Oxidation & Identification of an Unknown Alcohol
of Experiment--see below.
Hornback; 2nd ed.; pp 380-385.
In this experiment, you will use common household bleach
as the oxidizing agent. Most bleaches are aqueous sodium hypochlorite,
NaOCl(aq). This is created by adding chlorine to sodium hydroxide:
When sodium hypochlorite
is added to acetic acid, the following acid-base reaction occurs:
NaOCl, Cl2, and
hypochlorous acid (HOCl) are all possible sources of positively charged
Although the existence of discrete Cl+ ions in aqueous solutions
has never been found, it is apparent that a key step in these reactions
is the transfer
of electrons from the organic substrate to the Cl+ species
to generate Cl-. One possible transformation for the oxidation
of an alcohol with these reagents, using cyclopentanol as an example,
step in the mechanism shows the replacement of the hydroxyl proton with
the positive chlorine. The following step is the elimination of HCl from
alkyl hypochlorite to form the ketone, cyclopentanone. In the first step,
Cl+ is transferred to the substrate; and in the second, Cl-
is lost. The change is a reduction by two electrons. Cyclopentanol provides
those two electrons and is therefore, oxidized.
Hypochlorite oxidations provide a distinct advantage over other oxidizing
reagents, such as Cr(VI) reagents, since the toxicity of the chromium
reagents provide difficulties in handling and waste disposal. The salt
formed in the hypochlorite oxidations can be rinsed down the sink.
In this experiment, you will use the NaOCl in a water/acetic acid mixture
to oxidize one of seven possible alcohols into a ketone. Due to the possible
low boiling points of some of the ketone products, we will never completely
isolate your ketone product. Instead, your product will remain in a solution
of dichloromethane (methylene chloride) that can be injected into the
GC/MS for separation
and identification of individual compounds in your product. Therefore,
the GC/MS will be the only instrument that will allow us to identify the
compounds present in your product mixture. Identification of your product
by GC/MS should allow you to determine the ketone you have created. From
this, you should be able to determine which one of the following seven
alcohols you were given at the beginning of the lab.
1: List of Possible Alcohols
Weigh out 1.5 grams of your unknown alcohol into a 125-mL Erlenmeyer flask.
Add 1.0 mL of glacial acetic acid and place the flask on a stir plate.
Add a stir bar to the flask and gently stir your solution.
Add 20 mL of aqueous sodium hypochlorite solution dropwise to the flask
over a 10-minute span making sure to keep the temperature of the solution
After complete addition of the aqueous sodium hypochlorite, stir the
mixture for an additional 20 minutes. After approximately 20 minutes
add 5 mL of isopropanol and stir for 1-2 minutes. (What does the isopropanol
Pour the product mixture from the flask into a 125-mL separatory funnel.
Add 20-30 mL of NaCl solution. Shake and vent frequently! (Why is the
salt solution added?) Extract your organic products from the aqueous layer
by adding approximately 10 mL of dichloromethane. Shake and vent,
remove the aqueous layer which should now be void of any organic products.
Wash the organic layer with approximately 10 mL of saturated
hydrogen carbonate solution. Vent often! Dry the organic layer with phase
paper and anhydrous magnesium sulfate and fill a labeled GC/MS vial
the dried organic layer.
Run a GC/MS on this organic product mixture.
Analyze your GC/MS to determine the ketone that you have formed.
Special Waste Disposal
Place all aqueous solutions down the sink rinsing with plenty of water.
- What was the purpose
of adding isopropanol to your reaction?
- Why did you add
salt before trying to isolate your organic product from the aqueous
- Using your mass
spectrum, prove which ketone was synthesized in your reaction?
- Using your mass
you identify any other compounds, or any functional groups on other
in your product mixture?
- Using your partner's
mass spectrum, prove which ketone was synthesized in her reaction.
- Using your partner's
mass spectrum, can
you identify any other compounds or any other functional groups on
in her product?
- Which alcohols
did you and your partner start with in this oxidation reaction? (Make
sure to mention their unknown numbers.)
- What errors occurred
in your oxidation and what would you do differently if you were to do
this reaction again?