What is Acetonitrile?

Acetonitrile is a transparent liquid with an aromatic odor, with chemical formula CH3CN. It is the simplest organic nitrile.

Acetonitrile is also known as cyanomethane, ethyl nitrile, ethanenitrile, methanecarbonitrile, and methyl cyanide.

Acetonitrile is used to make pharmaceuticals, perfumes, rubber products, pesticides, acrylic nail removers, and batteries. It is also used to extract fatty acids from animal and vegetable oils.

Sigma Aldrich Acetonitrile Lewis Structure

Acetonitrile is a polar aprotic solvent. The electronegativity difference between carbon and nitrogen and the triple bond between them produces a dipole moment that makes this substance polar.

It is an aprotic solvent, because, unlike of protic solvents such us 2-propanol, the acetonitrile molecules are not capable of forming protons (H+) upon dissociation.

As a leading supplier of high-purity solvents, we offer the right product for your application, whether you need HPLC acetonitrile, acetonitrile for biotech, anhydrous acetonitrile, or other grades available.

Acetonitrile Formulas and Structures

Acetonitrile has a central carbon atom that is triple bound to one nitrogen atom (nitrile functional group) and has a single bond to a methyl group.

Type Formula or Structure
Acetonitrile Molecular Formulas C2H3N or CH3CN
Acetonitrile Ball and Sticks Structural Model Sigma Aldrich Acetonitrile  Ball-Stick Structure
Acetonitrile Sticks Structural Model Sigma Aldrich Acetonitrile Stick Structure
Acetonitrile Skeletal Structural Model Sigma Aldrich Acetonitrile Skeletal Structure
Acetonitrile Space-Filling Structural Model Sigma Aldrich Acetonitrile Space-Filling Structure

Acetonitrile Identification

Chart listing the various names, identifiers and synonyms of acetonitrile.

ID Type Identification
Synonym Methyl cyanide
Molecular Formula CH3CN
CAS Number 75-05-8
Beilstein Registry
EG/EC Number 2008352
MDL Number MFCD00001878
RIDADR UN 1648 3/PG 2


Acetonitrile Physical and Chemical Properties

Chart including the physical and chemical properties of acetonitrile.

Property Value
Molecular Weight 41.05
Density 0.786 g/mL at 25ºC
Boiling Point 81-82ºC
Melting Point -48ºC
Flash Point 5.5ºC
Viscosity (cP)
0.369 at 25ºC
Dielectric Constant 36.64 at 20ºC
Dipole Moment 3.924
UV cutoff 190 nm
Refractive Index 1.344 at 20ºC
Vapor Pressure 72.8 mm Hg (20°C)
Vapor Density 1.41 (vs. air)
Water Solubility 24.36 M 
Heat of Combustion 31.03X10+6 J/kg at 250
Heat of Vaporization 72.7X10+4 J/kg at 800
Dissociation Constants pKa = -4.30 (conjugate acid) 
Surface Tension 29.04 dyn/cm at 200

Acetonitrile Miscibility and Immiscibility

Property Chemical
Miscible Acetic Acid, Acetone, Acetonitrile, Benzene, Butanol, Methyl ethyl ketone (MEK), Butyl Acetate (n-), Methyl tert-butyl ether (MTBE), Carbon Tetrachloride, Chloroform, Dichloroethane (1, 2), Dichloromethane, Diethyl ether, Diisopropyl ether, Dimethylformamide, Dimethyl Sulfoxide (DMSO), Dioxane, Ethanol, Ethyl Acetate, Methanol, 1-Propanol, Isopropanol, Tetrahydrofuran (THF), Toluene, Trichloroethylene, Water, Xylene
Immiscible Cyclohexane, Heptane, Hexane, Pentane, Isooctane
Miscibility Information and Solvent Miscibility Table

Acetonitrile Hazard Statements

Hazard Statements H225-H302 + H312 + H332-H319
Signal Word Danger
P210-P280-P305 + P351 + P338

GHS Information

GHS Pictogram Statement

Flammable gases, category 1
Flammable aerosols, categories 1,2
Flammable liquids, categories 1,2,3
Flammable solids, categories 1,2
Self-reactive substances and mixtures, Types B,C,D,E,F
Pyrophoric liquids, category 1
Pyrophoric solids, category 1
Self-heating substances and mixtures, categories 1,2
Substances and mixtures, which in contact with water,
emit flammable gases, categories 1,2,3
Organic peroxides, Types B,C,D,E,F
Acute toxicity (oral, dermal, inhalation), category 4
Skin irritation, category 2
Eye irritation, category 2
Skin sensitisation, category 1
Specific Target Organ Toxicity – Single exposure, category 3

Acetonitrile SDS Information

An SDS (safety data sheet) is available for each acetonitrile product. Start your search for an SDS

Acetonitrile Uses

The most common uses of acetonitrile are:

  • In organic synthesis as starting material for acetophenone, α-naphthaleneacetic acid, thiamine, and acetamidine.
  • To remove tars, phenols, and coloring matter from petroleum hydrocarbons.
  • To extract fatty acids from fish liver oils and other animal and vegetable oils.
  • As a polar solvent in non-aqueous titrations;
  • As a non-aqueous solvent for inorganic salts.
  • In reverse-phase chromatography (RPC), HPLC, UV, and electrochemistry applications.
  • To facilitates reactions between organic substrates and inorganic materials.

The Ritter reaction is a good example of acetonitrile in a common application. This reaction converts a nitrile and a carbocation precursor to an amide using strong acid and water.


Sigma Aldrich Acetonitrile Ritter Reaction


Acetonitrile Advantages in RPC

RPC is a liquid chromatography technique used to separate molecules. These interactions occur between two phases, the mobile and stationary phases. The mobile phase of a solvent carries molecules through the column. The stationary phase is the inner surface of the column.

In normal-phase chromatography, the stationary phase is polar and the mobile phase is non-polar. Dissolved polar components are attracted to the stationary phase. Due to this attraction, polar components remain in the column longer. Non-polar components are not attracted to the stationary phase. Without an interaction, non-polar components continue through the column with the mobile phase.

In reverse-phase chromatography, the stationary phase is non-polar, and the mobile phase is polar. Non-polar molecules interact with the stationary phase by hydrophobic interactions. Water is the mobile phase in RPC, but many solutes are not soluble in water.

Organic solvents, that are miscible in water, are often added during RPC to improve solute solubility. These solvents are called organic modifiers. Organic modifiers cannot be too non-polar or they affect the interaction between the solute and stationary phase. Acetonitrile and methanol are the common organic modifiers of choice for reverse-phase chromatography. Both solvents provide advantages and disadvantages in this analytical technique.

There are many criteria to select an organic modifier, including its: miscibility with water, polarity, UV cut-off, viscosity, and safety.

Both solvents are miscible with water and are compatible with common mobile phases and buffers.

These are the pros and cons of each one:

  • Acetonitrile costs more than methanol,
  • Methanol is less toxic than acetonitrile
  • Acetonitrile has a lower UV cut-off than methanol,
  • Acetonitrile is more suitable for use in applications requiring low UV detection wavelengths
  • Acetonitrile and water mixes have a lower viscosity than methanol and water mixes
  • Acetonitrile generate substantially lower back pressures across the LC column
  • Acetonitrile has a higher elution strength than methanol for RPC
  • Acetonitrile has shorter analyte retention than methanol
  • Acetonitrile is a polar aprotic solvent and possesses a stronger dipole moment. This can have a powerful effect on chromatographic selectivity

Research both methanol and acetonitrile before developing a new reversed-phase method. It's useful to understand how your organic modifier will affect your project.