The present invention relates to monomeric and oligomeric unsaturated vicinal dithioethers. Furthermore the present invention relates to the use of unsaturated vicinal di ^¬ thioethers according to the invention in methods for se ^¬ lective palladium ( I I ) separation from secondary raw materials.

In the following for the novel unsaturated vicinal di ^¬ thioethers the terms compound and ligand are used synony- mousyl .

The recovery of platinum group metals (PGM) from secondary sources has gained increasing importance, especially in countries without platinum-group metal mines. As meas ^¬ ured by the annual demand palladium is one of the most important platinum-group metal. In industrial process streams it occurs in the divalent oxidation state and forms chloro complexes, with the tetrachloropalladate an ^¬ ion, [PdCl ₄ ] ^2~ , being the most common species.

Nowadays one of the secondary sources for selective re ^¬ covery of palladium is derived from the production and recovery of automotive catalysts. But this is only one application area for the compounds and methods of the in ^¬ vention .

The selective recovery of Pd ( II) from automobile cata- lysts is a very challenging task because the sources usu- ally are acidic and oxidizing media .

The most common automotive catalysts consist of ceramic monoliths, that are mainly coated with aluminium oxide but also rare earth and base metal oxides as well as al ^¬ kaline earths. Furthermore platinum group metals are fixed at the surface of that washcoat. Beside palladium, these are particularly platinum and rhodium.

In the state of the art it is known to leach the automo ^¬ bile catalysts with a strongly oxidising acidic medium containing chloride, like aqua regia, in order to obtain the PGM chloro complexes.

The liquid gained in this hydrometallurgical way, natu ^¬ rally also contains a wide spectrum of other metals, some of which are in a large excess. Moreover, compared to feed solutions originating from pyrometallurgical enrich ^¬ ment processes, the concentration of the PGM is rela ^¬ tively low (some hundred milligrammes per litre) .

Nowadays the separation of the individual platinum group metals like palladium is mainly done via extraction proc ^¬ esses namely solvent extraction and solid phase extrac ^¬ tion methods.

In solvent extraction methods the palladium ions con- tained in an aqueous liquid phase are chelated with an appropriate ligand, transferred to an organic phase and afterwards released from the complex and thereby sepa ^¬ rated . However solid phase extraction methods offer a number of advantages over solvent extraction methods, caused by a less problematic handling of the solid material compared to flammable and volatile solvents. Moreover, in solid phase extraction methods the formation of stable emul- sions is avoided, which makes it a lot easier to separate the two phases and reduces the loss of extractant. An alternative approach consolidates selective extrac- tants used in solvent extractions with the benefits of solid phase operations. In solvent impregnated resins (SIRs) the ligand is physically impregnated into a poly ^¬ meric support, making preparation of these materials rather convenient.

In these methods the ligand used mainly accounts for the selectivity, whereas the support influences the extrac ^¬ tion kinetics and should provide certain properties, such as a high surface area and porosity as well as chemical and mechanical resistance [1] . Commonly one reverts to the same solid supports as they are used in ion exchange resins. In this way, solid phase extraction studies on SIRs can be also seen as a preliminary step to testing with covalently bound extractants.

Considering the composition of a solution from a recovery process, the development of a selective extractant for Pd(II) is a challenging task. The extractant has on the one hand to be selective in respect of the metal and on the other hand has to withstand the reaction conditions that can be strong acidic.

Therefore it is an aim of the invention to provide novel compounds that can be utilized in extraction processes for palladium ( I I ) and to investigate their usefulness in different extraction methods.

Malik and Paiva [2] have given an overview of relevant works dealing with the separation of Pd(II), Pt(IV) and Rh(III) from chloride solutions. A major drawback of most extracting agents presented there for Pd(II) is the in- sufficient selectivity. It was reported that especially when using ion exchangers the separation from Pt(IV) and Rh(III) is not taking place, but also with solvent extractants like malonamide or organophoshine ligands Pd(II) is not separated during the extraction step.

In industrial processes in the state of the art it is known to recover palladium via solvent extraction with hydroxyoximes or long chain thioethers through the forma- tion of inner-sphere complexes [3,4,5].

