The African black soap from Elaeis guineensis (Palm kernel oil) and Theobroma cacao (Cocoa) and its transition metal complexes

Abstract

African black soap is an indigenous African organic soap formed by esterification. This was prepared by reacting palm kernel oil and the filtrate of cocoa pod ash. Chemical analyses revealed the moisture content was 26% (w/w), total fatty matter (TFM) was 44.75% (w/w), total fatty alkaline (TFA) was 0.22% (w/w), total alkaline (TA) was 11.78% (w/w) and pH was 10. The metal complexes were formed by the reaction of the synthesized black soap with some transition metal salts which included Cu(CH3COO)2.H2O, Pb(CH3COO)2.3H2O and FeCl3. The metal:ligand ratio, that is, M:L = 3:1, while the reaction was carried out in an aqueous medium to afford [Pb(C11H23COO-K+)2(C11H23COO-)2].9H2O, [Cu(BL)4(C11H23COO-)2].4H2O and [Fe(BL)2(C11H23COO-)Cl2] with the percentage yield of 56, 48 and 41%, respectively. Characterization of the black soap and complexes was done by spectroscopic analyses and determination of physicochemical properties. The solubility of the metal complexes was determined at room temperature in various solvents. Results showed that solubility increased as polarity decreased and it was most effective with non-polar organic solvents. Potassium ester (C11H23COO-K+), commonly called African black soap, has acted either as a monodentate or bidentate ligand forming metal complexes by coordinating through one or two of its oxygen donor atoms and also by entirely replacing the potassium ion with the transition metal (displacement reaction). Spectra analyses corroborate an octahedral structure for the Pb(II), a distorted octahedral structure for the Cu(II) and an octahedral Fe(III) complex.