CHEM 351
INTRODUCTORY MODULE IN EXPERIMENTAL CHEMISTRY
CHEM 351 INTRODUCTORY MODULE IN EXPERIMENTAL
CHEM Credits 1.00 Fall 00
- Experiments illustrating techniques in
synthetic inorganic chemistry and instrumental methods of
analysis. Required for chemistry majors. Taught in the first half
of the semester.
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- Freshmen may take the course with
permission from instructor.
Prereq-CHEM 121 AND 122, 151 AND 152 or
permission of intsructor
BH Rm. 280 01:00 PM - 5:00 PM Instructor:
Andrew R. Barron
Introductory
Laboratory Module
Syllabus
Instructor:
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Andrew R. Barron
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Office:
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Butcher Hall 410, Ext. 5610
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Email Address:
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arb@rice.edu
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Office Hours by Appointment
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Teaching Assistants:
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Chris Edwards, BH410, ext. 3456,
chrised@rice.edu
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Jake Ciszek, Room #GRB 213E,
ciszek@ruf.rice.edu
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Grading:
The course grade is based upon the performance
in the laboratory. This includes attendance (10%), preparation (10%),
actual experimental skills developed (10%), results (20%) and the
laboratory notebook (50%). You will work in pairs, but you should
each keep a completely independent notebook. In addition, I will rely
heavily on the opinions of the teaching assistants and my own
observations of your work in order to assess your progress in the
course. Your lab notebooks will be due by 5 PM, Friday, October 29;
late notebooks will be penalized 3% per weekday late. It is
recommended that you keep your lab notebook in your lab desk drawer
to prevent loss.
Safety:
You must at all times were safety glasses and
you must follow reasonable safety precautions when working in the
lab!!! Failure to abide by the safety regulations could get you
kicked out of the lab. This is an extremely serious issue with dire
consequences to health and safety of yourself and your colleagues.
Wearing a lab coat or apron is recommended but not required. Specific
safety precautions concerning the use of hazardous chemicals and
operation of scientific equipment will be indicated whether by myself
or by one of the teaching assistants. These procedures must be
followed. If you have any doubts about the safety of something you
are about to do, ask first!!! We will be most happy to answer your
questions. Finally, and very importantly, at least one T.A. or myself
must be physically present at all times for you to work in the
lab.
If you have a documented disability that will
impact your work in this class, please contact me to discuss your
needs. Additionally, you will need to register with the Disability
Support Services Office in the Ley Student Center.
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- Introductory
Laboratory Module
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- Laboratory
Notebooks
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- Your laboratory notebook should be a clear
and accurate record of your experiments and calculations as they
happen. Thus, when you are done with an experiment and all of the
chemicals used have been washed away, and all the apparati taken
down, the notebook will serve as an infallible "memory" of what
happened and how. This is especially true for thesis work where
some time may elapse before results are written up for the thesis
or publication. Industrial standards for keeping notebooks are
rigorous, due to patent and other legal concerns, so that all
entries may need to be witnessed, dated and signed. The following
guidelines will be used in this course:
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- 1. Use a durable, sewn notebook, preferably
cloth bound.
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- 2. Always record data in permanent
ink.
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- 3. Do not record any data on scrap paper.
Scrap paper used for this purpose will be taken up, and your data
will be lost. Record all data directly into your notebook and
date. Quantities including the raw measurements should be
included.
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- 4. Cross through mistakes in such a manner
so that they may still be read.
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- 5. Include your name, section number, desk
number, course title, semester date, college affiliation, and
phone number in case your notebook is lost.
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- 6. Number all pages in ink if this is not
already done.
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- 7. Include an updated table of contents at
the beginning of the notebook. Blank space may be left at the
beginning of the book for this purpose.
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- 8. Leave no blank pages after the table of
contents in your notebook.
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- 9. The usual rules regarding significant
figures should be observed. Never report more significant figures
than warranted by the data.
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- 10. Adopt a numbering scheme based on the
date or notebook page for all samples and spectra. These numbers
should appear on the sample/spectrum and when the sample/spectrum
is mentioned in the notebook. ARB II 101 means the first sample on
page 101 of A. R. Barron's second notebook. Also on the spectrum
should be written the composition of the sample and the sample
number.
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- 11. A compressed scan or sketch of the
spectrum placed directly in the notebook is a useful aid when the
data are being reviewed.
