Toward reactive extraction processes for synthesizing long-chain esters: A general approach by tuning bifunctional deep eutectic solvent

An abnormal strong interaction was identified, which was found to be the key to prepare non-ionic DES, that may be classified as type V. Mixtures of non-ionic compounds have been reported as DES but most are just ideal mixtures. In the thymol–menthol system, an abnormal strong interaction was identified stemming from the acidity difference of the phenolic and aliphatic hydroxyl groups. This type of interaction is found to be the key to prepare non-ionic DES, that may be classified as type V.