Synthesis And Properties Of Novel Quaternary Phosphonium Ionic Liquid Surfactants

Quaternary phosphonium ionic liquid?IL?surfactants combine the characteristics of ILs and surfactants with low foaming properties and antibacterial properties.However,one limitation of quaternary phosphonium ILs is that their preparation is usually not"green".Generally,phosphonium-based ILs are prepared by quaternarization of tertiary phosphine with halogenated alkanes or dimethyl sulfate?DMS?.However,the traditional synthetic route has its own limitations.It can cause the problems of environmental pollution and equipment corrosion during the synthesis process because of the toxicity and corrosion of halogenated alkanes and DMS.In addition,halogen ions will remain in products due to the incomplete quaternization reaction,resulting in environmental pollution.The effective way to solve this problem is to select a"green"alkylation reagent.Dimethyl carbonate?DMC?is a multifunctional compound that becomes an environmentally friendly alternative to halogenated alkanes?or DMS?and phosgene,during methylation and carbonylation,respectively.At present,there are many reports on the synthesis of quaternary ammonium salts by using DMC and tertiary amines,and the synthesis methods and processes are relatively mature.However,there are few reports on the synthesis of quaternary phosphonium ILs by the reaction of DMC with tertiary phosphine.Also,there is little research on the properties of the synthesized quaternary phosphonium ILs,which has great research prospects.In this paper,quaternary phosphonium ILs were synthesized using triphenylphosphine?TPP?,DMC and carboxylic acids.The optimum reaction conditions were determined by orthogonal experimental design.The physicochemical properties and application properties of these ILs were studied.There are three main experimental sections in this paper:1.Synthesis and characterization of quaternary phosphonium ILs.A series of quaternary phosphonium IL surfactants were synthesized by quaternization of TPP with DMC and followed anion exchange with different acids.The optimum reaction conditions were optimized and determined by orthogonal experimental design.Under these conditions,the conversion of TPP could reach 80%.FT-IR?¹H-NMR and ³¹P-NMR characterization of the quaternary phosphonium ILs confirmed the synthesis of the target products.The active content of the methyl carbonate quaternary salt intermediate was determined by two-phase chemical titration with tetraphenylboron sodium.2.Physicochemical properties of quaternary phosphonium ILs.The melting point,viscosity,electrical conductivity,density and surface tension of these quaternary phosphonium ILs were measured.Meanwhile,the effects of temperature and alkyl chain length on their viscosity,electrical conductivity,density and surface tension were also investigated.The critical dissolution temperature,critical micelle concentration?CMC?and minimum surface tension(?_CMC)of quaternary phosphonium ILs in aqueous solution were measured.The surface excess concentration?_max of quaternary phosphonium ILs at gas-liquid interface was calculated according to the surface tension curve.The aggregation behavior of these quaternary phosphonium ILs in aqueous solution was investigated by transmission electron microscopy measurements?TEM?.The viscosity,density and surface tension of quaternary phosphonium ILs decrease significantly with the increase of temperature,while the electrical conductivity shows an opposite trend.The longer the alkyl chain,the higher the viscosity,the lower the electrical conductivity,density and surface tension of quaternary phosphonium ILs.The value of CMC decreases with the increase of alkyl chain length,while?_max increases and?_CMC decreases first and then increases.The logarithm of CMC is linear with the length of hydrophobic group.TEM results indicated that quaternary phosphonium ILs could self-assemble into regular spherical aggregates in aqueous solution.The diameter of the spherical aggregates is about 50¹00 nanometers and does not change much with the change of alkyl chain length.3.Application properties of quaternary phosphonium ILs.The wetting,foaming,and emulsification properties of these quaternary phosphonium IL surfactants were investigated.The results indicate that the alkyl chain length has a significant effect on wettability,foam properties and emulsification.These quaternary phosphonium ILs show lower foaming properties than quaternary ammonium salts with the same anionic units.They also show better emulsification ability to soybean oil than that of liquid paraffin.