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Identification of an Unknown Oxygen-Containing Compound

Identification of an Unknown Oxygen-Containing Compound. CH344 Bruce A. Hathaway. Goals of This Lab. Gain experience with some common functional group tests. Determine the functional group in your unknown: 1°, 2° or 3° Alcohol, Aldehyde, Ketone.

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Identification of an Unknown Oxygen-Containing Compound

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  1. Identification of an Unknown Oxygen-Containing Compound CH344 Bruce A. Hathaway

  2. Goals of This Lab • Gain experience with some common functional group tests. • Determine the functional group in your unknown: 1°, 2° or 3° Alcohol, Aldehyde, Ketone. • Determine the identity of your unknown, using physical constants, IR and NMR.

  3. General Procedure • Determine some physical properties. • Run the chemical tests. • Determine which functional group you have. • Determine the identity of your compound by making derivatives and interpreting spectra.

  4. Physical Properties Boiling Point Range, by simple distillation. • You have about 12 mL of unknown, so distill from a 25 mL flask. • Collect distillate in clean test-tubes or vials. • Collect the material that boils over a relatively constant boiling range. • Do not distill to dryness. • I have added a high-boiling impurity!

  5. Test Procedures • The following slides, and the handout, summarize the test procedures. • You need to read the complete procedures in the text, and use them.

  6. Ignition Test, Page 574 • Place 3-4 drops of unknown on a clean watch-glass, and ignite them. • Observe the color of the flame. • A blue flame usually indicates oxygen. • A sooty flame usually indicates C=C’s or benzene rings.

  7. Water-Solubility • 4-5 drops of unknown + 3 mL of water, shake: • Does the unknown dissolve?

  8. 2,4-DNPH test, C-11 & D-3, p. 601 • Dissolve 4-5 drops of unknown in 4 mL of 95% ethanol, then add 3 mL of 2,4-DNPH reagent. Cool, filter, wash with water and NaHCO3 solution, then recrystallize from ethanol. • A yellow to orange precipitate indicates an aldehyde or a ketone. • You can use the precipitate as a derivative. • Acetone is a ketone!

  9. Chromic acid Test, C-9, p. 585-6 • Add 1-2 drops of unknown to 1 mL of reagent acetone in a small test tube. • Add 1 drop of chromic acid solution. • For comparison, add 1 drop of chromic acid solution to 1 mL of acetone in another small test tube. • A relatively quick formation of a green to blue-green solution usually indicates a 1o or 2o alcohol. • A slow (30-60 seconds) formation of a green to blue-green solution indicates often indicates an aldehyde.

  10. Chromic Acid Test

  11. Iodoform test, C-16, p. 590-1 • Add 3 drops of unknown to 2 mL of water in a large test tube. • Add 1 mL of 3M sodium hydroxide solution. Add a dropper-full of iodine-KI solution. • If a yellow ppt. forms, it is a positive test. • See text if no yellow ppt. forms. • 2° methyl alcohols also give a positive test.

  12. Semicarbazone and Oxime Derivatives: D-4 and D-5, p. 602

  13. Semicarbazone and Oxime Derivatives: D-4 and D-5, p. 602 • Mix 0.20 g of semicarbazide HCl or hydroxylamine HCl, 0.30 g of sodium acetate, 2 mL of water and 2 mL of 95% ethanol in a large test tube. • Add 0.20 g of unknown. • Cork and shake for a couple minutes. Cool and see if crystals form. • If not, heat in a boiling water bath for about 5 minutes, then cool and filter. • Wash with cold water, then recrystallize with ethanol or ethanol-water mixture.

  14. 3,5-Dinitrobenzoates, D-1, p. 600 • This reaction also works with 4-nitrobenzoyl chloride, to give 4-nitrobenzoate derivatives.

  15. 3,5-Dinitrobenzoates, D-1, p. 600 • Dry the alcohol first with Na2SO4 or MgSO4. • 0.2 g 3,5-dinitrobenzoyl chloride + 4-5 drops of alcohol in a medium test tube, heated in a small flame just enough to maintain in a liquid state for 5-10 minutes. • Cool, break up with a spatula, add 4 mL of sodium carbonate solution, heat in a boiling water bath for a few minutes. • Cool, filter, wash with water. Recrystallize from ethanol or ethanol-water.

  16. -Naphthylurethanesand Phenylurethanes, D-2, p. 600-1 • We don’t have any -naphthylisocyanate, so we will use phenyisocyanate instead.

  17. -Naphthylurethanesand Phenylurethanes, D-2, p. 600-1 • Dry the alcohol first with Na2SO4 or MgSO4. • Mix 5-drops of alcohol with 5 drops of -naphthyl isocyanate in a medium test tube. • If no reaction takes place immediately, heat in a boiling water bath for 5-15 minutes. • Cool, filter, recrystallize from heptane.

  18. Spectroscopy • Take an IR spectrum. • Submit a sample of your pure, distilled unknown for NMR.

  19. Putting It All Together • The chemical tests should point you to a particular functional group. • You can rerun the tests if you have conflicting results with yourself. • Make at least two derivatives, crystallize them, let them dry, and take melting points. • The boiling point, derivative melting point data, and the spectral data should point you to a particular unknown.

  20. Finishing up • Pour the test solutions/solids into the appropriate waste beakers in the hoods. • Keep all of the unknown you have left (distilled or undistilled). We will appropriately dispose of it later.

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