turd
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K(acac)
Howdy, any acetylacetonate experts here?
I want to make dry K(acac) and followed the method of Ger.Pat. 2402399: 7.8g KOH in 5.7g H2O was slowly added to 12.6g acetylacetone in 30 ml acetone.
Temperature stayed below 15°C. Stirred for 2h, filtered, washed with 50ml acetone, got a white crystalline powder (yellow mother liquor).
Now the patent says to dry it at 60-100°C under vacuum. Do I have to? I don't want to let the aspirator run for hours. Does the oxygen oxidise it?
The CO2 displace the acac? Does it not get sufficiently dry at 1 bar?
And can I store it or is it unstable?
Thanks..
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Dr. Beaker
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I'm not really familiar with the K organometallics, but if you want to keep your acac complex clean you should keep it in inert conditions: it will be
protonated by water, slowly giving of acetylacetone, which will slowly evaporate and thus favor hydrolysis.
I also doubt you'll be able to get read of water so easily, since they are coordinated to K. I made (acac)Li*TMEDA by reacting dry H-acac with BuLi
and adding TMEDA. I think you should make your reaction under inert conditions in the 1st place. you can react H-acac with KH or KCH2C6H5 or even KCP
(if the 2 later exists, since I'm quit sure alkyl-K are not stable). unless it is harmfull to your next step I'd advise to add a complexing reagent
such as TMEDA or 1,2 dimethoxyethane. that way you can get an easily soluble and crystalizable mononuclear complex.
[Edited on 2-1-2007 by Dr. Beaker]
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turd
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Thanks, I gather from you post that acetylacetonates are rather "bitchy". :/ It's probably a good idea to make them right before use. Unfortunately I
don't have potassium hydride or other organyls.
I tried to dry the powder on a hotplate set to 100°C and it showed signs of decomposition at the hotplate/powder interface. Next time I'll use an
oilbath or maybe azeotropic distillation with toluene...
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Sauron
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How about a vacuum dessicator over something aggressive like P2O5?
You'd only have to pump the dessicator down periodically. I would suggest using a mechanical pump rather than an aspirator. If you must use an
aspirator, put a drying tube between it and the dessicator.
A recirculating aspirator would have the advantage of not wasting all that water. I've got a Japanese one with a vacuum gauge and a cooling coil for
the water. I plumb it inline with the recirculating chiller for the condenser(s) and that way the water reservoir stays cold and maximizes the vacuum.
Or just add some ice to the reservoir from time to time. However this requires that you have a recepticle for overflow.
The other way the level stays constant.
The cooline coils were locally made and are of plated copper tubing. The plating will resist halogen acids that accumulate in the water if I am
running reactions that offgas HCl, HBr etc. Eventually they will get eaten but they are cheap enough that this is not a headache, I have them made 2
at a time so when one goes I just order two more.
I suppose tossing the water is an option, or neutralizing the HX. Don't want to corrode the aspitatots themselves, there are two of them inside.
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Sauron
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Also the hassle with KOH is that you'd better start with a fresh bottle or you will have some potassium carbonate in there.
Which at the minimum will lower your yield.
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Ramiel
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Yea, and trying to keep KOH anhydrous.... well, snowball in hell is what comes to mind.
I've never tried with Li/K/Na acac. but my experience with the transition metals is you need all your reagents impeccably dry to get good yields. If
you've managed this, you take a lot of labour out of drying.
Like I said I've never tried Potassium acac. But I Imagine proper drying will require a dry atmosphere like Sauron says.
Storing acac is a bit of a hassle, we usually just make them when we need them in the lab. I've heard of people ordering them in, but those special
ones like Cu(I) require completely inert conditions, any CO<sub>2</sub>, H<sub>2</sub>O <i>etc.</i> and you can
kiss a pure sample goodbye.
