tert-Butyl alcohol

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tert-Butyl alcohol
Skeletal formula of tert-butanol
Ball and stick model of tert-butanol
Sample of partially crystalised tert-butanol
Names
IUPAC name
2-Methylpropan-2-ol1
Other names
tert-Butanol1
Trimethyl carbinol2
2-Methyl-2-propanol1
Identifiers
75-65-0 YesY
906698
ChEBI CHEBI:45895 YesY
ChEMBL ChEMBL16502 YesY
ChemSpider 6146 YesY
DrugBank DB03900 YesY
EC number 200-889-7
1833
Jmol-3D images Image
MeSH tert-Butyl+Alcohol
PubChem 6386
RTECS number EO1925000
UNII MD83SFE959 YesY
UN number 1120
Properties
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
miscible3
log P 0.584
Vapor pressure 4.1 kPa (at 20 °C)
Acidity (pKa) 16.54 4
1.387
Thermochemistry
215.37 J K−1 mol−1
189.5 J K−1 mol−1
−360.04–−358.36 kJ mol−1
−2.64479–−2.64321 MJ mol−1
Hazards
Safety data sheet 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
H225, H319, H332, H335
P210, P261, P305+351+338
EU classification Highly Flammable F Harmful Xn
R-phrases R11, R20, R36/37
S-phrases (S2), S9, S16, S46
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 11 °C (52 °F; 284 K)
480 °C (896 °F; 753 K)
Explosive limits 2.4–8.0%
Lethal dose or concentration (LD, LC):
3559 mg/kg (rabbit, oral)
3500 mg/kg (rat, oral)5
US health exposure limits (NIOSH):
TWA 100 ppm (300 mg/m3)2
TWA 100 ppm (300 mg/m3) ST 150 ppm (450 mg/m3)2
1600 ppm2
Related compounds
Related butanols
2-Butanol

n-Butanol
Isobutanol

Related compounds
2-Methyl-2-butanol
Trimethylsilanol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.6 It is also found in cassava7 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 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.8

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:

0-SN1-tBuOH-to-tBuCl-2D-skeletal.png

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. ^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0078". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ http://www.inchem.org/documents/icsc/icsc/eics0114.htm
  4. ^ Reeve, W.; Erikson, C.M.; Aluotto, P.F. Can. J. Chem, 1979, 57, 2747.
  5. ^ "Tert-Butyl alcohol". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH). 
  6. ^ http://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+50
  7. ^ http://www.sc.mahidol.ac.th/scbc/bc_internet/publication/696.pdf
  8. ^ Johnson, W. S.; Schneider, W. P. (1950). "β-Carbethoxy-γ,γ-diphenylvinylacetic acid". Org. Synth. 30: 18. ; Coll. Vol. 4, p. 132 

External links