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2-Butanol
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| Names | |
|---|---|
| Preferred IUPAC name
Butan-2-ol[2] | |
| Other names | |
| Identifiers | |
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3D model (JSmol)
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| 773649 1718764 (R) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.001.053 |
| EC Number |
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| 1686 396584 (R) | |
| MeSH | 2-butanol |
PubChem CID
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| RTECS number |
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| UNII |
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| UN number | 1120 |
CompTox Dashboard (EPA)
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| |
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| Properties | |
| C4H10O | |
| Molar mass | 74.123 g·mol−1 |
| Density | 0.808 g cm−3 |
| Melting point | −115 °C; −175 °F; 158 K |
| Boiling point | 98 to 100 °C; 208 to 212 °F; 371 to 373 K |
| 390 g/L[3] | |
| log P | 0.683 |
| Vapor pressure | 1.67 kPa (at 20 °C) |
| Acidity (pKa) | 17.6 [4] |
| −5.7683×10−5 cm3 mol−1 | |
Refractive index (nD)
|
1.3978 (at 20 °C) |
| Thermochemistry | |
Heat capacity (C)
|
197.1 J K−1 mol−1 |
Std molar
entropy (S⦵298) |
213.1 J K−1 mol−1 |
Std enthalpy of
formation (ΔfH⦵298) |
−343.3 to −342.1 kJ mol−1 |
Std enthalpy of
combustion (ΔcH⦵298) |
−2.6611 to −2.6601 MJ mol−1 |
| Hazards | |
| GHS labelling: | |
 
| |
| Warning | |
| H226, H319, H335, H336 | |
| P261, P305+P351+P338 | |
| NFPA 704 (fire diamond) | |
| Flash point | 22 to 27 °C (72 to 81 °F; 295 to 300 K) |
| 405 °C (761 °F; 678 K) | |
| Explosive limits | 1.7–9.8% |
| Lethal dose or concentration (LD, LC): | |
LCLo (lowest published)
|
16,000 ppm (rat, 4 hr) 10,670 ppm (mouse, 3.75 hr) 16,000 ppm (mouse, 2.67 hr)[5] |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
|
TWA 150 ppm (450 mg/m3)[5] |
REL (Recommended)
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TWA 100 ppm (305 mg/m3) ST 150 ppm (455 mg/m3)[5] |
IDLH (Immediate danger)
|
2000 ppm[5] |
| Safety data sheet (SDS) | inchem.org |
| Related compounds | |
Related butanols
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n-Butanol Isobutanol tert-Butanol |
Related compounds
|
Butanone |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Butan-2-ol, or sec-butanol, is an organic compound with formula CH3CH(OH)CH2CH3. Its structural isomers are 1-butanol, isobutanol, and tert-butanol. 2-Butanol is chiral and thus can be obtained as either of two stereoisomers designated as (R)-(−)-butan-2-ol and (S)-(+)-butan-2-ol. It is normally encountered as a 1:1 mixture of the two stereoisomers — a racemic mixture.
This secondary alcohol is a flammable, colorless liquid that is soluble in three parts water and completely miscible with organic solvents. It is produced on a large scale, primarily as a precursor to the industrial solvent methyl ethyl ketone.
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| (R)-(−)-2-butanol | (S)-(+)-2-butanol |
Manufacture and applications
[edit]Butan-2-ol is manufactured industrially by the hydration of 1-butene or 2-butene:
Sulfuric acid is used as a catalyst for this conversion.[6]
In the laboratory it can be prepared via Grignard reaction by reacting ethylmagnesium bromide with acetaldehyde in dried diethyl ether or tetrahydrofuran.