Caveat Orator
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Sauron
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If you can't afford a glove box, or aren't handy enough to build one like the one described in a J.Chem.Ed. article that used to be posted on
rhodium/the hive, a low cost alternative is a dry bag. I think Aldrich sells "atmos-bags". You will still need a N2 r Ar tank (or lecture bottle) but
this way you can ensure your KOH is dry and carbonate free. Buy small bottles of the purest grade you can find and afford. Select sizes that fit the
scale you will work on. Don't use any leftovers at least not for this K(acac) prep. You can pool leftovers and use them in less demanding
applications.
Anhydrous conditions and reagents and inert atmosphere are hradly uncommon requirements in synthetic work. If you keep an eye peeled on LabX sometimes
you can get a bargain on a used glove box. The one I got was only $300, it cost me that much again to truck it to SF CA from KC MO and cost me lots
more to ship it by ocean to Thailand. But, it works, the seals are good, the light fixure and electricals are OK, it's 110 V so I fun it on a
transformer here, stepdown from 220. Maybe I have $1300 in it, not counting a new $400 pair of gauntlets and O-rings. But new, this is a $5-10,000
Labconco product. Door with toggles and an airlock. Plexiglass window about 1/2" thick. Weighs about 230 lbs. Not bad for $300.
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Rosco Bodine
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Just a note here on dessicants ....
and it is one of my long established pet peeves
concerning lab methods that it is virtually never mentioned , what is possibly the most aggressive
dessicant that is easily and cheaply available .....
*aluminum amalgam*
If you want absolutely *dry* , deoxygenated air ,
and a bit of byproduct hydrogen atmosphere which
is itself extremely dessicating , is no problem ....
then try some pieces of aluminum which have been
amalgamated with mercuric chloride , placed beneath the peforated plate in a petri dish , for a dessicant . The
alumina which comes off as a byproduct is also a dessicant . I don't know exactly what would be the ultimate pulldown of moisture and oxygen from
the
chemical reaction with the amalgamated aluminum .....
but i would bet it is favorably comparable with about anything else that will be found useful as a dessicant ,
and probably a good bit better than many common
dessicants which are way more expensive , and require
baking out to recycle .
Probably if you combined a preliminary dessication , followed up by an evacuation of the dessicant chamber
containing some aluminum amalgam and just lock it down
tight for a few days ....you have about as close to space
vacuum as you are going to ever need without resorting
to more expensive dessicants like metallic sodium , or P2O5 and the like .
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Dr. Beaker
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do you have access to K metal?
if so I've some crazy idea.. to use a direct metalation:
K + H-acac ----> K(acac) +1/2 H2
if K can react with alcohols then it probably can react with acac which is much more acidic. you should try it in small scale 1st to avoid runaway
reaction.
if, on the other hand, the reaction is slow or NR then try to add complexing reagents like ether THF or TMEDA. you can also heat it to K's m.p (about
60 I think) + stirring.
all solvents and equipment should be dry offcourse
the nice thing with this methode is that K will also eat up any CO2 H2O or O2 remaining in your starting materials.
[Edited on 2-1-2007 by Dr. Beaker]
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Nick F
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Yes, K will eat up any H2O etc in your starting materials, and leave them in your product...
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Dr. Beaker
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I guess recrystalization is not foriegn to any serious member here...
you rarely complete a reaction by mixing A+B. seperation and cleaning are many times the major obsticle.
and there some bizzar thing about acac... it somehow has such a large affinity to iron that it can disolve it, in pH of 5-6 (tap water in air). We use
acac to quench alkyl Al compounds (by creating Al(acac)3 which is soluble in acetone\methanol).
I once stirred such mixture of H-acac+ Al(acac)3+water and after 1 day to my surprise the solution turned orange (the Al complex is colorless). I then
realized that I used an old stirrer bar that lost parts of its teflon coating, so iron was exposed.
this solution later on gave very large (about 1/2 cm!) perfect hexagon plates shaped red crystals.
[Edited on 3-1-2007 by Dr. Beaker]
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turd
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Ummm... Maybe y'all going a bit over the top... 
K(acac) is not very moisture sensitive:
Patent DE2402399: K(acac) from acetone and KOH(aq).
