What Type of Alcohol Is Isobutyl Alcohol (CAS 78-83-1)?
Isobutyl alcohol, also written isobutanol or 2-methylpropan-1-ol, is a four-carbon, branched, saturated primary alcohol with the formula C4H10O, molecular weight 74.12 and EC number 201-148-0. In the alcohol family it is classified as a primary aliphatic monohydric alcohol: the carbon atom carrying the hydroxyl group is attached to one other carbon atom, which is the structural definition of primary. Because that carbon is bonded to two methyl groups it is branched rather than straight-chain, and that branching is what separates it from its isomer.
The distinction matters commercially, because technical documentation is often confused. The straight-chain isomer is n-butanol, CAS 71-36-3, with a boiling point near 117.7 degrees C and a freezing point near minus 89 degrees C. Isobutanol is a different substance with a different boiling point, freezing point, density and solvent behaviour, and a purchase order should be pinned to CAS 78-83-1 so that the correct isomer is delivered.
Physical and Chemical Properties
| Property | Typical value | Reference method |
|---|---|---|
| Assay as C4H10O | 99.0 % minimum, industrial grade | Gas chromatography |
| Water | 0.10 % maximum | ASTM E203 (Karl Fischer) |
| Colour | 10 Pt-Co maximum | ASTM D1209 |
| Density at 20 degrees C | 0.802 g/cm3 | ASTM D4052 |
| Boiling point at 101.3 kPa | 107.9 degrees C | ASTM D1078 |
| Melting point | minus 108 degrees C | Freezing curve |
| Flash point, closed cup | 28 degrees C | ASTM D93 |
| Solubility in water | Approximately 8.5 g per 100 mL at 20 degrees C | Phase equilibria |
| Transport classification | UN 1212, Class 3, Packing Group III | UN Model Regulations |
Why the Structure Decides the Solvent Behaviour
The hydroxyl group gives isobutanol a polar end and hydrogen bonding, while the branched butyl chain supplies a non-polar tail. That balance makes it a medium-polarity solvent that is fully miscible with most organic liquids and only partly soluble in water, and it gives the ester derived from it, isobutyl acetate, the mild odour and low viscosity valued in lacquer and ink systems. Compared with n-butanol, the branched chain evaporates slightly faster and produces a lower viscosity in resin solutions, which is a practical selection criterion in coatings formulation.
Industrial Uses
Coatings and inks: a latent solvent and diluent in amino, urethane, nitrocellulose and acrylic systems. Ester production: feedstock for isobutyl acetate and for plasticisers such as diisobutyl phthalate and diisobutyl adipate. Automotive and industrial fluids: a component of some brake fluids and a pour-point and octane improver in fuel blends. Chemical synthesis: an intermediate for pharmaceuticals, agrochemicals, antioxidants and specialised esters. Extraction and purification: a solvent for purification and crystallisation steps where a water-immiscible alcohol is required.
Handling, Storage and Safety Classification
Isobutanol is a flammable liquid, classified UN 1212, Class 3, Packing Group III, with a closed cup flash point of 28 degrees C, so it is stored in grounded steel drums or tanks away from ignition sources and oxidising agents, and transferred with bonding and grounding. It is irritant to eyes and respiratory tract, and inhalation exposure above the occupational exposure limit causes headache, dizziness and narcosis; local exhaust ventilation at filling and drumming points is normal practice. Bulk storage in carbon steel is acceptable if the water content is controlled, because dry alcohol has limited corrosivity, but moisture uptake through vents should be monitored.
Frequently Asked Questions
Q: Is isobutyl alcohol a primary, secondary or tertiary alcohol?
A: It is a primary alcohol. The carbon atom that carries the hydroxyl group is bonded to only one other carbon atom, a branched methyl-substituted carbon. Secondary alcohols have the hydroxyl carbon bonded to two carbons and tertiary alcohols to three.
Q: Is isobutanol the same as n-butanol?
A: No. They are isomers with the same formula C4H10O but different structures and different properties. Isobutanol is CAS 78-83-1 with a boiling point near 107.9 degrees C; n-butanol is CAS 71-36-3 with a boiling point near 117.7 degrees C. Always order against the CAS number.
Q: What is isobutanol used for?
A: The main outlets are coatings and ink solvents, esters such as isobutyl acetate and plasticisers, fuel and brake fluid additives, and intermediates for pharmaceuticals, agrochemicals and antioxidants.
Q: How should isobutanol be stored?
A: In closed, grounded steel or HDPE containers at ambient temperature, away from heat, ignition sources and strong oxidisers, with ventilation at filling points. Drums are opened only when required because the alcohol absorbs atmospheric moisture.
Q: What purity do industrial buyers normally specify?
A: 99.0% minimum assay by gas chromatography, water at 0.10% maximum, colour at 10 Pt-Co maximum, and controlled limits on aldehydes and acidity for use in esterification or in coatings where colour stability matters.