One disadvantage of the known methods is that due to slow extraction rates the equilibration times of such known systems are quite long [4,5] . These equilibration times can be reduced with the help of phase transfer catalysts, like amines in the case of β-hydroxyoximes [5], but that decreases the selectivity towards other metals. In addi ^¬ tion when using long chain thioethers, stripping the palladium from the organic phase is found to be difficult [5] .

General requirements of a solvent extractant suitable for use in commercial operations have been specified 1987 by Tavlarides et al . [6] . Besides the key focus - a selec- tive extraction of the metal with a high loading capacity under the required pH - they include aspects like accept ^¬ able equilibrium times, an easy stripping of the loaded metal from the organic phase, the stability of the ex ^¬ tractant throughout the several stages and a high solu- bility of the extractant in the organic phase (mostly aliphatic and aromatic diluents) along with a low solu ^¬ bility in the aqueous phase. Moreover the extractant should be non-flammable, non-volatile and non-toxic for security and environmental reasons as well as relatively inexpensive. In the state of the art thioethers are widely known to be soft donors and to form complexes with a range of transi ^¬ tion metals. Dithioethers based on (cis) -1, 2-dithioethene possess a rigid chelating unit, which perfectly meets the geometrical demand for the square planar complexation of Pd(II) [7] . Recently Ananikov et al . have reported on sulfur-containing alkenes and their Pd(II) complexes [8].

To overcome the drawbacks of the state of the art one ap- proach is to design ligands with a reduced electron density on the sulfur atoms. This can be achieved by intro ^¬ ducing electron withdrawing groups on the double bond, such as cyano groups, or the double bond being part of an aromatic ring.

Studies on maleonitrile-dithiocrown ethers have shown that they form stable Pd(II) complexes and have also dem ^¬ onstrated their potential to extract Pd(II) with a good selectivity towards other soft metal ions [9,10]. Another important attribute is their high surface activity caused by the ether groups. Yet because of the low yields in their synthesis these compounds have never been used on a large scale for solvent extraction. As Pd(II) is coordinated exocyclically via the two sulfur atoms, the steric design does not stringently need to contain macrocycles. Hence the open-chain equivalents, which are easier to synthesise, are promising ligands to be utilised in industrial processes.

Pd(II) complexes of 1 , 2-bis (methylthio) maleonitrile [11], 1,2 bis (methylthio) -benzene [7,11,12] and 1 , 2-bis (methyl ^¬ thio) -4-methylbenzene [12] have already been investigated earlier, but the ligands themselves have not received any attention concerning a possible applicability in solvent extraction . Since the complexation of the metal occurs at the inter ^¬ face or the aqueous phase, it is important that the ex- tractant used is not too nonpolar - otherwise it takes very long until the equilibrium establishes.

In the solid phase extraction methods the operation can be done in a column-process realising a high contact sur ^¬ face without additional mixing [13] . Usually solid phase extraction is associated with ion exchangers, but often these materials show a much poorer selectivity than coor ^¬ dinating extractants.

Negatively charged chloro complexes of Pd(II) and Pt(IV) and to a lesser extent also Rh(III) are often co- extracted when using anion exchangers [14, 15] . With so- called selective chelating ion exchange resins - polymers with covalently bound side chains containing chelating functional groups with sulfur, nitrogen or oxygen donor atoms - different extraction mechanisms can occur. De ^¬ pending on the acidity of the feed solution an inner- sphere coordination mechanism or outer sphere ionic mechanism predominates [16, 17] . Yet the linking of the functional groups to the backbone of the resin is complex and time-consuming, resulting in a costly production process. For this reason there is only a small number of those resins available on the mar ^¬ ket [13, 1] . In addition, these materials are often too hydrophobic and sometimes the selectivity of the coordi ^¬ nating ligand is not preserved [18] .

Until now, no compounds have been disclosed that are suitable as complex forming agents for the extraction of Pd(II) at different pH values from a wide range of secon ^¬ dary raw materials. It is therefore an aim of the present invention to pro ^¬ vide such complex forming compounds that can be utilized in solid phase extraction processes of Pd(II) and be used as solid phase extractants in solvent impregnated resin extraction processes.

