Introduction
C14H14 is a molecular formula that corresponds to a class of aromatic hydrocarbons in which the skeleton contains fourteen carbon atoms and fourteen hydrogen atoms. The most commonly referenced compound with this formula is 1,2,3,4‑tetrahydroanthracene, a partially hydrogenated derivative of the polycyclic aromatic hydrocarbon anthracene. The formula can also be realized by other structural isomers, such as the bicyclic hydrocarbon 1,2,3,4‑tetrahydroindene and certain fused ring systems containing a cyclohexadiene core attached to a benzene ring. Because the compound is not chiral and possesses planar conjugated systems, it is frequently employed in studies of polycyclic aromatic chemistry, polymerization, and materials science. The compound is available commercially in the form of a colorless liquid or solid, depending on its purity and degree of crystallinity, and is used as a reagent, monomer, or intermediate in organic synthesis.
Structure and Nomenclature
IUPAC Name
The International Union of Pure and Applied Chemistry (IUPAC) nomenclature for the most studied form of C14H14 is 1,2,3,4‑tetrahydroanthracene. This name indicates that four hydrogen atoms have been added to the anthracene framework at the 1, 2, 3, and 4 positions, reducing the central ring from an aromatic benzene to a cyclohexadiene. The parent hydrocarbon anthracene (C14H10) consists of three linearly fused benzene rings. The numbering of the anthracene core begins at one of the outer rings, continues through the central ring, and ends at the opposite outer ring. The addition of hydrogens at positions 1, 2, 3, and 4 produces a partially saturated system that retains planarity at the benzene rings but introduces a conjugated double bond within the reduced central ring.
Common Names
Outside of formal nomenclature, the compound is often referred to as tetrahydroanthracene or simply THA. In polymer chemistry literature, it may appear as 1,2,3,4‑tetrahydroanthracene (THA) or as 1,2,3,4‑tetrahydroanthracene (1,2,3,4‑THA). Because the molecule can adopt several stereoisomeric forms (E/Z configurations at the internal double bond), some authors distinguish between the cis and trans isomers, labeling them as cis‑1,2,3,4‑THA and trans‑1,2,3,4‑THA. In the context of materials science, the compound is also described as a monomer for the synthesis of conjugated polymers due to its ability to participate in radical-initiated polymerization.
Structural Isomerism
While 1,2,3,4‑tetrahydroanthracene is the most studied isomer, the molecular formula C14H14 can be satisfied by numerous other skeletal frameworks. Among these are bicyclic systems such as 1,2,3,4‑tetrahydroindene, which consists of a cyclohexadiene fused to a benzene ring. Another isomer, 1,2,3,4‑tetrahydrofluorene, contains a five‑membered ring fused to a benzene ring and a cyclohexadiene. Each isomer exhibits distinct physical properties, reactivity patterns, and potential applications. Isomeric diversity is commonly explored in synthetic organic chemistry to investigate structure–property relationships in aromatic systems. The distribution of isomers in a sample can be analyzed by chromatographic techniques such as gas chromatography coupled with mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC).
Physical Properties
State and Appearance
At room temperature and atmospheric pressure, 1,2,3,4‑tetrahydroanthracene is typically observed as a pale yellow to colorless liquid. The compound crystallizes into a monoclinic lattice when cooled below 20 °C under controlled conditions, yielding colorless plates that are translucent to opaque. The melting point of the trans isomer is reported to be 22 °C, while the cis isomer melts at 17 °C, reflecting the difference in crystal packing due to stereochemical orientation. The boiling point of the liquid form is approximately 140 °C under reduced pressure (1 atm) and is readily distilled in a laboratory setup. The density at 20 °C is measured to be 0.92 g cm⁻³, indicating a slight expansion relative to its aromatic counterpart anthracene.
Thermal Properties
The heat capacity of 1,2,3,4‑tetrahydroanthracene at constant pressure is 1.68 kJ mol⁻¹ K⁻¹ in the temperature range 298–400 K. The compound exhibits a relatively low thermal conductivity of 0.12 W m⁻¹ K⁻¹, typical of organic liquids. Thermogravimetric analysis (TGA) shows no weight loss up to 250 °C, after which the compound begins to decompose, releasing small amounts of volatile products such as ethylene and hydrogen. Differential scanning calorimetry (DSC) indicates an endothermic peak at 140 °C corresponding to the phase transition from liquid to vapor. The compound is stable under normal atmospheric conditions for extended periods, although exposure to concentrated oxidizing agents may lead to gradual degradation.
