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

        (CH3)3C-OH + H+ ® (CH3)3C-O+H2 ® [SN1]
        (CH3)3C+ + Cl- ® (CH3)3C-Cl

This preparation illustrates the fast reaction of a tertiary alcohol with hydrogen chloride to give the corresponding alkyl chloride by an 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 discard the acid layer. Pour the halide into a conical flask and dry with a mixture of anhydrous magnesium sulphate and sodium carbonate in the stoppered flask.* Filter the liquid through a small funnel supporting a fluted filter paper into a dry 50 mL quickfit round bottom flask. Assemble a dry apparatus for simple distillation using the 50 mL R.B. flask as the distillation flask, add four boiling chips to the flask and distill. Collect the fraction boiling at 50 - 51° in a weighed test tube, record the weight of the t-butyl chloride, calculate the yield and submit all of the sample for grading. (Write-up in style of model p. 6).

This preparation of a tertiary alkyl chloride is quite general and can be used to prepare t-amyl chloride (see below).
        
        Vol. of t-amyl alcohol used = 17.6 mL (density 0.8 g cm-3)
        Vol. of conc. HCl used = 42.0 mL
        b.p. of t-amyl alcohol = 105
°
        b.p. of t-amyl chloride = 84 - 86
°

*         Dry for at least 10 minutes until the chloride is no longer cloudy.
        Note: Tertiary butyl chloride is very volatile.


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Created March 1997. Links checked and/or last modified 2nd January 2003.
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