Answer Happy

Give a brief description of what is meant by primary (1°), secondary (2%), tertiary (39) and secondary methyl alcohols, giving a correct name for one alcohol in cach of these categories. Give a different example for a secondary methyl alcohol than you give for the secondary alcohol; both examples may end up being secondary methyl alcohols, but not necessarily. Give a brief description of the reaction that takes place with cach of the 4 tests being used and indicate whether the test you are describing will be positive reaction) or negative (no reaction) or positive with some conditions, such as longer waiting time for the reaction or having to warm the mixture for each of the 4 examples of alcohols that you gave above. The 4 test you are describing are: 1) chromic acid oxidation; 2) Ritter test or permanganate oxidation: 3) Lucas test to form alkyl chlorides, and 4) iodoform test with sodium hypoodite (NaOl). It will be important to write a conclusion or make a table showing each of the 4 alcohols you have named and whether that alcohol gives a positive test in each of the 4 tests that are performed in this experiment. You could set up a table as follows: Ritter Test Lucas Test Jodoform Test Alcohol Example Chromic Acid Test 1° Example 2° Example 3° Example 2° Methyl Example Give the correct nume you are using for cach alcohol where 1,2,3 and 2' Methyl are entered here. Briefly describe in cach box what change, if any, is observed and whether the change requires special conditions, such as after a longer time or with heating,
/-swatson/downloads/files/Experiment_6.pdf Qualitative Tests for Alcohols, Alcohol Unknown, IR of Unknown In this experiment you are going to do a series of tests in order to determine whether or not an alcohol is a primary (1º), secondary (29) or tertiary (3") alcohol. The tests can also determine whether or not there is a secondary methyl alcohol functionality in the molecule. You will do four chemical tests: (1) Chromic Acid Test (or Jones Oxidation), (2) Ritter Test using potassium permanganate (3) the Lucas Test using ZnCl, and HCI, and (4) the lodoform Test The experiment has three parts, all of which can be done in one laboratory session. First, you will practice all four of the chemical test using known alcohols. You will perform each of the first three tests three times, once with a primary, once with a secondary and once with a tertiary alcohol. The fourth test we will do two times, once with a secondary methyl containing alcohol and once with a not secondary methyl alcohol. The tests on the three known alcohols can be done at the same time. Then you will perform all four chemical tests on your unknown. Finally, you will take an Infrared Spectrum of your unknown. You will identify your unknown alcohol and as many peaks as you can using our IR tables at the back of this manual. PLEASE RETURN THE REAGENT BOTTLES TO THE CENTRAL BENCH WHEN YOU ARE FINISHED WITH THEM SO THAT OTHERS CAN USE THEM. Test 1: Chromic Acid Oxidation This test distinguishes primary and secondary alcohols from tertiary. Chromic acid will oxidize a primary alcohol first to an aldehyde and then to a carboxylic acid and it will oxidize a secondary alcohol to a ketone. Tertiary alcohols do not react. The OH-bearing carbon must have a hydrogen atom attached. Recall, that a carbon is oxidized when it loses a hydrogen or hydrogens or gains a more electronegative atom. Since the carbon atom is being oxidized in primary and secondary, the orange chromium Cr" ion is being reduced to the blue-green Crion. The reactions involved are shown in Figure 6.1. Figure 6.1 Chronic Acid Oxidation of Alcohols Primary Akobol Cry(SO) Info + + H6,0 -OH blue-green orange Secondary Alcohol H.SO -OH HCO, orange + Crash blue-green Tertiary alcohol H.COM Orange R СОН H.SO No action, no color change Procedure: Set-up three small test tubes in your test tube rack. The tubes do not need to be dry, Label the first test tube as a primary alcohol, the next as a secondary alcohol and the third as a tertiary alcohol. Write down in your notebook which alcohols you are going to be using. Add 2 mL of acetone to cach test tube and then add 3- mentalna Date de collima TOA TY
a vigorously using a small tight fitting cork. You should see a color change to a blue or blue-green or similarly colored precipitate within a few seconds to indicate a positive test. Record your results in your notebook. Test 2: Ritter Test This test is similar to the Chromic Acid Oxidation and provides the same information. It is the oxidation of primary and secondary alcohols to carboxylic acids and ketones using potassium permanganate (KMnO.). Again, tertiary alcohols cannot be oxidized by this reagent because there is no hydrogen to be lost from the carbon that bears the OH group. In the Ritter Test the Mn of KMnO, (bright purple) is reduced to Mn". The Mn" is brownish in color. The reactions involved are as follows. Figure 6.2 Potassium Permangante Oxidation RCH,OH R_CHOH KMnO4 AcОН + MnO purple Lohorte R brown R.COH + KMnO AcOH purple No reaction, no color change Procedure: As for the Chromic Acid Oxidation, set-up three small, labeled tests tubes. Add 2 ml acetic acid (CAUTION: Stench!) to each tube. Add 3-4 drops of the test alcohol to each tube and then add ONE drop of saturated KMnO, solution to each test tube. Shake vigorously to mix, using a small cork as before. For the 1° and 2° alcohols you should see a brownish color develop as the purple KMnO, color disappears. Do not add too much KMnO, If you add an excess of this reagent, the purple color will persist even though you have a primary or secondary alcohol. With the tertiary alcohol you should see no color change since the purple color remains. Record your observations in your notebook. Test 3: Lucas Test
