What Is Acetonitrile (CAS 75-05-8)?
Acetonitrile, also known as methyl cyanide or cyanomethane, is the simplest organic nitrile. Its chemical formula is CH3CN (C2H3N) and its molecular weight is 41.05 g/mol. The compound is a colorless, volatile liquid with a mild ether-like odor. It is fully miscible with water and with most common organic solvents, which makes it one of the most frequently used polar aprotic solvents in laboratories and industrial plants. Typical applications include high-performance liquid chromatography (HPLC), pharmaceutical synthesis, pesticide formulation, extractive distillation, and lithium battery electrolyte formulation.
What Is Acetone (CAS 67-64-1)?
Acetone, also known as propanone or dimethyl ketone, is the simplest ketone. Its chemical formula is CH3COCH3 (C3H6O) and its molecular weight is 58.08 g/mol. Acetone is a colorless, highly volatile liquid with a characteristic sweet odor. Industrially, most acetone is produced by the cumene process, in which cumene is oxidized to phenol and acetone, or by catalytic dehydrogenation of isopropanol. It is widely used as a solvent for paints, coatings, adhesives, nail polish removers, and laboratory glassware cleaning.
Key Differences Between Acetonitrile and Acetone
Both acetonitrile and acetone are polar aprotic solvents that are completely miscible with water. However, they belong to different functional group families and show clear differences in physical properties, toxicity, and applications.
| Property | Acetonitrile (CAS 75-05-8) | Acetone (CAS 67-64-1) |
| Chemical family | Nitrile | Ketone |
| Molecular formula | C2H3N (CH3CN) | C3H6O (CH3COCH3) |
| Molecular weight | 41.05 g/mol | 58.08 g/mol |
| Boiling point | 81.6 °C | 56.1 °C |
| Melting point | -45 °C | -94.7 °C |
| Flash point (closed cup) | 2 °C | -20 °C |
| UV cutoff | Around 190 nm | Around 330 nm |
| Primary use | HPLC, pharmaceutical synthesis | Cleaning, coatings, nail polish remover |
| Toxicity profile | Moderately toxic, metabolized to cyanide | Low acute toxicity, naturally present in the body |
Why Acetonitrile Is Preferred in HPLC.
Acetonitrile is the standard organic modifier in reversed-phase HPLC because of its low UV absorbance. Its cutoff of about 190 nm allows detection of analytes at short wavelengths. Acetone, by contrast, absorbs strongly above 300 nm, which makes it unsuitable for most UV detection systems. Acetonitrile also has lower viscosity than methanol, which reduces column backpressure and shortens analysis time.
How to Choose Between Acetonitrile and Acetone
Choose acetone when the task requires an inexpensive, low-toxicity solvent for cleaning, degreasing, or resin dilution. Choose acetonitrile when you need a solvent with high elution strength, low UV background, or stable performance in pharmaceutical and analytical applications. Do not substitute one for the other without revalidating the process, because differences in boiling point, toxicity, and UV transparency can change both results and safety requirements.
Safety and Handling Considerations
Acetonitrile is moderately toxic. It is absorbed through the skin, by inhalation, and by ingestion, and the body metabolizes it to cyanide, which can cause serious systemic poisoning. Acetone has low acute toxicity but is highly flammable and can form explosive vapor-air mixtures. Both solvents require adequate ventilation, grounded containers to prevent static discharge, and storage away from oxidizers and ignition sources. Routine quality control for solvent grades includes gas chromatography purity assay, water content by Karl Fischer titration per ASTM E203, density measurement per ASTM D4052, and color measurement per ASTM D1209.
Frequently Asked Questions
Is acetonitrile the same as acetone? No. Acetonitrile (CAS 75-05-8) is a nitrile with the formula C2H3N, while acetone (CAS 67-64-1) is a ketone with the formula C3H6O. They are both polar aprotic solvents miscible with water, but their structures, physical properties, and applications differ.
Can acetone replace acetonitrile in HPLC? No. Acetone has a UV cutoff near 330 nm and absorbs strongly in the detection range used by most HPLC methods, while acetonitrile with a cutoff near 190 nm keeps the baseline clean at short wavelengths.
Why is acetonitrile more expensive than acetone? cetonitrile is a byproduct of acrylonitrile production and requires costly purification steps, whereas acetone is manufactured in very high volume by the cumene process, which gives it a lower unit cost.
Is acetonitrile toxic to humans? Yes. Acetonitrile is moderately toxic and is metabolized in the body to cyanide. Exposure through inhalation, ingestion, or skin contact must be controlled with ventilation, gloves, and eye protection.
What are the main uses of acetone? acetone is used as a solvent in coatings, adhesives, and cleaning products, as a carrier for nail polish remover, and as a raw material for methyl methacrylate and bisphenol A production.
How is bulk acetonitrile packaged? Bulk acetonitrile is commonly supplied in 160 kg drums, 1000 L IBC containers, and ISO tank containers. Nitrogen blanketing is recommended to prevent moisture pickup during long-term storage.