Short description of the invention

Therefore it is an object of the invention to provide compounds that are comparably easy and cost effective to synthesise and at the same time are ligands to be util ^¬ ised in industrial processes.

First and foremost to be utilized in industrial applica- tions a compound is preferred that can be synthesized in a method with few steps and most preferred in a one-pot synthesis .

To solve the problem of the invention the inventors have provided a number of novel monomeric and oligomeric vici ^¬ nal unsaturated dithioethers and have investigated the use thereof in solvent extraction and solid phase extrac ^¬ tion of Pd (II) . To show the usefulness of the novel unsaturated vicinal dithioethers their potential for selective extraction of Pd(II) from different media was investigated. In a part of these experiments the acidic and oxidizing media from the recovery of automobile catalysts were simulated.

The problem of the invention is solved by providing unsaturated vicinal dithioethers of general formula I

wherein n is an integer from 1 to 12, wherein m is 0 or 1, wherein X is selected from

wherein Y is selected from the group consisting of

CH,+CH,— O CH,+CH,—

~CH ₂ — CH ₂ ^— CH ₂ — -CH ₂ — CH ₂ — O O CH ₂ — CH ₂ - CH ₂ — CH ₂ — O— CH ₂ -

, , and

CH2 O CH ₂ — CH ₂ —

r

wherein, under the proviso that n is 1, m is 1 and Ri and R ₂ each are H; wherein, under the proviso that n > 1, R _x and R ₂ are selected from the group consisting of H, Na, CI, and Br, or R _x and R ₂ together form a bond making up a cycle .

In an embodiment of the invention preferred unsaturated vicinal dithioether are provided, namely 1, 2-bis (2-hydroxyethylthio) -4-methylbenzene

, 2-bis (2-methoxyethylthio) -4-methylbenzene

, 2-bis (2-hydroxyethylthio) benzene

, 2-bis (2-methoxyethylthio) benzene

(Z) -1, 2-bis (2-hydroxyethylthio) -1, 2-dicyanoethene (5)

( Z) -1 , 2 -bis (2-methoxyethylthio) -1 , 2-dicyanoethene ( 6)

Especially preferred are unsaturated vicinal dithioethers according to the invention, namely oligomeric unsaturated dithioethers of the following structures:

To solve the problem of the invention a mixture (7) is preferred, comprising at least two oligomeric unsaturated dithioethers according to the invention with the follow

wherein m in general formula I is 0 or 1, and wherein the unsaturated dithioethers with identical m values differ at least in the value of n or in the meaning of Ri or ]¾ .

In a particularly preferred embodiment a mixture (8) is provided, comprising at least two oligomeric unsaturated dithioethers according to the invention with the following structures:

wherein m in general formula I is 0 or 1, and wherein the unsaturated dithioethers with identical m values differ at least in the value of n or in the meaning of Ri or ]¾ .

In a further preferred embodiment of the invention a mix ^¬ ture (9) is provided, comprising at least two oligomeric unsaturated dithioethers according to the invention with the following structures:

wherein m in general formula I is 0 or 1, and wherein the unsaturated dithioethers with identical m values differ at least in the value of n or in the meaning of Ri or R2.

In an particularly preferred embodiment of the invention the a compound or mixture according to the invention is used in the separation of Pd(II) from secondary raw materials.

Especially preferred is the use of a compound or mixture according to the invention, wherein the separation is a solvent extraction method.

In a preferred embodiment a compound or mixture according to the invention is used in a solid phase extraction method .

Preferred is an embodiment of the invention wherein the use of a compound or mixture according to the invention is a solvent impregnated resin (SIR) extraction method.

Particularly preferred is the use according to the inven- tion wherein the secondary raw material is derived from the production or recovery of automobile catalysts.

The problem of the invention is furthermore solved by providing a solid support comprising a compound or mix- ture according to the invention.

In a preferred embodiment of the invention the solid sup ^¬ port is silica gel or a polymeric resin. Particularly preferred is a support, wherein the poly ^¬ meric resin is a macroporous styrene-divinylbenzene co ^¬ polymer .