Although some butan-2-ol is used as a solute, it is mainly converted to butanone (methyl ethyl ketone, MEK), an important industrial solvent and found in many domestic cleaning agents and paint removers. Though most paint removers have ceased using MEK in their products due to health concerns and new laws. Volatile esters of butan-2-ol have pleasant aromas and are used in small amounts as perfumes or in artificial flavors.[6]
Solubility
[edit]The listed solubility of butan-2-ol is often incorrect,[3] including some of the most well-known references such as the Merck Index, the CRC Handbook of Chemistry and Physics, and Lange's Handbook of Chemistry. Even the International Programme on Chemical Safety lists the wrong solubility. This widespread error originated because of Beilstein's Handbuch der Organischen Chemie (Handbook of Organic Chemistry). This work cites a false solubility of 12.5 g/100 g water. Many other sources used this solubility, which has snowballed into a widespread error in the industrial world. The correct data (35.0 g/100 g at 20 °C, 29 g/100 g at 25 °C, and 22 g/100 g at 30 °C) were first published in 1886 by Alexejew and then similar data was reported by other scientists including Dolgolenko and Dryer in 1907 and 1913, respectively.[3]
Precautions
[edit]Like other butanols, butan-2-ol has low acute toxicity. The LD50 is 4400 mg/kg (rat, oral).[6]
Several explosions have been reported[7][8][9] during the conventional distillation of 2-butanol, apparently due to the buildup of peroxides with the boiling point higher than that of pure alcohol (and therefore concentrating in the still pot during distillation). As alcohols, unlike ethers, are not widely known to be capable of forming peroxide impurities, the danger is likely to be overlooked. 2-Butanol is in Class B Peroxide Forming Chemicals[10]
References
[edit]- ^ "Alcohols Rule C-201.1". Nomenclature of Organic Chemistry (The IUPAC 'Blue Book'), Sections A, B, C, D, E, F, and H. Oxford: Pergamon Press. 1979.
Designations such as isopropanol, sec-butanol, and tert-butanol are incorrect because there are no hydrocarbons isopropane, sec-butane, and tert-butane to which the suffix "-ol" can be added; such names should be abandoned. Isopropyl alcohol, sec-butyl alcohol, and tert-butyl alcohol are, however, permissible (see Rule C-201.3) because the radicals isopropyl, sec-butyl, and tert-butyl do exist
- ^ "2-butanol - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification and Related Records. Retrieved 12 October 2011.
- ^ a b c Alger, Donald B. (November 1991). "The water solubility of butan-2-ol: A widespread error". Journal of Chemical Education. 68 (11): 939. Bibcode:1991JChEd..68..939A. doi:10.1021/ed068p939.1.
- ^ Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc., p. 989
- ^ a b c d NIOSH Pocket Guide to Chemical Hazards. "#0077". National Institute for Occupational Safety and Health (NIOSH).
- ^ a b c Hahn, Heinz-Dieter; Dämbkes, Georg; Rupprich, Norbert (2005). "Butanols". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. ISBN 978-3-527-30673-2..
- ^ Doyle, R. R. (1986). "2-Butanol safety warning". Journal of Chemical Education. 63 (2): 186. Bibcode:1986JChEd..63..186D. doi:10.1021/ed063p186.2.
- ^ Peterson, Donald (11 May 1981). "Letters: Explosion of 2-butanol". Chemical & Engineering News. 59 (19): 3. doi:10.1021/cen-v059n019.p002.
- ^ Watkins, Kenneth W. (May 1984). "Demonstration hazard". Journal of Chemical Education. 61 (5): 476. Bibcode:1984JChEd..61..476W. doi:10.1021/ed061p476.3.
- ^ "Classification List of Peroxide Forming Chemicals". ehs.ucsc.edu.
External links
[edit]- International Chemical Safety Card 0112
- NIOSH Pocket Guide to Chemical Hazards. "#0077". National Institute for Occupational Safety and Health (NIOSH).
- IPCS Environmental Health Criteria 65: Butanols: four isomers
- IPCS Health and Safety Guide 4: 2-Butanol
2-Butanol
View on Grokipediafrom Grokipedia
Chemical identity and nomenclature
Structural formula and molecular properties
2-Butanol, also known as butan-2-ol, is an organic compound with the molecular formula C₄H₁₀O.[1] Its structural formula is CH₃CH(OH)CH₂CH₃, featuring a linear four-carbon chain where a hydroxyl group (-OH) is attached to the second carbon atom.[1] This configuration classifies 2-butanol as a secondary alcohol, in which the hydroxyl group is bonded to a carbon atom that is itself connected to two alkyl groups (a methyl and an ethyl group).[1] The molecule has a molar mass of 74.12 g/mol.[4] In terms of molecular geometry, the carbon atoms in the chain adopt tetrahedral arrangements with typical C-C bond lengths of approximately 1.54 Å and C-O bond lengths of about 1.43 Å, consistent with sp³ hybridization in aliphatic alcohols.[5] The O-H bond length is around 0.96 Å, and bond angles at the hydroxyl-bearing carbon and oxygen are near 109.5°.[https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/09:_Alcohols_Ethers_and_Epoxides/9.02:_Structure_and_Bonding] Key identifiers for 2-butanol are summarized below:| Identifier | Value |
