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Organic Chemistry Lab: Qualitative Analysis of Unknown Compounds

Conduct chemical and spectroscopic tests to identify unknown aldehydes or ketones. Record results, perform distillation, and report findings following lab instructions.

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Organic Chemistry Lab: Qualitative Analysis of Unknown Compounds

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  1. Organic Chemistry Lab 318 Spring, 2012

  2. DUE DATES • Today • At beginning of lab – Grignard Reaction Report • At end of lab -- copy of laboratory notebook pages for today's experiment • Next Week • Qualitative Analysis Report

  3. The Experiment • Qualitative Analysis • Identification and characterization of unknown compounds • Chemical and spectroscopic methods • Chemical classification – “test tube” reactions that are fast and give a visual result • Spectroscopy – IR; H-NMR/C-NMR; mass spectroscopy • The unknowns are either aldehydes or ketones • You will perform chemical tests, take an IR and receive/take an NMR

  4. Experiment Notes • Follow the instructions in the Manual and in Pavia, beginning on p. 446. • Simple distillation to purify unknown and get a b.pt. or m.pt. determination • Refractive index – remember to record room temp. • Perform “qual tests”. • Record all observations in your notebook; do not merely record “positive” or “negative”. • Do not fill in the table on the Handout – it is part of your report. • Use 1,2-dimethoxyethane instead of di(ethylene glycol) diethyl ether for Tollens

  5. Experiment Notes • When you are finished with your qual tests, write a paragraph in your notebook that summarizes the results. • You then should be able to justify the conclusion that you have either an aldehyde or a ketone (and if you have a ketone, whether it is a methyl ketone or not). • After you have successfully convinced me of your conclusion (orally and in writing), you can take an IR. • (Of course, you will be able to tell whether or not you have an aldehyde by the specific IR absorptions)

  6. Experiment Notes • Solubility test – H2O and conc. H2SO4 • Watch for color change or heat evolution with concentrated H2SO4. Positive results indicates a reaction of >C=O with H+ • 2,4-DNP [no reagent available!!!] Precipitate color: yelloworangered Extent of conjugation in ald/ket: unconjugated some highly

  7. Experiment Notes • Chromic Acid • Aldehydes are easily oxidized – ketones are not orange sol’n green ppt. • Tollens Test • Aldehydes are easily oxidized – ketones are not • Show me the results of your test. silver mirror

  8. Experiment Notes • Iodoform Test • Test for methyl ketones yellow ppt • Use a large test tube. • It may take a long time, so do this test first. • Show me the results of your test.

  9. Experiment Notes • Each student gets his/her own unknown. • You may work in groups on the known compounds (I will divide the class). • One person sets up each test for knowns and unknowns. Both people perform the tests and observe and interpret results. • Both people are responsible for the results. • DO NOT divide the work by giving one person sole responsibility for a test.

  10. Experiment Notes • Pavia tells you what knowns to use for each test. Use them. • This should correspond to the Table that is part of the Handout (please let me know of any discrepancies). • Unknown possibilities are listed in the Manual appendix.

  11. Experiment Notes • All waste goes into the WASTE JAR in the Hood

  12. Experiment Notes • Clean-up: Michael Chung and Cindy Tran

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