2-Methyl-2-butanol (75-85-4) Physical and Chemical Properties
2-Methyl-2-butanol
Branched tertiary alcohol used industrially as a protic solvent and building-block intermediate for fragrances, specialty chemicals and formulation R&D.
| CAS Number | 75-85-4 |
| Family | Tertiary aliphatic alcohol |
| Typical Form | Colorless liquid |
| Common Grades | BP, EP, JP, USP |
2-Methyl-2-butanol is a branched tertiary aliphatic alcohol (molecular formula \(\ce{C5H12O}\)) featuring a tertiary hydroxyl group bound to a quaternary carbon. The tertiary substitution pattern produces significant steric protection of the hydroxyl group relative to primary and secondary alcohols; this influences its acid–base and redox behavior (weaker Bronsted acidity, greater resistance to oxidation), lowers hydrogen-bonding capacity per mole, and reduces biodegradability compared with less-branched isomers. As a protic solvent it can donate a hydrogen bond but has limited acceptor/donor capacity (one hydrogen-bond donor and one acceptor) and a modest topological polar surface area, resulting in intermediate polarity and limited water miscibility.
Physicochemical descriptors indicate modest lipophilicity (XLogP = 0.9; log Kow ≈ 0.89) with a relatively low dielectric constant (\(5.78\) at \(25\ ^\circ\mathrm{C}\)) and low molecular weight (88.15). The compound is a volatile, flammable liquid with measurable vapor pressure at ambient temperature and a boiling point in the range typical for C5 alcohols; it forms a binary azeotrope with water and is miscible with many organic solvents (alcohols, ethers, benzene, chloroform, acetone). Industrially and pharmaceutically it is used principally as a solvent and intermediate; it also appears as a fragrance/flavor component and as a human/animal metabolite of certain ether oxygenates.
Common commercial grades reported for this substance include: BP, EP, JP, USP.
Basic Physical Properties
Density
Reported density: 0.8096 at 20 °C/4 °C. This low liquid density relative to water is consistent with its branched hydrocarbon skeleton and moderate volatility.
Melting Point
Reported melting points: −9.1 °C and −8.4 °C. Small variability reflects measurement method and sample purity.
Boiling Point
Reported boiling point: 102.4 °C at 760 mm Hg. A binary azeotrope with 27.5% (wt) water has a boiling point of 87.35 °C; this is relevant for distillation and dehydration operations.
Vapor Pressure
Reported vapor pressure values include 16.8 mm Hg (unspecified temperature), 1.215 kPa (9.113 mm Hg) at 20 °C, and 16.7 mm Hg at 25 °C. These values indicate significant volatility at ambient temperatures and justify vapor-control measures in industrial settings.
Flash Point
Measured flash points reported include 67 °F (NFPA, 2010), 19 °C, and 67 °C (closed cup). Differences reflect differing test methods/protocols; use the closed-cup value appropriate to the method specified by regulatory or quality procedures in procurement and safety documentation.
Chemical Properties
Solubility and Phase Behavior
Water solubility is limited and temperature-dependent: 12.1% wt at 20 °C; 11.0% wt at 25 °C; 10.1% wt at 30 °C. Other reported solubility values include 99,100 mg/L at 25 °C and 110 mg/mL at 25 °C (note these reflect different reporting conventions and should be reconciled with analytical specifications). The compound is miscible with common organic solvents (alcohols, ether, benzene, chloroform, glycerol, oils) and is very soluble in acetone. The presence of a water azeotrope (27.5% wt water, b.p. 87.35 °C) affects separation strategies during purification and solvent recovery.
Reactivity and Stability
The tertiary alcohol function confers relative resistance to oxidation compared with primary and secondary alcohols, but the substance remains chemically reactive with strong oxidizers and certain electrophiles. Documented incompatibilities and reactivity hazards include: strong oxidizers, strong acids (violent reactions possible), hydrogen trifluoride, and alkaline earth metals (formation of hydrogen). It may attack some plastics and reacts violently with acetyl bromide; mixtures with concentrated hydrogen peroxide or hypochlorite can be explosive. The material is reported as sensitive to light and should be stored protected from light in tightly closed containers. Flammability and vapor–air explosion risks are significant; physical containment, grounding/bonding for transfers, and control of ignition sources are required.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
Reported thermochemical properties (experimental): - Heat of combustion: 789.45 kcal/mol at 25 °C. - Heat of vaporization: 40.11 kJ/mol at boiling point. - Heat of fusion: 90.71 kcal/mol at 25 °C. - Specific heat (reported): 3.15 J/g·deg K (reported at "20 deg K" in source; verify units and reference before process calculations). These values are useful for energy-balance calculations in formulation, distillation, and combustion scenarios. Where standard formation enthalpies or tabulated heat capacities across a broad temperature range are required, consult validated thermodynamic datasets or primary literature.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \(\ce{C5H12O}\).
- Molecular weight: 88.15.
- Exact/monoisotopic mass: 88.088815002.
LogP and Polarity
- XLogP: 0.9 (computed).
- Experimental/log Kow: 0.89.
