dormouse (Member)
04-22-00 22:51
No 108680
      The Next Level: Nickel Oxide---> NiCL2 -spiceboy  Bookmark   


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Author  Topic:   The Next Level: Nickel Oxide---> NiCL2 
spiceboy
Member   posted 03-23-99 10:34 AM          
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Yesterday, I got a nice visit from a friend. She dropped off my nice, little pkg of Black Nickel Oxide she ordered for me thru mail-orde ceramic co.
Boy, this stuff is heavy.

It appears to be a fine, dense black dust.
I know that Nickel is in the same transition
metal family as our buddies Pd and Pt., has the +2, all good.

Took some garden variety muriatic(same kind I make CuCL2 with) and added it to the nickel oxide in a pyrex pan.

(Cough, Hack!)

Yeah, it's nasty. Apparently, the rxn goes;

NiO + 2HCL-----> NiCL2 + 2H2O

anyway, it turns emerald green ( like cucl2)
and goes to completion slower.

This is where I woke up.

The intent is to attempt an SRV with an assload of this stuff and CuCL2, just for shits-n-grins.

Any ideas,(c'mon,)?

Stay tuned.


Osmium
Member   posted 03-23-99 11:16 AM          
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Good luck!
(Although I don't think that it will work...  )
 
Piglet
Member   posted 03-23-99 11:46 AM          
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Maybe O2 stand's a chance? Or, at least, NiCl2 + PdCl2 (trace) + CuCl2?
 
spiceboy
Member   posted 03-23-99 01:54 PM          
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Oh, using O2, for sure.
No air.
The idea is to get the ooomph the O2 packs to
work for you rather than against. Perhaps piglets idea of mainly NiCL2 w/ CuCL2 and a trace of pdcl2 will run.....

I dunno, it might just work if you use a lot, and NiCL2 is VERY CHEAP TO MAKE. Over a pound for ~30.00$ amerikan...


Bright Star
Member   posted 03-23-99 03:20 PM          
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Sorry gentlemen.
Its not going to work. There is a quantum mechanical reason for it.

You see, the pi* antibonding orbitals are not big enough on the Ni+2 atom to overlap with the carbon pi orbitals.

And the Ni+2 isn't a good pi bond coordinational element. IE Is does not complex well with high electron density.

However, I do have several ideas for you spiceboy ... and an intimate knowledge of the mechanism.

Are you still at pagan spice?

But you know I invite you to prove me wrong. As a matter of fact .... PLEASE prove me wrong.


hellman
Member   posted 03-23-99 05:36 PM          
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Wouldn't it work, if you upgraded the nickle to w-2 raney?, the proceedure is somewhere around here or in vogels pract.
I hope it works,
Although stranger things have happened,.

Goodluck Spice!!!!!

Hellski!


rev drone
Member   posted 03-23-99 05:38 PM          
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Bright Star,
Just the person I wanted to talk to. Please, let's start discussing; I have a few ideas that I think you'll be very interested in. E-mail me drone342@hotmail.com , and let's get talking -- damn soon.

Still, this does bring up an interesting problem. If there are indeed quantum mechanical issues here, then why should Raney nickel be an effective catalyst for hydrogenation, where a similar complex intermediate exists?

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-the good reverend drone


 
The Cook
Member   posted 03-23-99 10:53 PM          
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I was thinking about that the other day, as I read over the patent for oxidizing toluene->benzaldehyde. It seems that Fe or Ag will oxidize at the 1-position when coupled with a copper salt. and Pd (what about Pt) oxidizes at the 2-. There has to be SOMETHING else that will fit in that gap.
Maybe isomerizing first would ease the transition from the platinum metals. Hmmmm.
-cook
 
Piglet
Member   posted 03-24-99 03:28 AM          
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TC: Interesting stuff.
My idea was that the Pd complex swaps with the Ni complex (freeing up the Pd) wuth the CuCl2 as the reoxidant for both?


Bright Star
Member   posted 03-24-99 10:33 AM          
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Well the only reason I know this, is that I just got done writing a paper on this particular reaction. I have never studied the Rainey-Nickel reaction ... but I'll look into it.
Its just an idea, but I'd think it takes less energy to move a hydride than an oxygen. Just a guess.

The Wacker:

1. It would work alot better with an equimolar amount of water in it. The Oxygen on the ketone comes from the water. The mechanism actually forms the enol, then it rearranges to the ketone.

2. A base is required. It would go alot faster if a 0.5 molar equivalent amount of Na2CO3 (or K2CO3) were added. NaOH might be a bit too stong ...

3. The Oxygen you put into it, is only there to complete this reaction:

2Pd(o) + 2CuCl2 + O2 -> 2PdCl2 + 2CuO

If Pd(o) is allowed to float about .. it isomerizes the olfin at an incredible rate. It can also polymerize at a slower rate.