Patent US20040127690: K(acac) from KOH(aq)
Bull. Chem. Soc. Jpn., 54, 207-211(1981): K(acac) from MeOH:H2O 1:1
Using dry KOH seems a bit excessive, since water is generated during the reaction anyway. I'm sure elemental K would work, but local overheating and
double deprotonation could be a problem.
As has been noted carbonates can be removed by recrystalisation.
I tried to dry another batch on a 95°C oil bath, but after 8h it clearly starts to darken. I will make an IR to see if it picked up notable amounts
of CO2.
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Nick F
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"I guess recrystalization is not foriegn to any serious member here...
you rarely complete a reaction by mixing A+B. seperation and cleaning are many times the major obsticle."
So if you're going to recrystalise to remove hydroxides etc anyway, why bother to use metallic potassium?
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Dr. Beaker
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it all depend on what the Kacac will be used for.
If you need it, for instance, as a ligand carier to transfer it to, say, early transition metals/lanthanides/actinides then why enter "hydro-oxic
acid" to your system in the 1st place?
if it is needed to some organic prep. that doesn't need ultradry cond. then, as posted here there are many aquos preps.
[Edited on 3-1-2007 by Dr. Beaker]
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turd
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Heh, sorry, with dry I didn't mean free of any traces of water, just that I don't want hydrates.
I don't have the equipment for working in ultra-dry conditions anyway. Ok, maybe with some improvisation, but being used to standard Schlenk
techniques, I just can't bother. In my private lab I just work with drying tubes and drying the glassware with a heat gun. This is enough for
grignards, but of course not for most other metal-organics.
Anyway, this acac-chemistry seems interesting. So far the only time I used it was to reduce the reactivity of alkoxides.
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ferrocene
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Acacs are pretty easy to do. I remember a number of preps from old Inorganic Syntheses, but don't have them on hand.
Drying under vacuum doesn't require that the aspirator be on all the time. In fact, that's counter-productive, as water can diffuse back into your
system from the aspirator. If you have a vacuum desiccator, pull a vacuum then seal it. The vacuum helps the desiccant work much faster.
To further purify the Kacac, try sublimation.
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guy
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How efficient is the condensation of acetone and ethyl acetate using a base catalyst? It gives the acac salt right away.
Wikipedia
| Quote: | The second synthesis involves the base-catalyzed condensation of acetone and ethyl acetate,
NaOEt + EtO2CCH3 + CH3C(O)CH3 → NaCH3C(O)CHC(O)CH3 + 2 EtOH
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From Vogel
| Quote: | All moisture must be excluded during
the preparation in order to avoid the formation of sodium hydroxide,
which markedly lowers the yield. Return the condenser to the reflux
position and add 800 ml. of pure, dry ethyl acetate (3) through the
dropping funnel to the warm solid sodium ethoxide as rapidly as
possible. Start the stirrer immediately and add at once 116 g. (147 ml.)
of pure dry acetone during about 15 minutes ; if the mixture does not
reflux, warm gently on a water bath. After about half of the acetone
has been introduced, the mixture generally sets to a solid mass and
mechanical stirring is impossible ; turn the stirrer by hand and continue
the addition of the acetone. In a few minutes the mass can again be
stirred mechanically. During the addition of the acetone, the solution
acquires a red colour and eventually the mixture turns brown. Reflux
the mixture for 1 hour : stop the stirrer and allow to stand for 12 hours,
during which time crystals of the sodium salt separate. |
[Edited on 1/6/2007 by guy]
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reckless explosive
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Sorry to bump an old thread but does anyone know if the above reaction would actually work? If i can make some dry acetone, ethyl acetate, and sodium
ethoxide i wouldnt mind trying this on a small scale but i wanna get the acac in pure form and the wikipedia mentions acidifying with HCl to produce
the acac and sodium chloride would this mean HCl is to be bubbled through or an equimolar solution of hydrchloric acid was to be added? Also could the
acac and water be simply distilled apart or is an azeotrope between it and water from?
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Nicodem
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If it works, then the procedure is in the literature, so the obvious solution is to find the reference.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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