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Propylene Carbonate - Polar Aprotic Solvent CAS 108-32-7

 

Propylene Carbonate (4-Methyl-1,3-dioxolan-2-one) - Properties, Applications, and Safety

Propylene carbonate (CAS 108-32-7) is a cyclic organic carbonate with the molecular formula C₄H₆O₃ and a molecular weight of 102.09 g/mol. It is a colorless, odorless, and highly polar aprotic liquid with a faint sweet ester-like odor. Known for its excellent solvating properties, high dielectric constant, wide liquid range, low toxicity, and biodegradability, propylene carbonate is one of the most versatile solvents in industrial and research applications.

Physicochemical Properties

  • Molecular Formula: C₄H₆O₃

  • Molecular Weight: 102.09 g/mol

  • Appearance: Colorless liquid

  • Density: 1.204 g/mL at 25°C

  • Melting Point: –49°C (some sources report –55°C)

  • Boiling Point: 240–243°C at 760 mmHg

  • Flash Point: 116–135°C (closed cup)

  • Vapor Pressure: 0.13 mmHg at 20°C

  • Refractive Index: 1.4210 at 20°C

  • Solubility in Water: 240 g/L at 20°C

  • Dielectric Constant: Approximately 64.9 at 25°C – one of the highest among organic solvents

  • EC Number: 203-572-1

  • MDL Number: MFCD00005385

Mechanism of Action

Propylene carbonate functions primarily as a polar aprotic solvent. Its high dielectric constant (≈64.9) enables effective dissociation and solvation of ionic compounds, making it particularly valuable in electrochemical applications. The molecule contains a carbonyl group and two oxygen atoms in the cyclic ring, providing strong dipole-dipole interactions and hydrogen bonding capability. Its aprotic nature means it does not donate protons, allowing it to dissolve a wide range of polar and ionic species without interfering in acid-sensitive reactions.

Applications

Lithium-Ion Battery Electrolytes: Propylene carbonate is widely used as a solvent or co-solvent in lithium-ion battery electrolytes due to its high dielectric constant, low melting point (–49°C), and ability to dissolve lithium salts. Its low-temperature performance makes it a valuable component in electrolytes for cold-weather applications.

Paints, Coatings, and Adhesives: Used as a solvent and coalescing aid in paints, coatings, and adhesives, improving film formation and reducing viscosity.

Paint Strippers and Cleaners: An effective component in paint strippers, hard surface cleaners, and resin cleaners, including fiberglass, polyester, and polyurethane cleaning formulations.

Cosmetics and Personal Care: Used as a solvent, plasticizer, and skin-conditioning agent in cosmetics and personal care products.

Plasticizer: Functions as a plasticizer for various polymers, enhancing flexibility and processability.

Chemical Synthesis: Serves as a solvent in organic synthesis, including electroorganic synthesis, where it acts as a greener alternative to acetonitrile or dichloromethane.

Gas Processing: Used in gas processing for the removal of acid gases such as CO₂ and H₂S.

Safety and Toxicology

Propylene carbonate is considered a safe and low-toxicity solvent. The Cosmetic Ingredient Review (CIR) Expert Panel has concluded that propylene carbonate is safe as a cosmetic ingredient.

  • Acute Toxicity (Oral): LD50 (rat, oral) is approximately 33,520 mg/kg – indicating very low acute oral toxicity.

  • Acute Toxicity (Dermal): LD50 (rabbit, dermal) >2,000 mg/kg.

  • Skin Irritation: Undiluted propylene carbonate is moderately irritating to skin and eyes. However, formulations containing up to 20% propylene carbonate showed moderate skin irritation.

  • Inhalation Toxicity: Non-toxic by inhalation exposure.

  • Environmental Profile: Propylene carbonate is readily biodegradable.

  • Regulatory Status: Not listed on the U.S. DOT list of hazardous materials. It is considered a low-hazard solvent and an acceptable replacement for flammable ketones such as acetone and methyl ethyl ketone.

Storage and Handling

Propylene carbonate should be stored in tightly sealed containers in a cool, dry, well-ventilated area, away from strong oxidizers and acids. The compound is stable under normal storage conditions. Use appropriate personal protective equipment (gloves, safety goggles) when handling. In case of skin or eye contact, rinse thoroughly with water. The compound has a shelf life of typically 24–36 months under recommended storage conditions.

Conclusion

Propylene carbonate (CAS 108-32-7) is a highly versatile, polar aprotic solvent with a unique combination of properties: high dielectric constant, wide liquid range, excellent solvating power, low toxicity, and biodegradability. Its applications span lithium-ion battery electrolytes, paints and coatings, adhesives, cosmetics, paint strippers, and chemical synthesis. With a favorable safety profile and environmental acceptability, propylene carbonate continues to be a solvent of choice in both established and emerging technologies, particularly in energy storage and green chemistry applications.

 

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