Adipic acid: Uses and Synthesis

Adipic acid is an organic compound that contains six carbon atoms, along with two total carboxylate groups, one attached to each terminal end of the carbon chain. Adipic acid can be referred to as a di-acid since it has two carboxylate groups.

Uses in Medicine

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. Additional controlled-release formulations have included adipic acid with the intention of obtaining a late-burst release profile.

Uses in Foods

Minor but significant amounts of adipic acid are used as a food ingredient as a flavorant and gelling aid. It is used in some calcium carbonate antacids to make them tart. As an acidulant in baking powders, it avoids the undesirable hygroscopic properties of tartaric acid. Adipic acid, rare in nature, does occur naturally in beets, but this is not an economical source for commerce compared to industrial synthesis.

Laboratory Synthesis

Adipic acid can be synthesized by taking cyclohexene as the starting material and exposing it to oxidation-type conditions. Cyclohexene is a six-carbon ring that contains a double bond and is a perfect substrate to make adipic acid because it already contains the six carbons we need for the final product.

Industrial Synthesis

The primary method of making adipic acid involves taking what's known as 'KA oil', which stands for ketone-alcohol oil, and oxidizing the mixture with concentrated nitric acid. The ketone-alcohol oil is a mixture of cyclohexanol and cyclohexanone and both of these starting materials ultimately produce adipic acid as the final product of the reaction. 

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