ANTHRACENE: STRUCTURE, PROPERTIES, TOXICITY AND USES - CHEMISTRY - 2025

The anthracene is a polycyclic aromatic hydrocarbon (PAH) which is formed by the fusion of three benzene rings. It is a colorless compound, but under the irradiation of ultraviolet light it acquires a fluorescent blue color. Anthracene easily sublimates.

It is a white solid (bottom image), but it can also appear as colorless monoclinic crystals, with a mild aromatic odor. Solid anthracene is practically insoluble in water and is partially soluble in organic solvents, especially carbon disulfide, CS ₂.

Anthracene crystals. Source: Leiem via Wikipedia.

It was discovered in 1832 by August Laurent and Jean Dumas, using tar as a raw material. This material continues to be used in the production of anthracene, since it contains 1.5% of the aromatic compound. It can also be synthesized from benzoquinone.

It is found in the environment as a product of the partial combustion of fossil hydrocarbons. It has been found in drinking water, in atmospheric air, in motor vehicle exhausts, and in cigarette smoke. It is listed by the EPA (United States Environmental Protection Agency) of the most important environmental pollutants.

Anthracene is dimerized by the action of ultraviolet light. Furthermore, it is hydrogenated to 9,10-dihydroanthracene by the action of zinc, maintaining the aromaticity of the remaining benzene rings. It is oxidized to anthraquinone by reaction with hydrogen peroxide.

By rubbing it can emit light and electricity, darkening by exposure to sunlight.

It is used as an intermediate in the production of inks and colorants, such as alizarin. It is used in the protection of wood. It is also used as an insecticidal, miticidal, herbicidal and rodenticidal agent.

Structure of anthracene

The three aromatic rings of anthracene. Source: Jynto

The upper image shows the structure of anthracene represented with a model of spheres and bars. As can be seen, there are three six-carbon aromatic rings; these are benzene rings. Dotted lines indicate aromaticity present in the structure.

All carbons have sp ² hybridization, so the molecule is in the same plane. Therefore, anthracene can be considered as a small, aromatic sheet.

Note also that the hydrogen atoms (the white spheres), on the sides, are practically exposed to a series of chemical reactions.

Intermolecular forces and crystal structure

Anthracene molecules interact through London scattering forces and stacking their rings on top of each other. For example, it can be seen that two of these "sheets" come together and as the electrons of their π cloud move (the aromatic centers of the rings), they manage to stay together.

Another possible interaction is that hydrogens, with some positive partial charge, are attracted to the negative and aromatic centers of neighboring anthracene molecules. And therefore, these attractions exert a directional effect that orients the anthracene molecules in space.

Thus, anthracene is ordered in such a way that it adopts a long-range structural pattern; and therefore it can crystallize in a monoclinic system.

Presumably, these crystals exhibit yellowish colorations as a result of their oxidation to anthraquinone; which is a derivative of anthracene whose solid is yellow.

Properties

Chemical names

-Anthracene

-Paranaphthalene

-Anthracine

-Green Oil

Molecular formula

C ₁₄ H ₁₀ or (C ₆ H ₄ CH) ₂.

Molecular weight

178.234 g / mol.

Physical description

White or pale yellow solid. Monoclinic crystals product of recrystallization in alcohol.

Color

When pure anthracene is colorless. With yellow light the yellow crystals fluoresce with a blue color. It can also present certain yellowish tones.

Odor

Mild aromatic.

Boiling point

341.3 ° C.

Melting point

216 ° C.

ignition point

250ºF (121ºC), closed cup.

Water solubility

Practically insoluble in water.

0.022 mg / L of water at 0 ºC

0044 mg / L of water at 25ºC.

Solubility in ethanol

0.76 g / kg at 16ºC

3.28 g / kg at 25 ° C. Note how it is more soluble in ethanol than in water at the same temperature.

Solubility in hexane

3.7 g / kg.

Solubility in benzene

16.3 g / L. Its greater solubility in benzene shows its high affinity for it, since both substances are aromatic and cyclic.

Carbon disulfide solubility

32.25 g / L.

Density

1.24 g / cm ³ at 68 ° F (1.25 g / cm ³ at 23 ° C).

Vapor density

6.15 (relative to air taken as a reference equal to 1).

Steam pressure

1 mmHg at 293 ° F (sublime). 6.56 x 10 ^-6 mmHg at 25 ° C.

Stability

It is stable if stored under recommended conditions. It is triboluminescent and triboelectric; This means that it emits light and electricity when rubbed. Anthracene darkens when exposed to sunlight.

Auto-ignition

1,004 ° F (540 ° C).

