What is 2-methyl-2-propanol?
The 2-methyl-2-propanol or terbutanol (t-BuOH) is a tertiary alcohol (the simplest of its homologous series). Its molecular formula is (CH3)3COH and molecular mass of 74.123 g-mol−1, it is also known as trimethyl carbinol. It is one of the four isomers of butanol. Its IUPAC name it is the 2-methylpropan-2-ol.
It is used as a solvent, in denatured ethanol, as an ingredient in paint cleaners and as a chemical intermediate to produce methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE) by reaction with methanol and ethanol, respectively. It is also used to obtain tertiary butyl hydroperoxide (TBHP) by reaction with hydrogen peroxide.
It is one of the four isomers (with the same molecular formula C4H10O) of butanol. The other three are isobutanol (CH3)2CHCH2OH, 2-butanol CH3CH2CH(OH)CH3, and n-butanol CH3CH2CH2CH2OH. It has a dipole moment of 1.31 Debye.
The 2-methyl-2-propanol is a colorless solid, which melts at near room temperature (25-26 ºC) and has a camphor-like odor. It is miscible in water, ethanol and diethyl ether. Its boiling point is 82-83 ºC and its density is 0.775 g-mL−1 .
Like all tertiary alcohols, it is more difficult to oxidize than the other butanol isomers.
Terbutanol is deprotonated with a strong base such as an alkoxide, e.g. potassium terbutoxide, which is prepared by treatment of terbutanol with potassium metal.
- K + t-BuOH → t-BuO−K+ + 1/2 H2
Thus, the terbutoxide obtained is a strong, non-nucleophilic base widely used in Organic Synthesis. It has the ability to remove acidic protons (H+) from substrates, and its steric hindrance prevents it from participating in nucleophilic substitutions, such as the Williamson ether synthesis or an SN2 nucleophilic substitution reaction.
On the other hand, terbutanol reacts with HCl to yield tert-butyl chloride.
Chlorination in oxygen (O-chlorination) of terbutanol with hypochlorous acid (HOCl) gives tert-butyl hypochlorite according to the following reaction:
(CH3)3COH + HOCl → (CH3)3COCl + H2O
Method of production
Terbutanol is obtained commercially from isobutane as a by-product of propylene oxide production. It can also be produced by catalytic hydration of isobutylene, or by a Grignard reaction between methyl magnesium chloride and acetone.
Because it forms an azeotrope with water, its purification cannot be carried out by simple distillation. An initial drying (when it contains large amounts of water) can be done by adding benzene (tertiary azeotrope terbutanol/water/benzene) and removing the water by distillation.
If small amounts of water are present in the terbutanol, they can be removed by drying with an anhydrous salt such as calcium oxide (CaO), potassium carbonate (K2CO3), calcium sulfate (CaSO4) or magnesium sulfate (MgSO4), followed by fractional distillation. In a next step, anhydrous terbutanol can be obtained by refluxing and distilling from iodine-activated magnesium or alkali metals such as sodium and potassium.
Other methods used to obtain anhydrous terbutanol are 4 Å molecular sieves, aluminum terbutylation or calcium hydride (CaH2).