posted on Jan, 17 2006 @ 12:32 PM
This past semester, I replaced my Advanced Senior Inorganic Chemistry Lab by working in the professor's laboratory. I worked under a graduate student
on her project, and I got the job of synthesizing some cobaltocene for her. I'm posting this in case anyone has to do a project in school and wants
Keep in mind that after the first step, none of your chemicals are allowed to be in contact with air or water (unless you desire to have fewer
fingers/eyes than you currently have), so everything you do is enclosed in air-tight glassware filled with N2 gas. You will need to learn how to work
a Schlenck Line and have access to a Dry Lab (you know... the funny looking glass box with gloves you can reach through with).
Background about Cobaltocene:
Cobaltocene is a metallocene like ferrocene, in that it is a metal atom sandwiched between two 5-membered carbon rings. The carbon rings are missing a
hydrogen atom each, thus giving each of them a (1-) charge. The central metal atom takes a (2+) charge. For iron, this gives it an 18 electron count.
If you have taken Inorganic Chemistry, this is the happy number of the 18-electron rule. However, cobalt has 19 electrons in this configuration, and
is prone to ejecting an electron to get down to 18 electrons, and would carry a (3+) if this happens, giving the entire molecule a (1+) charge. It in
turn would pick up a counterion to balance the charge.
Cobaltocene has been found to be a useful reactant with fluorocarbons (the most inert compounds created by man). One example is the reaction of
cobaltocene with perfluorodecalin to form perfluoronaphthalene.
Na = Sodium
CP = cyclopentadiene ( C5H6 )
diCP = dicyclopentadiene
NaCP = sodium cyclopentadieneide ( Na+ )( C5H5- )
CoCP2 = cobaltocene ( bis(eta-C5H5)cobalt(II) )
N2 = nitrogen gas
H2 = hydrogen gas
Cut 5.0 g Na into 200 mL diCP (degased)
Reflux and stir in 500 mL RB flask w/ schlenck at 160 C for 5 hours under N2
During this time, diCP will "crack" into monomeric CP.
Na will react with CP to made NaCP and H2.
2Na + 2CP -> NaCP + H2
Transfer NaCP to Schlenck Frit w/ attached 250 mL RB flask w/ Schlenck.
Wash 2x with 50 mL pentane.
Transfer 100 mL THF to 15.0 g NaCP in an RB flask w/ Schlenck ON ICE, and 50 mL THF to 7.5 g CoCl2 in another RB flask w/ Schlenck, with a stir bar in
Allow both to reach room temperature (1/2 to 1 hour).
Inject CoCl2 solution into NaCP solution (will turn black).
Reflux and stir on LOW heat for 15-20 hours.
Remove THF under reduced pressure. Wash solution w/ pentane if needed.
Scrape away black solid from walls of flask.
Sublimate black solid on small sublimator for 15 hours at 85 C.
Beautiful purple prismatic crystals will form on the cold finger in the sublimator. That is your cobaltocene. Make sure that you don't expose it to
air, or it will catch on fire.
The experiment is one big fat pain in the behind, but you will learn a lot, especially as far as methodology is concerned. I can post my report if
anyone so desires. It's about 4 pages, and focuses primarily on methodology.
[edit on 17-1-2006 by Ralph_The_Wonder_Llama]