Lab 9: SODIUM HYPOCHLORITE OXIDATION: PREPARATION OF CAMPHOR
From: http://www.wou.edu/las/physci/ch335/preparation%20of%20camphor.doc
Oxidation has a somewhat different meaning in organic chemistry than you have been used to
in inorganic, where oxidation is defined as a process involving loss of electrons, as in the
conversion of Fe+2 to Fe+3. Oxidation of organic compounds also normally involves electron
transfer, but because the valence of carbon usually remains at four, it is more useful to define
oxidation as either (a) loss of hydrogen atoms or (b) addition of oxygen or other electronegative
atoms. Thus, all of the following reactions are classified as oxidations:
H
CrO3
O
OH
OH
KMnO4
C
CH 3
O
OH
H2O2
OsO4
OH
Oxidations of alcohols provides one of the most general methods for the preparation of
carbonyl compounds; oxidation of primary alcohols affords aldehydes (or carboxylic acids, if
oxidation is continued), while oxidation of secondary alcohols affords ketones. Tertiary
alcohols cannot be oxidized without breaking carbon-carbon bonds.
H
R
Aldehyde
Primary alcohol
R'
R
O
R
OH
OH
R
O
Carboxylic Acid
R'
OH
R
O
The most common oxidizing agents for the conversion of alcohols to aldehydes and ketones are
chromium trioxide (CrO3) and its relatives, chromate and dichromate ions (CrO4-2 and Cr2O7-2),
as well as a series of modified forms of CrO3, such as Collins reagent, in which CrO3 is
complexed with pyridine (Collins reagent is used in nonaqueous media, and is especially useful
for oxidizing primary alcohols to aldehydes without overoxidation to the carboxylic acid).
KMnO4 can also be used to oxidize alcohols.
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An alternative oxidizing agent for the preparation of ketones, sodium hypochlorite (NaOCl) in
acetic acid, was introduced by Stevens, Chapman, and Weller in 1980 (J. Org. Chem. 45, 2030).
This reagent offers several advantages: it is cheap (sodium hypochlorite is the reagent in Clorox
and "swimming pool chlorine"); it oxidizes secondary alcohols rapidly and in high yield; and it
avoids the problem of disposing of toxic wastes associated with chromium and manganese
reagents.
The example chosen to illustrate the oxidation of alcohols is the sodium hypochlorite oxidation
of isoborneol to camphor:
H3C
H3C
CH 3
CH 3
NaOCl
CH3CO2H
OH
H3C
H3C
O
Camphor is a bridged bicyclic ketone widely distributed in nature, especially in trees of the Far
East. It is used as a plasticizer for the production of celluloid film, for smokeless powders and
explosives, as an insect repellent, and for medicinal purposes (you will recognize the
characteristics odor of Vicks). Borneol, one of the stereoisomeric related alcohols, is found in
certain trees of Borneo, and isoborneol, used in today's experiment, is made commercially from
pinenes (the C10 hydrocarbons of turpentine).
Safety and Waste Disposal
1. Sodium hypochlorite (Clorox) is a strong oxidizing agent and bleach; be careful to keep it off
your skin and clothing. Wash spills with water.
2. Excess Clorox, as well as the filtrate from the collection of camphor, can be poured down the
drain if diluted well with water.
3. If you distill the methylene chloride at the end of the experiment, put the distillate in the
bottle labeled "RECOVERED METHYLENE CHLORIDE"
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EXPERIMENTAL PROCEDURE
Dissolve 5 g of isoborneol in 15 mL of glacial acetic acid in a 125-mL Erlenmeyer flask. Add 50
mL of Clorox by the milliliter over 5 minutes, cooling the flask as necessary to keep the internal
temperature in the range 15-25ºC. A white precipitate will separate out at this point. Allow the
mixture to stand at room temperature for 30 mins with swirling (every 3 mins). A positive KIstarch test should be obtained at this point (White KI-starch paper will turn blue-violet for
positive test).
Add saturated NaHSO3 (Sodium bisulfite: Quenches excess oxidizing agent) solution carefully
until the yellow color of the reaction mixture disappears and the KI-starch test is negative
(White paper stays white). Pour the mixture over 100 mL of brine (Saturated NaCl) and
ice[take 100 ml brine and add a fistful of ice], collect the solid by filtration on a Buchner funnel,
and wash it with saturated NaHCO3 (Sodium bicarbonate) solution until foaming is no longer
evident. Air-dry your solid for 15 minutes (use high vacuum) by using the Buchner filtration
system.
Weigh the dry product so that you can calculate the yield.
Wait until the product dries above; you will need to get all the material needed for this step!
Once the product dries, you will need to prepare the 2,4 Dinitrophenyl hydrazone derivative of
camphor: Dissolve about 0.2 g of your camphor in 5 mL of 95% ethanol, add 10 mL of the 2,4dinitrophenylhydrazine reagent solution, heat to boiling on a hot plate for 3 minutes (The
solution will turn deep yellow or yellow-orange at this point. Don’t worry if some of you don’t
observe this. You will see crystals upon cooling the flask on ice!), and allow the mixture to cool
(1-2 min). Scratch the bottom of the flask with a clean spatula and keep the flask on ice.
Crystallization (yellowish crystals) usually occurs within a few minutes. Filter the yellow
precipitate by suction filtration, wash with 2-3 mL of chilled water, and allow drying to occur
(high vacuum for 5 min).
Determine the melting point (reported mp 164 oC) of your 2,4-DNPH-derivative of camphor
from above.
Calculate the percent yield of your product (camphor).
Post-lab Questions: (Answer these in your notebook).
1. Write a balanced equation for the oxidation of isoborneol by NaOCl.
2. What do you actually observe in a "positive KI-starch test"? What does it mean when it is
mentioned at the end of the first paragraph in the Experimental Procedure that the KI-Starch
test is positive?
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3. What is the purpose of adding NaHSO3 at the end of the oxidation? Write a balanced
equation for the reaction it undergoes.
Notes.
1. Commercial Clorox contains about 6.5% NaOCl.
2. Preparation of 2,4-dinitrophenylhydrazine reagent:
Add 50 mL of concentrated sulfuric acid to 10 g of 2,4-dinitrophenylhydrazine in a 500-mL
Erlenmeyer flask and mix well. Add 75 mL of water dropwise (CAREFUL! HEAT EVOLUTION),
with stirring or swirling, until solution is complete. To this warm solution add 250 mL of 95%
ethanol. This scale provides enough reagents for 35 students. The solution should be prepared
fresh each day.
3. For alternative oxidations of secondary alcohols with Clorox, see
(a)
Oxidation of cyclohexanol: N.M. Zuczek and P.S. Furth, in J. Chem Educ. 58, 824 (1981).
(b)
Oxidation of cyclic and acyclic secondary alcohols: R.A. Perkins and F. Chau, in J. Chem.
Edu. 59, 981 (1982).
(c)
Oxidation of 9-fluorenol: C.S. Jones and K. Albizati, in J. Chem. Educ. 71, A271 (1994).
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