# Tert-Butyl alcohol

**Tert-Butyl alcohol** (tert-butanol, TBA; IUPAC name 2-methylpropan-2-ol) is the simplest tertiary alcohol, a four-carbon alcohol with the formula (CH₃)₃COH in which the hydroxyl-bearing carbon is bonded to three methyl groups. It is a colorless solid or liquid above 77 °F (about 25 °C) with a camphor-like odor, is fully miscible with water, and is used industrially as a solvent, gasoline octane booster, and chemical intermediate.<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup><sup> • </sup><sup>[2](https://assessments.epa.gov/risk/document/&deid=348442)</sup>

| Key fact | Detail |
|---|---|
| Identity | CAS 75-65-0; formula (CH₃)₃COH; synonyms 2-methyl-2-propanol, trimethyl carbinol<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup> |
| Physical state | Colorless solid or liquid above 77 °F; melting point about 25 °C; boiling point 180 °F (82.3–83 °C)<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup><sup> • </sup><sup>[3](https://pubchem.ncbi.nlm.nih.gov/compound/tert-Butanol)</sup>  |
| Solubility | Miscible with water; molecular weight 74.1<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup> |
| Main uses | Solvent, ethanol denaturant, octane booster, dehydrating agent, intermediate for methyl methacrylate, flotation agents, fruit essences, perfumes<sup>[2](https://assessments.epa.gov/risk/document/&deid=348442)</sup> |
| Production | Acid-catalyzed hydration of 2-methylpropene (isobutene); also a by-product of propylene oxide production<sup>[4](https://onlinelibrary.wiley.com/doi/full/10.1002/cite.202000077)</sup> |
| Occupational limits | NIOSH REL TWA 100 ppm (300 mg/m³), ST 150 ppm; OSHA PEL TWA 100 ppm; IDLH 1600 ppm<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup> |
| EPA toxicity values (2021) | Oral RfD 4 × 10⁻¹ mg/kg-day; inhalation RfC 5 mg/m³; suggestive evidence of carcinogenic potential<sup>[5](https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1036)</sup> |
| Environmental behavior | Highly mobile in soil; anoxic soil half-life about 200 days; atmospheric half-life 14 days<sup>[6](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)</sup> |

## Physical and chemical properties

Tert-butyl alcohol is unusual among the four butanol isomers in melting just above room temperature, at about 25 °C, so it is often handled as a solid that liquefies in a warm room or as an aqueous solution.<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup><sup> • </sup><sup>[3](https://pubchem.ncbi.nlm.nih.gov/compound/tert-Butanol)</sup>  It boils at 180 °F (reported values include 82.3 °C and 83 °C), has a flash point of 52 °F, and forms flammable mixtures in air between 2.4% and 8.0% by volume; it is classified as a Class IB flammable liquid and a combustible solid.<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup> Its vapor pressure at 77 °F is 42 mmHg, and its specific gravity as a solid is 0.79.<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup>

As a tertiary alcohol, the carbon bearing the hydroxyl group is attached to three other carbon atoms, which distinguishes it from its isomers n-butanol, sec-butanol, and isobutanol.<sup>[7](https://www.vaia.com/en-us/textbooks/chemistry/organic-chemistry-6-edition/chapter-1/problem-8-draw-lewis-structures-and-condensed-structural-for/)</sup>

In water, tert-butanol behaves as a [hydrotrope](https://www.edgepedia.org/hydrotrope) (a substance that boosts water's ability to dissolve hydrophobic molecules), forming dynamic hydrogen-bonded molecular clusters rather than assembling into stable structures, and its mixtures with water show micro-heterogeneity and phase-transition-like anomalies.<sup>[8](https://arxiv.org/abs/1910.03699)</sup><sup> • </sup><sup>[9](https://arxiv.org/abs/1402.4970)</sup>  The TBA–water system has a eutectic at approximately −8 °C at 22.5% w/w TBA; in frozen solutions TBA first crystallizes as a dihydrate, which transforms to a heptahydrate on warming.<sup>[10](https://pubs.rsc.org/en/content/articlehtml/2020/cp/c9cp06576h)</sup>

