Tert-Butanol

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tert-Butanol, or 2-methyl-2-propanol, is the simplest tertiary alcohol. It is one of the four isomers of butanol. tert-Butanol is a clear liquid with a camphor-like odor. It is well soluble in water and miscible with ethanol and diethyl ether. It is unique among the isomers of butanol because it tends to be a solid at room temperature, with a melting point slightly above 25 degrees Celsius.

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Applications

tert-Butyl alcohol is used as a solvent, as a denaturant for ethanol, as an ingredient in paint removers, as an octane booster for gasoline, as an oxygenate gasoline additive, and as an intermediate in the synthesis of other chemical commodities such as flavors and perfumes.

Preparation

tert-Butyl alcohol can be manufactured industrially by the catalytic hydration of isobutylene.

Chemistry

As a tertiary alcohol, tert-butanol is more stable to oxidation and less reactive than the other isomers of butanol.

When tert-butanol is deprotonated with a strong base, the product is an alkoxide anion. In this case, it is tert-butoxide. For example, when tert-butanol is deprotonated with sodium hydride, the resultant is sodium tert-butoxide.

NaH + tBuOH → tBuO⁻Na⁺ + H₂

The tert-butoxide species is itself useful as a strong, non-nucleophilic base in organic chemistry. It is able to abstract acidic protons from the substrate molecule readily, but its steric bulk inhibits the group from participating in nucleophilic addition, such as in a Williamson ether synthesis or an S_N2 reaction.

Conversion to alkyl halide

tert-Butanol (also tert-butyl alcohol) reacts with hydrogen chloride to form tert-butyl chloride and water via an S_N1 mechanism.

The overall reaction, therefore, is:

Because tert-butanol is a tertiary alcohol, the relative stability of the tert-butyl carbocation in the Step 2 allows the S_N1 mechanism to be followed. Primary alcohols generally require an S_N2 mechanism because the energy barrier to produce a primary carbocation is so high that it will not reasonably happen. The S_N2 mechanism allows the carbocation intermediate to be avoided.

References

1. ^ Merck Index, 11th Edition, 1542