In contrast to thioethers of the state of the art the novel compounds are not volatile and do not have the characteristic odour, which is advantageous for practical application .

To investigate the usefulness of the novel unsaturated 1 , 2-thioethers of the invention solvent extraction batch experiments with the unsaturated dithioethers (1) to (6) and various reference compounds were performed.

All tests were carried out in a chloroform / water sys- tern, where the extractant was present in excess in the organic phase. The composition of the aqueous phase, which contained Pd(II), has been progressively modified from a model solution closer to industrial conditions. The invention is further detailed by reference to the ac ^¬ companying drawings . Brief discussion of the drawings

Figure 1 shows the solvent extraction kinetics of the di- thioethers (2), (4), (5), and (6) compared to dihexylsul- fide and Aloxime®840 in CHC1 ₃ /H ₂ 0 = 1/1 (c(L) ₀ = 10 ^"2 M, Co(Pd) _w = 10 ^"4 M, cCCl) _w = 1.5 x 10 ^"2 M) . The extraction yield E was determined by measuring c(Pd) _w with ICP OES.

Figure 2 shows the solvent extraction kinetics of dithio- ether (2), 4-methylbenzodithio-12-crown-4 and 1,2- bis (methylthio) -4-methylbenzene in CHCI3/H ₂ O = 1/1

(c(L)o = 10 ^"2 M, Co(Pd) _w = 10 ^"4 M, c(Cl) _w = 1.5 10 ^"2 M) . The extraction yield E was determined by measuring c(Pd) _w with ICP OES.

Figure 3 shows the dependency of the extraction yield E of maleonitrile-dithio-12-crown-4 , dithioethers (2), (4) and (6) on the HC1 concentration added to the aqueous phase (CHC1 ₃ /H ₂ 0 = 1/1, c(L) ₀ = 10 ^"2 M, c ₀ (Pd)„ = 10 ^"4 M, Co(Ol)„ = 1.5 x 10 ^"2 M) . The extraction yield E is deter ^¬ mined by measuring c(Pd) _w with ICP OES.

Figure 4 shows the results of a solvent extraction batch experiment with a solution gained by leaching of an auto- motive catalyst with aqua regia (subsequent dilution with the same volume of water) and extractant (4) in chloro ^¬ form. Composition of the feed solution (dark grey) and organic phase (light grey) as determined with ICP OES (c(4) ₀ = 10 ^"2 M, H ₂ O/CHCI3 = 1/1).

Figure 5 shows SPE kinetics of the SIRs in batch tests (10 ^~4 M Pd(II) , 0.02 M HC1) .

Figure 6 shows the elution of the loaded SIRs (see Table 2 for the initial Pd content) in batch tests with 0.5 M thiourea, 0.1 M HC1. Detailed description of the invention

Figure 1 clearly demonstrates the ability of the ligands (2), (4) and (6) to transfer Pd(II) from the aqueous into the organic phase. Compared to the two industrially used extractants dihexylsulfide [19] and Aloxime®840 [20] all of compounds of the invention containing 2-methoxyethyl end groups establish the extraction equilibrium extremely fast. Especially (2) and (4), which show extraction yields near 100 % within only 30 minutes, are preferred compounds according to the invention.

Compound (5) formed an insoluble precipitate, which accu ^¬ mulated in between the phases and could not be analysed. Thus, although the palladium content of the aqueous phase instantly drops when getting in contact with (5) , it is unsuitable to be used as an extractant. Surprisingly the compounds (1) and (3) did not extract any Pd(II) . This was caused by their high water solubility, as revealed by scanning of both phases via UV/Vis spectroscopy. Both ligands form palladium complexes, but under the condi ^¬ tions chosen their concentration in the aqueous phase has been high enough to keep the palladium there. Figure 2 illustrates the influence of the end groups on the extraction kinetics within a series of 1 , 2-dithio-4- methylbenzene derivatives: the acyclic 1 , 2-bis (2-methoxy- ethylthio) -4-methylbenzene (2) has been tested in com ^¬ parison to the analogue crown ether 4-methylbenzodithio- 12-crown-4 [21] and the non-polar acyclic 1,2-bis-

