The molecular weight of 1-butanol (n-butanol, CAS 71-36-3) is 74.12 g/mol, calculated from its molecular formula C₄H₁₀O. This value is a fixed physical constant - it doesn't change with purity grade, only the amount of non-butanol material (typically water) present in a given product affects the measured mass of a sample.
| Parameter | Value |
|---|---|
| Compound | 1-Butanol (n-Butanol) |
| CAS Number | 71-36-3 |
| EC Number | 200-751-6 |
| Molecular Formula | C₄H₁₀O |
| Molecular Weight | 74.12 g/mol |
1-Butanol is a straight-chain, four-carbon primary alcohol - the "n-" (normal) designation distinguishes it from its three structural isomers: isobutanol, sec-butanol, and tert-butanol, all of which share the same molecular formula and molecular weight but differ in how the carbon chain is arranged around the hydroxyl group.
Molecular Formula
1-Butanol's structure is written as CH₃CH₂CH₂CH₂OH, showing a straight four-carbon chain with the hydroxyl group (-OH) attached to the terminal carbon - making it a primary alcohol. This is the structural detail that differentiates it from its isomers: isobutanol has a branched carbon chain, sec-butanol carries the -OH on an internal carbon, and tert-butanol has the -OH attached to a carbon bonded to three other carbons. All four isomers share the formula C₄H₁₀O and the molecular weight of 74.12 g/mol, but their differing structures give them distinct boiling points, reactivity, and industrial uses.
Physical Properties
| Property | Value |
|---|---|
| Appearance | Colorless liquid |
| Odor | Strong, mildly sweet, alcoholic odor |
| Density (20°C) | ~0.810 g/cm³ |
| Boiling Point | ~117.7°C |
| Melting/Freezing Point | ~-89°C |
| Flash Point (closed cup) | ~35-38°C |
| Autoignition Temperature | ~343°C |
| Refractive Index (20°C) | ~1.3993 |
| Vapor Pressure (20°C) | ~6 mmHg |
| Water Solubility | ~7.7-9% (w/w) at 20°C - partially miscible |
Unlike lower alcohols such as ethanol or isopropanol, 1-butanol is only partially miscible with water - at 20°C, roughly 7.7-9% of a butanol-water mixture will dissolve as butanol in the water phase, while water itself dissolves into butanol at about 20% by weight. This partial miscibility is a direct consequence of the longer, more nonpolar four-carbon chain relative to the polar hydroxyl group, and it's a property that matters directly in extraction and solvent-recovery applications.
Chemical Properties
1-Butanol is miscible with most common organic solvents, including ethanol, ether, and many other organics, but only partially with water as noted above. As a primary alcohol, it can be oxidized stepwise - first to butyraldehyde, then further to butyric acid - under appropriate oxidizing conditions, a reactivity pattern that distinguishes primary alcohols from secondary alcohols (which oxidize only to ketones) and tertiary alcohols (which resist oxidation entirely).
1-Butanol reacts with carboxylic acids under acid catalysis to form butyl esters - this esterification reaction is the basis for two of its largest industrial derivatives, butyl acetate and butyl acrylate. It also reacts with ethylene oxide to form butyl glycol ethers, and with phthalic anhydride in the production of dibutyl phthalate. Like other flammable alcohols, it is incompatible with strong oxidizers, which can trigger vigorous or exothermic reactions.
Industrial Applications
Solvent for Coatings and Paints: 1-Butanol's moderate evaporation rate and solvency make it a common component in lacquers, enamels, and other coating formulations, where it helps control flow and drying characteristics.
Plasticizer Production: It is a raw material for dibutyl phthalate (DBP) and related plasticizers used in flexible PVC and other polymer formulations.
Ester Production: 1-Butanol is the feedstock for butyl acetate (a widely used coatings and printing solvent) and butyl acrylate (a monomer in acrylic polymers, adhesives, and coatings).
Glycol Ether Manufacturing: Reaction with ethylene oxide produces butyl glycol ethers, used as solvents in cleaning products and coatings.
Extraction Solvent: Its partial water miscibility makes 1-butanol useful as an extraction solvent in organic synthesis and in the isolation of biochemical and pharmaceutical intermediates.
Chemical Intermediate: Beyond esters and glycol ethers, 1-butanol serves as a building block across broader organic synthesis processes in the specialty and fine chemical industries.
Safety Information
| Category | Value |
|---|---|
| GHS Classification | Flammable Liquid Category 3; Acute Toxicity Category 4; Skin/Eye Irritant; STOT SE (single exposure) |
| OSHA PEL (TWA) | 100 ppm (300 mg/m³), skin notation |
| NIOSH REL (Ceiling) | 50 ppm (150 mg/m³), skin notation |
| ACGIH TLV | 20 ppm (8-hour) |
| IDLH | 1,400 ppm |
| Flammable Range | 1.4% – 11.2% by volume in air |
| DOT Classification | UN 1120, Class 3, Flammable Liquid |
1-Butanol carries a skin notation from both OSHA and NIOSH, indicating that dermal absorption can contribute meaningfully to overall exposure - appropriate gloves and skin protection are recommended in addition to standard ventilation controls. As with other flammable alcohols, vapors are heavier than air and can travel to distant ignition sources, so storage away from heat, sparks, and open flame is essential. Always consult the current Safety Data Sheet (SDS) before handling.
FAQs
What is the exact molecular weight of 1-butanol?
74.12 g/mol, based on the molecular formula C₄H₁₀O. Some sources round this to 74.1 g/mol.
Do n-butanol and its isomers (isobutanol, sec-butanol, tert-butanol) have the same molecular weight?
Yes. All four C4 alcohol isomers share the molecular formula C₄H₁₀O and therefore the same molecular weight (74.12 g/mol), but they differ in structure, boiling point, and industrial application because of how the carbon chain and hydroxyl group are arranged.
How do I use 1-butanol's molecular weight to prepare a solution?
Multiply the target molarity by 74.12 g/mol to get the mass needed per liter - for example, a 1 mol/L solution requires 74.12 g of 1-butanol per liter, or approximately 91.5 mL by volume given its density of ~0.810 g/mL.
Is 1-butanol fully soluble in water?
No. 1-Butanol is only partially miscible with water - about 7.7-9% by weight dissolves at 20°C - unlike shorter-chain alcohols such as ethanol or isopropanol, which are fully water-miscible.
What is 1-butanol's CAS number and EC number?
CAS Number: 71-36-3. EC (EINECS) Number: 200-751-6. These identifiers are the most reliable way to confirm you are sourcing or referencing the correct compound, distinct from its structural isomers.
Is 1-butanol dangerous to handle?
It is classified as a flammable liquid with skin and eye irritation potential, and carries OSHA and NIOSH skin notations indicating dermal absorption risk. Standard flammable-liquid precautions - ventilation, ignition-source control, and appropriate PPE - apply. Always consult the current SDS before handling.