|---|---|
| CAS Number | 78-92-2 |
| SMILES | CCC(C)O |
| InChI | InChI=1S/C4H10O/c1-3-4(2)5/h4-5H,3H2,1-2H3 |
Naming and stereochemistry
The IUPAC name for 2-butanol is butan-2-ol.[1] It is also known by common names such as sec-butanol, sec-butyl alcohol, and ethyl methyl carbinol.[6] 2-Butanol is one of four structural isomers of butanol (C₄H₁₀O), the others being 1-butanol (butan-1-ol), 2-methyl-1-propanol (isobutanol), and 2-methyl-2-propanol (tert-butanol).[1] 2-Butanol possesses a chiral center at the carbon atom in position 2, which bears four different substituents: a hydroxyl group, a methyl group, an ethyl group, and a hydrogen atom. This chirality results in two enantiomers: (2R)-butan-2-ol, also denoted as (R)-(-)-2-butanol, and (2S)-butan-2-ol, or (S)-(+)-2-butanol. These enantiomers are non-superimposable mirror images of each other and exhibit identical physical properties except for their optical rotation. In most industrial and laboratory contexts, 2-butanol is produced and utilized as a racemic mixture, containing equal proportions of the (R) and (S) enantiomers.[7] The specific rotation for pure (S)-(+)-2-butanol is +13.52°, while for (R)-(-)-2-butanol it is -13.52°. These values indicate that the (S) enantiomer rotates plane-polarized light to the right (dextrorotatory), and the (R) enantiomer rotates it to the left (levorotatory).[8] Enantiomerically pure forms of 2-butanol can be obtained through classical resolution methods, which involve forming diastereomeric salts with a chiral resolving agent, such as a chiral acid or base, followed by separation based on differing solubilities; subsequent liberation of the alcohol yields the individual enantiomers.[9]Physical properties
Appearance and basic physical data
2-Butanol appears as a clear, colorless liquid at standard conditions, exhibiting a strong, fruity odor often described as pleasant and alcoholic. The odor threshold is approximately 3.2 ppm.[1][10] Key physical measurements include the following:| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 0.808 g/cm³ | 20°C | https://www.chemeo.com/cid/46-479-0/2-Butanol.pdf |
| Refractive index | 1.3978 | 20°C | https://pubchem.ncbi.nlm.nih.gov/compound/2-Butanol |
| Viscosity | ~3.5 mPa·s | 20°C | https://www.chemicalbook.com/ChemicalProductProperty_EN_CB0751661.htm |
| Flash point | 22–27°C (closed cup) | - | https://pubchem.ncbi.nlm.nih.gov/compound/6568 |
| Autoignition temperature | 405°C | - | https://www.chemeo.com/cid/46-479-0/2-Butanol.pdf |
Thermodynamic properties
2-Butanol exhibits typical thermodynamic behaviors of a secondary alcohol, remaining in the liquid phase at room temperature and atmospheric pressure due to its melting point of -114.7 °C and boiling point of 99.5 °C. These phase transition temperatures indicate that the compound freezes at moderately low temperatures and vaporizes near 100 °C under standard conditions, consistent with its role in various industrial processes involving heating or cooling.[11] The vapor pressure of 2-butanol is 1.67 kPa at 20 °C, reflecting its moderate volatility and potential for forming flammable vapors in air.[12] The heat of vaporization is approximately 40.8 kJ/mol at the boiling point, corresponding to 583 kJ/kg, which quantifies the energy required for phase change from liquid to gas and influences distillation efficiency.[11] The liquid heat capacity is 197.1 J/mol·K at 298.15 K, providing a measure of the energy needed to raise its temperature in liquid form.[13] At higher pressures and temperatures, 2-butanol reaches its critical temperature of 536 K (263 °C), beyond which it cannot be liquefied regardless of pressure, marking the end of distinct liquid and vapor phases.[14] The phase diagram of 2-butanol shows a stable liquid region between its melting and boiling points at 1 atm, with vapor pressure curves describing the equilibrium between liquid and gas phases up to the critical point.[11]| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -114.7 °C | 1 atm | PubChem |
| Boiling point | 99.5 °C | 1 atm | PubChem |
| Vapor pressure | 1.67 kPa | 20 °C | Sigma-Aldrich |
| Heat of vaporization | 40.8 kJ/mol (583 kJ/kg) | Boiling point | NIST WebBook |
| Heat capacity (liquid) | 197.1 J/mol·K | 298.15 K | NIST WebBook |
| Critical temperature | 536 K (263 °C) | Critical point | NIST WebBook |
Solubility
