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

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Presentation on theme: "Identification of an Unknown Oxygen-Containing Compound CH344 Bruce A. Hathaway 1."— Presentation transcript:

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

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. 2

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. 3

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! 4

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. 5

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. 6

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

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 NaHCO 3 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! 8

9 Chromic acid Test, C-9, p 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 1 o or 2 o alcohol. A slow (30-60 seconds) formation of a green to blue- green solution indicates often indicates an aldehyde. 9

10 Chromic Acid Test 10

11 Iodoform test, C-16, p 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. 11

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

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. 13

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

15 3,5-Dinitrobenzoates, D-1, p. 600 Dry the alcohol first with Na 2 SO 4 or MgSO g 3,5-dinitrobenzoyl chloride 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. 15

16  -Naphthylurethanes and Phenylurethanes, D-2, p We don’t have any  -naphthyl isocyanate, so we will use phenyisocyanate instead. 16

17  -Naphthylurethanes and Phenylurethanes, D-2, p Dry the alcohol first with Na 2 SO 4 or MgSO 4. 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. 17

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

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. 19

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. 20


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