Tert-Butanol

Chembox new
Name = "tert"-Butanol
Reference = ["Merck Index", 11th Edition, 1542]
ImageFileL1 = Tert-butanol-2D-skeletal.png ImageSizeL1 = 120px
ImageNameL1 = "tert"-Butanol
ImageFileR1 = Tert-butanol-3D-balls.png ImageSizeR1 = 120px
ImageNameR1 = "t"-BuOH
IUPACName = 2-Methyl-2-propanol
OtherNames = "t"-Butanol
"tert"-Butanol
"t"-Butyl alcohol
"tert"-Butyl alcohol
"tertiary"-Butyl alcohol
Section1 = Chembox Identifiers
CASNo = 75-65-0
SMILES = C(C)(C)(C)O
Section2 = Chembox Properties
Formula = C₄H₁₀O
MolarMass = 74.1216(42) g/mol
Density = 0.78086 g/cm³
MeltingPtC = 25.69
BoilingPtC = 82.4
Section7 = Chembox Hazards
ExternalMSDS = [http://physchem.ox.ac.uk/msds/BU/tert-butyl_alcohol.html Oxford MSDS]
NFPA-H = 1
NFPA-F = 3
NFPA-R =

"tert"-Butanol, or 2-methyl-2-propanol (colourless liquid or white solid, depending on the ambient temperature), 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 °C.

Preparation

"tert"-Butanol can be manufactured industrially by the catalytic hydration of isobutylene.

Applications

"tert"-Butanol 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.

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, the commonly used organic reagent potassium "tert"-butoxide is prepared by refluxing dry "tert"-butanol with potassium metal. [OrgSynth | author = William S. Johnson and William P. Schneider | title = β-Carbethoxy-γ,γ-diphenylvinylacetic acid | collvol = 4 | collvolpages = 132 | prep = cv4p0132 | year = 1963]

:K + "t"BuOH → "t"BuO⁻K⁺ + ¹/₂ 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 substitution, 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