2-Butanol has a solubility in water of 35.0 g per 100 g of water at 20°C, decreasing with increasing temperature to 29 g per 100 g at 25°C and 22 g per 100 g at 30°C.[15] These values reflect the compound's ability to form hydrogen bonds with water molecules, though solubility diminishes as thermal energy disrupts these interactions.[15] Earlier reports citing a solubility of 12.5 g/100 g at 20°C, found in many textbooks and databases, stem from a historical miscalculation based on volume measurements rather than mass, as clarified in experimental re-evaluations.[15] The compound is completely miscible with ethanol, diethyl ether, chloroform, and most organic solvents, owing to compatible intermolecular forces such as hydrogen bonding and van der Waals interactions. The octanol-water partition coefficient (log P) for 2-butanol is 0.61, signifying moderate hydrophilicity where the polar -OH group promotes aqueous affinity while the butyl chain confers some lipophilicity.[16] 2-Butanol is miscible with non-polar hydrocarbons such as hexane.[17] This behavior arises primarily from hydrogen bonding enabled by the -OH group, which favors polar environments over purely hydrocarbon ones.Synthesis
Industrial production
The primary industrial production of 2-butanol involves the acid-catalyzed hydration of butene isomers, particularly 1-butene and 2-butene, sourced from petroleum refining streams such as raffinate-2.[18][19] This process has become the dominant method since the mid-20th century, replacing earlier, less efficient routes as petrochemical feedstocks became abundant and cost-effective.[19] The conventional approach is an indirect hydration using concentrated sulfuric acid as the catalyst. In the first step, butene reacts with sulfuric acid to form sec-butyl hydrogen sulfate (and some di-sec-butyl sulfate as a byproduct):
This intermediate is then hydrolyzed with water under controlled conditions (typically at 70–90°C and atmospheric pressure) to produce 2-butanol while regenerating the sulfuric acid for recycling:
The overall process operates in a continuous or semi-continuous manner, with butene absorption in acid followed by hydrolysis and distillation to separate the product. Yields typically reach 90–95%, depending on butene composition and process optimization, with byproducts like di-sec-butyl sulfate converted during hydrolysis to minimize waste.[20] Acid corrosion and effluent management are key engineering challenges addressed through material selection and neutralization steps.[21]
Alternative industrial routes include direct hydration using solid acid catalysts such as zeolites (e.g., H-ZSM-5 or beta zeolites) in fixed-bed reactors, which avoid liquid acid handling but are less widespread due to ongoing deactivation issues from water and coke formation. Direct hydration processes have been commercialized, for example, using phosphoric acid catalysts or supported ion-exchange resins.[21] Another option is the catalytic hydrogenolysis of butanone (methyl ethyl ketone), often over supported copper or nickel catalysts under mild hydrogen pressure (1–10 bar, 100–200°C), though this is typically integrated into solvent production chains rather than standalone for 2-butanol.[22]
Global production of 2-butanol occurs on the scale of thousands of metric tons annually, largely as a co-product in multi-output butene hydration processes that also yield butanes, with major capacity in Asia and North America.[23][20]
Laboratory methods
One common laboratory method for synthesizing 2-butanol involves the Grignard reaction, where ethylmagnesium bromide reacts with acetaldehyde to form the magnesium alkoxide intermediate, followed by acidic hydrolysis to yield the alcohol.[24] The reaction proceeds as follows:
This approach is suitable for small-scale preparations due to the availability of reagents and straightforward workup under anhydrous conditions.[24]
Another widely used laboratory route is the reduction of butanone (methyl ethyl ketone) to 2-butanol. Sodium borohydride (NaBH₄) serves as a mild, selective reducing agent for this transformation, typically performed in protic solvents like methanol or ethanol at room temperature.[25]
The reduction equation is:
Catalytic hydrogenation using nickel or palladium catalysts under hydrogen gas pressure offers an alternative, often achieving high yields in laboratory settings with controlled stereochemistry potential.[25]
For the preparation of enantiomerically enriched 2-butanol, asymmetric synthesis via catalytic hydrogenation of butanone employs chiral ruthenium-BINAP complexes, pioneered by Noyori, enabling high enantioselectivity (up to 100% ee) for simple aliphatic ketones lacking directing groups.[26] These reactions utilize Ru(II) catalysts with diphosphine ligands like BINAP and diamine co-ligands, proceeding under mild hydrogen pressure (4–100 atm) in alcoholic solvents, with substrate-to-catalyst ratios up to 10,000.[26]
