SYNOPSISPreparation of sodium salt of di (2-ethylhexyl) dithiophosphoric acid ( DTPANa) by reaction of the corresponding DTPA with sodium hydride has been described. Nucleophilic substitution of chlorine on poly( vinylchloride) (PVC) by a di( 2-ethylhexy1)dithiophosphate group resulting in modified polymer (MP) was characterized by the second order rate constant equal to 6.6 X M-'
INTRODUCTIONIn recent years, a great amount of work has been done on the substitution of chlorine in poly( vinylchloride) (PVC) by nucleophiles such as thiolate, xantate, and dithi~carbamate.'-~ The substitution of chlorine in PVC was reported to produce a material for membranes used in per~aporation.~ A gelled membrane composed of PVC modified by dialkyldithiocarbamate with a specific extractant played as both an ion carrier and a solvent was recently de~cribed.~ The membrane was shown to be capable of selective separation of mercury or silver from many other cations when di(2-ethylhexyl) dithiophosphoric acid (DTPA) was used as an ion carrier. DTPA is a very strong extractant for a number of metals with the extraction sequence as follows:The excellent extraction properties of DTPA are already used in solvent-extraction plants in which metals are being recovered from low grade residues in the hydrometallurgical i n d~s t r y .~ Hence, it was of interest to find a way to introduce DTPA into a polymeric system giving material to be packed in ion exchange columns. To do so, we modified PVC by dithiophosphate. The resulting modified polymer ( M P ) formed stable gelled phases with DTPA. The synthesis and performance of the above MP are outlined below.
EXPERIMENTAL Synthesis of DTPANaDTPA was synthesized by the reaction of 2-ethylhexyl alcohol ( Merck) with phosphorus pentasulfide (BDH Chemicals) according to a procedure described recently.' DTPA (0.01 mol) was carefully mixed with sodium hydride (0.01 mol) suspension (Merck) in water-free conditions until no more hydrogen was evolved from the reactionary mixture. The NaH was added slowly into DTPA with stirring to avoid excessive frothing. Bis [ di ( 2-ethylhexyloxy) thiophosphoryl] disulfide (BTPD) was synthesized and purified as was described elsewhere.' The resulting DTPANa, DTPA, and BTPD were analyzed by 'H and 31P NMR. To this solution DTPANa (0.03 mol) in DMF (20 mL) was added. The mixture was stirred under a stream of nitrogen at 45°C. Samples were withdrawn intermittently from the reactionary mixture and precipitated in methanol. The polymer was washed with water to remove the unreacted DTPANa, washed again with methanol, and dried under vacuum at room temperature.The sulfur and chlorine content of each sample was measured by elemental sulfur and chlorine analysis. NMR spectra were recorded at 400 MHz on a Bruker AMX400 spectrometer. A Nicolet 510 FTIR spectrometer was used to record infrared spectra of the modified polymer cast as thin films.
Preparation of Beads and Ion Exchange ProcedureThe mixture of MP (S, 4.1%; C1,42.1%), PVC, and DTPA in the weight ratio 1.0 : 0.9 : 1.1 wa...