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- 12. The origin of solvents and reagents
should be clearly stated.
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- 13. Make it clear what apparatus was used.
Whenever an unusual piece of equipment is first used, a sketch of
it should be included.
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- 14. If physical data are used, or if
spectral comparisons are made with the literature, the reference
should be recorded.
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- Your notebook should
contain:
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- 1. Date. Be sure and date all entries in
your notebook.
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- 2. Title. The title should be as brief and
as informative as possible. Titles should also be included for all
drawings, charts, or graphs.
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- 3. Introduction. The introduction should
include the purpose of the experiment, descriptions of any
chemical or physical processes expected to occur, and any known
literature values or other data pertinent to the experiment. For
chemical processes, include all pertinent balanced chemical
equations.
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- 4. Procedure. Reference the source of the
experimental procedure you are following. Explicitly note any
alterations you make in the procedure, and any differences in the
outcome. Securely attach any pertinent handouts directly to the
notebook page.
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- 5. Observations. Include all numeric data
obtained during the experiment. Label all numeric data clearly.
Also include detailed descriptions of all pertinent physical or
chemical processes that you observe.
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- 6. Results. Label all numeric results
clearly. Include, when appropriate, any final values obtained,
standard deviations of measurements, and percent errors, when a
theoretical result is available.
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- 7. Conclusion. Did the experiment work?
List possible sources of error, and explain whether they would
lower or raise numeric results, if possible. If you have
suggestions for improving the experimental procedure, you should
include them as well.
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- More About Lab Write Ups for Your
Notebook;
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- What do I want for the lab write up? The
compiled report should be in the format listed in the above
Laboratory Notebooks handout. It should be concise.
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- In the experimental section, the most
important thing is to note details about things changed from the
written procedure. You do not need to repeat the detailed
experimental from the lab handout.
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- The results section is very important and
should detail what happened (color changes, gas evolution, heat
production, etc.). It should also list the analytical results (IR
spectra, NMR spectra, melting points, etc.). It will probably be
the longest section.
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- The discussion section is your chance to
shine. Here you should describe problems you had with the
synthesis, if any, and ways the experiment might be done better.
You get to interpret the spectroscopic and spectrometric data.
Concentrate on the highlights of the techniques as we discussed
them in class. You might wish to explain why a given compound is
expected to be diamagnetic or paramagnetic. You might wish to note
specific IR bands and what they might mean based on the structure
of your compound, etc. What are possible sources of error? Of low
yields? Of impure materials? What did you learn about porphyrins
and metalloporphyrins, in general? Feel free to discuss the
experiments with the other lab groups, but write your own
discussion in your own words.
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Introductory
Laboratory Module
- Synthesis,
Purification, and Structural
Characterization
- of Porphyrin and
Metalloporphyrin Compounds
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- Abstract:
p-methyltetraphenylporphyrin (Me4TPPH2) is a
commonly studied ligand which displays similar characteristics to
the porphyrin ligands present in hemoglobin and other human
metalloproteins. In this project, Me4TPPH2
is synthesized and purified by column chromatography. After
synthesis of the porphyrin molecule, you will metallate this
unique ligand's center with zinc(II), one of the metals commonly
found associated with porphyrins in humans. Each group will
prepare a different iron(III) complex, some of which have never
been synthesized previously and none of which have been
structurally characterized.
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- What you learn: You will learn how
porphyrins form synthetically. Wet chemical techniques learned
include distillation, reflux reactions, mixed-solvent extraction,
and purification by column chromatography and recrystallization.
Next, an introduction to Infrared (IR) spectroscopy, Mass
Spectrometry (MS), Nuclear Magnetic Resonance (NMR) spectroscopy
and the magnetic properties of materials (diamagnetism/
paramagnetism) will allow for the structural and electronic
characterization of the porphyrin and metalloporphyrin molecules
using modern research methods. Finally, you will learn how to
prepare and isolate a new compound.
