Tert-Butyl alcohol

tert-Butyl alcohol
IUPAC name 2-Methylpropan-2-ol[1]
Other names tert-Butanol[1] 2-Methyl-2-propanol[1]
Identifiers
CAS number	Y
PubChem
ChemSpider	Y
UNII	Y
EC number
UN number	1120
DrugBank
MeSH
ChEBI	Y
ChEMBL	Y
RTECS number	EO1925000
Beilstein Reference	906698
Gmelin Reference	1833
Jmol-3D images	Image 1
SMILES CC(C)(C)O
InChI InChI=1S/C4H10O/c1-4(2,3)5/h5H,1-3H3 Y Key: DKGAVHZHDRPRBM-UHFFFAOYSA-N Y
Properties
Molecular formula	C4H10O
Molar mass	74.12 g mol−1
Appearance	Colorless liquid
Odor	Camphorous
Density	0.775 g/mL
Melting point	25 to 26 °C; 77 to 79 °F; 298 to 299 K
Boiling point	82 to 83 °C; 179 to 181 °F; 355 to 356 K
Solubility in water	miscible[2]
log P	0.584
Vapor pressure	4.1 kPa (at 20 °C)
Acidity (pKa)	16.54 [3]
Refractive index (nD)	1.387
Thermochemistry
Specific heat capacity C	215.37 J K−1 mol−1
Std molar entropy So298	189.5 J K−1 mol−1
Std enthalpy of formation ΔfHo298	−360.04–−358.36 kJ mol−1
Std enthalpy of combustion ΔcHo298	−2.64479–−2.64321 MJ mol−1
Hazards
MSDS	inchem.org
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H225, H319, H332, H335
GHS precautionary statements	P210, P261, P305+351+338
EU Index	603-005-00-1
EU classification	F Xn
R-phrases	R11, R20, R36/37
S-phrases	(S2), S9, S16, S46
NFPA 704	3 1 0
Flash point	11 °C (52 °F; 284 K)
Explosive limits	2.4–8.0%
Related compounds
Related butanols	2-Butanol n-Butanol Isobutanol
Related compounds	2-Methyl-2-butanol Trimethylsilanol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Y   Y/N?)

tert-Butyl alcohol (TBA), or 2-methyl-2-propanol (2M2P), is the simplest tertiary alcohol. It is one of the four isomers of butanol. tert-Butyl alcohol is a clear liquid (or a colorless solid, depending on the ambient temperature) with a camphor-like odor. It is very 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.

Natural occurrence

t-Butyl alcohol has been identified in beer and chickpeas.^[4] It is also found in cassava^[5] which is used as fermentation ingredient in certain alcoholic beverages.

Preparation

tert-Butyl alcohol is derived commercially from isobutane as a co-product of propylene oxide production. It can also be produced by the catalytic hydration of isobutylene, or by a Grignard reaction between acetone and methylmagnesium chloride.

Applications

tert-Butyl alcohol is used as a solvent, ethanol denaturant, paint remover ingredient, and gasoline octane booster and oxygenate. It is a chemical intermediate used to produce MTBE and ETBE by reaction with methanol and ethanol, and TBHP by reaction with hydrogen peroxide.

Chemistry

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

When tert-butyl alcohol is deprotonated with a strong potassium tert-butoxide is prepared by refluxing dry tert-butanol with potassium metal.^[6]

K + tBuOH → tBuO⁻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-Butyl alcohol reacts with hydrogen chloride to form tert-butyl chloride and water via an S_N1 mechanism.

• Step 1

• Step 2

• Step 3

The overall reaction, therefore, is:

Because tert-butyl alcohol 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 undergo an S_N2 mechanism because the relative stability of a primary carbocation intermediate is very low. The tertiary carbocation in this case is stabilized through hyperconjugation where the neighboring C–H sigma bonds donate electrons into the empty p-orbital of the carbocation.

References