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Organic Chemistry Lab 315 Fall, 2013

Organic Chemistry Lab 315 Fall, 2013. 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 Nothing Due In Two Weeks Qualitative Analysis Report (two-week experiment). Last Week’s Report.

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Organic Chemistry Lab 315 Fall, 2013

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  1. Organic Chemistry Lab 315 Fall, 2013

  2. 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 • Nothing Due • In Two Weeks • Qualitative Analysis Report (two-week experiment)

  3. Last Week’s Report • You took an experimental IR. The report instructions said to attach it, along with a copy of a literature spectrum. The spectrum should have the important characteristic peaks marked. • Separation Scheme: You need to review the concept, and the statements in the t-BuClpowerpoint, and the experiment itself. Look over your graded scheme to see what you did wrong. You will probably need to revise the cyclohexene separation scheme. • To learn from your t-BuCl report, and to improve your cyclohexene report, you can take the cyclohexene report back, amend it, and return it to me by Thursday noon.

  4. In Lab Today • Begin Qualitative Organic Analysis • Text p. 446 ff • Manual p. 69 ff • Classes of compounds: hydrocarbons (alkanes, alkenes, alkynes, aromatic); hydrocarbyl halides (1°, 2°, 3°, Ar); alcohols (1°, 2°, 3°). • All test solutions are ready for use. • Dispose of all waste in designated containers. • Continue the experiment next week.

  5. Experiment Notes • See Pavia p. 447 “How to Proceed-Option 1.” • Receive a liquid unknown. • Determine its boiling point (simple distillation) and refractive index. • Distill over ice • Proper precision in refractive index • Perform solubility and qual. tests on known compounds (see Manual table p. 73) and unknown.

  6. 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.

  7. 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.) • You will then be given permission to take an IR of your unknown. • Store unknown in tightly capped vial (labeled with your name) for use next week.

  8. Notes on Qualitative Analysis Tests After every test, read the “Discussion” in Pavia for an explanation of what a positive/negative test means. • 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”

  9. 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)

  10. Notes on Qualitative Analysis Tests • Tests for Unsaturation • Br2/methylene chloride Bromine reacts with pi 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 pi 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).

  11. Notes on Qualitative Analysis Tests • Tests for Alcohols • Acetyl chloride Alcohols react with acetyl chloride to give acetate esters 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 green-blue when 1° and 2° alcohols are oxidized.

  12. 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. cylinger 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.

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