- Topological polar surface area (TPSA): 20.2 Å^2. These descriptors indicate modest lipophilicity and limited polarity consistent with partial water solubility and readiness to partition into organic phases.
Structural Features
2-Methyl-2-butanol is a tertiary alcohol (IUPAC name: 2‑methylbutan-2-ol). Structural and computed identifiers:
- SMILES: CCC(C)(C)O
- InChI: InChI=1S/C5H12O/c1-4-5(2,3)6/h6H,4H2,1-3H3
- InChIKey: MSXVEPNJUHWQHW-UHFFFAOYSA-N
- Hydrogen-bond donor count: 1; acceptor count: 1.
- Rotatable bond count: 1; heavy atom count: 6; complexity ≈ 39.2.
The tertiary center reduces availability of the OH hydrogen for intermolecular hydrogen bonding relative to less hindered alcohols, lowering associational enthalpies and affecting volatility and solvent behavior.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS RN: 75-85-4
- EC number: 200-908-9
- UNII: 69C393R11Z
- UN number (listed): 1105 (TERT-AMYL ALCOHOL)
- ChEBI: CHEBI:132750
- ChEMBL: CHEMBL44658
- Other registry/inventory identifiers are available in supplier and regulatory documentation.
Also provided molecular identifiers:
- SMILES: CCC(C)(C)O
- InChI: InChI=1S/C5H12O/c1-4-5(2,3)6/h6H,4H2,1-3H3
- InChIKey: MSXVEPNJUHWQHW-UHFFFAOYSA-N
Synonyms and Structural Names
Common synonyms and trade/structural names reported include: tert-amyl alcohol; tert‑pentyl alcohol; 2‑methylbutan-2-ol; t‑Amyl alcohol; tertiary amyl alcohol; tert‑pentanol; 2‑METHYL-2-BUTANOL; amylene hydrate. Use exact supplier nomenclature and CAS RN when specifying procurement or regulatory submissions.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Typical uses: solvent for flavors and fragrances, pharmaceuticals, resins and gums, coatings and adhesives; intermediate in organic synthesis; flotation and frothing agent in mineral processing; surfactant/stabilizer applications in petroleum recovery and solvent formulations. It is listed as a fragrance ingredient and as a solvent for specialty chemical applications. Production routes include hydration of pentenes and oxo-process-derived routes; also obtained by fractionation of fusel oil in small quantities.
Role in Synthesis or Formulations
Functionally, 2‑methyl‑2‑butanol serves as a protic polar solvent for reactions where moderate polarity and proticity are beneficial, and as a stabilizer for certain chlorinated solvents. Its tertiary structure makes it a less reactive alcohol toward oxidation; however it can serve as an intermediate for derivatization (e.g., esterification under controlled conditions). In formulations, its volatility, solvency profile (miscibility with many organics), and odor profile (camphor-like characteristic) inform its selection in flavor and fragrance applications.
Safety and Handling Overview
Acute and Occupational Toxicity
Toxicological data (select values): - LD50, rat (oral): 1.0–2.0 g/kg. - LD50, rabbit (oral): 2.0 g/kg. - LD50, mouse (iv): 0.61 g/kg. - LD50, rabbit (dermal): 1.72 g/kg. - LCLo (rat, inhalation): 5,700 ppm for 6 h. - Chronic/subchronic inhalation effect levels and reference concentrations have been derived in toxicological assessments (example chronic reference concentration: 0.003 mg/m^3 reported in some regulatory summaries). Clinical and animal data indicate the potential for central nervous system depression at high exposures, dermal and ocular irritation, and target‑organ effects (CNS, liver) in subchronic inhalation studies. Exposure via inhalation, ingestion, or dermal absorption can lead to systemic effects; volatilization and inhalation are primary occupational exposure routes.
Reported GHS hazard statements (as used for classification and labelling) include: - H225: Highly flammable liquid and vapor. - H315: Causes skin irritation. - H319/H318: Causes serious eye irritation/damage (varies by notification). - H332: Harmful if inhaled. - H335: May cause respiratory irritation. - H336: May cause drowsiness or dizziness (reported in some classifications). Appropriate interpretation of these codes for a specific product must follow the product safety information supplied by manufacturers.
Storage and Handling Considerations
General handling and storage guidance: - Store in tightly closed containers in a cool, well-ventilated area away from heat, sparks, open flame, and incompatible materials (strong oxidizers and strong acids). - Protect from light; many suppliers specify "KEEP TIGHTLY CLOSED & PROTECTED FROM LIGHT." - Use grounded and bonded equipment for transfer to avoid static-ignition hazards; use non-sparking tools and equipment. - Provide appropriate local exhaust ventilation and vapor monitoring where bulk quantities are handled. - Personal protective equipment: solvent-resistant gloves, splash goggles/face shield, and respiratory protection where vapor exposure may exceed occupational limits. Structural firefighters' protective clothing provides thermal protection but limited chemical protection; use positive-pressure SCBA for fire response. - In case of spills, eliminate ignition sources, ventilate area, and absorb with inert material; contain runoff to avoid environmental release. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