(methylthio) -4-methylbenzene [12]. All of them exhibit very good extraction yields, but the time taken to reach the extraction equilibrium differs widely. Using the non- polar 1 , 2-bis (methylthio) -4-methylbenzene the extraction takes the longest. The reaction rate increases according to an enhancement of the surface activity in the order of: methyl < 2 meth- oxyethyl group. 4-Methylbenzodithio-12-crown-4 , possessing a similar polarity to 2, reacts fastest. Without in- tending to be bound to a theory this difference in kinet ^¬ ics could be explained by the rigidity of the crown ether. Compared to the open-chain ligand (2), it features a better preorganisation for a complexation of Pd(II) . Interestingly the extraction yield of the dithiomaleoni- trile derivative (6) is less than that of the extractants (2) and (4) based on the dithiobenzene unit.

For media containing a high concentration of hydrochloric acid, like the streams in platinium group metals refining industries, the extractants used have to be strong enough to compete with Cl ^~ for a complexation at Pd(II) .

As can be seen from Figure 3 there is a huge difference in the extraction performance between extractant (2), (4) and (6) . The extraction yield of the dithiomaleonitrile derivative dramatically decreases even by the addition of very small quantities of HCl. At a concentration level of 0.26 M HCl ligand (6) extracts almost no Pd(II) at all. The same trend is observed when using the corresponding crown ether maleonitrile-dithio-12-crown-4 [22], although it is shifted to higher HCl concentrations. Being more preorganised the crown ether is a stronger chelating agent than the open-chain analogue (6) . However, utilis ^¬ ing HCl concentrations higher than 1 M also depresses the extraction yield to negligible values.

In contrast, extractants (2) and (4) constantly exhibit extraction yields near 100 % even at extremely high HCl concentrations . Figure 4 demonstrates the capability of extractant (4) under conditions close those in recovery proceses for automotive catalysts.

A solution was extracted, which was gained by leaching an automotive catalyst with aqua regia and diluting that 1:1 with water. Beside a HC1 concentration of nearly 4.5 M, this solution did not only contain a higher concentration of Pd(II) but also Pt(IV) and Rh(III), as well as a num ^¬ ber of base metals, partially in 10 fold excess.

The selectivity of compound (4) was found to be excel- lent. The organic phase contained 133 mg/L palladium, whereas the concentration of all the other metals was smaller than 0.2 mg/L. This experiment also demonstrates the redox stability of the system under strongly oxidis ^¬ ing conditions.

This shows that the novel chelating compounds (1) to (6) can be utilised for the selective coordination of Pd(II) . They proved to have a high stability towards oxidation, which makes them interesting for application in solvent extraction industries.

In batch experiments it were the ligands (2) and (4), which particularly substantiated the capability to be used as solvent extractants. They are based on 1,2- dithio-4-methylbenzene and o-dithiobenzene, respectively and contain 2-methoxyethyl side-chains.

Compared to conventionally used extractants like dihexyl- sulfide or hydroximes the novel ligands enable a drastic increase of the reaction rate. The influence of the vary ^¬ ing backbones of our ligands on the complex stabilities reflects in a dramatic disparity of the extraction per ^¬ formance in the presence of chloride. Like mentioned above, for an application in industry it is important that the extractant is cheap to produce, very stable against oxidation and also able to extract Pd(II) out of a medium containing a high content of hydrochloric acid. On the other hand the complex formed should not be too stable to enable a fast elution. These criteria are perfectly met by ligand (4) rendering it the extractant of choice.

With the above referenced results the high potential of compound (4) by selectively extracting Pd(II) in solvent extraction methods out of a solution of a leached automo ^¬ tive catalyst was demonstrated, which also contained a high concentration of other PGM and base metals as well as hydrochloric acid. In the following the usefulness of a selection of the compounds according to the invention was investigated in the solid phase extraction of Pd(II) . In these experi ^¬ ments three different kinds of solid supports were im ^¬ pregnated with the ligands of the invention.

