Author Topic: Base-catalyzed polymerization of P2P  (Read 3773 times)

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Rhodium

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Base-catalyzed polymerization of P2P
« on: July 25, 2002, 11:31:00 AM »
Action of Solid Sodium Hydroxide on Phenylacetone JACS 75, 1134 (1952)

A mixture of phenylacetone (60 g., 0.448 mole) and sodium hydroxide (19.7 g., 0.49 mole) was stirred and heated at 90-100°C for 16 hours. A dark brown, viscous paste resulted. Upon working up the mixture in the usual manner, only 4.2 g. (7%) of the original phenylacetone, bp 95-98°C/14mmHg was recovered. The remainder of the product was an amber, viscous, non-distillable polymer.

Glossary: amber, viscous, non-distillable polymer = the dreaded red tar

Aurelius

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What
« Reply #1 on: July 25, 2002, 12:22:00 PM »
Hey Rhodium, why are you interested in polymerization of P2P?  (btw, is it reversible?)

Tricky

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Don't try this at home.
« Reply #2 on: July 25, 2002, 12:30:00 PM »
It's like most of typical examples of condensation of carbonil compounds in base...

IMHO, such experiments are Vandalism  :)  :)  :)


There's a hole in our soul that we fill with dope
And we're feeling fine.

lugh

  • Guest
Ketone Polymerization
« Reply #3 on: July 25, 2002, 12:32:00 PM »

Hey Rhodium, why are you interested in polymerization of P2P?  (btw, is it reversible?)


 
 


Because the same mechanism can probably occur with any methyl ketone, and any such polymerization is probably irreversible  :(


GC_MS

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polymerization
« Reply #4 on: July 25, 2002, 12:34:00 PM »
I don't think its purpose is to polymerize our beloved ketone, but to give a reference where they have tested the effects of NaOH on the ketone. Or in other words: too much NaOH will destroy your ketone  ;) .
I wonder if the polymerization is reversible as well, but for that, I'd need to know what kind of polymerization products are formed. Some of the Leuckart polymerization products for instance can be reversibly converted to your active amphetemine derivative, while others cannot.

Doped(TM) since 19.... euhm... a long time  :)

Aurelius

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Revisibility
« Reply #5 on: July 25, 2002, 12:49:00 PM »
aurelius was just curious as to whether is was possible- however, aurelius doesn't think that it is so because of the C-C bond formation.  if there was condensation with a heterocompound there would be inherent weaknesses in the product to give a target area for possible reverse rxns.

hest

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Aldolcondensation
« Reply #6 on: July 25, 2002, 12:55:00 PM »
It's an usual aldolcondensation, base and ketones is a big no no. (unles you are trying to remove methylethylketon from denaturated alcohol ;D )

goiterjoe

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NaOH will turn MDP2P into crap
« Reply #7 on: July 25, 2002, 06:37:00 PM »
NaOH and heat will turn MDP2P into crap, and this is very important to those bees out there using peracid techniques since the washes you perform are done with sodium hydroxide solutions.  I remember a while back I was washing some ketone and hadn't used enough DCM to properly solvate it.  The sodium hydroxide washes weren't separating out properly.  I had also ran out of distilled water to finish washing with, and was thinking "Fuck it, I'll just let the distillation get rid of the residual water."  There wasn't that much water left, maybe 10ml or so.  I distilled off the DCM, followed by the first small fraction of isosafrole that came over.  When I cranked up the heat to collect the ketone, it proceded to become more and more viscuous until I finally got frustrated with it and turned off the heat to see what was wrong.  Upon cooling, the liquid quickly turned into a tarry substance, and within a few minutes what was supposed to have been ~35g of ketone was now a solid dark red chunk at the bottom of my flask that took almost two days of soaking in Acetone to get rid of.  I was pissed about that one, and ever since then I always doubled the amount of DCM I used for solvating the ketone, made sure to let all my washes separate out completely, and always followed the NaOH washes with a water wash.

All paths are the same: they lead nowhere

Antoncho

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Re: It's an usual aldolcondensation, base and ...
« Reply #8 on: July 25, 2002, 07:19:00 PM »

It's an usual aldolcondensation, base and ketones is a big no no. (unles you are trying to remove methylethylketon from denaturated alcohol)




Which brings me sorta offtopic, but still..... Wouldn't one xpect an aromatic aldehyde (you know which one ;) ) to react with acetone, when a K2CO3/acetone methylation is performed?

Antoncho



Rhodium

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K2CO3 is not a strong enough base to enolize ...
« Reply #9 on: July 25, 2002, 09:36:00 PM »
K2CO3 is not a strong enough base to enolize acetone to any appreciable extent, and you shouldn't be using more base than needed to neutralize the phenol anyway.

(And, yes, the reason I posted the excerpt above was to show intentional scientific destruction of 50 grams of P2P...)

