Austin Peay State University Department of Chemistry CHEM 1021 TESTING FOR ORGANIC FUNCTIONAL GROUPS

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1 TESTING FOR ORGANIC FUNCTIONAL GROUPS Caution: Chromic acid is hazardous as are many of the organic substances in today s experiment. Treat all unknowns with extreme care. Many organic substances are flammable. Purpose: In this lab you will use traditional chemical tests to identify a variety of functional groups in known chemicals, and to use those positive results to identify the functional groups present in an unknown chemical. Background: Chemists today are trained to use elaborate technologies and instrumentation to determine chemical structure and makeup. However, many years ago, these technologies were not yet available, and there were very few ways for chemists to determine the composition of any chemical. Chemists would use a series of tests to characterize the structure and makeup of a chemical. You will be doing some of these tests in this lab, in particular, ones that indicate functional groups present on a molecule. Functional groups can be defined as the parts of organic molecules that are prone to chemical reactions. Molecules with carbon chains full of hydrogens (saturated hydrocarbons), are not especially susceptible to reactions, but chemicals that contain oxygen, nitrogen, halogens (Br, Cl, F, and I) and multiple bonds between carbon atoms can react quite easily in specific conditions. The following functional groups will be tested in this experiment: Alkenes alkenes are chemicals that contain a carbon-carbon double bond. They react with the magenta-colored chemical potassium permanganate (KMnO 4 ) to product manganese dioxide (MnO 2 ), which is a brown solid. In other words, you can determine if a chemical has a double bond by adding KMnO 4 and looking for the development of the brown solid MnO 2. Example: 1-butene OH H 3 C H 2 C C H CH 2 KMnO 4 H 3 C H 2 C H C CH 2 + MnO 2 (s) OH Alcohols alcohols consist of a hydroxyl group (-OH) attached to a carbon chain. Alcohols are oxidized with chromic acid (H 2 CrO 4 ) to give a carbonyl (C=O) and a green chromium compound (a chromium oxide). Positive identification of an alcohol will be evident when the addition of chromic acid results in a green solution. This reaction is quick, working on the order of 2-3 seconds. Aldehydes also react with chromic acid to produce the green chromium compound, but the reaction takes a bit longer, seconds or so. Revision S10 Page 1 of 12

Purpose: In this lab you will use traditional chemical tests to identify a variety of functional groups in known chemicals, and to use those positive results to identify the functional groups present

2 Example: 2-propanol (iso-propanol) Ketones/aldehydes a carbon-oxygen double bond, where the carbon is also attached to two other carbons (ketone) or to a carbon and a hydrogen (aldehyde). Ketones and aldehydes react with a chemical called 2,4-dinitrophenylhydrazine (2,4-DNPH) to form a yellow or orange solid within a few minutes. Example: propanone (a ketone) Example: ethanal (an aldehyde) H C CH 3 + NO 2 H N NH 2 NO 2 H N N CH 3 C H O O 2 N O 2 N 2,4-DNPH Alkyl halides alkanes that have a halogen in place of a hydrogen. Bromines, chlorines, and iodines attached to carbons are all alkyl halides. It is quite easy to test for halogens on an organic compound by way of a Beilstein test. A copper wire can be heated under a flame to from a layer of copper II oxide (CuO) on the wire. Dipping the coated wire in your compound to coat it, and put it under the flame. A green flame indicates the burning of a copper halide, which shows a reaction between an alkyl halide and the copper oxide. Example: methyl bromide Revision S10 Page 2 of 12

Example: propanone (a ketone) Example: ethanal (an aldehyde) H C CH 3 + NO 2 H N NH 2 NO 2 H N N CH 3 C H O O 2 N O 2 N 2,4-DNPH Alkyl halides alkanes that have a halogen in place of a hydrogen.

