I'll post it myself.
JOC 1990, 55, 2924-27

A benzo-Wacker with added acids, like HClO4, HBF4, HNO3. Solvent aq. MeCN, yields >90%, finished in 10mins. 50 times faster than a comparable Wacker without added acids. So acids are indeed compatible with the wacker, at least with this one. They even speed it up! Only ten minutes to completion! Do it in a tubular reactor, and you have a continuous process for ketone production.


 
rev drone
Member   posted 08-06-99 06:15 AM          
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Os,
Wow! I suppose the acids do a nice job homogeneously regenerating the oxidized Pd species (Pd being the "least noble" of the precious metals, it doesn't hesitate to react with HNO3, or even HCl in the right conditions.)

One of the nice things about Pd catalysts is the very fact that, among the precious metals used as redox catalysts, its the only one that really stands up to acidic conditions and stil does its job. Off to the library I go!


rev drone
Member   posted 08-07-99 01:19 PM          
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Os,
How would you suggest engineering this into process?

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-the good reverend drone


 
rev drone
Member   posted 08-07-99 01:22 PM          
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Argh! That should read: "How would you suggest engineering this into a continuous process?"


rev drone
Member   posted 08-07-99 06:24 PM          
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Now here' the next question: are we looking at nitration as a side reaction? According to Rhodium, nitric acid, even without the presence of an activator like H2SO4, will nitrate the benzodioxole, as it is activated on its own, due to the electron dontation from the two oxygens. I'd like so see evidense of that, but maybe he has a point. I'll dig around my library, but somehow I feel this side reation can be kept to a minemum by keeping the concentrations of available NO2+ low.
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-the good reverend drone


 
Rhodium
Administrator   posted 08-08-99 10:04 AM          
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Perhaps I should add that the observation I referred to involved chilled concentrated nitric acid (compare the nitration of 2C-H to 2C-N in Pihkal). Just a little HNO3 or HNO2 in the solution probably won't nitrate the ring.
 
Osmium
Member   posted 08-09-99 05:57 AM          
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A long thin SS pipe, coiled up to conserve space, is used as the tubular reactor. The ingredients are continuously introduced, pushing the reaction mix slowly through the pipe. At the end, the now finished reaction is worked up batchwise, as usual, or with an improved procedure (flashing away the acetonitrile for reuse, flooding with water, extraction etc).
Drone, forget HNO3. It nitrates or activated benzenes instantly, that's what you learn in basic organic chemistry lectures. Or from the buddy in school who is into pyro/explosives.


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