Spectroscopic Data
In the infrared (IR) spectrum, 1,2,3,4‑tetrahydroanthracene displays characteristic absorptions at 3020 cm⁻¹ (aromatic C–H stretch), 2950 cm⁻¹ (aliphatic C–H stretch), 1620 cm⁻¹ (C=C stretch of the reduced ring), and 1510 cm⁻¹ (aromatic C=C stretch). The Raman spectrum is dominated by peaks at 1605 cm⁻¹ (C=C) and 1330 cm⁻¹ (C–H out-of-plane bending). In the nuclear magnetic resonance (NMR) domain, the ^1H NMR spectrum recorded in CDCl₃ at 400 MHz shows six aromatic proton signals between 7.30 and 7.70 ppm, and two alkenic protons appearing as a multiplet at 5.50 ppm. The ^13C NMR spectrum features signals at 140.2, 138.7, 129.6, 128.3, 128.0, and 126.5 ppm for aromatic carbons, and at 115.7 and 108.3 ppm for the double bond carbons. High-resolution mass spectrometry (HRMS) confirms the molecular ion at m/z 182.1075, consistent with the formula C14H14 (calculated 182.1075). Elemental analysis results for the pure compound yield carbon 79.12 %, hydrogen 4.93 %, nitrogen
Synthesis and Production
Laboratory Synthesis
Laboratory preparation of 1,2,3,4‑tetrahydroanthracene is typically achieved through partial hydrogenation of anthracene or related polycyclic aromatics. A common procedure involves the catalytic hydrogenation of anthracene using palladium on carbon (Pd/C) as the catalyst under hydrogen pressure of 5 bar at 80 °C. The reaction mixture is stirred for 4 h, after which the catalyst is filtered off and the solvent removed under reduced pressure. The crude product is purified by column chromatography on silica gel, employing a gradient of hexane/ethyl acetate (9:1 to 7:3) as the eluent. The resulting fraction corresponds to the trans isomer, with an isolated yield of 72 %. To obtain the cis isomer, the hydrogenation is performed at lower temperatures (25 °C) with a catalyst such as platinum oxide (PtO₂) in the presence of a Lewis acid promoter, yielding 68 % isolated yield.
Alternative synthetic routes exploit Birch reduction of anthracene in liquid ammonia with sodium or lithium metal and an alcohol as proton source. This method affords a mixture of diastereomers that can be resolved by chromatography or by recrystallization from toluene. The resulting product is a 1,4‑diol that can be dehydrated to give 1,2,3,4‑tetrahydroanthracene via acid-catalyzed elimination. Although more laborious, this approach provides access to functionalized derivatives, as the diol intermediate can be substituted before dehydration.
Industrial Production
Commercial production of 1,2,3,4‑tetrahydroanthracene is carried out at scale by catalytic hydrogenation of anthracene or phenanthrene in a flow reactor. The process employs a packed-bed catalyst of Pd/C or Raney nickel with hydrogen pressures ranging from 10 to 20 bar and temperatures between 90 and 120 °C. Continuous removal of the product by distillation at atmospheric pressure allows for high throughput and reduces the residence time of the reactive intermediates. The industrial process typically yields a product that is 99.5 % pure with respect to the desired isomer, with impurities consisting primarily of unreacted anthracene and minor amounts of dihydroanthracene. The final product is formulated as a clear liquid and shipped in sealed containers to laboratories and polymer manufacturers worldwide. Environmental controls include catalytic recirculation of hydrogen and solvent recovery systems to minimize waste and emissions.
Chemical Reactions
Oxidation
1,2,3,4‑Tetrahydroanthracene can undergo oxidation to regenerate the aromatic anthracene core. Typical oxidants include potassium permanganate in aqueous alkaline solution or ozone in a dry solvent. The reaction proceeds via a two-electron oxidation at the alkenic bond, restoring the central ring to an aromatic state. In the presence of catalytic amounts of copper(II) acetate, the oxidation can be performed at room temperature, yielding anthracene in >90 % isolated yield. Overoxidation, however, can lead to the formation of anthraquinone, a dihydroxy derivative, when strong oxidants such as sodium dichromate are employed.
Reduction
Further reduction of 1,2,3,4‑tetrahydroanthracene to tetrahydroanthracene derivatives with saturated rings is possible using catalytic hydrogenation under higher hydrogen pressures (20–30 bar) and lower temperatures (25 °C). The resulting product, 1,2,3,4‑tetrahydroanthracene, has a fully saturated central ring and is typically obtained as a mixture of stereoisomers. Another reduction pathway involves the use of a hydride donor such as lithium aluminium hydride (LiAlH₄) in tetrahydrofuran (THF), which reduces the alkenic double bond to a single bond while maintaining the aromatic rings. The reaction requires careful temperature control (
Functional Group Introduction
Because the alkenic bond in 1,2,3,4‑tetrahydroanthracene is reactive toward electrophilic addition, a variety of functional groups can be introduced. For example, bromination using N-bromosuccinimide (NBS) in carbon tetrachloride yields 1,2,3,4‑dibromo‑1,2,3,4‑tetrahydroanthracene. The brominated product can undergo Suzuki–Miyaura cross-coupling with arylboronic acids to generate extended conjugated systems. Similarly, a radical addition of acetyl radicals produced by the decomposition of diacetyl can append acetyl groups at the alkenic positions, yielding 1,4‑diacetyl‑tetrahydroanthracene. Such functionalized intermediates serve as building blocks for the synthesis of polymeric materials with tailored electronic properties.
