Download Colorful Oxidation of Alcohol

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Colorful Oxidation of Alcohol
Source: Summerlin, L. R., Borgford, C. L., and Ealy, J. B. (1987)
Chemical Demonstrations: A Source Book for Teachers Volume 2. p. 210.
Description: When a yellow solution, K2CrO7, is added to three different alcohols, the
solution turns blue in two of the alcohols and remains yellow in one.
Concept: Potassium dichromate will oxidize propyl alcohol and sec-butyl alcohol, but
not tert-butyl alcohol. Primary and secondary alcohols are easily oxidized. The carbons
holding the OH groups in propyl and sec-butyl alcohol are also holding at least one
hydrogen. This hydrogen is removed by the oxidizing agent along with the H from the
hydroxyl group leaving a carbonyl group and forming water.
Materials:
 0.015 M K2Cr2O7 in 3 M H2SO4
 propyl alcohol (1-propanol)
 sec-butyl alcohol (2-butanol)
 tert-butyl alcohol (2-methyl-2-propanol)
 three large test tubes
 25 mL graduated cylinder
 Stirring rods
Safety: Wear safety goggles and gloves. Sulfuric acid is irritating. Potassium
dichromate is extremely destructive to the mucous membranes of the upper respiratory
tract, skin, and eyes. Exposure could be fatal. Also it is a carcinogen.
Procedure:
Add about 25 mL of each alcohol to the large test tubes.
Add 25 mL of the K2Cr2O7 solution to each tube and stir quickly.
Clean-Up: Collect the contents of the test tubes in a waste bottle, label a waste tag, and
take to EH&S collection site.
Notes:
This demo has never been done in class. It was requested by Prof. Richardson for C102.
See diagram next page for information about the reactions.
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H
H
H
H
H- C- C- C- OH
H
H
H
H
H
(yellow)
H
H
H
H
O
H
CH
H
(yellow)
tert
H
(blue)
H
H
O
methyl ethyl ketone
H O
2
H
(blue)
3
HO - C - CH
CH
H O
2
H- C- C- C- C- H +
+ (O)
H
sec -Butyl Alcohol
O +
H
propylaldehyde
H- C- C- C- C- H
H
H
H- C- C- C
+ (O)
H
1-Propanol
H
3
+ (O)
NR
(no color change)
remains yellow
3
-Butyl Alcohol
(yellow)
The aldehyde would be further oxidized to form a carboxylic acid. The ketone
would not be further oxidized. Another demo in this manual, The Silver Mirror (Tollen's
Test for Aldehydes) illustrates this principle
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