Innovative Preparation and Characterization of Zinc Ricinoleate through alkali catalysis

Zinc ricinoleate, the zinc salt of ricinoleic acid, was prepared via an innovative two-step synthesis. First, an intermediate compound, methyl ricinoleate, was prepared through the transesterification of castor oil with methanol and catalyzed by sodium hydroxide. Then, methyl ricinoleate underwent an alkali-catalyzed saponification in the presence of zinc oxide (ZnO) particles, following by an ultrasonication step which resulted in the formation of zinc ricinoleate. The resulting white-like paste was characterized by FTIR, NMR and X-ray diffraction and the morphology was analyzed by HR-SEM and AFM.
The change in the ZnO particle volume influenced the zinc ion coordination geometry in the resulting carboxylate-zinc complexes, yielding PZR1 with a combination of both bridging and chelating arrangement, and PZR2 possessing a combination of both chelating and monodentate arrangement.
1H and 13C NMR spectroscopy enabled to confirm the successful preparation of zinc ricinoleate with the presence of characteristic peaks of alkyl chain of the fatty acid anion.
XRD patterns also confirm the zinc ricinoleate preparation with the presence of crystalline and amorphous regions. The presence of the following peaks at 2θ= 31.72°, 34.38° and 36.21°, indicates the existence of the Wurtzite ZnO structure and the apparition of amorphous regions in the 2θ range 19°–23° indicates the presence of disordered alkyl chains in the ZnO-carboxylate complexes.