Polymerization
Radical polymerization of 1,2,3,4‑tetrahydroanthracene is a key reaction for the creation of conjugated polymers used in organic electronics. In a typical scheme, the monomer is dissolved in anisole and subjected to initiation by a azo-initiator such as azobisisobutyronitrile (AIBN) at 90 °C. The radical initiator generates a carbon-centered radical that adds to the alkenic bond of the monomer, propagating the chain and preserving conjugation across the polymer backbone. The resulting polymer, poly(1,2,3,4‑tetrahydroanthracene), exhibits an intrinsic conductivity of 1.2 S cm⁻¹ at 300 °C and a glass transition temperature of 120 °C. By copolymerizing with electron-withdrawing comonomers such as 4‑vinylpyridine, the bandgap can be tuned between 1.8 and 2.4 eV, making the material suitable for photovoltaic applications.
Applications
Polymer Science
The conjugated nature of 1,2,3,4‑tetrahydroanthracene enables its use as a monomer in the synthesis of semi-conducting polymers. When polymerized under radical initiation, the resulting polymer chain retains a delocalized π-electron system that provides charge transport pathways. Applications include the fabrication of organic field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs). Additionally, the polymer can act as a donor material in bulk heterojunction solar cells, offering high power conversion efficiencies when blended with acceptor molecules such as phenothiazine derivatives.
Medicinal Chemistry
Although primarily used as a synthetic intermediate, derivatives of 1,2,3,4‑tetrahydroanthracene have been investigated for their potential anti-cancer activity. In particular, the cis isomer, due to its specific spatial arrangement, can intercalate into DNA double helices, disrupting replication processes in tumor cells. In vitro assays against human cervical carcinoma cell line HeLa revealed an IC₅₀ value of 45 µM for cis‑1,2,3,4‑THA. Trans‑1,2,3,4‑THA, in contrast, displayed negligible cytotoxicity in the same assay. Further structural modifications, such as the introduction of electron-withdrawing groups, have improved selectivity toward malignant cells, suggesting a pathway for drug development.
Material Science
1,2,3,4‑Tetrahydroanthracene serves as a feedstock for the synthesis of high-performance thermoplastic polymers due to its high melting point and ability to form a semi-crystalline matrix. When polymerized with diynes such as bis(4-ethynylphenyl)acetylene, the resulting polymer demonstrates exceptional tensile strength (550 MPa) and modulus (15 GPa). The polymer's semi-crystalline nature allows for the formation of nanofibrous mats that are used in filtration membranes and gas separation membranes. The high thermal stability of the polymeric material (Tg 210 °C, decomposition >300 °C) positions it for use in aerospace and automotive industries where lightweight yet durable polymers are required.
Safety and Handling
1,2,3,4‑Tetrahydroanthracene is classified as a moderately hazardous organic substance. It is combustible under normal conditions, with a flash point of 35 °C in the presence of an ignition source. The compound is toxic when inhaled or ingested, producing symptoms such as headache, dizziness, and gastrointestinal distress. Exposure limits for occupational settings are established at 0.1 mg m⁻³ for an 8‑hour work shift. Protective equipment such as gloves, eye protection, and respirators should be used when handling the liquid form. In the event of a spill, the material should be collected with a non-reactive absorbent and disposed of according to institutional hazardous waste protocols.
In a laboratory context, standard operating procedures include the use of a fume hood, personal protective equipment, and an inert atmosphere for reactions involving flammable or reactive intermediates. Disposal of waste solutions containing the compound should involve neutralization with a weak base to precipitate any acidic by-products, followed by solvent evaporation and incineration of the solid residue. The environmental impact of large-scale production is mitigated by the use of catalytic hydrogen recovery systems and the recycling of solvent streams.
Future Directions
Research on 1,2,3,4‑tetrahydroanthracene continues to explore its potential as a platform for functional material design. Novel polymerization strategies aim to increase chain alignment and conjugation length, thereby improving charge transport properties in organic electronic devices. In medicinal chemistry, derivative screening seeks to identify analogues that exhibit selective cytotoxicity while minimizing side effects. Advances in catalytic hydrogenation techniques, including the development of earth-abundant metal catalysts, promise to reduce the environmental footprint of industrial production. Additionally, computational modeling of isomeric distributions and reaction pathways offers insight into optimizing reaction conditions for specific product outcomes.
Conclusion
1,2,3,4‑Tetrahydroanthracene, a partially saturated aromatic system, presents a versatile platform for a wide range of chemical transformations and material applications. Its synthesis by catalytic hydrogenation is straightforward, and its physical and spectroscopic properties are well characterized. Ongoing research seeks to harness the compound’s reactivity for the creation of advanced conjugated polymers and to uncover potential therapeutic uses through systematic structure–activity investigations. As a commercially available monomer, it remains a staple in the toolkit of synthetic chemists, polymer scientists, and materials engineers seeking to exploit the unique attributes of partially saturated aromatic systems.
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