SCH4C          Lab #14 - Some Reactions of Hydrocarbons and Alcohols

In the first part of this experiment you will investigate the reactivity of some examples of different classes of hydrocarbons - compounds containing carbon and hydrogen only.  You will use cyclohexane, cyclohexene, xylene and toluene.

You will investigate the relative ease of oxidation of these compounds by a strong oxidizing agent, and an alkaline solution of potassium permanganate.  You will also compare their ability to add or substitute a bromine atom for a hydrogen atom when they are treated with a solution of bromine Br2, in an organic solvent.

In the second part of the experiment you will investigate some of the reactions of alcohols - organic compounds that contain the functional group - OH.  Alcohol's are classified as primary, secondary or tertiary, according to the number of other groups that are bonded to the carbon atom to which the -OH group is attached.  You will use the following alcohols:   methanol, ethanol, butan-1-ol, butan-2-ol, and t-butyl alcohol.

You are dealing with organic compounds.  Safety glass must be worn at all times.
No open flames during this lab.

1.       First you will study oxidation.  Label a clean, dry, 13 X 100 mm test tube for each of the hydrocarbons to be tested: cyclohexane, cyclohexene, toluene and xylene.  Add about 10 drops of the appropriate hydrocarbon to each test tube.  Prepare about 4 mL of 0.005 M alkaline potassium permanganate solution by adding 2 mL of 0.01 M KMnO4 to 2 mL of 6 M NaOH.  Add 20 drops (about 1 mL) of this solution to each of the test tubes containing different hydrocarbons.  Stopper each test tube and shake gently to obtain more complete contact between the two phases.    Note any changes in the colour of the aqueous layer after about 1 minute.  Shake the contents occasionally, and observe the tubes after 5 minutes.

2.    Now you will observe addition and substitution of Br2.  Place about 10 drops of each hydrocarbon into four small test tubes, properly labeled.  Add about 20 drops (about 1 mL) of bromine water, Br2(aq),  drop by drop, to each of the test tubes.  Stopper each tube and shake the contents occasionally as you add the bromine solution.  Note any changes in colour.  If a change is noted, continue the addition of the bromine until the bromine colour persists.  Record the number of drops of Br2 requird to achieve a persistent colour.

Part 2: Some Reactions of Alcohols

1.    Observe the reaction of ethanol, C2H5OH, with neutral, acidic, and basic solutions of potassium permanganate.
Place about 2 mL of 0.01 M KMnO4 in each of three small test tubes.  Add 2 mL of distilled water to one, 2 mL of 6 M H2SO4 to the second,  and 2 mL of 6 M NaOH to the third.  Label them neutral, acidic, and basic KMnO4.  Now add 2 drops of C2H5OH to each, shake the contents, and note any changes in colour of the permanganate solutions.  Add another drop or two of ethanol and observe any further changes that may take place after 5 minutes.   Note any differences in the rate of oxidation as well as in the reaction products. Note: The colour of a solution containing the manganate ion MnO4-2, is green; manganese dioxide, MnO2, is a brown precipitate; and a solution containing the manganese(II) ion, Mn+2, is very light pink, almost colourless.

2.      Now you will observe the reaction of methanol, CH3OH, with hot copper oxide.  Wrap a penny with a few turns of heavy copper wire so that it can be suspended above about 10 mL of methanol in a small beaker.  Place a glass stirring rod across the beaker, and hook the wire over it so that the penny is suspended about 1 cm above the surface of the methanol.  Remove the penny and wire to a flame placed well away from the beaker and heat to a dull red hot.  Quickly suspend the hot penny above the methanol in the beaker and note the interesting cyclical reaction that occurs.
    Note the change in the appearance of the copper.  Cautiously smell the vapours and compare then with those of the methanol.  The new substance formed is formaldehyde, HCHO, which you may recognize as the liquid used to preserve specimens in the biology laboratory.

3.       Compare the behaviour of three isomeric alcohols in the following reactions.
    First, you will observe the reaction with concentrated HCl. (Note: concentrated HCl is used to compare the ease with which the -OH group of the alcohol R-OH reacts with 12 M HCl to form H2O and the alkyl chloride, R-Cl.  The alkyl halide is only slightly soluble in the aqueous phase and its presence is shown by a cloudiness due to the suspension of R-Cl droplets in the water.)
    Place about 1 mL of butan-1-ol in a small test tube.  Add about 5 mL of 12 mL HCl.  Stopper the test tube, shake the mixture very carefully, and after a minute look for the presence of the slightly soluble alkyl chloride.
    Repeat this test with the other two isomeric alcohols.
    Second, observe the reaction with a neutral solution of 0.01 M KMnO4.   Place about 2 mL of 0.01 M KMnO4 solution in a small test tube.  Add an equal volume of butan-1-ol. Add 1 mL of distilled water, stopper the tube, and shake the contents.  Observe the color of the permanganate solution over a period of five minutes.  Shake occasionally during this period.
    Repeat this test with the other two isomeric alcohols.
    Third, observe the reaction with metallic sodium.  Place about  1 mL of the butan-1-ol in a small dry test tube.  Add a very small piece of freshly cut metallic sodium metal.  Note any reaction that occurs.  (Caution: Sodium is a very reactive and potentially dangerous metal.   Keep it away from water or acids.)
    Repeat this test with the other two isomeric alcohols.

1.    Examine models of the various hydrocarbons you tested.  Which contain double bonds?  Which of the models are planar, and which are non-planar.  Is there an alternate structure for cyclohexane?

2. (a)  Which of the hydrocarbons were readily oxidized by the alkaline solution of KMnO4?
    (b)  Which hydrocarbon were reactive with the bromine solution?
    (c)   What is the relationship between the reactivity noted in (a) and (b) and the structure of the hydrocarbons?

3.    Write the balanced equation for the reaction in which methanol was oxidized by the hot copper oxide.

4.    What differences were noted when C2H5OH reduced the neutral, acidic, and basic solutions of KMnO4?  Assuming that in each case C2H5OH was oxidized to acetic acid, CH3COOH, write balanced equations for each reaction.  Be sure to use the reduction half-cell reaction that involves the reduction product of manganese you observed.

5.    In the reactions involving the three isomeric alcohols with the formula C4H9OH, what did each of the following tests show about the functional group - OH and its position in the alcohol in
(a)    the test with concentrated hydrochloric acid;
(b)    the test with neutral potassium permanganate; and
(c)    the test with metallic sodium?

6.    Write a balanced equation for each case in question 5 where a reaction occurred.

7.    There is a fourth alcohol with the formula C4H9OH.  Draw a structural formula for it and name it.  How so you predict that it would react with each of the tests in question 5.