What Is the Boiling Point of Isobutanol?
Isobutanol (2-methyl-1-propanol, CAS 78-83-1) has a boiling point of 108°C (227°F) at standard atmospheric pressure (760 mmHg). This value is confirmed by multiple independent sources, including the CDC/NIOSH Pocket Guide to Chemical Hazards and the OECD SIDS (Screening Information Data Set) dossier, which cites the Merck Index and Aldrich reference catalogues. Some analytical suppliers report a slightly more precise figure of 107.66°C, reflecting minor variation in measurement methodology and purity of the tested sample - but 108°C is the generally accepted reference value.
| Property | Value |
|---|---|
| Boiling point | 108°C (227°F) |
| Melting/freezing point | −108°C (−162°F) |
| Molecular formula | C₄H₁₀O |
| Molecular weight | 74.12 g/mol |
| Density | ~0.80–0.806 g/cm³ |
| Vapor pressure | 9 mmHg (at room temp) |
| Flash point | 82–100°F (28–37°C, varies by source) |
Why Isobutanol's Boiling Point Matters?
At 108°C, isobutanol sits in a moderate range among the butanol isomers - lower than n-butanol (117.7°C) but higher than most common solvents like ethanol (78°C) or acetone (56°C). This intermediate volatility is precisely why it's chosen over lighter or heavier solvents in formulations that need controlled evaporation - fast enough to dry within a reasonable process window, slow enough to avoid flash-off problems during application (e.g., in coatings and inks).
Physical and Chemical Properties of Isobutanol
Isobutanol is a colorless liquid with a mild, sweet-to-musty odor. It's flammable (flash point in the 28–37°C range depending on the reference), only slightly soluble in water, but miscible with common organic solvents like ethanol and ether. Chemically, it behaves as a typical primary alcohol: it can be oxidized to isobutyraldehyde or isobutyric acid, esterified with acids to form compounds like isobutyl acetate, and it reacts predictably with strong oxidizers and alkali metals - standard alcohol chemistry rather than unusual reactivity.
Industrial Applications
Isobutanol's combination of moderate volatility, solvency power, and low water solubility makes it useful across several sectors:
- Solvent - Used in paints, inks, resins, and adhesive formulations, where its evaporation rate helps control drying time and finish quality.
- Chemical intermediate - A precursor for isobutyl acetate (used in flavors, fragrances, and as a solvent), isobutyl acrylate/methacrylate, and various plasticizers and pharmaceutical/agrochemical intermediates.
- Fuel additive - Used in some gasoline blends to improve octane rating; it's also studied as a biofuel component since it can be produced via fermentation.
- Personal care and cleaning products - Used in some cosmetic and industrial cleaning formulations, generally as a solvent or carrier.
- Other uses - Additive in rubber processing, textile treatment, and certain electronics manufacturing processes.
Frequently Asked Questions
What is the boiling point of isobutanol?
Isobutanol boils at approximately 108°C (227°F) at standard atmospheric pressure. Some analytical references cite 107.66°C, reflecting minor differences in sample purity and test method, but 108°C is the commonly accepted value.
Is isobutanol flammable?
Yes. Isobutanol is classified as flammable, with a flash point in the range of 28–37°C (82–100°F) depending on the source. It can form explosive vapor-air mixtures, so it should be stored away from open flames, sparks, and strong oxidizers.
Is isobutanol soluble in water?
Only slightly. Isobutanol dissolves in water at roughly 95 g/L at 20°C, meaning it's partially miscible rather than fully soluble. It is, however, fully miscible with common organic solvents like ethanol and ether.
How is isobutanol different from n-butanol?
Both are four-carbon alcohols (C₄H₁₀O) with the same molecular formula, but different structures. Isobutanol (2-methyl-1-propanol) has a branched carbon chain and boils at 108°C, while n-butanol (1-butanol) is straight-chained and boils higher, at about 117.7°C. The branching in isobutanol also gives it slightly different solvency behavior and a somewhat lower density.
What is isobutanol used for?
Its main uses are as a solvent in paints, inks, resins, and adhesives; as a chemical intermediate for isobutyl acetate, acrylates, and plasticizers; as a fuel additive; and in select personal care and industrial cleaning formulations.
Can isobutanol be used as a fuel?
Yes. Isobutanol can be blended into gasoline to boost octane rating, and it's also produced via fermentation as a biofuel candidate. Compared to ethanol, isobutanol has a higher energy density and lower water affinity, which are advantages for blending and pipeline transport - one reason it's been studied as a "drop-in" biofuel alternative.