To this end several extractants, including compound 1,2- bis (2-methoxyethylthio) benzene (4) but also oligomeric mixtures of (7), (8) and (9), have been applied onto sil ^¬ ica gel and amberlite XAD-2.

Table 1 shows the composition of the SIRs that were pre ^¬ pared utilizing the compounds according to the present invention .

Table 1

Denotation and composition of SIRs.

wherein : mSupport is the ratio between mass of extractant and mass of solid support and xs is the sulphur content.

The measured sulfur content xs directly depends on the content of dithioether units. As a result of differences of the distribution of the oligomeric species with dif- ferent lengths within the mixtures, the sulfur content of the oligomeric mixtures (7) - (9) differs more than would be assumed from the repetition units. This also reflects in the xs values of the SIRs. The oligomeric compounds according to the invention con ^¬ sist of chelating o-dithiobenzene or maleontrile dithio ^¬ ether units, which are connected via ether or alkyl chains . The inorganic, hydrophilic silica gel is a typical sup ^¬ porting material for solid support extraction materials [23, 24] . In the case of the use of silica gel as solid support in the SIRs the bonding to the extractant occurs via hydrogen bonds from the hydroxyl groups of the silica gel to ether groups of the oligomers. Amberlite XAD-2, a macroporous styrene-divinylbenzene co ^¬ polymer, is a commonly used, organophilic substrate that adsorbs the ligands via n-n-dispersion forces. Generally XAD resins are more stable against acid and al ^¬ kali solutions than Cis-bonded silica gel, which also had been widely used as adsorbent.

The batch experiments performed with the SIRs of Table 1 revealed that the extraction behaviour of the SIRs varies widely (Fig. 5) . Generally, the SIRs SG-1 and SG60-2 con ^¬ taining polar silica gel as supporting material, estab ^¬ lish the extraction equilibrium much faster than those that contain organophilic XAD 2. Especially a comparison of SG60-2 and XAD2-2, both being impregnated with the same amount of extractant 8, shows that the kinetics strongly depend on the kind of the solid support used, whereas in terms of the extraction yields in the equilib ^¬ rium state comparable values were obtained (94.9% and 91.4%, respectively) . The extractant on the surface of the solid support determines the extraction yields.

In analogy to the above referenced observations from sol ^¬ vent extraction experiments with acyclic dithioethers, SG-1, which is impregnated with a dithiomaleonitrile ex ^¬ tractant, gave poorer extraction yields than SG60-2, that contains the dithiobenzene analogue (66.2% and 94.9~6 , re spectively) . In the context of the investigations of the momomeric un ^¬ saturated dithioethers of the present invention it was shown that due to the higher electron withdrawing effect of the dithiomaleonitrile backbone the stability of the respective Pd(II) complex formed is less than that of a dithiobenzene derivative. On the other hand the percent ^¬ age of metal extracted during one extraction step also depends on the hydrophilicity of the extractant, which is varied via the number of oxygen atoms within the chains connecting the chelating dithioether units. Although, due to the shorter chains and missing oxygen, XAD2-3 contains a higher sulfur content than XAD2-2 (Table 1) it ex ^¬ tracted only 51.7% of the Pd(II) in the feed solution. With 69.8% the SIR XAD2-4a comprising the monomeric ex ^¬ tractant, exhibited an extraction yield in between the other two amberlite resins. XAD2-4b was overloaded and the extractant washed off the solid support, which re ^¬ sulted in an oily film at the surface of the aqueous phase. Hence this SIR was not used for further experi ^¬ ments. That shows that amount of the extractant chosen for XAD2-4a is already near the maximal possible value.

Furthermore in successive batch extraction experiments the effective Pd(II) capacity g _Pd of the SIRs was deter ^¬ mined according to equation (2), where n is the number of extraction steps until the SIR was fully loaded, m is the mass of the SIR and Vi the volume of the aqueous phase.

(2)

In Table 2 the results of these experiments are shown. Table 2 shows the contact times for each extraction step, the number of steps and the palladium capacities as de ^¬ termined via batch experiments (10 ^~4 M Pd(II), 0.02 M HC1) .

