The preparation of tertiary butyl chloride (2-chloro-2-methylpropane).

(CH3)3C-OH + H+ → (CH3)3C-+OH2 → (CH3)3C+ + Cl- → (CH3)3C-Cl
tertiary alcohol                                             carbocation          alkyl halide


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.


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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