3 Equipment: Copper wire Methylene Chloride Hexane standard Pentene Bunsen burner Unknown chemicals Test tube rack Hexanal Spatulas 2% KMnO 4(aq) Sand paper Ethanol Disposable pipettes Acetone Small test tubes/stoppers Chromic acid reagent 2,4-DNPH reagent Procedure: This experiment will consist of adding chemicals to test tubes. You will want to keep track of each test tube, and keep them until the end of the experiment for comparison to your unknown chemical. I. Testing for alkenes: Set up two test tubes in the test tube rack. In tube one, put in 4 drops of hexane. In tube two, put in 4 drops of pentene. Add 2 ml of ethanol to each tube. Add two drops of the permanganate solution, stopper, and shake (be careful you know which tube is which!) Record the results on the data sheet. II. Testing for alcohols: Set up two new test tubes in the test tube rack. In tube one, put in 1 drop of hexane, and in tube two put in one drop of ethanol. Add 1 ml of acetone to each tube followed by 1 drop of the chromic acid reagent. Gently swirl the tubes. Record the results on the data sheet. III. Testing for ketones: Set up two test tubes in the test tube rack. In tube one, put in 2 drops of hexane, and in tube two, put in 2 drops of acetone. Add 2 ml of ethanol to each tube followed by 3 ml of the 2,4-DNPH reagent. Stopper and shake well. Let the solution stand for up to 15 minutes. You can go onto the next test in this time. Record the results on the data sheet. IV. Testing for aldehydes: You will be using two tests for aldehydes, the chromic acid test as well as the 2,4-DNPH test. Because you already know what the negative tests for these look like, you will only be doing the positive tests. Set up two test tubes in the test tube rack. In tube 1, put in 1 drop of hexanal, 1 ml of acetone, and 1 drop of chromic acid. Swirl the tube. In tube 2, put in 2 drops of hexanal, 2 ml of ethanol, and 3 ml of the 2,4-DNPH reagent. Stopper and shake the tube. Wait up to 15 minutes for a reaction in tube 2. Compare the tests to the positive and negative tests in 2 and 3 above. Record the results on the data sheet. V. Testing for alkyl halides: Take a small length of copper wire and brush it clean using the sand paper. Hold it over a flame for about 30 seconds. Take it out of the fire and let it cool down. Dip the wire in hexane and hold over the flame. Repeat the procedure using methylene chloride. Record the results on the data sheet. Revision S10 Page 3 of 12

You will want to keep track of each test tube, and keep them until the end of the experiment for comparison to your unknown chemical. I.

4 VI. Testing your unknown: Obtain your unknown and 3 test tubes. Do the alkene, alcohol/aldehyde, and aldehyde/ketone test on it as well as the alkyl halide test. Record your results on the data sheet. Compare to the positive results for the known chemicals above to determine the functional groups present in your compound. Waste Disposal and Cleanup: When you are finished, pour the chemicals in the appropriate waste container. Wash your glassware thoroughly with soap and water followed by a distilled water rinse. *Techniques and Experiments for Organic Chemistry Revision S10 Page 4 of 12

Compare to the positive results for the known chemicals above to determine the functional groups present in your compound.

5 TESTING FOR ORGANIC FUNCTIONAL GROUPS DATA SHEET Name: Partner: Unknown #: I. Alkene test a. Hexane control observations: b. Propene observations: II. Alcohol test a. Hexane control observations: b. Ethanol observations: Revision S10 Page 5 of 12

6 III. Ketone test a. Hexane observations: b. Acetone observations: IV. Aldehyde tests a. Chromic acid test observations: b. 2,4-DNPH test observations: Revision S10 Page 6 of 12

7 V. Alkyl halide test a. Hexane observations: b. Methylene chloride observations: VI. Unknown tests: a. Alkene test observations: Is this test positive or negative? b. Alcohol/aldehyde test observations: Is this test positive or negative? c. Ketone/aldehyde test observations: Revision S10 Page 7 of 12

Alkene test observations: Is this test positive or negative? b.

8 Is this test positive or negative? d. Alkyl halide test observations: Is this test positive or negative? Which functional groups are present in your unknown chemical? Revision S10 Page 8 of 12

9 Name: TESTING FOR ORGANIC FUNCTIONAL GROUPS POST-LAB Imagine you have 3 separate chemicals, an aldehyde, an alcohol, and a ketone. How could you determine the functional group of each chemical? Explain. Using what you have learned in this lab, is there a way to distinguish between a chemical that has an alcohol functional group and a chemical that has an aldehyde functional group on it? Explain. What about one that has an aldehyde and one that has a ketone? Explain. Revision S10 Page 9 of 12

Using what you have learned in this lab, is there a way to distinguish between a chemical that has an alcohol functional

10 THIS PAGE INTENTIONALLY LEFT BLANK. Revision S10 Page 10 of 12

11 Name: TESTING FOR ORGANIC FUNCTIONAL GROUPS PRE-LAB 1. Name and circle the functional groups below. Which test would you use for the following chemicals? Revision S10 Page 11 of 12

12 2. Draw the Lewis-dot structures below of chemicals that you will be using in this lab, circle the functional group, and name the functional group. Hexane: Acetone: Propene Ethanol: Hexanal Methylene chloride: Revision S10 Page 12 of 12

Identification of Unknown Organic Compounds

Identification of Unknown Organic Compounds Introduction The identification and characterization of the structures of unknown substances are an important part of organic chemistry. Although it is often