2-Methyl-1-propanol, also known as isobutanol or isobutyl alcohol, is a colorless, flammable organic compound with a characteristic penetrating odor. With the chemical formula C4H10O and CAS number 78-83-1, it is one of the four isomeric butanols, alongside n-butanol, sec-butanol and tert-butanol. Because of its alcohol functionality and moderate volatility, isobutanol is widely used as a solvent in chemical reactions and as an important building block for organic synthesis.
What Is 2-Methyl-1-Propanol (Isobutanol)?
Isobutanol is a branched primary alcohol in which the hydroxyl group is attached to a carbon chain that branches at the second carbon atom. Its IUPAC name is 2-methyl-1-propanol, and its molecular weight is approximately 74.12 g/mol. In commerce it is commonly referred to as isobutyl alcohol (IBA) or 2-methyl propanol. The compound is produced industrially by hydroformylation of propylene followed by hydrogenation, or by the carbonylation of isobutene, and it is also a by-product of certain fermentation processes.
Physical Properties of Isobutanol
Appearance: colorless transparent liquid with a special, slightly sweet odor
Melting point: approximately -108 °C
Boiling point: approximately 107.9 °C
Density: approximately 0.803 g/cm³ at 20 °C
Flash point: approximately 27.8 °C (closed cup), flammable liquid
Refractive index: approximately 1.393 at 20 °C
Solubility: slightly soluble in water, about 8.7 mL per 100 mL of water at 20 °C; readily soluble in ethanol, diethyl ether and most organic solvents
Vapor pressure: about 9 mmHg at 20 °C, giving the liquid a noticeable volatility
Chemical Properties and Reactivity
Isobutanol is a flammable liquid whose vapor can form explosive mixtures with air. The explosive range in air is approximately 1.7% to 10.9% by volume, so exposure to open flames, sparks or high heat must be avoided. As a primary alcohol, it reacts with strong oxidizing agents, and heating may cause decomposition with the release of toxic gases.
From a synthetic perspective, isobutanol undergoes the typical reactions of primary alcohols: oxidation to isobutyraldehyde and further to isobutyric acid, esterification with carboxylic acids to give isobutyl esters, and dehydration to isobutene under catalytic conditions. These reactions make it a valuable intermediate for the production of many commercial chemicals.
Key Industrial Applications of Isobutanol
Production of isobutyl acetate, a solvent widely used in lacquers, coatings and printing inks, and also approved as a food flavoring substance
Synthesis of diisobutyl phthalate (DIBP) and other isobutyl esters used as plasticizers for rubber and plastics
Manufacture of the antioxidant 2,6-di-tert-butyl-p-cresol (BHT)
Production of isobutyl acrylate and other acrylate monomers for polymer industries
Use as a solvent and extractant in paints, adhesives and cleaning formulations
Raw material for synthetic musk, fruit flavor oils and pharmaceutical intermediates
Additive in petroleum products and in some fermentation-derived applications
Toxicity and Handling Precautions
Isobutanol possesses moderate toxicity and can be harmful to humans if swallowed, inhaled in high concentrations or absorbed through the skin. It is classified as an eye irritant, and high vapor exposure may cause headache, dizziness and drowsiness. Occupational exposure limits are commonly set at around 50 ppm as an eight-hour time-weighted average, and local regulations should always be consulted.
When handling isobutanol, use adequate ventilation, wear chemical-resistant gloves and safety goggles, and keep ignition sources away from the working area. In case of skin contact, wash thoroughly with soap and water; in case of eye contact, rinse with plenty of clean water and seek medical attention.
How to Store Isobutanol Safely
Store isobutanol in a cool, well-ventilated, dry environment, away from fire, heat sources and direct sunlight. Keep the material in tightly sealed containers made of compatible metal or approved plastic, and isolate it from strong oxidizing agents, acids and alkalis. Because the vapor can form explosive mixtures with air, storage areas should be equipped with explosion-proof electrical equipment, and containers should be grounded during transfer to prevent static discharge.
Frequently Asked Questions
Is isobutanol the same as isobutyl alcohol?
Yes. Isobutanol, isobutyl alcohol and 2-methyl-1-propanol all refer to the same compound with CAS number 78-83-1 and formula C4H10O.
Is 2-methyl-1-propanol toxic?
Isobutanol has moderate toxicity. It is harmful if swallowed, can irritate the eyes and respiratory tract, and high vapor concentrations may affect the central nervous system. Proper ventilation and personal protective equipment are required when handling it.
What is isobutanol mainly used for?
Its main uses include the production of isobutyl acetate solvents, diisobutyl phthalate plasticizers, the antioxidant BHT, synthetic musk, fruit flavor oils and pharmaceutical intermediates, as well as direct use as an industrial solvent.
Is isobutanol soluble in water?
Isobutanol is only slightly soluble in water, with a solubility of about 8.7 mL per 100 mL of water at 20 °C, and it is readily soluble in ethanol, diethyl ether and most organic solvents.
What is the flash point of isobutanol?
The flash point of isobutanol is approximately 27.8 °C in a closed cup, which classifies it as a flammable liquid. Its vapor can form explosive mixtures with air.
What is the CAS number and molecular formula of isobutanol?
Isobutanol has the CAS number 78-83-1 and the molecular formula C4H10O, with a molecular weight of about 74.12 g/mol.
