Cerritos Community College
Organic Chemistry 211 Laboratory
Nucleophilic Substitution of Alkyl Halides
(Part 2: Solvent Effects on SN1 Reactivity)
Waste Disposal: All the reaction mixtures should be placed in the halogenated organic waste
container.
Objective: To study the effects of solvent polarity and proticity on the rate of SN1 reactions.
Experiment Overview: Several types of solvent systems, varying in polarity and proticity (All else
being equal) the rates of the reactions will be measured.
The solvent systems are shown in the table below:
It is useful at this point, to think about the polarities of the solvent systems (disregarding the
different mixing percentages) and rank the solvent systems utilized, according to their polarities.
Also, think about the effect of changing the percentage of water in changing the polarities of the
given solvent systems.
The general equation for the reactions is shown below, where the substrate, tert-butyl chloride reacts
with the alcohol (or water) to form an ether and hydrochloric acid byproduct. A certain concentration
of the acidic byproduct will serve as the visual indicative for the endpoint of the reaction, since there
will be an NaOH concentration and some phenolphthalein indicator present in the reaction mixture.
Once enough acid gets produced in the reaction to neutralize the base present, the indicator will
change color, which will be marked as the reaction endpoint.
t-Bu_____Cl + ROH t-Bu___OR + HCl
Procedure:
With your instructor’s help, choose 3 solvent systems, using either different ratios of one solvent
system or the same ratio for different solvent systems. Label 3 clean and dry test tubes. To each test
tube add 2.0 mL of the solvent system and 3 drops of 0.5 M NaOH solution containing
phenolphthalein indicator. Cork the test tubes and place them into a water bath equipped with a
thermometer and water at 30.0 + 1 oC. A Styrofoam cup placed in an empty beaker makes a
convenient insulated container for the bath. After a few minutes of allowing the test tubes to
equilibrate with the temperature of the bath, add 3 drops of tert-butyl chloride to each test tube.
Record the time of addition and shake the contents of the test tubes thoroughly, in order to insure
complete mixing. Also, swirl the test tubes intermittently. Record the time required for the
disappearance of the pink indicator color. This will be the visual indicative for the completion of the
reactions. Remember to monitor the temperature and keep it within 1oC of 30oC (the temperature is a
constant value and not a variable).
Solvent System
Percentage
acetone: water
55:45
60:40
65: 35
*
ethanol: water
55:45
60:40
65: 35
70:30
methanol: water
55:45
60:40
65: 35
70:30