Spiceboy- I actually tried the KRV reaction with Ni(OAc)2 many moons ago .... It didn't work ... but please post your findings. I'm very intersted.

Droney- Change your email! (but check it first)


spiceboy
Member   posted 03-25-99 09:49 AM          
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Well, y'know, it's strange you say it, but I have noticed success with added water to the
SRV/Wacker.
The ref says water is where the O comes from.
So, again, I agree.

What I am leaning towards believing is maybe Nickle as a third partner, a la Piglet.

Nickle will work in some form, but if I can't replace Pd, I probably won't dream it.


 
ChemHack
Member   posted 03-25-99 10:50 AM          
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enol ?
ketal ?

Huh? What is the mechanism here?

Is this one of those things where you might say:
"I could explain it to you but your head would explode!"

The Wackers are one of a very few Hive topics with more PRACTICAL guesses than THEORETICAL chemistry...

Where is Droney?


 
ChemHack
Member   posted 03-25-99 10:58 AM          
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Bright Star: Please tell more about the base requirement. You say that this will speed the reaction. Could there be oxygen availability issues in such an accelerated rxn?
Doesn't Osmium's explaination of this rxn directly contradict yours regarding the water? Is this ketal vs enol? I'm confused.


Bright Star
Member   posted 03-25-99 11:38 AM          
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With all due respect to Osmium, he must have been thinking of something else. This is not a flame, or an attempt to be 'The Man' ... it is meary a rehash of what I have learned. You know I love you Big O.
My aging inorganic prof showed me and several other 'interested parties' the whole mechanism for Wacker type oxidations. Its amazing what they'll tell you if you show genuine interest

Since I don't know how to post ChemDraw art ... just visualize it with me.

PdCl2 looses a Cl-, and a water molecule forms a loose connection to the Pd. PdCl-OH2 finds the olefin's double bond insolution. Pd's pi bonds and the double bonds pi* anti-bonding orbitals match up perfectly! This causes a quantum mechanical energy change that coaxes a pair of electrons into the pi* anti-bonding orbits that is shared between the Pd and the double bond. Now the double bond has a lack of electron density between the two carbons! The oxygen (on the water molecule) dives into the double bond because its two lone pairs fit perfectly in the gap. The double bond keeps the electrons, and reduces the Pd to Pd(o). The Pd(o) is ejected due to an abundance of electron density where it eventually finds the CuCl2 to complex with. A base comes in and steals the proton from the water, creating an enol. The enol rearranges to form the ketone.

The Oxygen is needed to grab the Pd(CuCl2) out of solution, creating PdCl2 and CuO in another oxidation reduction reaction. Thats O2's only purpose. However, you need to keep the O2 in there, because Pd(o) will isomerize the olefin (to iso-saf and a crazy polymer (that red shit)).

Have you noticed that the SRV contents after the rxn is a little acidic? H20 is a strong enough base to grab the extra proton and create H3O+.

Perhaps an equimolar amount of Na(OAc) would be better. Its my guess that the reaction stops prematurlly because the solution gets too acidic. Perhaps another base would be better ... something that sucks up the protons but doesn't contribute too strongly to the pH of the solution. The water in the first step could be repaced with an -OH, but making the solution REALLY basic would stop the reaction. Something VERY mild is needed. Or perhaps tossing a chip of NaOH in the solution at the 3rd, 6th, 9th, and 12th refills .... that actually sounds better.

Discussion?


Osmium
Member   posted 03-25-99 12:40 PM          
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In an alcoholic solution, without water present, the Pd will simply substitute the water with an alcohol, forming the ketal. When water is present, both reactions will take place, their respective rates depending (among other things) on concentration. Since the usual alcohol Wacker contains A LOT of alcohol, this reaction becomes independent on alcohol concentration. We are talking about a solvolysis reaction, right? That's why almost exclusively the ketal is formed, even when some water is present. Fact is: the alcoholic Wacker runs best (FASTEST!) with no water at all. Now the carbonyl oxygen comes from the solvent (alcohol, not water). Water only becomes important during the ketal hydrolysis during workup. When water is absent, the reaction will still work.
What your professor told you there was the classical, industrial Wacker (done in water), which works great for ethene--->acetaldehyde, but of course is useless for our needs.
And adding base to a Wacker is definitely a bad idea. There are several refs out there claiming that this reaction can be speeded up considerably by addition of acid, as long as it doesn't interfere with the complex formations.
 