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- Introduction
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- Coordination compounds are extremely
important in biological systems. A classic example is hemoglobin
which uses an iron-centered macrocyclic ligand to carry oxygen
reversibly from the lungs to other parts of the body. The
functioning of hemoglobin is a delicate balance of structure and
environment as the iron compound is expected to bind well to
oxygen in an oxygen-rich environment and release it in an
oxygen-poor one. In this experiment we will synthesize
p-methyl-tetraphenylporphyrin which is a macrocyclic ligand that
is very similar to the ligand around the iron center in
hemoglobin. The iron-ligand complex in hemoglobin is known as
heme. p-methyltetraphenylporphyrin
(Me4TPPH2) and heme are shown below for
comparison purposes. As you might expect,
(Me4TPPH2) is much easier to synthesize than
the heme ligand and consequently it has been widely studied. While
its iron complex is a reasonable model compound, it unfortunately
does not have all the properties of heme. Other much more complex
porphyrin systems have also been synthesized which attempt to more
closely mimic the function of heme.
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- Many other transition metal species are
found to be important in biological systems. There is a class of
very important cluster molecules which function as
electron-transport agents. These are often clusters of iron with
sulfur ligands and may also contain molybdenum. Copper is
important in cytochrome c oxidase. Vanadium has been found in
certain algae. Cobalt is found in vitamin B12. These are just a
few examples. Just as p-methyltetraphenylporphyrin has been used
to model the hemoglobin system, chemists are seeking to make
compounds which mimic the function of these biologically-active
compounds. In many cases the protein portion of the active
molecules is so complex that model compounds may be the only way
that a clearer picture of what is happening in the biological
system may be obtained.
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- p-methyltetraphenylporphyrin
(Me4TPPH2)
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- Heme
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- Synthesis of crude
p-methyltetraphenylporphyrin
(p-Me4TPPH2)
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- Heat 350 mL of propionic acid to reflux in
a 500 mL roundbottom flask using a heating mantle, a stirrer, and
a reflux condenser. Add freshly distilled pyrrole (6.0 mL) and
p-tolualdehyde (11mL) to the refluxing acid, making the final
solution approximately 0.25 M in each reagent. After refluxing for
30 min., cool the solution to room temperature and collect the
purple crystalline product by vacuum filtration. Wash the filter
cake with methanol to remove excess propionic acid. The solid
product contains about 3% tetraphenylchlorin (TPCH2) an
undesired by-product. Calculate the yield based on
pyrrole.
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- Purification of
p-MeTPPH2
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- Prepare an alumina column (6.5 cm diameter)
by filling it 12 cm high with a dense slurry of chloroform and
activated neutral alumina. Allow the alumina to settle evenly
while draining excess solvent. Add a solution with 350 mg of crude
porphyrin (about 1/2 your sample) dissolved in 60 mL hot
chloroform to the column and elute with fresh chloroform.
Me4TTPH2 will elute first as a thick purple
band, and TPCH2 will elute second as a minor green
band. Collect the purple band and take it to dryness under reduced
pressure. Collect the purple crystalline product. Recrystallize
the solid product from chloroform. Calculate the percent yield
based on Me4TPPH2. Determine if the material
is diamagnetic or paramagnetic.
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- Preparation of
[ZnII(Me4TPP)]
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- Dissolve 250 mg of pure
Me4TPPH2 in 200 mL of chloroform using a 500
mL roundbottom flask. Bring the solution to reflux using a heating
mantle, stirrer, and reflux condenser. Add an excess of zinc
acetate (1.0 g) dissolved in a minimum of hot methanol. Reflux the
solution for 2 hours and then remove all the solvent under reduced
pressure. Dissolve the resulting solid in a minimum of
CH2Cl2 and filter to remove excess zinc
acetate. Discard the filter cake. Remove the solvent under reduced
pressure and redissolve the resulting solid in a minimum amount of
hot chloroform (approx. 50 mL). Purify on a silica column as
above, eluting with chloroform. The
[ZnII(Me4TPP)] band should be
reddish purple and should elute first. Recrystallize the solid
product as above. Calculate the percent yield based on
Me4TPPH2. Determine if the material is
diamagnetic or paramagnetic.
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Introductory
Laboratory Module
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- Research
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- Synthesis and
Characterization of Unknown Iron Porphyrin Compounds
- Abstract: In this project you will
prepare a new (previously unknown) iron(III) porphyrin compound.
Each team will prepare a compound with a different substituent.
After the synthesis of these new compounds you will determine its
structure by IR spectroscopy, magnetic properties and (if you can
obtain suitable crystals) X-ray crystallography. The results from
all the groups will be combined to allow comparison of these new
compounds. If the results warrant, the new compounds will be
written-up for publication in a peer-reviewed chemistry journal.
