Download Experiment # 8 Synthesis and Reactivity of tert

Experiment # 8
Synthesis and Reactivity of tert-Butyl Chloride
Introduction:
The purpose of this experiment is to synthesize tert-butyl chloride via an SN1
reaction and to characterize it using simple chemical tests to describe its reactivity.
HCl
OH
Cl
tert-butyl chloride
tert-butyl alcohol
Tertiary alcohols can easily be converted to their corresponding alkyl chlorides by
the addition of concentrated hydrochloric acid to the alcohol. In this experiment,
concentrated hydrochloric acid is used to prepare tert-butyl chloride from tert-butyl
alcohol via SN1 reaction.
The mechanism of this SN1 reaction involves three steps. First, is the rapid (and
reversible) protonation of the alcohol, followed by the much slower rate-determining
step, the loss of water to give a relatively stable tertiary carbocation. In the final step, the
carbocation is rapidly attacked by the chloride ion to form the alkyl halide. The alkyl
halide is insoluble in water, and thus it separates from the aqueous layer.
H-Cl
OH
OH2
-H2O
Cl
Cl
Characterization of alkyl halides takes advantage of the fact that the halogen can
easily be displaced. The two tests that you will use are complementary, and are useful for
classifying the structure of alkyl halides. The silver nitrate test proceeds via an SN1
reaction, and the sodium iodide test proceeds via an SN2 reaction.
When a halide is treated with a solution of AgNO3 in ethanol, the silver ion
initially coordinates with the halogen electron pair. This in turn weakens the carbon
halogen bond, and a molecule of insoluble silver halide is formed. The resulting
carbocation reacts with the ethanol to form an ethyl ether. Since this reaction is an SN1
reaction, the order of reactivity for this test tertiary > secondary > primary > methyl.
The sodium iodide test is used to test for the presence of bromine or chlorine.
Alkyl halides that can react by an SN2 mechanism to give a precipitate of sodium halide
salt. The order of reactivity of alkyl halides in this reaction is methyl > primary >
secondary > tertiary.
Procedure:
Part A: Synthesis of tert-butyl chloride
To a 125 mL separatory funnel, carefully add 15 mL of concentrated acid and 5
mL of tert-butyl alcohol. Swirl the contents of the funnel, place the stopper on, and invert
it. Open the stopcock immediately to release excess pressure, pointing the funnel towards
the back of the fumehood. Shake the funnel and vent at regular intervals. Place the funnel
in a ring stand and allow the two layers to separate. Drain the lower aqueous layer into a
250 mL Erlenmeyer flask (labeled H2O to remind you that this is the aqueous layer). Add
40 mL of saturated sodium bicarbonate solution to the organic layer remaining in the
funnel. Gently swirl the funnel several times until the bubbling ceases. Then, stopper the
funnel, invert it, and vent immediately. Shake the funnel and vent it at regular intervals.
Place the funnel back in the ring stand and allow the two layers to separate. Drain the
lower aqueous layer in the Erlenmeyer flask. Wash the organic layer with 30 mL of
water. Again, drain the lower aqueous layer into the Erlenmeyer flask. Transfer the
organic layer (the crude product, tert-butyl chloride) into a clean and dry 50 mL
Erlenmeyer flask and dry using calcium chloride. Decant or pipet off the liquid into a preweighed 10 mL beaker. Get the weight of your crude product, and calculate the percent
yield (the tert-butyl alcohol is your limiting reagent).
Part B: Qualitative Chemical Tests for Reactivity
Obtain a test tube rack, and label the four small test tubes. Into two tubes add a
couple drops of your synthesized tert-butyl chloride. Into the other two test tubes add a
couple drops of 1-chlorobutane. To one test tube of each compound add 1 mL of sodium
iodide solution, stopper the test tube, and shake the contents vigorously. Note the time it
takes for any precipitate to form (at the first appearance of any precipitate). To the other
two test tubes, add 1 mL of the silver nitrate solution, stopper the test tube, and shake the
contents vigorously. Avoid getting the AgNO3 solution on your skin! Again, note the time
it takes for any precipitate to form (at the first appearance of any precipitate).
Equipment:
Each pair will obtain the following glassware/equipment from the cart at the front of the
room before starting the experiment. All equipment should be cleaned and returned to the
cart before leaving the lab.
- 1 125 mL separatory funnel with stopper
- 1 250 mL erlenmeyer flask
- 1 50 mL erlenmeyer flask
- 1 10 mL beaker
- 1 test tube rack with 4 test tubes and stoppers
- 1 pipet bulb
- 1 10 mL graduated cylinder
- 1 50 mL graduated cylinder
Glass pipets will be on the bench tops. All chemicals will be in the fume hood. There will
be a ring stand in each fumehood. All aqueous waste can be washed down the drain with
water. Organic liquid waste should go into the waste container that will be in the
fumehood.
Safety Considerations:
- Take care when using the concentrated acid and the silver nitrate solution to not
get it on your skin or clothing. Since we are using a larger volume of concentrated
acid this week, you may want to choose what you wear to lab carefully!
- There will be a waste container for organic liquid waste
- Dispose of used glass pipets in the broken glass container