Purification of laboratory-synthesized 2-butanol typically involves fractional distillation to remove impurities and unreacted materials. Due to its formation of a minimum-boiling azeotrope with water (boiling at approximately 90°C), anhydrous conditions or additional drying agents like molecular sieves are often required post-distillation to obtain pure product.[27]
Chemical properties and reactions
General reactivity
2-Butanol is a secondary alcohol, characterized by a hydroxyl group attached to a carbon bearing two alkyl substituents, which imparts specific reactivity patterns dominated by the functional group. This structural feature makes it susceptible to oxidation under mild conditions, typically yielding ketones such as butan-2-one, and to dehydration, which eliminates water to form alkenes like but-1-ene, (E)-but-2-ene, and (Z)-but-2-ene. The acidity of 2-butanol arises from the -OH proton, with a pKa value of approximately 17.7, rendering it a weaker acid than water (pKa 15.7); this reduced acidity stems from the electron-donating effects of the adjacent alkyl groups, which stabilize the neutral alcohol relative to the alkoxide ion.[16] In terms of basicity, the lone pairs on the oxygen atom allow 2-butanol to act as a weak base by accepting a proton, though it is only marginally basic, as indicated by the pKa of its protonated conjugate acid (2-butanolium ion) at about -1.6.[16] Under neutral conditions at ambient temperatures, 2-butanol exhibits good chemical stability, showing no significant decomposition. However, upon strong heating, it undergoes thermal decomposition, primarily through dehydration pathways to produce butene and water, along with potential formation of other byproducts.[28] Additionally, like certain other alcohols, 2-butanol has the potential to form unstable peroxides when exposed to air over extended periods, particularly if concentrated by distillation or evaporation; these peroxides can be explosive and require careful handling to mitigate risks.[29] Spectroscopic methods provide reliable identification of 2-butanol's functional group and structure. In infrared (IR) spectroscopy, the characteristic O-H stretching vibration manifests as a broad absorption band centered around 3300 cm⁻¹, indicative of hydrogen bonding in the alcohol.[30] Proton nuclear magnetic resonance (¹H NMR) spectroscopy reveals key signals, including a doublet for the three protons of the methyl group attached to the carbinol carbon (C1 in CH₃-CHOH-), typically around 1.1 ppm, and a multiplet for the single methine proton at the carbinol carbon (C2), appearing near 3.8 ppm due to coupling with adjacent protons and the hydroxyl group.Specific reactions
One key transformation of 2-butanol involves its oxidation to butan-2-one (methyl ethyl ketone, MEK), a secondary alcohol to ketone conversion. This reaction proceeds using pyridinium chlorochromate (PCC) in dichloromethane, which selectively oxidizes the secondary alcohol without over-oxidation, yielding the ketone and chromium byproducts.[31] Alternatively, chromic acid (Jones reagent, CrO₃ in aqueous sulfuric acid) achieves the same oxidation, forming a chromate ester intermediate that eliminates to the ketone.[32] The general equation is:
where [O] represents the oxidant.[31]
Dehydration of 2-butanol eliminates water to form butene isomers, typically using concentrated sulfuric acid at 140°C, following an E1 mechanism via a secondary carbocation intermediate.[33] Zaitsev's rule dictates the major product as the more substituted alkene, 2-butene (cis and trans isomers), with 1-butene as the minor product.[33]
Esterification of 2-butanol with carboxylic acids, such as acetic acid, occurs via the Fischer method under acidic catalysis (e.g., H₂SO₄ reflux), forming sec-butyl esters through protonation of the carbonyl, nucleophilic attack by the alcohol, and elimination of water.[34] For acetic acid, the product is sec-butyl acetate.[35] The equation is:
This equilibrium reaction favors the ester with excess alcohol or removal of water.[34]
Halogenation converts 2-butanol to 2-bromobutane using phosphorus tribromide (PBr₃), where the alcohol oxygen coordinates to phosphorus, forming a phosphite ester that undergoes bromide attack.[36] This SN2 pathway results in inversion of configuration at the chiral carbon for enantiopure 2-butanol.[36]
Due to its chirality, 2-butanol exhibits stereospecific behavior in reactions; acidic conditions, such as dilute sulfuric acid, lead to racemization via protonation of the hydroxyl group, carbocation formation, and nucleophilic attack from either side.[37] In contrast, enzymatic oxidations, such as by yeast alcohol dehydrogenase (ADH1), preserve stereochemistry, preferentially oxidizing (S)-2-butanol over the (R)-enantiomer with high enantioselectivity.[38]