Transcript DUE DATES - George Mason University

Organic Chemistry Lab 315
Fall, 2014
DUE DATES
• Today
– At beginning of lab – Synthesis of Cyclohexene
– At end of lab -- copy of laboratory notebook pages
for today's experiment
• Next Week
– Written summary of progress in identifying
unknown, on a new continuation page in your
notebook. See example in Manual, p. 70.
• In Two Weeks
– Qualitative Analysis Report (two-week
experiment)
In Lab Today
• Classes of compounds: hydrocarbons (alkanes,
alkenes, alkynes, aromatic); hydrocarbyl
halides (1°, 2°, 3°, Ar); alcohols (1°, 2°, 3°).
• Begin Qualitative Organic Analysis
– Text p. 446ff
– Manual p. 69ff
• All test solutions are ready for use.
• Dispose of all waste in designated containers.
• Continue the experiment next week.
Experiment Notes
• See Pavia p. 447 “How to ProceedOption 1.”
• Receive a liquid unknown.
• Determine its boiling point (simple
distillation) and refractive index.
– Distill over ice. Use boiling stones. Do not
distill to dryness.
– Proper precision in refractive index. Room
temperature will be given to you.
• Perform solubility and qual. tests on
Experiment Notes
• It is necessary to see both a positive
and negative result for each test.
• It is necessary to perform all tests,
even if you think you have already
classified your unknown.
• You may perform the tests on knowns
and your unknown with the other
students who share your bench.
– Remember, you are personally responsible for the
outcome of all tests. Don’t let anyone test your
unknown for you.
Experiment Notes
• When you have finished all the qual.
tests, deduce what class of compound
your unknown is, based on the qual
tests, and justify it to me. (See Manual,
p. 70.)
– Only then will you be given permission to
take an IR of your unknown.
• Store unknown in tightly capped vial
(labeled with your name) for use next
week.
Notes on Qualitative
Analysis Tests
After every test, read the “Discussion” in Pavia for
an explanation of what a positive/negative test
means.
• Tests for solubility
– H2O General idea of the number of carbons
and/or presence of heteroatoms O, N, and S.
– H2SO4 Conc. H2SO4 reacts with Lewis bases
(compounds with non-bonding or pi electrons) such
as alkenes, alkynes, some aromatics, alcohols.
• Heat or color change is designated “soluble”
Notes on Qualitative
Analysis Tests
• Tests for Halides
X = Cl, Br, I
– Beilstein Use a Bunsen burner. Copper wire +
hydrocarbyl halide → CuX2 (blue-green flame)
– AgNO3/ethanol Forms a AgX↓ precipitate with
hydrocarbyl groups that form stable carbocations
(SN1 reactivity: 3°; 2°, 1° with heating; aryl, vinyl
NR)
– NaI/acetone Forms NaBr or NaCl precipitate
(SN2 reactivity: 1°; 2°, 3° with heating; aryl, vinyl
NR)
Notes on Qualitative
Analysis Tests
• Tests for Unsaturation
– Br2/methylene chloride Bromine reacts with p
bonds of alkenes and alkynes. Red color of Br2
disappears.
• Interpret immediately – eventually Br2 reacts with sat’d.
C-H
– KMnO4 Potassium permanganate reacts with p
bonds of alkenes and alkynes. Purple color of
permanganate changes to brown precipitate.
• Interpret immediately – eventually EtOH solvent oxidizes
– Ignition Sooty yellow flame in Bunsen burner is an
indication of unsaturation/aromaticity (incomplete
combustion).
Notes on Qualitative
Analysis Tests
• Tests for Alcohols
– Acetyl chloride Alcohols react with acetyl
chloride to give acetate esters (CH3CO2R) and
generate heat and HCl gas (test with moist litmus)
DO THIS RXN IN THE HOOD!
– Lucas test (ZnCl2/HCl) Forms a hydrocarbyl
halide precipitate (SN1 reactivity: 3°; 2° after
time; 1°, aryl, vinyl NR).
– Chromic acid Orange chromic acid turns greenblue when 1° and 2° alcohols are oxidized.
Notes on Qualitative
Analysis Tests
• Set up a hot water bath using a large beaker
of water on a hot plate.
• Use an eye-dropper and small grad. cylinder
to count # drops in ml of liquid.
• I will assist in the Beilstein and ignition tests.
Please be ready to conduct these tests in
your group when I give you notice.
• Keep vial of unknown in a small beaker so it
doesn’t tip over and drips are contained.
Weekly Clean-up
• Lozano
• Postol