Written and maintained by CASRAI Editorial Board
Last updated
Short answer
The boiling point of 1-butanol (n-butanol) at 760 mmHg is about 117.6 °C (390.7 K). NIST gives a compiled average of 390.6 ± 0.8 K, and the CRC Handbook value cited by PubChem is 117.6 °C. Related properties: density 0.8098 (20/4 °C), polarity index 3.9, refractive index 1.3993 at 20 °C, pKa 16.1 at 25 °C. This page is a lab solvent reference sheet, not safety or purchasing advice; use the supplier safety data sheet for handling.
Definition and scope: which butanol
“Butanol” names four isomeric C4 alcohols: 1-butanol (n-butanol), 2-butanol, isobutanol and tert-butanol. They are different compounds, so a number copied from another isomer’s page is not valid for your bottle. Every value below is for 1-butanol (CAS 71-36-3, NIST WebBook ID C71363, PubChem CID 263), the isomer normally meant by “butanol” in laboratory solvent contexts.
Property reference card for 1-butanol
Values are from the NIST Chemistry WebBook and PubChem’s Experimental Properties section, both read 2026-11-08. Where sources report different numbers, the spread is shown instead of being averaged away.
| Property | Value | Source as cited |
|---|---|---|
| Boiling point, 760 mmHg | 117.6 °C; 117.73 °C; 117.7 °C. NIST average 390.6 ± 0.8 K | CRC Handbook 94th ed.; PubChem; PhysProp; NIST WebBook |
| Melting / freezing point | -88.6 °C; -89.8 °C. NIST average 188 ± 9 K; triple point 184.54 K | CRC; PhysProp; NIST (Wilhoit 1985) |
| Density | 0.8098 (20/4 °C); 0.8095 g/cm³ at 20 °C | CRC; PubChem |
| Vapor pressure | 7.0 mmHg at 25 °C; 0.67 kPa at 20 °C | Daubert and Danner 1989; PubChem |
| Viscosity | 5.186 cP at 0 °C; 2.544 cP at 25 °C; 0.533 cP at 100 °C | CRC via PubChem |
| Refractive index | 1.3993 at 20 °C, sodium D line | CRC via PubChem |
| Polarity index (Burdick and Jackson scale) | 3.9 (n-butyl alcohol; the same value that table gives isopropyl alcohol) | Burdick and Jackson solvent table, LSU copy |
| pKa | 16.1 at 25 °C (IUPAC 16.10) | Serjeant and Dempsey 1979 via PubChem |
| Flash point (closed cup) | about 29 °C (ACGIH 28.89 °C); NFPA lists 37 °C (98 °F) | PubChem |
| Water solubility | 63.2 g/L; 68 g/L (25 °C); 7.7 g/100 mL (20 °C) | PubChem (Tewari 1982; Yalkowsky 2010) |
Why the numbers differ between sources
NIST’s boiling point is an average of 137 of 146 compiled measurements, so it carries an explicit uncertainty; the 117.6 and 117.7 °C figures are individual handbook or database picks. For melting point the NIST uncertainty is ±9 K because only six values were averaged and they spread widely. Flash point and water solubility differ by method and temperature (a closed-cup flash point near 29 °C against NFPA’s 37 °C). In a lab note, cite one source and edition and record the temperature and pressure each value applies to.
What each number means at the bench
Boiling point and vapor pressure: removing butanol under vacuum
At 117.6 °C butanol boils far above room temperature, and its 7.0 mmHg vapor pressure at 25 °C shows it evaporates slowly, so removing it usually means reduced pressure. NIST publishes vapor pressure as Antoine parameters (log10 P = A – B/(T + C), P in bar, T in K; A = 4.54607, B = 1351.555, C = -93.34, valid 295.8 to 391.0 K, Kemme and Kreps 1969). Calculating from those parameters gives about 0.0089 bar (6.6 mmHg) at 25 °C, consistent with the 7.0 mmHg handbook value; about 0.046 bar at 50 °C; and a boiling temperature near 64 °C at 0.1 bar (100 mbar). These are our calculations from the NIST equation, not instrument settings; real evaporator performance also depends on the flask, bath and condenser. The DMSO boiling point sheet applies the same pressure logic to a higher-boiling solvent.
Density: which layer is butanol
At about 0.81 g/mL butanol is less dense than water. With 63 to 68 g/L water solubility at 25 °C it is only partly miscible, so in a simple water extraction it is the upper phase unless a dense co-solvent changes that. The solubility figures disagree across sources, so treat them as order-of-magnitude.
Viscosity: temperature matters
Viscosity falls from 5.186 cP at 0 °C to 2.544 cP at 25 °C and 0.533 cP at 100 °C, so a viscosity value is meaningless without its temperature.
Polarity index versus elution strength
The polarity index of 3.9 comes from the Burdick and Jackson table and matches the number that table gives isopropyl alcohol. It is a different scale from the Snyder eluent-strength series used for alumina chromatography, where butanol is listed at 0.70 (Stenutz compilation of Snyder 1983). Do not exchange values between scales. For plate-based work see the thin-layer chromatography guide.
pKa and refractive index
A pKa of 16.1 at 25 °C means butanol is a very weak acid; it does not ionize appreciably under ordinary aqueous buffer conditions. The refractive index of 1.3993 is quoted at 20 °C for the sodium D line, the basis to match when comparing a refractometer reading.
Common misunderstandings
- “Butanol” is one compound. It is four isomers; confirm the CAS number (71-36-3 for 1-butanol) on the label.
- Freezing point is a single exact number. The handbook melting point is -88.6 °C, but NIST’s fusion average has a ±9 K spread, with triple-point measurements near 184.5 K.
- One polarity number fits all. Polarity index and eluent strength are separate scales.
- Handbook values are exact. They are compiled from measurements at a stated temperature and pressure.
FAQ
What is the boiling point of butanol?
For 1-butanol at 760 mmHg, about 117.6 °C (390.7 K); sources range from 117.6 to 117.73 °C.
What is the density of butanol?
0.8098 at 20/4 °C (CRC Handbook), or about 0.8095 g/cm³ at 20 °C.
What is the polarity of butanol?
Its Burdick and Jackson polarity index is 3.9.
What is the polarity index of butanol?
3.9 on the Burdick and Jackson scale; 0.70 on the separate Snyder alumina eluent-strength scale.
What is the vapor pressure of butanol?
7.0 mmHg at 25 °C (Daubert and Danner 1989) and 0.67 kPa at 20 °C.
What is the viscosity of butanol?
2.544 cP at 25 °C, 5.186 cP at 0 °C and 0.533 cP at 100 °C.
What is the refractive index of butanol?
1.3993 at 20 °C for the sodium D line.
What is the freezing point of butanol?
About -88.6 °C by the CRC melting point; NIST triple-point values are near 184.5 K.
What is the pKa of butanol?
16.1 at 25 °C.
What is the dielectric constant of butanol?
This sheet does not quote one, because a dielectric constant is only meaningful with its measurement temperature; take it from the CRC Handbook table at your working temperature.
Related CASRAI pages
For other solvent reference sheets see CDCl3 properties and xylene substitutes.
Sources
- NIST Chemistry WebBook, 1-Butanol, https://webbook.nist.gov/cgi/cbook.cgi?ID=C71363&Mask=4 (read 2026-11-08).
- PubChem, 1-Butanol (CID 263), Experimental Properties, https://pubchem.ncbi.nlm.nih.gov/compound/263 (read 2026-11-08).
- Burdick and Jackson solvent polarity index table (LSU copy), https://macro.lsu.edu/howto/solvents/polarity%20index.htm (read 2026-11-08).
