Introduction
Mesitylene is an organic compound that belongs to the class of aromatic hydrocarbons. It is a clear colorless liquid with a pleasant odor. Mesitylene has important industrial applications and is widely used as a chemical intermediate in the production of various materials. In this article, we will discuss in detail about mesitylene including its properties, production methods, uses and safety considerations.
Chemical Properties and Structure
Mesitylene has the chemical formula C9H12 and molecular weight of 120.19 g/mol. It is classified as a trimethylbenzene isomer as it contains three methyl substituents attached to a benzene ring. The methyl groups can be arranged in three different configurations namely 1,3,5-trimethylbenzene; 1,2,4-trimethylbenzene and 1,2,3-trimethylbenzene. Out of these, 1,3,5-trimethylbenzene is the most stable configuration and constitutes about 80-90% of technical grade mesitylene.
As an aromatic hydrocarbon, mesitylene is non-polar and hydrophobic in nature. It is insoluble in water but miscible with organic solvents like ethanol, acetone and ether. Mesitylene has a boiling point of 165°C and melting point of -35°C. The density of liquid mesitylene is 0.862 g/cm3. Due to the presence of methyl substituents, mesitylene is less chemically reactive as compared to benzene.
Production Methods
Currently, the largest volume production route for mesitylene involves catalytic isomerization of trimethylbenzenes obtained during the catalytic reforming of petroleum naphtha feedstocks in petroleum refineries. In this process, 1,2,4-trimethylbenzene undergoes isomerization into the more thermodynamically stable 1,3,5-isomer i.e. mesitylene.
The isomerization is catalyzed by acid catalysts typically based on zeolites. Process conditions involve temperatures between 200 to 300°C and pressures from atmospheric to 50 bars. This results in mesitylene yields exceeding 90% with traces of other trimethylbenzene isomers.
In the laboratory, mesitylene can be synthesized by Friedel-Crafts alkylation of toluene with propene using aluminum chloride as the catalyst. It may also be prepared by heating a mixture of acetone and benzene in the presence of aluminium chloride. However, these routes are not economically viable for large scale production.
Uses and Applications
Some key applications and uses of mesitylene include:
- Agrochemicals: It is used as an intermediate in the manufacturing of herbicides, insecticides and fungicides like isoxaflutole and mesotrione.
- Perfumes and Fragrances: Many perfume formulations incorporate mesitylene to impart pleasant floral and herbal notes to fragrances.
- Plastics and Resins: Mesitylene serves as a precursor in producing thermosetting resins and several classes of polymers like poly(phenylene oxide), polyimides and epoxies.
- Dyestuffs: It acts as a solvent and reactive intermediate in manufacturing various azo, anthraquinone and industrial dyestuffs.
- Extractive Metallurgy: Used as a solvent for extracting and purifying metals like uranium and copper through solvent extraction processes.
- Fuel Additives: Possess cetane improving properties for use as a diesel fuel additive in small quantities.
Safety Profile and Handling
Being an aromatic hydrocarbon, mesitylene is considered moderately toxic and hazardous material. The occupational exposure limit set by ACGIH is 25 ppm. Prolonged or repeated exposure can cause irritation of eyes, respiratory tract and skin. Ingestion may result in nausea, vomiting and diarrhea. Mesitylene is readily absorbed through inhalation as well as dermal contact.
It is classified as a flammable liquid and its vapors can form explosive mixtures in air in concentration between 1-7%. The autoignition temperature is >500°C. Standard precautions include ensuring proper ventilation, using masks and gloves while handling. Mesitylene must be stored away from heat, sparks and open flames in accordance with fire and building codes. Spills should be contained using absorbents and the area well ventilated before cleanup and disposal of wastes.
Conclusion
In summary, mesitylene is an industrially important aromatic hydrocarbon that serves as a key intermediate for producing various agrochemicals, plastics, dyes and other fine chemicals. The petroleum refining route is currently the major commercial process adopted for large scale mesitylene production. While offering numerous economic benefits, adequate safety measures are warranted given its flammable and toxic potential when not handled properly. With increasing societal demands, future applications of this versatile solvent are expected to grow further.