Decomposition

Hazardous compounds are produced by combustion (carbon oxides). It decomposes on heating under the influence of strong oxidants, producing a pungent and toxic smoke.

Heat of combustion

40,110 kJ / kg.

Caloric capacity

210.5 J / mol · K.

Maximum absorption wavelength (visible and ultraviolet light)

Maximum λ 345.6 nm and 363.2 nm.

Viscosity

-0.602 cPoise (240 ºC)

-0.498 cPoise (270 ºC)

-0.429 cPoise (300 ºC)

As can be seen, its viscosity decreases as the temperature increases.

Nomenclature

Anthracene is a uniform polycyclic molecule, and according to the nomenclature established for this type of system, its real name should be Tricene. The prefix tri is because there are three benzene rings. However, the trivial name anthracene has spread and rooted in popular culture and science.

The nomenclature of the compounds derived from it is usually somewhat complex, and depends on the carbon where the substitution takes place. The following shows the respective carbon numbering for anthracene:

Carbon numbering in anthracene. Source: Edgar181

The order of numbering is due to the priority in reactivity or susceptibility of said carbons.

The end carbons (1-4, and 8-5) are the most reactive, while those in the middle (9-10), react by other conditions; for example, oxidative, to form anthraquinone (9, 10-dioxoanthracene).

Toxicity

In contact with the skin it can cause irritation, itching and burning, which are aggravated by sunlight. Anthracene is a photosensitizer, which enhances skin damage caused by UV radiation. May cause acute dermatitis, telangiectasia, and allergy.

In contact with the eyes it can cause irritation and burns. Breathing anthracene can irritate the nose, throat, and lungs, causing coughing and wheezing.

Anthracene intake has been associated in humans with headache, nausea, loss of appetite, inflammation of the gastrointestinal tract, slow reactions, and weakness.

There have been suggestions of a carcinogenic action of anthracene. However, this presumption has not been corroborated, even some anthracene derivatives have been used in the treatment of certain types of cancer.

Applications

Technological

-Anthracene is an organic semiconductor, used as a scintillator in detectors of high energy photons, electrons and alpha particles.

-It is also used for coating plastics, such as polyvinyl toluene. This in order to produce plastic scintillators, with characteristics similar to water, to be used in radiotherapy dosimetry.

-Anthracene is commonly used as a UV radiation tracer, applied in coatings on printed circuit boards. This allows the coating to be inspected under ultraviolet light.

Bipedal molecule

In 2005 chemists at the University of California, Riverside, synthesized the first bipedal molecule: 9.10-dithioanthratracene. It propels itself in a straight line when heated on a flat copper surface, and it can move as if it were two feet.

The researchers thought the molecule was potentially usable in molecular computing.

Piezochromaticity

Some anthracene derivatives have piezochromatic properties, that is, they have the ability to change color depending on the pressure applied to them. Therefore, they can be used as pressure detectors.

Anthracene is also used in the making of so-called smoke screens.

Ecological

Polycyclic aromatic hydrocarbons (PAH) are environmental pollutants, mainly water, so efforts are made to reduce the toxic presence of these compounds.

Anthracene is a material (PAH) and is used as a model to study the application of the hydric pyrolysis method in the degradation of PAH compounds.

Hydric pyrolysis is used in industrial water treatment. Its action on anthracene produced the formation of the oxidation compounds: anthrone, anthroquinone and xanthone, as well as derivatives of hydroanthracene.

These products are less stable than anthracene and therefore are less persistent in the environment and can be more easily eliminated than PAH compounds.

Others

-Anthracene is oxidized to produce anthroquinone, used in the synthesis of dyes and colorants

-Anthracene is used to protect wood. It is also used as an insecticide, miticide, herbicide, and rodenticide.

-The antibiotic anthracycline has been used in chemotherapy, since it inhibits the synthesis of DNA and RNA. The anthracycline molecule is sandwiched between the DNA / RNA bases, inhibiting the replication of rapidly growing cancer cells.

References

1. Fernández Palacios S. et al. (2017). Piezochromic properties of pyridil divinyl anthracene derivatives: a joint Raman and DFT study. Malaga University.
2. Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. Amines. (10 ^th edition.). Wiley Plus.
3. Wikipedia. (2018). Anthracene. Recovered from: en.wikipedia.org
4. PubChem. (2019). Anthracene. Recovered from: pubchem.ncbi.nlm.nih.gov
5. Somashekar MN and Chetana PR (2016). A Review on Anthracene and Its Derivatives: Applications. Research & Reviews: Journal of Chemistry.