## Production

The main industrial route is the acid-catalyzed hydration of 2-methylpropene (isobutene), the same chemistry used for 2-butanol from 1- or 2-butene; a tendency to use raffinate II, a refinery C₄ stream, instead of pure butenes has been reported.<sup>[4](https://onlinelibrary.wiley.com/doi/full/10.1002/cite.202000077)</sup> Tert-butanol is also formed as a by-product in several industrial processes, notably the production of propylene oxide from 2-methylpropane.<sup>[4](https://onlinelibrary.wiley.com/doi/full/10.1002/cite.202000077)</sup> Industrially, isobutene can be recovered from C₄ fractions by hydration to tert-butanol and later regenerated by dehydration, a route used when producing methyl tert-butyl ether (MTBE).<sup>[11](https://patents.google.com/patent/RU2076091C1/en)</sup> In the laboratory, hydration of isobutene catalyzed by strong acids such as H₂SO₄ yields tert-butanol; theoretical work predicts the reaction proceeds faster with the superacid HSbF₆ than with sulfuric acid.<sup>[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC6667991/)</sup>

## Uses

Tert-butyl alcohol serves as a solvent; a denaturant for ethanol and several other alcohols; a raw material for flotation agents, fruit essences, and perfumes; an octane booster in gasoline; a dehydrating agent; and a chemical intermediate in the manufacture of methyl methacrylate.<sup>[2](https://assessments.epa.gov/risk/document/&deid=348442)</sup> As a gasoline additive it acts as an oxygenate, facilitating complete combustion, and it is a starting compound for other oxygenates such as methyl tert-butyl ether and ethyl tert-butyl ether.<sup>[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC6667991/)</sup> It is also used to prepare potassium tert-butoxide, a strong non-nucleophilic base for [Williamson ether synthesis](https://www.edgepedia.org/williamson-ether-synthesis) that must be made in situ because of its high reactivity.<sup>[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC6667991/)</sup>

**Pharmaceutical freeze-drying.** TBA–water mixtures are used as co-solvent systems in lyophilization (freeze-drying) of pharmaceuticals, where they offer increased solubility of hydrophobic drugs, decreased drying time, and improved product stability and reconstitution characteristics.<sup>[10](https://pubs.rsc.org/en/content/articlehtml/2020/cp/c9cp06576h)</sup> Reviews of the practice list high freezing temperatures, very short sublimation times, low sublimation enthalpies, and low toxicity among the advantages of these systems.<sup>[13](https://www.tandfonline.com/doi/full/10.1080/07373937.2011.628133)</sup> The commercial product CAVERJECT Sterile Powder is significantly more stable when freeze-dried from a 20% v/v tert-butanol/water co-solvent system than from a simple aqueous solution.<sup>[14](https://www.sciencedirect.com/science/article/abs/pii/S0928098701002214)</sup>

## Occurrence as a metabolite and environmental behavior

Tert-butanol is a primary metabolite of the fuel oxygenates MTBE and ethyl tert-butyl ether (ETBE), and some toxicological effects observed for those compounds are attributed to tert-butanol.<sup>[6](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)</sup> In humans, the urinary half-life of tert-butanol after MTBE exposure was 8.1 ± 2.0 hours and after ETBE exposure 7.9 ± 2.7 hours.<sup>[6](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)</sup> It has been detected in MTBE-contaminated wells in the United States (1993–1998) at concentrations of 5.5–397 µg/L.<sup>[3](https://pubchem.ncbi.nlm.nih.gov/compound/tert-butanol)</sup>

Environmentally, tert-butanol is expected to be highly mobile in soil because of its low affinity for soil organic matter, so percolating water can transport it into groundwater; as a tertiary alcohol it degrades more slowly than primary or secondary alcohols, with an estimated half-life of about 200 days in anoxic soil.<sup>[6](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)</sup> Vapor-phase tert-butanol in the atmosphere is degraded by reaction with hydroxyl radicals with a half-life of 14 days.<sup>[6](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)</sup> EPA does not have a maximum contaminant level for TBA in drinking water, but several states have passed drinking water action levels because of its potential human toxicity.<sup>[15](https://www.epa.gov/sites/default/files/2015-06/documents/raton_basin_report_508_km.pdf)</sup>

## Toxicology and regulation

The EPA's Integrated Risk Information System (IRIS) finalized its Toxicological Review of tert-butyl alcohol in August 2021, after a review process that began with preliminary assessment materials in 2013 and included Science Advisory Board review in 2017 and 2019.<sup>[2](https://assessments.epa.gov/risk/document/&deid=348442)</sup> The assessment derives an oral reference dose (RfD) of 4 × 10⁻¹ mg/kg-day and an inhalation reference concentration (RfC) of 5 mg/m³, both based on increased severity of nephropathy (kidney disease) with medium confidence.<sup>[5](https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1036)</sup> Under EPA's 2005 cancer guidelines, tert-butyl alcohol has "suggestive evidence of carcinogenic potential" for all routes of exposure based on some evidence in animals; the oral slope factor is 5 × 10⁻⁴ per mg/kg-day, based on increasing thyroid tumors in mice, with tumor types including renal adenomas and carcinomas and thyroid adenomas (NTP, 1995).<sup>[5](https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1036)</sup> No inhalation cancer estimate was derived because no PBPK model of tert-butanol in mice is available for route-to-route extrapolation.<sup>[5](https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1036)</sup> Animal studies also show suggestive evidence of developmental toxicity, including increased fetal loss, decreased fetal body weight, and increased skeletal variations.<sup>[6](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)</sup>