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- What you learn: You will learn to
prepare and characterize a previously unknown compound. You will
learn to adapt your synthetic and purification methods to an
unknown compound. The processes and methods that are required are
the basis for scientific research.
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- Introduction
- Nature's elaboration of the
fundamental iron porphyrin structure has resulted in a
multiplicity of functions for the hemeproteins. Thus, oxygen
transport in the hemeglobins, electron transfer in cytochromes c,
and oxygen redox chemistry in the cytochromes P450 and peroxidases
are all achieved at an iron heme active site. In understanding the
heme site a number of model compounds have been investigated
including iron(III) porphyrin complexes possessing an oxygen donor
ligand in the axial position. The simplest class of these
compounds include the carboxylato iron(III) porhyrins,
(por)Fe(O2CR), where R = an organic group. A number of
these compounds have been reported (H. Oumous, C. Lecomite, J.
Protas, P. Cocolios, and R. Guilard, Polyhedron, 1984,
3, 651-659, and S. A. Moy, J. A. Gonzalez, and L. J.
Wilson, Acta Cryst., 1995, C51, 1490-1494), however,
only two have been structurally characterized.
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- Preparation of
[FeIII(Me4TPP)Cl]
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- Dissolve 250 mg of pure
Me4TPPH2 in 200 mL DMF using a 500 mL
roundbottom flask. Add a few small boiling chips, and an excess of
FeIIICl3*6H2O (1.0 g) dissolved
in a minimum amount of hot methanol. Heat the solution to 145
°C using a hot plate and sandbath apparatus, a thermometer,
and a reflux condenser. After heating for 3 hours, remove the
roundbottom flask from the sandbath (caution: flask will be very
hot) and allow to cool to under 60 °C. Concentrate the
solution to 100 mL under reduced presure and slowly add 150 mL
deionized water to precipitate a crude sample of
[FeIII(Me4TPP)Cl]. Filter and wash
with cold water, then air dry on the filter paper.
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- Preparation of
[FeIII(Me4TPP)]2(m-O)
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- Weigh the dried sample of
[FeIII(Me4TPP)Cl] and the filter
paper. Add the sample and filter paper to 75 mL of
CH2Cl2. The of
[FeIII(Me4TPP)Cl] will dissolve and
the filter paper may be removed and dried. Re-weighing the filter
paper will allow you to calculate the yield of
[FeIII(Me4TPP)Cl]. To the
CH2Cl2 solution of
[FeIII(Me4TPP)Cl] add an equal
volume of 1 M perchloric acid. Stir for 1 h. The organic layer is
separated in a separation funnel and washed with distilled water.
(N.B. Make sure you retain both layers, just in case you use the
wrong one!) Separate the CH2Cl2 solution of
[FeIII(Me4TPP)
]2(m-O)
and add 150 mL of heptane to precipitate the red microcystalline
product. Filter and air dry on the filter paper. Determine if the
material is diamagnetic or paramagnetic.
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- Preparation of
[FeIII(Me4TPP)(O2CR)]
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- Weigh a sample of
[FeIII(Me4TPP)
]2(m-O)
into a round bottom flask. Add an excess of the carboxylic acid
you have chosen. It is usual to add at least a 10-fold excess. If
the carboxylic acid is a liquid, heat the mixture to reflux for 20
min. Then cool to room temperature. Check with TLC to make sure
all the [FeIII(Me4TPP)
]2(m-O)
has reacted. If it has not, continue heating the solution for
another 20 min. Once all the
[FeIII(Me4TPP)
]2(m-O)
has reacted, place the sample in the fume hood to evaporate the
excess acid. If the carboxylic acid is a solid, then heat the
mixture until the carboxylic acid melts (see the Aldrich
catalogue for the melting point ) and continue to heat for 20 min.
Check with TLC to make sure all the
[FeIII(Me4TPP)
]2(m-O)
has reacted. If it has not, continue heating the solution for
another 20 min. Once all the
[FeIII(Me4TPP)
]2(m-O)
has reacted wash the sample with 50 mL of hot isopropyl ether and
recrystallize the solid from a minimum amount of toluene.
Determine if the material is diamagnetic or paramagnetic. Caution:
Some of the carboxylic acids are very smelly! Use gloves and
handle in the fume hoods at all times.
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