What Is Acetonitrile and What Else Is It Called?
Acetonitrile (CAS 75-05-8) is the simplest organic nitrile, with the chemical formula CH3CN. It is a colourless, transparent liquid with a distinctive pungent odour and is one of the most widely used polar aprotic solvents in industry and in laboratory practice.
The compound appears in technical and commercial documents under several alternative names. The most common synonyms are methyl cyanide, methanecarbonitrile, ethanenitrile, cyanomethane, and the abbreviations ACN and MeCN. Because translated documents sometimes apply several of these names to the same drum, always match the CAS number 75-05-8 and the formula CH3CN on the label, the safety data sheet and the certificate of analysis.
Physical and Chemical Properties
Acetonitrile dissolves a broad range of organic compounds, inorganic salts and even some gases, which makes it a versatile medium for synthesis, extraction and analytical work. It combines strong solvent power with a relatively low boiling point, so it is easy to remove by distillation after a reaction.
| Property | Value |
|---|---|
| CAS number | 75-05-8 |
| Chemical formula | CH3CN |
| Common synonyms | Methyl cyanide; ethanenitrile; methanecarbonitrile; cyanomethane; ACN; MeCN |
| Molecular weight | About 41.05 g/mol |
| Appearance | Colourless liquid with a pungent odour |
| Boiling point | About 81.6 °C at atmospheric pressure |
| Freezing point | About -45 °C |
| Density at 20 °C | About 0.786 g/cm3 |
| Solubility | Completely miscible with water, alcohols, esters and many organic solvents |
| Solvent character | Polar aprotic |
Main Industrial and Laboratory Applications
Acetonitrile is best known as the mobile phase solvent in high-performance liquid chromatography, where its low absorbance in the short-wavelength ultraviolet region and its consistent purity are essential to reproducible results.
Mobile phase and sample solvent in HPLC and LC-MS analysis.
Extraction and recrystallisation of pharmaceutical compounds.
Reaction medium in organic synthesis and in the manufacture of fine chemicals.
Solvent in the production of battery electrolytes and agrochemical intermediates.
Purification of butadiene for the rubber industry.
Grades, Purity and Packaging
Different applications call for different specifications, and the grade should be stated on the purchase order to avoid a mismatch on arrival.
Gradient grade for HPLC, controlled for ultraviolet absorbance and gradient baseline.
Analytical grade for general laboratory work.
Technical grade for industrial synthesis and extraction duty.
Typical packaging: 200 L drums, intermediate bulk containers and road tankers for bulk users.
Key specification points to confirm are assay, water content, non-volatile residue and ultraviolet absorbance. Each delivery should arrive with a certificate of analysis that can be traced to the batch number on the container.
Handling, Storage and Safety
Acetonitrile is a flammable liquid with a low flash point, so it must be kept away from ignition sources and stored in tightly sealed containers in a cool, dry and well-ventilated area. It carries acute toxicity and irritant hazard classifications, and exposure by inhalation, skin contact or ingestion should be avoided.
Wear chemical-resistant gloves and safety goggles, and work in a well-ventilated space or under local exhaust ventilation.
Ground and bond containers during transfers to prevent static ignition.
Consult the safety data sheet before use, and keep it accessible to all operators.
In the event of a spill, ventilate the area and absorb the liquid with inert material before disposal.
Store separately from oxidising agents and strong acids.
Frequently Asked Questions
Q: What is the most common alternative name for acetonitrile?
Methyl cyanide is the most common alternative name, while ethanenitrile, methanecarbonitrile, cyanomethane, ACN and MeCN are also widely used.
Q: Is acetonitrile soluble in water?
Yes. Acetonitrile is completely miscible with water in all proportions, which is unusual for a nitrile solvent.
Q: What is acetonitrile mainly used for?
Its largest uses are as a solvent in HPLC analysis, in pharmaceutical synthesis and extraction, and as a reaction medium in organic chemistry.
Q: Is acetonitrile the same as acetone?
No. Acetonitrile is a nitrile with the formula CH3CN, while acetone is a ketone with the formula C3H6O; the two chemicals have different CAS numbers and different properties.
Q: How should acetonitrile be stored?
Store it in a tightly closed container in a cool, dry, well-ventilated area away from heat, sparks and open flames, and ground the containers during transfers.
Q: Does acetonitrile have a low boiling point?
Its boiling point is about 81.6 °C at atmospheric pressure, which is low for a dipolar aprotic solvent and convenient when the solvent has to be removed.
Q: Why is acetonitrile preferred for HPLC?
It has low absorbance in the short-wavelength ultraviolet region, low viscosity and consistent purity, which help produce stable baselines and reproducible retention times.