**Occupational exposure.** NIOSH sets a recommended exposure limit (REL) of 100 ppm (300 mg/m³) as an 8-hour time-weighted average with a short-term limit of 150 ppm (450 mg/m³); the OSHA permissible exposure limit is a TWA of 100 ppm, and concentrations of 1600 ppm are immediately dangerous to life or health (IDLH).<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup> Exposure routes are inhalation, ingestion, and skin or eye contact, with symptoms including irritation of the eyes, skin, nose, and throat, drowsiness, and narcosis; the eyes, skin, respiratory system, and central nervous system are the target organs.<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup> The chemical is incompatible with strong mineral acids, strong hydrochloric acid, and oxidizers.<sup>[1](https://www.cdc.gov/niosh/npg/npgd0078.html)</sup>

## References

1. [NIOSH Pocket Guide to Chemical Hazards: tert-Butyl alcohol, CDC/NIOSH](https://www.cdc.gov/niosh/npg/npgd0078.html)
2. [IRIS Toxicological Review of Tert-Butyl Alcohol (Tert-Butanol or TBA) (Final Report), US EPA](https://assessments.epa.gov/risk/document/&deid=348442)
3. [tert-Butanol, CID 6386, PubChem](https://pubchem.ncbi.nlm.nih.gov/compound/tert-Butanol)
4. [Gehrmann, S. and Tenhumberg, N. (2020). Production and Use of Sustainable C2-C4 Alcohols – An Industrial Perspective. Chemie Ingenieur Technik](https://onlinelibrary.wiley.com/doi/full/10.1002/cite.202000077)
5. [tert-Butyl Alcohol (tBA), CASRN 75-65-0, IRIS Chemical Landing Page, US EPA](https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1036)
6. [Toxicological Review of tert-Butyl Alcohol (tert-Butanol) CAS No. 75-65-0, US EPA](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100OV4L.TXT)
7. [Draw Lewis structures and condensed structural formulas (tertiary alcohol classification), Vaia](https://www.vaia.com/en-us/textbooks/chemistry/organic-chemistry-6-edition/chapter-1/problem-8-draw-lewis-structures-and-condensed-structural-for/)
8. [Structural, Rheological and Dynamic Aspects of Hydrogen-Bonding Molecular Liquids: Aqueous Solutions of Hydrotropic tert-Butyl Alcohol, arXiv](https://arxiv.org/abs/1910.03699)
9. [Fluctuating micro-heterogeneity in water–tert-butyl alcohol mixtures, arXiv](https://arxiv.org/abs/1402.4970)
10. [Bhatnagar, B. S. et al. (2020). A refined phase diagram of the tert-butanol–water system and implications on lyophilization process optimization of pharmaceuticals. Phys. Chem. Chem. Phys.](https://pubs.rsc.org/en/content/articlehtml/2020/cp/c9cp06576h)
11. [RU2076091C1 – Process of producing tertiary butanol, Google Patents](https://patents.google.com/patent/RU2076091C1/en)
12. [Brzeski, J. and Skurski, P. (2019). The mechanisms of isobutene hydration yielding tert-butanol catalyzed by H2SO4 and HF/SbF5. Heliyon](https://pmc.ncbi.nlm.nih.gov/articles/PMC6667991/)
13. [A Review on Freeze Drying of Drugs with tert-Butanol (TBA) + Water Systems, Drying Technology](https://www.tandfonline.com/doi/full/10.1080/07373937.2011.628133)
14. [Practical aspects of lyophilization using non-aqueous co-solvent systems, ScienceDirect](https://www.sciencedirect.com/science/article/abs/pii/S0928098701002214)
15. [Retrospective Case Study in the Raton Basin, Colorado, US EPA](https://www.epa.gov/sites/default/files/2015-06/documents/raton_basin_report_508_km.pdf)

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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Alcohols, ethers, and organooxygen groups › Alcohols and polyols › Lower alkanols (C1–C4)*

*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*

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