The physicochemical properties of a deep eutectic solvent (DES) and thus its area of application are influenced by the nature salt or hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), molar ratio, temperature and water content. The search for and discovery of new HBD would further widen the scope of DES versatility. In this study, the capacity of castor oil to serve as HBD and form DES with choline chloride (ChCl) was investigated. ChCl and castor oil were mixed in four molar ratios, namely 1:1, 1:2, 1:3, and 1:4. DES was formed at 1:3 and 1:4 molar ratios and code-named DES1 and DES2, respectively. The physicochemical properties of both DESs were measured as a function temperature from 313 K to 353 K. The results indicate that the densities of these castor oil-based DESs are uniquely low when compared to other DESs and ionic liquids. Their physicochemical properties generally follow the known trend for other DES, in terms of temperature variations. The viscosity, conductivity, surface tension and refractive index of castor oil based-based DES all fall within the known range for other choline chloride-based DESs. Based on its pH values, castor oil based DES is a Bronsted acidic deep eutectic solvent. This discovery offers significant potential to expand the possible combinations of salts and HBDs and further increase the areas of application of this solvent.
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