DFT study on the effects of substituents on the structure and properties of dithiophosphate collectors

Abstract

The structures and properties of seven substituted dithiophosphate (DTP) collectors containing three types of functional groups (O2PS2, C2PS2, and N2PS2) were studied using density functional theory. The collectors studied were dibutyl dithiophosphate (DNBDTP), diisobutyl dithiophosphate (DIBDTP), dibutoxyethyl dithiophosphate (DBOEDTP), xylenol dithiophosphate (DMPDTP), diisobutyl dithiohypophosphite (3418A), diphenylamine dithiophosphate (DTADTP), and dicyclohexylamine dithiophosphate (DCADTP). The structural analysis showed that the PS bond lengths in the C2PS2 and N2PS2 types are longer than those in the O2PS2 type, indicating that the strength of the PS bond is weaker in the former two. The frontier molecular orbital studies showed that the energy differences between the highest occupied molecular orbitals (HOMO) of 3418A (C2PS2 type) and DCADTP (N2PS2 type) and the lowest unoccupied molecular orbital (LUMO) of galena are significantly lower than those of the other collectors, suggesting that C2PS2 type and N2PS2 type with cyclohexane could enhance the interaction with galena. Using the Fukui function to calculate the nucleophilicity and electrophilicity of the sulfur atom indicated that the S atom exhibits nucleophilicity, especially in DMPDTP and DTADTP, which contain benzene rings, and the S atom exhibits strong nucleophilicity without electrophilicity. However, due to the lack of contribution from S atoms to the LUMO orbitals, the S atoms in these two compounds are not participate in any LUMO reactions. The adsorption results demonstrated that 3418A (C2PS2 type) and DCADTP (N2PS2 type) exhibit the strongest adsorption on Pb2+ ions, while DMPDTP (C2PS2 type) and DTADTP (O2PS2 type) which contain benzene rings, as well as DBOEDTP (C2PS2 type) which does not contain a benzene ring, exhibit weaker interaction compared to the other compounds. These are consistent with the results of the frontier molecular orbital and electrophilic nucleophilicity calculations.