Record your observations in your notebook. Test 3: Lucas Test This test distinguishes tertiary, secondary and primary alcohols from each other. It uses zinc chloride as the reagent in concentrated hydrochloric acid (Lucas Reagent). It is based on the rate of formation of insoluble alkyl chloride. An emulsion is formed. This test is reliable only for alcohols that are fairly soluble in water. Tertiary Alcohols Secondary Alcohols React immediately to form an emulsion of the alkyl halide and water (cloudy solution) React in 5-10 minutes. Heating in warm water and shaking is sometimes necessary with water-insoluble alcohols. These generally take more than one hour to react. Primary alcohols The rate of reaction of the alcohols is determined by the ease of formation of the carbocation intermediate. Tertiary alcohols react quickly because they form a relatively stable tertiary carbocation and secondary alcohols react more slowly because the secondary carbocation is less stabilized than the tertiary carbocation. The first step, shown below for a tertiary alcohol, involves a Lewis acid-base reaction between zinc chloride and a lone pair of elections on the alcohol oxygen. In the next step, which is the slow, rate determining step, the HO-ZnCl complex leaves and the carbocation is then attacked by a chloride anion from the HCI solvent to form the insoluble alkyl chloride which forms the cloudy emulsion indicative of a positive test. Again, the overall rate of the reaction is determined by the slow step, which is the breaking of the C-OH-ZnCI bond. This rate is determined by the stability of the carbocation being formed.
Figure 63 Lucas Test Tertiary alcohol R' R Ha -*+ R-OH + Zna, Lewis Acid Lewis Base Rz CI insoluble CT Recall: Stability of carbocations: H >> >R+ R Procedure: Set-up three small test tubes as above, labeling each of them. Add 0.5 mL of the test alcohol to each test tube. To the first test tube, add 3 mL of the Lucas reagent. Shake vigorously using a small cork to stopper the test tube. Wait at least 10 minutes. If you have a water insoluble alcohol (you see two layers in your test tube) then repeat the experiment using a hot water bath set at 60 °C, immersing the test tube in the water bath immediately after shaking and waiting the 10 minutes with occasional shaking. Also repeat the experiment using a water-soluble alcohol of the appropriate class. Record your results. Repeat on all three classes of alcohol. Test 4: Todoform Test This test is slightly different from the previous three tests. This test does not distinguish 1º, 2º, 3º alcohol but is specific for only one class of alcohol. This is the secondary methyl alcohol. If the alcohol contains a methyl group attached to a carbon that also has a hydrogen and an OH group then it will give a positive iodoform test. The formation of a yellow precipitate indicates a positive test. This is shown in figure 6.4. Figure 6.4 FOH ОН R=H. CH. CH.CH, etc This group must be present in the molecule in order to give a positive iodoform test The mechanism of the reaction is somewhat complex (Figure 6.5) and will be studied in detail in the second semester. Only the outline of the mechanism is shown here. Notice that the first step is the formation of the mild oxidizing agent sodium hypoiodite, NaOl, from sodium hydroxide and iodine. NaOl oxidizes the
Appendix 6.1: A possible mechanism for hypoiodite oxidation of Alcohols. Figure 66 - + NaOH Na OH OH R- CH, POH + CH H OH Rt-CH, LCH + 1 +HO OH Appendix 6.2 Infrared Spectra of Unknown Alcohols. Methyl Alcohol 80 60 % Transmittance 40 M 20 4000 3000 1000 2000 Wavenumbers (cm-1) Ethyl Alcohol 80 60 % Transmittance 40 20 4000 3000 1000 2000 Wavenumbers (cm-1)
1-Propanol 80 60 %Transmittance 40 20 4000 3000 1000 2000 Wavenumbers (cm-1) 2-methyl-2-Propanol 80 60 % Transmittance W. W 40 20 4000 3000 1000 2000 Wavenumbers (cm-1) 1-Butanol 80 60 % Transmittance 40 20 1000 4000 3000 2000 Wavenumbers (cm-1)
2.Methyl-2-butanol w mi Cyclohexanol 80 60 8 % Transmittance 40 20 1000 4000 3000 2000 Wavenumbers (cm-1)
2-Butanol (s-Butyl Alcohol) 80 60 % Transmittance 40 20 4000 3000 1000 2000 Wavenumbers (cm-1 w им 1-Pentanol (Amyl Alcohol) 80 % Transmittance 60 40 20 4000 3000 1000 2000 Wavenumbers (cm-1) 3-Methyl-1-butanol (Isoamyl Alcohol) N 80 . 60 % Transmittance 40 20 1000 4000 3000 2000 Wavenumbers (cm-1)