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What is acetonitrile?

The  acetonitrile  is a substance of organic origin formed by only carbon, hydrogen and nitrogen. This chemical species belongs to the group of nitriles, being acetonitrile the one with the simplest structure among those of the organic type.

Nitriles are a class of chemical compounds whose structure is made up of a cyanide group (CN  ) and a radical chain (-R). These elements are represented by the following general formula: RC≡N.

It is known that this substance is primarily originated during the production of another species called acrylonitrile (another simple nitrile, of molecular formula C 3 H 3 N, which is used in the manufacture of products in the textile industry) as a by-product of it.

Furthermore, acetonitrile is considered a solvent with medium polarity properties, which is why it is used fairly regularly in RP-HPLC (reverse phase high performance liquid chromatography) analyzes.

As previously mentioned, acetonitrile belongs to the functional group of nitriles, having a molecular formula commonly represented as C 2 H 3 N, which can be observed in the structural formula that is exemplified in the figure above.

This image shows a kind of lobe attached to the nitrogen atom, which represents the pair of unpaired electrons that this atom has, and which give it a large part of the reactivity and stability properties that are characteristic of it.

In this way, this species shows a very particular behavior due to its structural arrangement, which translates into weakness to receive hydrogen bonds and little ability to donate electrons.

Also, this substance originated for the first time in the second half of the 1840s, being manufactured by the scientist named Jean-Baptiste Dumas, whose nationality was French.

The structural conformation of this substance allows it to have characteristics of its own solvent of organic nature.

In turn, this property allows acetonitrile to be mixed with water, in addition to a series of other solvents of organic origin, with the exception of hydrocarbons or saturated-type hydrocarbon species.

Acetonitrile Properties

This compound has a series of properties that distinguish it from others of its same class, which are listed below:

  • It is in a liquid state of aggregation under standard conditions of pressure and temperature (1 atm and 25 ° C).
  • Its molecular configuration gives it a molar mass or molecular weight of approximately 41 g / mol.
  • It is considered as the nitrile that has the simplest structure, among the organic type.
  • Its optical properties allow it to be colorless in this liquid phase and with limpid characteristics, in addition to having an aromatic odor.
  • It has a flash point of around 2 ° C, which is equivalent to 35.6 ° F or 275.1 K.
  • It has a boiling point in the range of 81.3 to 82.1 ° C, a density of approximately 0.786 g / cm 3 and a melting point that is between -46 to -44 ° C.
  • It is less dense than water but miscible with it and with a variety of organic solvents.
  • It exhibits a dielectric constant of 38.8 in addition to a dipole moment of approximately 3.92 D.
  • It is capable of dissolving a great variety of substances of ionic origin and nonpolar nature.
  • It is widely used as a mobile phase in HPLC analysis, which has high flammability properties.

Uses / applications

Among the large number of applications that acetonitrile has, the following can be counted:

  • In a similar way, other nitrile species can undergo a process of metabolism in microsomes (vesicular elements that are part of the liver), especially in this organ, to produce hydrocyanic acid.
  • It is widely used as a mobile phase in the type of analysis called reverse phase high performance liquid chromatography (RP-HPLC); that is, as an eluting substance that has high stability, great eluting power and decreased viscosity.
  • In the case of industrial applications, this chemical compound is used in crude oil refineries as a solvent in certain processes, such as the purification of the alkene called butadiene.
  • It is also used as a ligand (chemical species that combines with an atom of a metallic element, considered central in the given molecule, to form a compound or coordination complex) in a large number of nitrile compounds with metals of the transition group .
  • Similarly, it is used in organic synthesis for a large number of such advantageous chemicals as α-naphthalene acetic acid, thiamine or acetamidine hydrochloride.

Risks

The risks associated with exposure to acetonitrile are diverse. Among these is a decreased toxicity when the exposure is for a reduced period of time and in low amounts, being metabolized for the production of hydrocyanic acid.

Likewise, rarely have there been registered cases of people who have been poisoned with this chemical species, being poisoned by the cyanide present in the molecule after having been in contact with acetonitrile in different degrees (by inhaling it, ingesting it or absorbing it through the skin ).

For this reason, the consequences of its toxicity are delayed because the body does not easily metabolize this substance into cyanide, since it takes two to twelve hours for this to occur.

However, acetonitrile is easily absorbed from the lungs and gastrointestinal tract. Subsequently, it is distributed throughout the body, happening in people and even animals and reaching the kidneys and spleen.

On the other hand, in addition to the flammability risks it presents, acetonitrile is a precursor of substances as toxic as hydrocyanic acid or formaldehyde. Its use in products belonging to the cosmetic area was even prohibited in the so-called European Economic Area in 2000.

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