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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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goals of this lab
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.
general procedure
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.
physical properties
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!
test procedures
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.
ignition test page 574
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.
water solubility
Water-Solubility
  • 4-5 drops of unknown + 3 mL of water, shake:
  • Does the unknown dissolve?
2 4 dnph test c 11 d 3 p 601
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!
chromic acid test c 9 p 585 6
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.
iodoform test c 16 p 590 1
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.
semicarbazone and oxime derivatives d 4 and d 5 p 6021
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.
3 5 dinitrobenzoates d 1 p 600
3,5-Dinitrobenzoates, D-1, p. 600
  • This reaction also works with 4-nitrobenzoyl chloride, to give 4-nitrobenzoate derivatives.
3 5 dinitrobenzoates d 1 p 6001
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.
naphthylurethanes and p henylurethanes d 2 p 600 1
-Naphthylurethanesand Phenylurethanes, D-2, p. 600-1
  • We don’t have any -naphthylisocyanate, so we will use phenyisocyanate instead.
naphthylurethanes and phenylurethanes d 2 p 600 1
-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.
spectroscopy
Spectroscopy
  • Take an IR spectrum.
  • Submit a sample of your pure, distilled unknown for NMR.
putting it all together
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.
finishing up
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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