Synthesis and characterization of metal soap (Zn-, Al-, and Mg-soap) from sunflower oil and its potential as sunscreen

Zinc, aluminum, and magnesium soaps are known as synthetic metal soaps. This research aims to synthesize zinc-, aluminum-, and magnesium soaps from sunflower oil and test its activity as a sunscreen. The synthesized was carried out with the following steps (1) synthesis of K-soap through the saponification of oil with KOH, (2) synthesis of metal soap through the trans-saponification of K-soap with its chloride salts, (3) characterization of physical properties and identification through IR, XRD, and XRF, and (4) sunscreen activity assay. The synthesized Zn-, Al-, and Mg-soap are white solids, melting points of 72–76, 76–90, and 102–120°C respectively. These three metal soaps are soluble in chloroform, but insoluble in water and n-hexane. Mg-soap soluble in methanol, while Zn- and Al-soaps are insoluble. XRD patterns of the synthesized Zn-soap showed the unique peaks from 2θ 4-12° that is unique for the layer zinc oleate, zinc linoleate, and zinc stearate structure. However, the broad peak from 2θ 14-28° was dominant for Al- and Mg- soap. The metal content in the synthesized soaps that were analyzed using the XRF revealed the percentage substitution of K- soap by Zn, Al, and Mg, i.e. 99, 76, and 81%, respectively. SPF value of Zn-soap, Al-soap, and Mg-soap sunflower seed oil was 2.78, 0.96, and 1.63, respectively. Based-on this SPF value, Zn-soap has the potential as a sunscreen.