Experiment Eight

Are Alkyl Halides Acidic or Basic?

(Are Alkyl Halides Electrophilic or Nucleophilic?)

Background:

Key Terms/Concepts and techniques:

Carbocations, carbanions and their stabilities
Principles of acid-base chemistry
Principles of mass spectrometry and fragmentation patterns
Principles of gas chromatography

Objectives:

To test the reactivity of a series of alkyl halides toward a variety of bases;
To test the reactive of a series of alkyl halides toward a specific base under varying conditions;
To propose mechanism(s) consistent with the results as determined by GC/MS analyses of product mixtures, and
Suggest additional experiments to validate proposed mechanisms.

Pre-lab and In-lab notes/questions:

1. You will work in teams. Each team of two will be assigned

an alkyl halide,
a base/solvent system to use, as well as
the temperature at which the reaction is to be run.

2. All reactions will be run for two hours. Some reactions will be run in a hood and some reactions will be run on the benchtop.

3. In your laboratory notebook, draw a Lewis structure of the alkyl halide assigned to you (hereafter referred to as your alkyl halide).

4. The alkyl halide is soluble in the solvent system, even at room temperature. The solvent system to be used is one of the following: ethanol; 1-propanol; ethyldiisopropylamine.

Discuss within your team how the solubility of your alkyl halide can be accounted for /accomplished.
Draw a picture to illustrate this solubility process..

5. The base involved in these reactions is either KOH or ethyldiisopropylamine.

Draw a structure for KOH and for ethyldiisopropylamine, as they might exist in the reaction medium, and indicate how each can function as a base.

Procedure:

Consult the Experiments Home page, Experiment 8, for the procedures, both general and specific.

Equipment/Apparatus:

The apparatus consists of a magnetic stirrer, heating mantle connected to a Powerstat. In the heating mantle is a 50 mL round bottom flask containing 0.02mole alkyl halide and 25 mL base/solvent. Connected to the flask is a water-cooled reflux condenser which is connected to a stillhead that has a thermometer in it. The still head is connected to a second water-cooled condenser which is connected to a takeoff adapter attached to a 25 mL round-bottom flask which serves as a receiver.

Click on the image at the left to see a larger picture of the apparatus.

You will need The Schockwave plug-in to do the following:

Click on the image at the left to see a larger picture of the apparatus in which you can see identified the various componensts of the apparatus. Once the image is opened click on the word Apparatus on the blackboard.

Reagents:

ethanol
1-propanol
1-bromohexane

1-chlorohexane
2-chloro-2-methylpentane
3-chloro-3-methylpentane

ethyldiisopropylamine
potassium hydroxide

Post-lab questions/notes:

Was there a chemical reaction between your alkyl halide and the base? How do you know?
Did you obtain "product" in your distillation?
If you obtained "product" in your distillate, how many components were there to that distillate? How do you know?
What were the molecular weights of your "products"?
What is the relationship between this value and that of your alkyl halide?
How can any differences be explained?

Compare your results with those of a team that used your alkyl halide but a different base or different solvent system or both.

How can you explain any differences between the reactions?
How can you explain any similarities between the reactions?

ethanol	1-propanol	1-bromohexane
1-chlorohexane	2-chloro-2-methylpentane	3-chloro-3-methylpentane
ethyldiisopropylamine		potassium hydroxide