Jan1983

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dump question
« Reply #10 on: July 26, 2002, 12:34:00 AM »
one short question, is there any stuff to avoid a Polymerizing ? as Hydratropic Aldehyde / H2SO4 also builds polimerized P2P .. i think there could be much more P2P recovered when there where anything to avoid the polimerization.

comments welcome

Chemistry are not only the things that stink. :)

Barium

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Rhodium: A system of solid K2CO3, toluene and a ...
« Reply #11 on: July 26, 2002, 12:57:00 AM »
Rhodium:
A system of solid K2CO3, toluene and a PTC can show remakable basic properties. I´ve seen a posting here about that....Will try to find it again.

Rhodium

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Yes, I know PTC catalysts simulate very high pH ...
« Reply #12 on: July 26, 2002, 03:03:00 AM »
Yes, I know PTC catalysts simulate very high pH in some reactions. In this example however, the K2CO3 should be neutralized with the phenol, and as the reaction is run in acetone, no PTC is added.

Greensnake

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You are right, Antoncho
« Reply #13 on: July 26, 2002, 09:29:00 AM »
It is kinda recomended specifically for phenolaldehydes better to use alcohol instead of acetone. (my fault, brains do not work very well in summer  :-[  )This method was invented by Claisen guy (the same who dicowered C. kondensation and C. rearrangement)

lab_bitch

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The chemistry of ketone polymerization
« Reply #14 on: July 29, 2002, 08:07:00 AM »
This is the same polymerization that happens to your MDP-2-P when you distill it.  Because of the highly conjugated structure of the aldol condensation product, this polymerization is EXTREMELY energetically favorable.  If enough of the motherfucker join together, it forms one entirely conjugated molecule.  Talk about resonance stablility!  The only reason that ketone doesn't spontaneously polymerize is that the rate is too slow.  The reaction is constantly occuring, though, and that is why ketone degrades it left at room temperature.  At 220C, however, this reaction is fast enough to turn a flask of ketone into tarry crap within a few minutes.

Also, remember from you organic class that aldol condensations are catalyzed by acids and bases.  Therefore, if the pH of the ketone is not neutral, it will polymerize faster.  I have actually experienced this before.  If the extracts are not washed several times with distilled water or sodium bicarb soln, I end up with a lot of undistillable crap in the flask.  If I do the proper washes, only about 1% of the initial mass does not distill out.

Another thing that I have noticed, is that when washing ketone with strong enough base, or acid, a lot of crap falls out of solution.  I used to think "Great! I'm cleaning my ketone!"  Little did I know, I was actually destroying my ketone, and what I thought was being removed by that wash was actually being formed by the wash!  The moral of the story is NEVER, NEVER, NEVER expose ketone to extreme pH, ESPECIALLY if you plan to heat it up (i.e. distillation).  Simple distilled water and sodium bicarb washed are sufficient. 

I have one more point to make, which happens to be the most important one.  Remember how I said that acid catalyzes ketone polymerization?  Well guess what happens to be fairly acidic -- a wacker.  While your ketone is being made, it is being destroyed at a rate relatative to the pH of the rxn mixture.  This really doesn't amount to much, but there is something else that happens.  Ever wonder why wackers never go to completion?  According to equilibrium, it is an irreversible reaction, so it should.  The reason lies in the precipitated solid found at the end of a wacker that appears just as the rate of oxidation starts to slow down.  This precipitate is your catalyst; well kind of.  Palladium forms pi-allylic complexes with certain olefins that can be very stable.  One of these olefins is the dimer of MDP-2-P.  As ketone is created, is dimerizes via aldol condensation due to the low pH of the rxn and subsequently forms a complex with the catalyst, thus deactivating it and precipitating it.  The formation of this complex actually lowers the pH further, increasing the rate of dimerization and complex formation further; thus it is an autocatalytic process.

There are three solutions to this problem. 

1) The first, is to increase the rate of safrole oxidation, thus increasing yield.  This works b/c the dimerization/complexing occurs at a constant rate relative to pH and ketone concentration.  It is somewhat like a timebomb - you have so much time to make ketone before the catalyst is all gone.  The rate of dimerization, is proportional to the square of the ketone concentration, however, so once you build up a critical product concentration, the poisoning really kicks into high gear.  Ways that you can speed up the oxidation are be raisin pH, using more catalyst, and lowering free chloride concentration.  Another way to speed the rxn is to run it in methanol.  The lower the alcohol (and the higher the dielectric constant), the faster the rxn runs.

2) Slow down the dimerization/complexation.  This can be done in two ways.  One is to operate at a higher pH.  This can be tricky, though, as the catalyst reoxidation needs a low pH to occur.  The other way is to keep a low ketone concentration.  One way to do this would be to add enough water or glycol to the reaction mixture so that one a certain amount of ketone is soluble and the rest seperates out as a second phase.

