Phenolic hydrogen bond donors in the formation of non-ionic deep eutectic solvents: the quest for type V DES

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.