Monomethyl Adipate: Properties, Synthesis & Safety

What is Monomethyl Adipate?

Monomethyl adipate, also known as monoethyl adipate, with synonyms including adipic acid monoethyl ester, has the English name: Monoethyl Adipate, monomethyl adipate CAS ID: 626-86-8, and the molecular formula: C8H14O4. Its chemical formula is C8H14O4, with a molecular weight of 174.19 g/mol. Monomethyl adipate is produced through the esterification reaction of adipic acid (a six-carbon dicarboxylic acid) with ethanol. It serves as a crucial raw material and intermediate in organic synthesis, pharmaceuticals, agrochemicals, and dye production.

Monomethyl adipate properties and Characteristics

Monomethyl adipate has a molecular formula of C8H14O4 and a molecular weight of 174.196. At room temperature, it is a white or pale yellow crystalline solid with a melting point of 28–29°C and monomethyl adipate boiling point of 285°C (at standard pressure). It has a relative density of 0.986, is insoluble in water, but easily soluble in alcohols, ethers, and other organic solvents. It is widely used as an intermediate in pharmaceutical applications.

Monomethyl Adipate Structure

The core structure of monomethyl adipate features a six-carbon chain, with one end attached to a carboxyl group (-COOH) and the other end to an ethyl ester group (-COOCH2CH3). The presence of two ester bonds imparts some polarity to the molecule, allowing effective interactions with both polar and non-polar solvents. The flexible carbon-hydrogen chain provides various conformations that affect its physical properties, such as melting point, boiling point, and solubility. Notably, monomethyl adipate has structural isomers, such as dimethyl adipate. Although similar in some properties, the difference in the position of the ester groups results in structural variations.

Monomethyl adipate Synthesis

Method One

The traditional synthesis process for monomethyl adipate involves dissolving adipic acid in excess ethanol in an organic solvent such as toluene. Under the action of acidic catalysts like concentrated sulfuric acid, the mixture is heated and refluxed for esterification. After the reaction, ethanol is first recovered, followed by the removal of adipic acid by adding toluene. The filtrate is then neutralized, extracted, and purified by distillation and drying to obtain the target product, monomethyl adipate.

Method Two

Adipic acid, ethanol, and dimethyl adipate are used in a molar ratio of 1:2:3 with concentrated sulfuric acid as an acidic catalyst. The reaction temperature is maintained at 70–100°C for 1–4 hours. This reaction produces a product containing substantial amounts of dimethyl adipate and adipic acid. After removing solid adipic acid, the filtrate is neutralized and extracted to separate dimethyl adipate and water. The resulting solution of monomethyl adipate is then dried and purified by distillation.

Method Three

Adipic acid and sulfuric acid are heated in a solvent to produce adipic anhydride. After removing sulfuric acid, ethanol is added dropwise to the adipic anhydride to obtain monomethyl adipate.

Safety and Handling

Handling Procedures and Safety Measures

When handling monomethyl adipate, strict adherence to safety guidelines is crucial to prevent accidents. Always wear appropriate personal protective equipment, including gloves, goggles, and laboratory coats. Ensure good ventilation when handling the substance. Avoid contact with skin, eyes, and mucous membranes. In case of contact, rinse the affected area with plenty of water and seek medical attention if necessary. Handle with care near open flames or heat sources as monomethyl adipate may be flammable. Its flash point is 235.4°F or 113°C.

Storage Recommendations

Proper storage is essential for maintaining product quality and safety. Store the chemical in a cool, dry, and well-ventilated area, away from incompatible substances. Keep the container tightly closed when not in use. Correct storage practices help prevent contamination, degradation, and potential hazards. Follow local regulations and guidelines for storing monomethyl adipate.

References

• Gao Caixia. Study on a Synthesis Method of Monomethyl Adipate. China Chemical Trade, 2015, 7(26): 211. DOI:10.3969/j.issn.1674-5167.2015.26.191.
• Shandong Xingwen Industrial Technology Research Institute Co., Ltd. A Method for Preparing Monomethyl Adipate. 2024-02-06.
• Fuzhou University. Selective Synthesis Process of Monomethyl Adipate. 2023-04-04.
• https://pubchem.ncbi.nlm.nih.gov/compound/Monoethyl Adipate