Today: Exp.6: Column Chromatography: The Separation of Ferrocene and Acetyl Ferrocene

Midterm next Friday in your lab!

starting at the beginning of your lab session 5 Problem Sets (Total 100 pts.) The exam will include today’s Exp. 6 material Review/study lab lectures, practice questions, experiments, calculations, graphs.

Do sample Midterm questions in ERES file

Midterm Rules:

Cell phones off and in your pack.

Do

bring a calculator, but not a "computer". No sharing ...

Do not leave the room during the exam.

No extra note paper; use back of pages if necessary.

Please no questions during exam (unless you discover a serious mistake). You can write: "if I understand the question this way ..." No "late" exams... A midterm not taken earns the grade "F".

Read questions carefully.

Proofread….

Exp.6: Column Chromatography: The Separation of Ferrocene and Acetyl Ferrocene (omit UV/VIS analysis)

CH 3

O

Fe Fe Ferrocene Acetylferrocene

1) Comment on the polarity of these two compounds.

2) Ferrrocene and Acetylferrocene are metal organic compounds. Do you know other metal organic compounds? Are there any in nature??

3) What is the color of ferrocene? Of acetyl ferrocene? What features in their molecules lead to absorption of light within the visible range (colored!).

Exp.6: Column Chromatography: The Separation of Ferrocene and Acetyl Ferrocene O

CH 3 Fe Fe Ferrocene Acetylferrocene

Cyclopentadienyl anion it aromatic?

is “aromatic”.

What makes

Column Chromatography

followed by Thin Layer Chromatography (TLC)

What is common to all methods of chromatography?

In our experiment: Stationary phase: Alumina III Moving phase: Pet. Ether. Later: 50/50 mixture pet. ether/diethyl ether

Column Chromatography

Setting up the micro-scale Column Chromatography (CC)

Procedure:

1. Assemble column . Check flow through the frit by using petroleum ether. Then bring the pet ether volume to a height of ¾ the column.

2. Slowly add Alumina powder. Goal is to have uniform packing. Do not let the top of the column packing go dry. 3. Add ~1 cm of sand after the column settled. (What could be the purpose of doing this?)

Alumina Stationary Phase Funnel

Column Chromatography Set up Tare

Separation of your mixture by CC

Save a small amount of unknown sample in the original vial for TLC.

1. Dissolve the weighed unknown in minimum of methylene chloride 2. Start pet ether flow through column and stop when solvent is just barely above the sand. Gently add your unknown sample with a pipette along the wall of the column 3. Elute ferrocene with petroleum ether (Do Not let the column go dry). Collect the

yellow

ferrocene band in a tared 50-mL E-flask.

4. To collect acetyl ferrocene, switch to a new tared 50-mL E-flask, add 50/50 petroleum ether/diethyl ether to column and start eluting the

orange

band of acetylferrocene.

5. Slowly evaporate the solvents in each of the E-flask on a steam cone or a sand bath.

Weigh

residues!

Evaluation of samples by Thin Layer Chromatography (TLC)

TLC plate (Silica is the stationary phase) 0.5 cm from top 1 cm from bottom

. .

Mix Fe

.

origin Ac Lightly mark with pencil, then spot samples

TLC Developing Jar TLC eluent (moving phase!) : (30:1) toluene/absolute ethanol Make sure that eluent level is

below

the spots Allow moving phase run up the plate to top line (NOT to top

edge

!), then remove TLC

Mark solvent front with pencil immediately after removing from developing chamber. Dry TLC and draw a circle around each spot.

TLC plate showing good separation:

solvent front origin

Calculate R

f

–values for each spot

Where would you find the spot of a sample with an R f value of 0.1, of 0.5, of 0.9?

How about an R f -value of 1.3 ????

A

. .

.

B

R f

=

A B

ACS Family Science Night Willard Middle School in Berkeley Thursday, Oct. 26, 6:30 – 8:30 pm

• • See also FSN link on my Home Page http://userwww.sfsu.edu/~msequin/

What would you do?

Help set up experiments Help middle school students (and their parents) do the experiments What would you get?

•

experience in working with youngsters and showing them the fun of science

•

a nice entry on your resume

•

a good impression with your instructor!

Next Friday Lab Lecture: Your questions….

Remaining Experiments: Exp.8, “Dehydration of 2-Butanol”; GC Exp.9, “Separation and Identification of an Unknown Mixture” (3 lab periods); IR, recryst., mp.s and other techniques you learnt this semester