Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
tert-butanol : (CH3)3COH
Class:
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elem=C,Cl
organic
Summary:
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Tert-butanol is very easily converted to tert-butyl chloride. Simply adding
tert-butanol to concentrated hydrochloric acid allows the formation of this
compound.
Description:
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Put a small volume of tert-butanol in a test tube (if the compound has
solidified then first heat slightly, its melting point is just above 25 C). Add
approximately 5 times its volume of concentrated hydrochloric acid (35% HCl)
and swirl: The liquid first becomes opalescent and after a few minutes, two
phases separate from each other. A thick lower layer is formed, which mainly is
hydrocloric acid and a thinner organic layer, which mostly is tert-butyl
chloride.
Add a lot of water (25 times or so of the volume of tert-butyl alcohol used)
and shake: Many small colorless droplets are formed and slowly, these droplets
go to the surface and a thin organic layer is formed on top of the aqueous
layer (which now is very dilute hydrochloric acid). The organic compound hardly
is soluble in water.
Pipette away the organic layer and transfer it to a watch glass. Carefully
smell the liquid: A sweet and fairly pleasant odor can be observed, the oder is
similar to the odor of chloroform. There is no choking smell of HCl, because
that was diluted strongly by adding a lot of water.
Light the liquid on the watch glass (do this outside): The liquid burns with a
very sooty flame and a choking black smoke is produced. This black smoke is
mainly carbon, but there also is formed a considerable amount of HCl and partly
charred compounds. Avoid inhaling this smoke!
The reactions, occuring in this experiment are the following:
Fast: (CH3)3COH + H(+) --> (CH3)3COH2(+) (protonation of alcohol)
Slow: (CH3)3COH2(+) --> (CH3)3C(+) + H2O (formation of carbocation)
Fast: (CH3)C(+) + Cl(-) --> (CH3)3CCl (formation of covalent end product)
The overal reaction hence is: (CH3)3COH + H(+) + Cl(-) --> (CH3)3CCl + H2O
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A counter experiment shows that indeed tert-butyl chloride is formed.
Take a small volume of tert-butyl alcohol and put this on a watch glass. When
this is smelled, then a fairly pungent and somewhat refreshing smell can be
observed. This smell is very different from the smell of tert-butyl chloride.
When the liquid is ignited, then it burns with an orange flame, but hardly any
soot is formed and the product of burning the alcohol is odorless.
Take a small amount of tert-butyl alcohol and add a small amount of water: The
liquids mix when they are swirled. Tert-butyl alcohol dissolves in water very
well and it looks as if these liquids can be mixed in any ratio.
These two counter experiments show that the tert-butyl alcohol has very
different properties, when compared to tert-butyl chloride.
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This experiment gives an example of an alcohol, which very easily can be
converted to its chloride. This is in strong contrast with most other alcohols,
where much more extreme conditions are needed for conversion to the chloride
(such as using PCl5 or SOCl2, or using anhydrous HCl and a strong drying
agent).