So we did an experiment where we reacted: ferrocene + acetic anhydride to produc

Question

So we did an experiment where we reacted:

ferrocene + acetic anhydride to produce acetylferrocene

I cant seem to come up with an answer to the following question:

Suppose you found that your final product was contaminated with unreacted ferrocene. Propose at least one method you could use for purifying you acetylferrocene, assuming ferrocene was the only contaminant. Provide as much detail as you can about the procedure you propose to use (ex: solvents you would use for recrystallization, temperatures you would look for in distillation, etc.)

Explanation / Answer

To separate the acetylferrocene from ferrocene and 1,1-diacetylferrocene, prepare a column
using silica gel.* Use your experience with TLC to guide your solvent choice for column
chromatography – in making your choice you may wish to consider the different goals of
TLC and column chomatorgraphy. Discuss you plan with your TA prior to preparing the
column.
To obtain a well packed column, fill with the initial solvent or solvent mixture chosen
(hereafter referred to as “solvent “) to about 70% of the desired column height. Weigh out about
1.5 g of silica gel in a 25 mL beaker, and prepare a slurry of the silica gel by adding a small amount
of the chosen solvent and swirling. Add the slurry through a funnel to the solvent in the column
until a column of 9 cm is obtained. In the course of adding the slurry it may be necessary to drain
some solvent from the column by opening the stopcock and to add more solvent to the silica gel in
the beaker. Do not allow the solvent level in the column to fall below the level of the silica gel.
Wash down any silica gel adhering to the sides of the column with additional portions of solvent.
Apply a 0.5 cm layer of sand to the top of the column to protect the surface of the adsorbent. Drain
the column to a point midway through the top sand layer.
To apply the sample, dissolve the dry crude product22 in as small a volume of ether as
possible (less than 1-2 mL). Apply it to the walls of the column with a disposable pipet. Wash
down any solution adhering to the sides of the column with a small (<1 mL) aliquot of the chosen
solvent system delivered from a disposable pipet. By alternately draining a small amount of
solvent from the column and adding more to the top, the sample may be washed from the layer of
sand onto the top of the adsorbent. Open the stopcock and add solvent cautiously to avoid
disturbing the top layer of sand and adsorbent.
Colored bands should appear as one species is eluted down the column more readily than
the other(s). Collect the eluant containing the first colored species in a tared 25 mL round bottom
flask. If necessary, add more solvent to complete the elution. Once the first band has been eluted,
you may wish to adjust the solvent system to favor the elution of subsequent bands. Collect each
colored eluant in a separate tared round bottom. You should have the same number of colored
fractions as spots on the original TLC plates.
Check the colored fractions by thin-layer chromatography to verify that each contains a
single component. Evaporate the solvent from each colored fraction with a rotary evaporator.
Determine the weight of each component and verify its identity by melting point. If the component
is not of satisfactory purity, it should be recrystallized. Acetyl ferrocene may be recrystallized
from hexane, diacetylferrocene from chloroform*-hexane.

or

To separate the acetylferrocene from ferrocene (and 1,1-diacetylferrocene if
present), prepare a column of acid washed alumina.* Clamp the empty column in a
vertical position. Note: Because this column has a built-in frit, unlike standard-scale
columns, it is not necessary to tamp down a plug of glass wool and add sand on top of it,
before adding alumina.
Add about 4 cm of the acid washed alumina (which has been previously dried in a
100 °C oven for at least 24 hours). Tap the column gently to pack down the alumina.
Add 5 mm sand on the top of the alumina.
Apply the crude acetylation product to the column using the “dry-loading”.
Dissolve the entire dry acetylation product in a minimum of methylene chloride (just a
few drops) in an Erlenmeyer flask. Add about 50 mg of dry alumina and stir. In the
hood evaporate the solvent completely until a fine, smooth flowing powder remains. Add
this powder to the top of the column. Apply a 3 mm layer of sand to the top of the
column. Add the solvent system chosen by TLC cautiously to avoid disturbing the sand;
allowing it to pickup any particles adhered to the wall of pipet (Note: The upper fitting
serves as solvent reservoir). Collect the eluant containing the first colored component in
a weighed 10 mL Erlenmeyer flask. Change flasks and collect the second colored
component in a second weighed 10 mL Erlenmeyer flask. (Note: the solvent coming off
the column which does not contain colored product may be collected separately from the
colored products). Be careful not to permit the column to go dry during this process.
Expect to remove the same number of fractions, as the number of colored spots observed
moving on the TLC plate. (Note: With this synthesis diacetylferrocene, if present at all,
will likely be present in such small amounts that it cannot be recovered from the column).
Check the colored fractions by thin-layer chromatography to verify that each
contains a single component. Evaporate the solvents in the hood using a very gentle
airflow. Dry the crystals in your desk until the next lab session.

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.