Adipic acid occurs as a white or almost white, odorless nonhygroscopic crystalline powder. The crystal structure of adipic acid is monoclinic holohedral.
- PhEur: Adipic Acid
- USP-NF: Adipic Acid
Synonyms: Acidum adipicum; acifloctin; acinetten; adilactetten; asapic; 1,4- butanedicarboxylic acid; E355; 1,6-hexanedioic acid; Inipol DS.
Chemical Name and CAS Registry Number: Hexanedioic acid [124-04-9]
Empirical Formula and Molecular Weight: C6H10O4 146.14
Functional Category: Acidifying agent; buffering agent; flavoring agent.
Applications in Pharmaceutical Formulation or Technology
Adipic acid is used as an acidifying and buffering agent in intramuscular, intravenous and vaginal formulations. It is also used in food products as a leavening, pH-controlling, or flavoring agent.
Adipic acid has been incorporated into controlled-release formulation matrix tablets to obtain pH-independent release for both weakly basic and weakly acidic drugs. It has also been incorporated into the polymeric coating of hydrophilic monolithic systems to modulate the intragel pH, resulting in zero-order release of a hydrophilic drug.
The disintegration at intestinal pH of the enteric polymer shellac has been reported to improve when adipic acid was used as a pore-forming agent without affecting release in the acidic media. Other controlled-release formulations have included adipic acid with the intention of obtaining a late-burst release profile.
- Acidity/alkalinity pH = 2.7 (saturated solution at 258͒C); pH = 3.2 (0.1% w/v aqueous solution at 258͒C)
- Boiling point 337.58͒C
- Dissociation constant pKa1: 4.418 at 258͒C; pKa2: 5.412 at 258͒C.
- Density 1.360 g/cm3
- Flash point 1968͒C (closed cup)
- Heat of combustion 17 653.9 kJ/mol (4219.28 kcal/mol) at 258͒C
- Heat of solution 33.193 kJ/mol (7.9 kcal/mol) at 258͒C
- Melting point 152.18͒CVapor pressure 133.3 Pa (1 mmHg) at 159.58C
- Viscosity (dynamic) 4.54 mPa s (4.54 cP) at 1608C for molten adipic acid.
Method of Manufacture
Adipic acid is prepared by nitric acid oxidation of cyclohexanol or cyclohexanone or a mixture of the two compounds. Recently, oxidation of cyclohexene with 30% aqueous hydrogen peroxide under organic solvent- and halide-free conditions has been proposed as an environmentally friendly alternative for obtaining colorless crystalline adipic acid.