Abstract: Novel compounds, viz., tris(perfluoroalkyl)phosphine oxides have the following general formula ##STR1## where R.sub.F is a perfluoroalkyl of normal and iso-structure, having from 2 to 8 carbon atoms.The method of preparing said compounds consists in that trialkylphosphine oxide having the general formula R.sub.3 PO, where R = C.sub.8 -C.sub.8, is fluorinated electrochemically in a medium of anhydrous hydrogen fluoride; whenever trialkylphosphine oxides having the general formula R.sub.3 PO, where R = C.sub.5 - C.sub.8, are used as the starting material, they are first brominated in a medium of anhydrous hydrogen fluoride, with subsequent isolation of the end product.The proposed novel compounds can be used as solvents for salts of rare earth elements and as complexing agents in the separation of valuable metals.

Abstract: The method for producing trialkylphosphine oxides having the general formula R.sub.3 PO, where R is an alkyl having from 1 to 16 carbon atoms, consists in that red phosphorus reacts with an alkyl iodide in the presence of a catalyst -- iodine or hexaalkyliodophosphoranephosphonium pentaiodide -- while gradually adding alkyl iodide to the reaction mixture, and maintaining the reaction temperature at 180.degree. - 230.degree. C., with subsequent isolation of the end product.The proposed method simplifies the process for preparing trialkylphosphine oxides, increases the yield of the end product to 80- 90 per cent by weight, rules out side reactions of dehydrohalogenation of alkyl iodides, and also shortens the process to 8- 10 hours.