Synthesis Of Heterocyclic Ligands Containing S,N Atoms And Study On Extraction Of Palladium Ion

Palladium as the one of Platinum Group Metals,it paly an important role of oil industry,automobile industry,nuclear industry,military,aerospace and other important industries due to the unique physical and chemical properties.The demand of Palladium metal was continue grow with the social development,and the Palladium mineral resources in the earth is low and uneven distribution that campared to the importance of recover Palladium from secondary resources.In Pd recovery feild,solvent extraction method has been wildely used and was a research hotspot for many researcher as a one of the best methods nowdays.Pd is a soft acid ligand,it has a good combine ability with S and N atoms and also has some combine ability with O atom,but Pd（II）combined with some oxygen-containing functional groups（such as carboxyl,carbonyl,etc.）will be reduced to Pd（0）to a certain extent.In many researchs,the structural design of extractants mostly used N atom as the active center,mainly ionic liquids containing amine groups,imidazole groups and pyridyl groups,and there were few studies on S atoms.In this paper,a ligand with multiple active centers formed by modified pyridine and thioether was designed and synthesized,and its Pd（II）extraction behavior in hydrochloric acid solution was studied.The results are as follows:（1）A novel three-coordinate extractant was synthesized,5-methoxy-2[（3,5-dimethyl-4-nitro-2-pyridyl）methylmercapto]-1-H-benzimidazole（MDNMB）,when chloroform was used as the organic phase solvent to extract Pd（II）in hydrochloric acid,it was found that when the concentration of hydrochloric acid solution was lower than 1 M,the extraction efficiency of Pd（II）was almost stably maintained at about100%.And when it higher than 1 M,the extraction efficiency decreased with the increase of the concentration of hydrochloric acid.Studies on other factors affecting extraction showed that 2 m M MDNMB could achieve the highest extraction of 0.5m M Pd（II）in 1 M hydrochloric acid under the condition that O/A was 1/2 and the extraction time was 10 min.The Pd Cl[MDNMB]⁺complexes were formed between the extractant and Pd（II）by FTIR,equimolar continuous variation method and maximum extraction capacity experiments,that is,the coordination ratio of Pd（II）to extractant was 1:1.（2）A novel chelating extractant with modified pyridyl groups and thioethers to form S and N tetracoordinates was synthesized,1,2-bis（（（3,5-dimethyl-4-nitropyridin-2-yl）methyl）thio）ethane（BDNMTE）.Dichloromethane was used as the solvent of the organic phase,when the concentration of hydrochloric acid solution was lower than 1M,the extraction efficiency of Pd（II）was almost stably maintained at about 100%,and then decreases with the increase of the concentration of hydrochloric acid.The extraction conditions were optimized for extraction:the extraction time was 10 min,the O/A was 1/1,and the extractant concentration was 1 m M.The experimental results of FTIR and equimolar continuous variation method showed that the coordination ratio of BDNMTE to Pd（II）was 1:2,namely[Pd Cl₂]₂BDNMTE.（3）A novel extractant was synthesized as 1-（5-（3,5-dimethyl-4-nitropyridin-2-yl）-2-（（3,5-dimethyl-4-nitropyridine-2-yl）methyl）-4-methylthiophen-3-yl）ethane-1（DNDNMME）.Compared with BDNMTE and MDNMB,the cyclic extraction performance of this extractant had been greatly improved.0.01 M hydrochloric acid+0.05 M thiourea was used as the eluent,the Pd（II）extraction rate of DNDNMTE after5 cycles was still above 80%,and it could achieve effective extraction of Pd（II）,and can be recycled.