Table 2

The effective capacities are generally lower than theo ^¬ retically possible, relating to the content of sulfur x _s listed in Table 1 (under the assumption that two sulfur atoms are needed to bind one Pd(II)) . In line with the trend deriving from Fig. 5 XAD2-3 has the lowest loading capacity within the series of SIRs investigated. The ca ^¬ pacity of the XAD2-2 is more than twice as much, although its content of chelating units is lower. Again, aside from the kinetics, there is no significant difference be ^¬ tween XAD2-2 and SG60-2, but the drop of the percentage of extraction plotted against the number of sequent ex ^¬ traction steps is much steeper for SG60-2 than for XAD2- 2. SG-1 has a relatively low effective loading capacity, although in terms of the utilisation of chelating groups it possesses the best value. The highest loading capacity has been achieved by XAD2-4a, which also contains the highest sulfur content. It is comparable to the loading capacity reported for SuperLig® from IBC (0.52 mmol/g) [25] .

To show the usability of the compounds of the present in ^¬ vention in solid phase extraction materials it is further shown that the solid supports impregnated with the com ^¬ pounds of the invention can be used for many extraction cycles .

For regeneration the extractant is treated with an elu- ent, which re-extracts the metal into an aqueous phase. In solvent extraction experiments with the monomeric ex- tractant (4), a mixture of thiourea in hydrochloric acid was found to be the most effective stripping agent [30] . Hence this solution was also used for the elution of Pd(II) from the SIRs via successive batch experiments with 3 mL eluent at a time.

As seen from Fig. 6, showing the Pd(II) content of each dose, the thiourea solution is a highly effective re- extractant that recovers the major part of the metal al ^¬ ready in the first elution step. From the two SIRs con ^¬ taining silica gel (SG-1, SG60-2) and XAD2-2 overall each 90% and 87% of the palladium, respectively, have been be re-extracted. In the cases of XAD2-3 and XAD2-4a the to ^¬ tal percentage of Pd(II) that could be recovered was only 68% for both SIRs. It is possible that the remaining Pd(II) had migrated into regions that have been inacces ^¬ sible for the eluent.

These experiments showed that the compounds of the pre ^¬ sent invention can be utilized as selective extractants for Pd(II) in solvent impregnated resins and have a po ^¬ tential to be used as solid phase extractants.

The problem of the present invention is solved by provid ^¬ ing the monomeric and oligomeric unsaturated vicinal di- thioethers of the present invention the synthesis and the investigation thereof is described in the following. Ad- ditionally the preparation of the SIRs provided in the present invention is disclosed.

Syntheses of the novel unsaturated vicinal dithioethers Synthesis of the monomeric compounds (l)-(6)

General: All reactions were carried out in dry solvents under an argon atmosphere. The melting points (m.p.) were measured with a capillary. NMR spectra of the compounds (l)-(6) were recorded with a Bruker Avance-300 spectrome ^¬ ter. The ^X H chemical shifts are reported relative to the TMS signal (0 ppm) and the ¹³ C chemical shifts relative to the solvent signal CDCI3 (77 ppm) . The assignments of the NMR signals were carried out under using 2D-NMR ex ^¬ periments HMBC and HMQC . IR spectra were recorded on a Thermo Nicolet NEXUS FTIR instrument. UV/Vis spectro ^¬ scopic measurements were done on a Perkin Elmer Lambda 950 spectrophotometer using quartz cuvettes. The EI MS spectra were recorded using Thermo Quest SSQ 710. Elemen ^¬ tal analyses (C,H,N,S) of the ligands 1-6 were performed with an Elementar Vario EL elemental analyser. The Pd content of the complexes [PdCl ₂ (L)] was determined by di- luting 1 mg in 1 mL 65 % HNO ₃ and measuring on an Optima 5300 DV ICP OES from Perkin Elmer (A = 340.458 nm) .

