SYNTHESIS AND CHARACTERIZATION OF A 1,2,4,5-TETRAZINE-MODIFIED ION-EXCHANGE RESIN

A novel 1,2,4,5-tetrazine functionalized polymer P-Tz was successfully synthesized by the reaction of an aminomethylated macroporous polysty rene-DVB-copolymer (P-Am) with 3-bromo-6-phenyl-1,2,4,5-tetrazine. The proposed structure of the functional groups of P-Tz was confirmed by synthesis of the model compound benzyl-(6-phenyl-1,2,4,5-tetrazine-3-y l)-amine and comparative FTIR-spectroscopic investigations, An applica tion of P-Tz as a redox polymer is not possible due to the cleavage of the tetrazine groups under reducing conditions. Metal sorption and de sorption studies of the resin P-Tz were carried out and the results co mpared with the properties of the weak base anion exchanger P-Am. Evid ence is given that the secondary amine spacer of P-Tz influences marke dly its over all sorption properties, i.e., the tetrazine-modified res in shows in dilute hydrochloric acid typical anion-exchange properties towards precious metal ions. Compared with the starting polymer P-Am the selectivity sequence found for P-Tz, Pd(II) > Au(III) much greater than Lr(IV) > Os(IV) > Pt(IV) > Ru(III) > Rh(III), revealed a signifi cantly higher selectivity for Pd(II) which is established even in the presence of an excess of base metals. The results of desorption studie s obtained by applying perchloric acid and thiourea as eluting agents led to the assumption that palladium is strongly N-coordinated by the functional tetrazine groups and the secondary amine spacer as well. Th is hypothesis is confirmed by the structural characterization of a Pd( II)-chelate which is formed during solvent extraction using a monomole cular tetrazine analogue.