3) Use an entirely different rxn mechanism.  Many researchers have used a Pd(NH3)4Cl2 catalyst at neutral pH to oxidize other olefins at about the same rate as the acidic wacker does.  In addition, selectivity is almost completely given to the methyl ketone (MDP-2-P) and isomerization is greatly inhibited.  This reaction looks very promising and needs further research for making MDP-2-P.

Currently, I am researching all of these topics and am trying different rxn parameters along with TLC analysis to determine optimum conditions.  Hopefully, I can come up with very good procedures for both the O2 and alkyl nitrite wackers soon.

SPISSHAK

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Thanks Lab-bitch
« Reply #15 on: July 31, 2002, 06:08:00 AM »
I admire your understanding of the wacker processes.
Very intelligent person you are.

SPISSHAK

  • Guest
Aldehydes ketones/ reactivity?
« Reply #16 on: August 05, 2002, 07:05:00 AM »
So in a non-regioselective wacker oxidation process I'm told that aldehydes are by-products.
I have a patent here I'm sure the subject has come up ad-nauseum about the formation of aldehydes in the wacker process.
Well in this patent they use additives to wacker oxidation systems like hydroquinone in catalytic amounts to inhibit aldhyde formation and notice a %20 increase in yeilds and a reduced impact of temperature on yeild.
So the theory here is that since aldehydes and ketones react via aldol condensation (or claisen can't remember) and aldehydes are more reactive species, I was thinking that the enhanced regioselectivity of this modification prevented the more reactive species (aldehydes) from being formed and retarded the catalyst deactivation that Lab-bitch was talking about.
Is this going in the right direction?
Another thing about the dilution of chloride ion concentration how does the cholide interfer with the rate?
Is this a consequence of pi complexing with Cl- ?
Does this hypothetical complex block the Pd(II) complex from being formed?
If so would just running a O2 wacker in a greater volume of methanol help to dilute things?

lab_bitch

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Chloride ion blocks the coordination sites on the ...
« Reply #17 on: August 05, 2002, 12:19:00 PM »
Chloride ion blocks the coordination sites on the palladium, so that less safrole can bind.  It is a competitive inhibitor, if you are familiar with enzyme chemistry.  Chloride is not a pi ligand, but a sigma ligand.  Safrole is a pi ligand.  Most likely, the ketone is more prone to polymerization than the aldehyde.  The enol tautomer of the ketone is much more stable than that of the aldehyde due to conjugation with the aromatic ring.  Since the rate of dimerization is proportional to the concentration of enol, the ketone would polymerize much faster.  In fact, it is possible that ketone exists mainly as the enol tautomer.

As far as diluting the wacker goes, it will give you better yields.  If the safrole concentration is not extremely low, the extensive rate of reaction (mol/s) is proportional to the amount of palladium in the rxn mixture.  Diluting does not change this.  Diluting does decrease the Cl- and H+ concentrations, which will increase the rxn rate up to a certain point.  If you dilute it too much, you may have trouble with the reoxidation of the catalyst.  Diluting the rxn definately slows down the rate of dimerization, since both the H+ and the ketone concentration is reduced.  The rate of dimerization is proportional to [H+][ketone]^2.  Since you are increasing the rate of conversion and reducing the rate of dimerization and catalyst deactivation, you will be able to process more safrole for a given amount of palladium.  It will take longer to go to completion if you add more safrole, but the deactivation will be slower, so you will have more rxn time available.

SPISSHAK

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My head is still spinning
« Reply #18 on: August 05, 2002, 12:32:00 PM »
From trying to understand that all but thank you Lab-bitch .
So since CuCl is only soluble in things like DMSO or DMF and CuCl2 has to be used in alcohol solvent-systems this presents a problem with having more CL- ions that coordinate
with the  catalyst.
I see anywhere from 3-6 parts being used with variable results.
What is the best proportion to use to recycle the  catalyst  without throwing too Many chloride ions into the system?

psychokitty

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Here's the PDF . . . buuuut????
« Reply #19 on: October 27, 2004, 04:50:00 PM »
Nowhere in the following PDF are there any experimental details regarding the base catalyzed aldol condesation/polymerization of P2P.  I think you listed the wrong citation information in your original post.

Preparation of Ketones and their Enol Esters by the Base-catalyzed Condensation of Acids and Acid Derivatives with Anhydrides
GRANT GILL SMITH
J.A.C.S. vol. 75, pp.1134-1137 (1953)



The condensation of phenylacetic acid with anhydrides in the presence of pyridine to produce benzyl ketones has been shown to be general for a number of aliphatic acid anhydrides, but not for aromatic acid anhydrides. Enol esters of the ketones were isolated as secondary products. Although condensation was slow with phenylacetic acid, the reaction rate was considerably increased by use of phenylacetic anhydride, phenylacetyl chloride or acids with more reactive a-hydrogens, such as fi-nitrophenylacetic acid. Under the same conditions ethyl phenylacetate and cinnamic acid did not condense.