Behavior and Toxicity of Phosphonium Based Ionic Liquids

Phosphonium based ionic liquids are having the advantages of enhancing chemical stability under varied conditions; more thermally stable than ammonium and imidazolium salts. These types of ionic liquids had been used in many industrial applications such as extractants for sulphur containing compounds, lubricants, electrolytes and media for metal deposition. In this study, three phosphonium based ionic liquids have been synthesized using quarternisation process. The three ionic liquids are: butyl triphenyl phosphonium chloride; hexyl triphenyl phosphonium bromide; octyl triphenyl phosphonium chloride. The toxicity of these ionic liquids is unknown and it might be toxic and harmful to the environment. Therefore, Fish Acute Toxicity Test and properties have been studied and conducted. The properties studies are including the melting point, molecular weight and solubility in water. The melting point of each synthesized ionic liquid was measured by using Stuart Melting Point Apparatus. The results are 222oC for butyl triphenyl phosphonium chloride, 202oC for hexyl triphenyl phosphonium bromide and 62oC for octyl triphenyl phosphonium chloride. The molecular weight of butyl triphenyl phosphonium chloride is 354.86 kg/mol, followed by hexyl triphenyl phosphonium bromide 427.36 kg/mol and octyl triphenyl phosphonium chloride 499.86 kg/mol. All of these phosphonium based ionic liquids are soluble in water. The Fish Acute Toxicity Test has been conducted according to Organisation for Economic Cooperation and Development (OECD) 203 Guideline. The results obtained have been analyzed using probit analysis method. Median lethal concentrations (LC50) have been calculated. LC50 for butyl triphenyl phosphonium chloride and for hexyl triphenyl phosphonium bromide were found 73.35 mg/L and 61.36 mg/L respectively. Both LC50 obtained can be identified as slightly toxic ionic liquids based on Acute Toxicity Rating Scale by Fish and Wildlife Service (FWS). On the other hand, no mortality of fish recorded for octyl triphenyl phosphonium chloride with highest concentration of 100 mg/L. According to the rating scale, if no mortality recorded after the fishes exposed to concentration of 100 mg/L and above, the ionic liquid will practically nontoxic. Next, the dose relationships by linear regression have been done and the empirical probit equations were developed to estimate the toxicity. In addition, the developed empirical probit equations also can be used to determine LC10, LC30, LC70 and LC99.