The preparation of tertiary butyl chloride
(2-chloro-2-methylpropane).
[SN1]
(CH3)3C-OH + H+ →
(CH3)3C-+OH2 →
(CH3)3C+ +
Cl- → (CH3)3C-Cl
tertiary alcohol
carbocation alkyl halide
Introduction
This preparation illustrates the fast reaction of a tertiary
alcohol with hydrogen chloride to give the corresponding alkyl
chloride by a SN1 mechanism, which goes via the
carbocation.
Procedure:
In a 100 mL separatory funnel place anhydrous t-butyl alcohol
(12.4 g, density 0.78 g cm-3), and concentrated
hydrochloric acid (21 mL) and shake the mixture very frequently
during 20 minutes. After each shaking, relieve any internal
pressure by opening the stopcock of the inverted separatory
funnel.
Allow the mixture to stand for a few minutes after the period of
shaking until the layers have separated sharply; separate the two
layers and set aside the aqueous acid layer in a beaker. Pour the layer
containing the halide product into a clean, dry conical flask and
dry with a mixture of anhydrous magnesium sulfate and
sodium carbonate in the stoppered flask.* Filter the liquid
through a small funnel supporting a fluted filter paper into a
dry pre-weighed test-tube.
Record the weight of the t-butyl chloride, calculate
the yield and submit the entire sample for grading.
Inspect the
infrared spectra of t-butanol and t-butylchloride.
On your worksheet, record the position of the band and name the
functional group that disappeared during the reaction.
* Dry for at least 10 minutes until the chloride is no longer cloudy.
Note: Tertiary butyl chloride is very volatile.
Reference: Solomons and Fryhle, 8th Edition, pg 501
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