ChemHack
Member   posted 03-25-99 12:42 PM          
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OK, let me preface this with a disclaimer that I know next to shit about what I'm about to say....
2(H2) + O2 --> 2(H2O) + HeatEnergy

2(H2O) + ElectricalEnergy --> 2(H2) + O2

So my little brain thinks that breaking up this water molecule will be an endothermic process, or at least require some energy to get going. But the Wacker seems exothermic rather than endothermic, especially bubble-gum-benzo variety.

Also, if water is being torn apart then 2 moles of H2 would be generated for 1 mol of O2 absorbed, right? This doesn't jive with the observation of an oxygen-filled SRV loosing pressure as the rxn progresses, it would gain pressure, no? Maybe that is what the H3O is all about?

I obviously couldn't theorize my way out of a wet paper sack so please don't laugh at me. I really WANT to understand this...


ChemHack
Member   posted 03-25-99 01:14 PM          
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Osmium: It is possible that you already answered this question with your "concentration" remark but here goes:
If 200ml of 95% ethanol is used in a SRV reaction of 50g safrole, there is about a 2:1 molar ratio of water to safrole and a >10:1 ratio of alcohol to safrole.

Is the catalyst more likely to complex the organic with alcohol or water?

It doesn't really matter in the end because they should both end up as ketone but it is interesting none-the-less...


sunlight
Member   posted 03-26-99 08:41 AM          
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Well, with all the respect with all you, good chemists, specially with you Bright Star, I want to try to clarify this topic.
The alcoholic wacker oxydation is, acording to the paper in JOC :
R-CH=CH2 +2CH3OH +PdCl2 -- > R-C2(CH3O)-CH3 +2HCl+ Pd
Pd + 2CuCl2 ------> PdCl2 + 2 CuCl
2CuCl + O2 +2HCl - --> 2CuCl2 +H2O
R-C2(CH3O)-CH3 +H2O ---> R-CO-CH3 +2CH3OH

Acording to that text only a few tenths of a percent of water is necessary to produce the hydrolisis of the ketal, and if more water is present the rxn runs slower, or even is inhibited.
And if you add a base, when the palladium is reduced to Pd(0) and HCl is formed, it will be formed a salt base+HCl, so no more HCl can dance in the rxn to recover the Pd, and it will end with no more product
It seems that Osmium is right.
And Osmium, are you absolutelly sure that stiring will not work ?


Bright Star
Member   posted 03-26-99 11:39 AM          
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Now it makes sense. I was having a real hard time visualizing the hydrolysis without water. Thanks sunlight!
Osmium is correct. I talked with said professor, and he lectured on the old industrial process. Although he made it sound universal ....

Well, back to the bench.


Osmium
Member   posted 03-26-99 12:02 PM          
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sunlight: actually no water at all is necessary for the ketal formation to proceed. This reaction will run in entirely anhydrous reactions, too. But for the ketal to hydrolyse, at least a stoichometric amount of water is necessary. It is best to do this hydrolysis after the reaction, during the workup (where it will proceed automatically), because water slows the alcoholic Wacker down, which is clearly stated in that JOC reference.
 
rev drone
Member   posted 03-26-99 05:01 PM          
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Sunlight,
I really have to disagree with your description of the mechanism. I don't have enough time right now to write up the whole thing, but I feel quite confidant in saying that your scenario is about 80% right, but with a few things quite off. First of all, the first step doesn't involve PdCl2 turning into PdClOH; it remains PdCl2. Your description of the overlapping is good, and that's what is essential, but where you describe water being involved, I'd make the arguement that that is where the oxidant would be involved, and that water doesn't play a role until considerably later, with its most important role being that in hydrolysis of the reagent; in other words, I'd say you're really close, but Osmium's comments are still quite valid, and I there's still much more to take into consideration. Otherwise, you did a great job, and many thanks for doing such.

Chemhack,

You're devling into thermodynamics here, and when it comes to redox reactions (of which you are asking), add the two half reactions, and if the number is zero, it can (theoretically) happen spontaneously, otherwise, it requires work (like electricity). I don't have time to elaborate, but I think that should be enough to get your brain juices flowing in the right direction. Good question.

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-the good reverend drone


 
sunlight
Member   posted 03-29-99 02:56 AM          
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Ufff, I'm not in conditions to argue with you about chemistry, you are chemists, I think really good chemists, professionals, and I'm a cooker, that's all. I have a basic knowledge of chemistry, enough to understand equations, recipes, mol ratios and so on, but not the mechanisms. What I have done is to copy exactly the equations and words of the JOC article of alcoholic oxydations of oleofins. And from my memory. I'll check again the article, but I trust my memory, I studied it seriously. And yes, if I play with this rxn, I'd do it in anhydrous conditions (except the water from CuCl2) and then I'd hydrolize it, just like with nitrites.
Anyway, from my condition of cooker, what is really important is that the honey is certainly good, and what I can make to cook it with less efforts, I like to cook but I like to dance, make love, meditate, and I have my job also... But I'm happy to lecture about this questions with you.
 
