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Tert-Butyl alcohol

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Tert-Butyl alcohol

tert-Butyl alcohol
Skeletal formula of tert-butanol Ball and stick model of tert-butanol
Sample of partially crystalised tert-butanol
Identifiers
CAS number  YesY
PubChem
ChemSpider  YesY
UNII  YesY
EC number
UN number 1120
DrugBank
MeSH
ChEBI  YesY
ChEMBL  YesY
RTECS number EO1925000
Beilstein Reference 906698
Gmelin Reference 1833
Jmol-3D images Image 1
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 The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
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 Highly Flammable F Harmful 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)
 YesY   YesY/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 → tBuOK+ + 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 SN2 reaction.

Conversion to alkyl halide

tert-Butyl alcohol reacts with hydrogen chloride to form tert-butyl chloride and water via an SN1 mechanism.

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 SN1 mechanism to be followed. Primary alcohols generally undergo an SN2 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

  1. ^ a b c "tert-Butyl Alcohol - Compound Summary". PubChem Compound. National Center for Biotechnology Information. 2005-03-26. Retrieved 2012-05-19. 
  2. ^ http://www.inchem.org/documents/icsc/icsc/eics0114.htm
  3. ^ Reeve, W.; Erikson, C.M.; Aluotto, P.F. Can. J. Chem, 1979, 57, 2747.
  4. ^ http://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+50
  5. ^ http://www.sc.mahidol.ac.th/scbc/bc_internet/publication/696.pdf
  6. ^ Johnson, W. S.; Schneider, W. P. (1950), "β-Carbethoxy-γ,γ-diphenylvinylacetic acid",  

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