Acetyl Ferrocene (shown below) is an aromatic organometallic compound that can b
ID: 954899 • Letter: A
Question
Acetyl Ferrocene (shown below) is an aromatic organometallic compound that can be prepared
using the reaction scheme shown below. Often time in this reaction two products form, acetyl
ferrocene and diacetyl ferrocene. If a scientist wanted to synthesize in lab acetyl ferrocene using
this reaction a purification technique such as column chromatography is usually employed to
purify and isolate the desired product. The column chromatography typically used has alumina
as the stationary phase and the mobile phase used has a gradient. First 100% hexanes is used to
elute the first band then the mobile phase is changed to 50/50 mixture of dichloromethane and
hexanes to elute the two remaining bands.
1. Assuming the reaction did not go to completion and starting material is present in
addition to the two product, which fraction should the scientist keep if the desired
compound is acetyl ferrocene? Explain your answer. (4 pts)
2. What would be the consequence of starting the experiment with 50/50 mixture of
dichloromethane and hexanes rather than 100% hexanes? (4 pts)
3. In our column chromatography of spinach most students obtain three or four bands.
However, a TLC of the same spinach extract can yield up to 7 spots on the TLC. Explain
why one can not isolate the same number of bands from the column as there are on the
TLC? (6 pts)
4. How would you need to adjust the column chromatography experiment in order to isolate
all the bands that are visible on the TLC? (2 pts)
Thank you.
Fe Fe Fe CI AlCl3 catalyst Ferrocene Acetyl ferrocene Diacetyl ferroceneExplanation / Answer
1)If you'd like to keep the acetyl-ferrocene, it is going to be in the second fractio, since first you are eluting with an apolar solvent, most probobla you are going to remove the starting materil since it hass less (or non) polar groups, the compound you are looking has one actyl,thus is more polar and less compatible with hexane.
2) That would be a disaster beacuse whe you elute with the mixture, you are going to elute everything together, since the dichloromethane has affinity for both acyl compunds and hexane for the starting material, hence there will be few space for them to separate.
3) in TLC you use really small sample, thus the plate is enough distance for all (or most of them) the components to separate; the column uses more sample, hence more to separate, the elution usually is faster, again if it moves faster you are reducing the chances to separate, and also the distance traveled in the column compared to the amount of sample is not enough space to separate.
4) most probable to separate 7 components you will need a larger column, and also a gradient in the solvent could help.