sunlight
Member   posted 03-29-99 03:07 AM          
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Lecture ? I don't know if that is the correct verb, I'm using a dictionary ... Well I'm happy to talk/comment/lecture/ with with you about these questions.
 
sunlight
Member   posted 03-30-99 02:25 AM          
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Yes, equations ar right. And may be a misundersunding, "a few thenths of a percent of water" means a > 99.5 % alcoholic solution, no water, just the water from CuCl2.2H2O.
 
rev drone
Member   posted 03-30-99 12:02 PM          
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Sunlight, Bright Star,
I should say preemptively, that my comments on the Wacker were actually directed to Bright Star, so I appologise for the confusion.

I guess it all comes back to one fact, and I hate to admit it: mechanisms are never proven. This is where the philosophical side of chemistry becomes evident. The best quote I ever read on this was from Collman's "Prinicples and Applications of of Organotransition Metal Chemistry"


quote:
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...However, the student should be aware, and the experienced chemist reminded, that a mechanism is never proven, but is only a hypothesis which best fits presently known experimental data."
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Now what does this mean? While mechanisms are quite useful, and great for predicting things, everything we know about them is essentially indirected percieved, and so all we can do is carefully piece the data together, and whatever image we come up with is the best we can do.

This isn't a discrediting of the value of studying and evaluating mechanisms; far from it. Its just a restatement that these paradigms that we create aren't necessarily "Truth" (it sounds lieka cop-out, but words like "truth" and "reality" are really more suited for religious discussions rather than science.)

The question is: who is right? Well, the answer here really is "well, everybody, sort of." The Wacker describes oxidation of terminal olefins with palladium catalysts, in all the variations. Soimetimes conditions are anhydrous, sometimes it isn't. Sometimes its been done in conjugation with cocatalysts and electrolysis, mothertimes not. Sometimes enol intermediates are isolatable, sometimes not. I've even seen examples of isolated intermediates with palladium sigma-bonded to the terminal carbon. In reality, there are a number of different routes this can go through, and completely different mechanisms can be reasonably rationalized for each of them.

Mechanisticly, from what I know of organometallic chemistry, I still think that a dimer complex is formed (following the 18-electron rule), where each palladium is pi-bonded (can't draw the right symbol) to the double bond through orbital overlapping, then the two palladium's are bridged by two chlorines (yes, chlorine bonded to two things at the same time!), with an additional chlorine dangling off each. The formula is Pd2Cl4(olefin)2. This much I think we can universally agree on.


The double bond is lengthened, weakened, and then various things can happen for the oxidation, including the reduction of the palladium metal (where the cocatalysts come into play, as well as possibly direct oxidation of palladium by the odixant being reasonable, as well as the thought that the palladium itself undergoes no redox reactions, but merely facilitates the oxidation, etc.) This is where debate can occur, and where it depends on the reagents and reaction conditions.

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-the good reverend drone


 
Bright Star
Member   posted 03-30-99 12:38 PM          
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Seems reasonable to me. Great in fact.
From this, my only hope is that, we as a community can improve the synthesis aspect of it. Osmium and my prof, mentioned that the water/Wacker is only really good for the oxidation of ethene (+98% yield). But what we all here want is an saf oxidation in a 98% yield. In alcohol? Water? Alcohol/water? Ratios? PdCl2? K2PdCl4? Pd(OAc)2?

Droney is completely correct. Unless someone can invent a microscope capable of following a pair of electrons (violation of Heisenberg's uncertianty ...) we'll never know about the true mechanism.

So all of us are essentially here for the same thing. And for me, All I ever wanted was an understanding of what was happening. heh. Good dreams ya'll.


dwarfer
Member   posted 03-31-99 03:18 PM          
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These latter synoptic posts are great: we guess, we try, we learn, we hypothesize, we create.
Our capacity to invent a paradigm translation of what really happens in the multi dimensional (more than the 3 we "intuit") world is highly limited. As intelligent or stupid as we are or aren't, compared to what it really takes to accurately talk about the macro or micro worlds, we are like a flea on an elephant describing Shakespeare.

Well, I'll discontinue my "rant", but it was nice following this interesting thread.

thanks
dwarfer


The Cook
Member   posted 04-06-99 11:04 AM          
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Or like a bee on an elephant....
What about other oxidation sources. Get rid of the O2 gas, and use H2O2 (gonna add water there), persulfate, etc.
Nickle Sulfate heptahydrate + Am. Persulfate + eugenol was not encouraging. (And it scored poorly on the iodoform test), but even if we're resigned to Pd, efficiency is still fun to tweak out..
-cook
 
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