Metal soaps of virgin coconut oil: Synthesis, characterization, and its potential physicochemical sunscreen

Abstract

Salts of fatty acids with metals other than sodium and potassium are known as metal soaps. Triglyceride oil is an excellent source of fatty acids. Virgin coconut oil (VCO) is a source of fatty acids, with the main content being lauric acid. This study aimed to synthesize zinc, aluminum, magnesium, and calcium soaps from VCO and test their activity as sunscreens. Metal soaps were synthesized from VCO by a double decomposition reaction through sodium-VCO (Na-VCO) soap followed by trans-saponification of Na-VCO soap with chloride salts of zinc, aluminum, magnesium, and calcium giving Zn-VCO, Al-VCO, Mg-VCO, and Ca-VCO, respectively. Changing the sodium with Zn, Al, Mg, and Ca lowers the melting point, particularly Za-VCO soap, melting in the 101–126 °C range. Trans-esterification of Na-soap with those metal ions gave a high yield of up to 88.0 %, which supported the similar FTIR spectra for all metal-VCO soap except the peak shifting in 1750–1250 cm^-1 as COO- stretching vibration. The SPF values of soaps of Na-VCO, Zn-VCO, Al-VCO, Mg-VCO, and Ca-VCO are 0.43, 13.77, 3.66, 11.27, and 19.41, respectively. Metal soaps (Zn-VCO, Al-VCO, Mg-VCO, and Ca-VCO) have the potential to act as sunscreen, and Na-VCO is not potential as sunscreen. Sunscreen activity of Ca-VCO > Zn-VCO > Mg-VCO > Al-VCO.