2-Ethyl anthraquinone
[CAS# 84-51-5]

Identification

• Classification: Organic raw materials >> Quinones
• Name: 2-Ethyl anthraquinone
• Synonyms: 2-Ethylanthraquinone; 2-Ethyl-9,10-anthracenedione
• Molecular Formula: C₁₆H₁₂O₂
• Molecular Weight: 236.27
• CAS Registry Number: 84-51-5
• EC Number: 201-535-4
• SMILES: CCC1=CC2=C(C=C1)C(=O)C3=CC=CC=C3C2=O

Properties

• Density: 1.2±0.1 g/cm³ Calc.^*
• Melting point: 108 - 111 °C (Expl.)
• Boiling point: 415.4±35.0 °C 760 mmHg (Calc.)^*, 180 - 190 °C (Expl.)
• Flash point: 155.4±22.9 °C (Calc.)^*
• Index of refraction: 1.629 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS08;GHS09 Danger
• Risk Statements: H350-H373-H400-H410
• Safety Statements: P203-P260-P273-P280-P318-P319-P391-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Carcinogenicity	Carc.	1B	H350
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413

Discovery and Applications

2-Ethylanthraquinone is an important organic compound with the molecular formula C₁₆H₁₂O₂. It belongs to the class of anthraquinone derivatives, which are characterized by a three-ring aromatic structure containing two ketone groups positioned at the 9 and 10 carbon atoms of the anthracene backbone. The ethyl group at the 2-position of the molecule distinguishes it from other anthraquinones and plays a crucial role in its chemical behavior and industrial applications.

The compound was developed and investigated in the early to mid-20th century as part of a broader effort to improve methods for hydrogen peroxide production. 2-Ethylanthraquinone emerged as a particularly effective working compound in the anthraquinone process, which is the predominant industrial method for the synthesis of hydrogen peroxide (H₂O₂). This process was introduced by the German chemical company IG Farben in the 1930s and later refined for large-scale commercial production.

In the anthraquinone process, 2-ethylanthraquinone serves as a carrier molecule that undergoes reversible hydrogenation and oxidation reactions. During the hydrogenation step, 2-ethylanthraquinone is converted to its corresponding anthrahydroquinone by reaction with hydrogen in the presence of a catalyst such as palladium supported on carbon. This reduced form is then oxidized with air or oxygen, regenerating the original quinone and producing hydrogen peroxide as a byproduct. The hydrogen peroxide is subsequently extracted with water, and the 2-ethylanthraquinone is recycled for reuse.

This cyclic process is highly efficient, with the working compound reused repeatedly without significant degradation over many cycles. 2-Ethylanthraquinone is favored over unsubstituted anthraquinone because the ethyl substituent enhances its solubility in the organic solvents used in the process and improves the kinetics of hydrogenation and oxidation reactions. It also provides a balance between chemical stability and reactivity, which is critical for sustained operation.

Beyond its role in hydrogen peroxide production, 2-ethylanthraquinone has been studied for its photochemical and redox properties. Anthraquinones in general are known for their ability to participate in electron transfer reactions and generate reactive oxygen species under light exposure. These properties have made them of interest in areas such as photodynamic therapy and organic electronics, although such uses of 2-ethylanthraquinone remain limited compared to its industrial significance.

In laboratory settings, 2-ethylanthraquinone can be synthesized by Friedel–Crafts alkylation of anthraquinone with ethyl halides using Lewis acid catalysts. Its structure and purity are typically confirmed by techniques such as nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), and melting point analysis. The compound appears as a yellow crystalline solid with moderate solubility in nonpolar organic solvents such as benzene and toluene.

From a safety perspective, 2-ethylanthraquinone is handled with standard laboratory precautions. It is considered to have low acute toxicity but may cause irritation upon contact with skin or eyes. As with other aromatic compounds, care must be taken to minimize inhalation and long-term exposure. Industrial processes involving this compound are conducted in closed systems to avoid environmental release and occupational hazards.

In summary, 2-ethylanthraquinone is a chemically stable and efficient redox carrier used in the large-scale production of hydrogen peroxide. Its favorable physical and chemical properties have established it as the preferred compound in the anthraquinone process, which remains the dominant method for hydrogen peroxide synthesis globally. Its contribution to this essential chemical process highlights its continued relevance in industrial chemistry.

References

2023. The Metal-Based Catalysts for Selective Hydrogenation of Anthraquinone to Produce Hydrogen Peroxide. Catalysis Surveys from Asia, 27(4).
DOI: 10.1007/s10563-022-09382-8

2021. Pd Nanoparticles on SBA-15 Containing F for 2-Ethyl-Anthraquinone Hydrogenation: Effects of Hydrophobicity. Catalysis Letters, 151(7).
DOI: 10.1007/s10562-021-03746-x

2019. Highly Dispersed Pd Nanoparticles Supported on Zr-Doped MgAl Mixed Metal Oxides for 2-Ethylanthraquinone Hydrogenation. Transactions of Tianjin University, 25(5).
DOI: 10.1007/s12209-019-00203-0