Isobutyl alcohol, also known as isobutanol or 2-methyl-1-propanol, is a colorless, transparent liquid with a characteristic odor and the CAS number 78-83-1. One of the most frequently asked questions about this alcohol is how well it dissolves in water and in common organic solvents. The answer matters for solvent selection, reaction design and safety planning in industrial processes.
What Is Isobutyl Alcohol?
Isobutyl alcohol is a branched-chain saturated alcohol with the molecular formula C4H10O and a molecular weight of 74.12 g/mol. It is one of the four isomeric butanols and carries a hydroxyl group on a primary carbon of a branched butyl skeleton. The compound is a flammable liquid, and its vapor can form explosive mixtures with air, so strict fire safety measures are required during storage and use.
Solubility of Isobutyl Alcohol in Water
Isobutyl alcohol is slightly soluble in water. At 20 °C, approximately 8.7 mL dissolves in 100 mL of water, which corresponds to a solubility of roughly 87 g/L. This partial miscibility reflects the molecular structure: the hydroxyl group can form hydrogen bonds with water, but the hydrophobic butyl chain limits the number of water molecules that can surround each molecule. As a result, isobutanol and water form a two-phase system when the alcohol is present above its saturation limit.
Solubility in Organic Solvents
In contrast to its limited water solubility, isobutyl alcohol is readily soluble in ethanol, diethyl ether, acetone and most common organic solvents. It also shows good compatibility with aromatic hydrocarbons and many ester and ketone solvents. This combination of slight water solubility and broad organic miscibility makes isobutanol useful as a mutual solvent and as an extraction medium in a variety of formulations.
Factors That Affect Solubility
Temperature: the water solubility of isobutanol increases modestly as temperature rises, but the change is small within normal handling ranges.
Isomer structure: n-butanol has a water solubility of about 7.7 g per 100 mL, isobutanol about 8.7 g per 100 mL, while the more compact tert-butanol is fully miscible with water in all proportions.
Presence of co-solvents: adding ethanol, acetone or other water-miscible solvents can create a homogeneous single-phase system even when isobutanol alone would separate.
Salt content: high concentrations of dissolved salts can reduce the effective water solubility by a salting-out effect, which is sometimes exploited in extraction and washing operations.
Industrial Uses Related to Its Solubility
Solvent for paints, lacquers, printing inks and adhesives, where its organic miscibility and moderate evaporation rate are valued
Extractant and reaction medium in organic synthesis and pharmaceutical processing
Raw material for esterification to isobutyl acetate, isobutyl acrylate and plasticizer esters such as diisobutyl phthalate
Component in fruit flavor oils, artificial musk and fragrance formulations
Additive in synthetic rubber production and in certain petroleum products
Safe Handling and Storage of Isobutyl Alcohol
Isobutyl alcohol is flammable, with a closed-cup flash point of approximately 27.8 °C, and its vapor can ignite or explode when exposed to open flames or high heat. Store it in a cool, well-ventilated, dry area away from ignition sources, in tightly sealed metal containers, and isolate it from strong oxidizing agents, acids and alkalis. Use explosion-proof equipment in storage and transfer areas, ground containers during dispensing, and wear appropriate gloves and eye protection when handling the liquid.
Frequently Asked Questions
Is isobutyl alcohol soluble in water?
Yes, but only slightly. Its solubility is approximately 8.7 mL per 100 mL of water at 20 °C, and it forms a separate layer when present above that limit.
Why is isobutanol only slightly soluble in water?
The molecule contains a polar hydroxyl group that hydrogen-bonds with water, but the nonpolar butyl chain limits overall water compatibility, resulting in partial solubility.
Is isobutyl alcohol soluble in ethanol and ether?
Yes. Isobutyl alcohol is readily soluble in ethanol, diethyl ether, acetone and most other common organic solvents.
Does temperature change the solubility of isobutanol in water?
The solubility increases slightly with temperature, but the effect is modest within typical handling temperatures, so the alcohol remains only partially miscible with water.
How does the water solubility of isobutanol compare with n-butanol?
Both are slightly soluble in water. n-Butanol dissolves to about 7.7 g per 100 mL, isobutanol to about 8.7 g per 100 mL, while tert-butanol is fully water-miscible.
What are the CAS number and molecular formula of isobutyl alcohol?
Isobutyl alcohol has the CAS number 78-83-1 and the molecular formula C4H10O.
