Bobber
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Wilkinson's Catalyst- Experience?
Hi everyone,
My research supervisor is... well, not personable. Some, including myself, have called him other names that i wont mention here.
The reason i'm asking this here is that he is of absolutely NO help with anything practical.
I have a reaction coming up that involves Wilkinson's catalyst refluxed in methanol (under Ar) for a catalytic rearrangement. Looking at the reaction
mechanism for the catalyst, it seems that phenylphosphine is released as a byproduct.
Could anyone share their experience with this catalyst including necessary real-world (i.e. not MSDS) safety precautions, disposal, etc.
Any help is much appreciated- i swear this guy is trying to kill his research group.
Cheers,
Bob
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Arrhenius
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Here's some advice. Call your research advisor all the names you want, but he's the one paying for you to learn chemistry. If he isn't helping you,
don't cry about it, take some initiative and invest time in teaching yourself.
This catalyst is totally benign. Won't catch fire, won't do anything exciting except be rather expensive. It's a fairly weak hydrogenation catalyst
compared to palladium on charcoal, but it's homogeneous. Throw it away however you dispose of other metal compounds.
There should be no triphenylphosphine released, though it may be eliminated and then substituted back in to release the product and the catalyst
again. You must get out the same molecule at the end of the reaction, or it won't be catalytic.
That being said, no one will offer you any help with a post that vague. What reaction are you doing? Or is it top secret?... Draw it up in ChemDraw
and upload it.
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JohnWW
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Wilkinson's catalyst is the common name for chlorotris(triphenylphosphine)rhodium(I), a chemical compound with the formula RhCl(PPh3)3 (Ph = phenyl),
a square planar complex. It is named after the late organometallic chemist and 1973 Nobel Laureate, Sir Geoffrey Wilkinson who popularized its use. A
good summary of it is given on http://en.wikipedia.org/wiki/Wilkinson%27s_catalyst .
It is made as red-violet crystals by reacting RhCl3 with an excess of triphenylphosphine (some of which is oxidized), but it would be quite expensive.
Its main use is hydrogenation of alkenes to alkanes, in the course of which one of the triphenyl groups is lost, and two H atoms are bonded to the Rh,
resulting in a trigonal-bipyramid intermediate complex which then gives up its H atoms to the alkene.
It does not appear to be advantageous for catalyzing hydrogenation compared to Pd or Raney Ni on charcoal or Pt or some other transition metals
(heterogenous), although it can be used as a solvent-based catalyst for other reactions such as hydroboration. If you want it only for hydrogenation,
Pd would be the best option, or more cheaply Raney Ni although that would probably require increased pressure to be as efficient.
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Nicodem
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Quote: Originally posted by Bobber  | Hi everyone,
My research supervisor is... well, not personable. Some, including myself, have called him other names that i wont mention here.
The reason i'm asking this here is that he is of absolutely NO help with anything practical. |
I have to agree with Arrhenius on this. You should not expect from supervisors to be reasonable and helpful (other than financially). Useful
supervisors are more of an exception than a rule. You should understand that he is most probably clueless about the chemistry you do (or any other
chemistry) and he lost touch with the lab reality long ago, so he could not help you even if he wanted to. The only person you should rely on is
yourself - you shouldn't even blindly trust the literature. His resentment and feelings of impotency might have made his personality unbearable as is
usually common in such cases (I think this phenomena is called "being an asshole" in English), but you should fight him with dignity nevertheless, or
he will drag you at his level and you will hardly ever recover.
Anyway, like Arrhenius told you, there is nothing special in regard to Wilkinson's catalyst. Once in solution it should not be exposed to air oxygen
or else the Ph3P ligand gets slowly oxidized. If you use lot's of it, you might spare the celite (or SiO2) you will use in the work up to remove the
catalyst. Otherwise, if you are not interested in rhodium recovery, just throw it in the solid waste chemicals bin.
…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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