| Section2 = {{Chembox Properties
|C=14|H=10
| Appearance = Colorless
| Density = 1.25 g/cm³ at 19.85 °C, Solid 0.969 g/cm³ at 220 °C, liquid
| MeltingPtC = 218
| BoilingPtC = 340
| Solvent = other solvents
| SolubleOther = Water: none Methanol: 0.908g per liter Hexane: 1.64g per liter
}}
| Section7 = {{Chembox Hazards
| EUClass = Dangerous for the Environment}}
}}
Anthracene is a solid
polycyclic aromatic hydrocarbon consisting of three fused
benzene rings. It is derived from
coal-tar or other residues of thermal pyrolysis. Anthracene is used in the artificial
production of the
red dye alizarin. It is also used in
wood preservatives,
insecticides, and coating
materials. Anthracene is colorless but exhibits a blue (400-500 nm peak)
fluorescence under
ultraviolet light.
In 2010, a strong
absorption band of anthracene was observed along a line of sight to a star in the
open cluster IC 348, and this may be associated with an intervening
molecular cloud.
Synthesis
A classic method for the preparation of anthracene in the laboratory is by cyclodehydration of o-methyl- or o-methylene-substituted diarylketones in the so-called
Elbs reaction.
Reactions
Anthracene has the ability to
photodimerize with irradiation by
UV light. This results in considerable changes in the physical properties of the material.
The
dimer is connected by two
covalent bonds resulting from the
4+4 cycloaddition. The dimer reverts to anthracene thermally or with
UV irradiation below 300 nm. The reversible bonding and
photochromic properties of anthracenes is the basis of many potential applications using poly and monosubstituted anthracene derivatives. The reaction is sensitive to
oxygen.
Reduction of anthracene generally yields 9,10-dihydroanthracene (destroying the aromaticity of the center ring) rather than 1,4-dihydroanthracene (which would destroy the aromaticity of one of the terminal rings). This preference for reduction at the 9 and 10 positions is explained by the fact that aromatic stabilization energy is directly correlated with the number of conjugated pi bonds in an aromatic system. Since 9,10-dihydroanthracene essentially preserves two "benzene" rings (a total of 6 conjugated pi bonds), whereas the 1,4-isomer only preserves one and a half such rings (a total of 5 pi bonds), the latter is not the thermodynamically favorable product. Similarly,
electrophilic substitution occurs at the "9" and "10" positions of the center ring;
oxidation occurs readily, giving
anthraquinone, C14H8O2 (below).
Uses
Anthracene derivatives having a
hydroxyl group are 1-hydroxyanthracene and 2-hydroxyanthracene, homologous to
phenol and
naphthols, and hydroxyanthracene is also called anthrol, and anthracenol.
1-Hydroxyanthracene NIST datapage
2-Hydroxyanthracene NIST datapage
Hydroxyanthracene derivatives are
pharmacologically active, and are contained in
aloe for example (specifically in the aloe latex - the references cited for this are inaccurate as they describe the aloe latex, which is typically not a part of the plant used in commerce or is removed during processing
IASC, 2009.
TGA News Herbals and Breastfeeding
Anthracene is an
organic semiconductor. It is used as a
scintillator for detectors of high energy
photons,
electrons and
alpha particles. Plastics such as
polyvinyltoluene can be doped with anthracene to produce a plastic scintillator that is approximately water equivalent for use in
radiation therapy dosimetry. Anthracene's
emission spectrum peaks at between 400 nm and 440 nm.
Bipedal derivative
In 2005, chemists at the
University of California, Riverside developed the first bipedal molecule,
9,10-Dithioanthracene, which propels itself in a straight line when heated on a flat copper surface. Researchers believe the molecule has potential for use in
molecular computers.
Toxicology
Unlike other polycyclic aromatic hydrocarbons (
PAH), anthracene is
not carcinogenic but has been recently included in the Substances of Very High Concern list (
SVHC) by the European Chemicals Agency (
ECHA)
link because it is considered Persistent, Bioaccumulative and Toxic (
PBT) for freshwater and marine ecosystems
link within the
REACH framework. Anthracene, as many other PAHs is generated during combustion processes: exposure to human happens mainly through tobacco smoke and ingestion of food contaminated with combustion products
link.
See also
References
External links