General procedure for the synthesis of compounds (l)-(4):

Benzene-1 , 2-dithiol or toluene-3, 4-dithiol respectively (9.5 mmol) in ethanol (3 mL) was added to a solution of sodium (20 mmol) in ethanol (21 mL) . The resulting solution was heated under reflux and 20 mmol of 2- bromoethanol or 2-chloroethylmethylether respectively were added. The solution was stirred under reflux for 15 hours. After that the precipitate was removed and the solvent was evaporated. The yellow, oily residue was pu ^¬ rified by column chromatography on silica gel using chloroform as an eluent to afford (1), (2) and (4) as colour ^¬ less oils and (3) as white crystals.

The maleonitril-dithioethers (5) and (6) were prepared by alkylation of disodium (Z) -1, 2-dicyanoethene-l , 2- dithiolate [26] with 2-bromoethanol and 2- chloroethylmethylether , respectively in the presence of Nal following a procedure reported by Lange and co ^¬ workers [27 ] . 1, 2-bis (2-hydroxyethylthio) -4-methylbenzene (1)

Yield: 2.16 g (93 %) ; Rf=0.12 (CHC1 ₃ ) ; n _D ²⁰ : 1.621;

XH NMR (300 MHz, CDCI ₃ , 25 °C, TMS) : 5=7.32 (d, ³ J(H, H) =8 Hz, 1H; CHCHCS), 7.21 (s, 1H; CCHCS), 7.01 (d,

3J(H,H)=8.0 Hz, 1H; CCHCH), 3.73 (t, ³ J(H,H)=5.7 Hz, 2H;

CH ₂ C ^h H ₂ 0) , 3.67 (t, ³ J(H,H)=5.7 Hz, 2H; CH ₂ C ^j H ₂ 0) , 3.12 (t, ³ J(H,H)=5.7 Hz, 2H; SC ^g H ₂ CH ₂ ) , ) , 3.07 (t, ³ J(H,H)=5.7 Hz, 2H; SC ⁱ H ₂ CH ₂ ), 2.65 (brs, 2H; OH), 2.32 ppm (s, 3H; C¾C) ; ¹³ C NMR (75 MHz, CDC1 ₃ , 25 °C, TMS) : 5=138.1 (CH ₃ CH) , 137.5 (CHC ^a S), 132.5 (CHC ^f S), 132.1 (CHCHCS), 131.1

(CCHCS), 128.4 (CCHCH), 60.0 (CH ₂ C¾ ₂ 0) , 59.8 (CH ₂ C¼0) , 38.5 (SC ^g H ₂ CH ₂ ), 37.7 (SC ⁱ H ₂ CH ₂ ), 21.0 ppm (CH ₃ C);

IR (KBr) : ΰ=3383 (O-H) , 2921 (C-H) , 2873 (C-H) , 1459 (C- C) , 1063 (C-OH) , 1039 (C-OH) , 1012 cm ^"1 (C-OH);

UV/Vis (H ₂ 0) : A _(max) (ε)=296 (1720), 247 (11704), 216 nm (22061 ; MS (70 eV) : m/z (%) : 244 (45) [M] ⁺ , 200 (75) [C ₉ H ₁₂ OS ₂ ] ⁺ , 167 (100) [C ₉ HuOS] ⁺ , 91 (65) [C ₇ H ₇ ] ⁺ ; elemental analysis ( % ) calcd for CnH ₁₆ 0 ₂ S ₂ : C 53.97, H 6.60, S 26.24; found: C 54.01, H 6.57, S 26.08.

1, 2-bis (2-methoxyethylthio) -4-methylbenzene (2)

Yield: 2.38 g (92 %) ; ¾=0.80 (CHCI ₃ ) ; n _D ²⁰ : 1.575;

¹ NMR (300 MHz, CDC1 ₃ , 25 °C, TMS) : 5=7.26 (d, ³ J(H, H) =7.9

Hz, 1H; CHCHCS), 7.13 (s, 1H; CCHCS), 6.96 (d,

3J(H,H)=7.9 Hz, 1H; CCHCH), 3.53-3.63 (m, 4H; CH ₂ C ^j ' ^h H ₂ 0), 3.38 (s, 3H; Ο^Η ₃ ) , 3.35 (s, 3H; OC ^m ¾) , 3.04-3.13 (m, 4H; SC ^i,g ¾CH ₂ ) , 2.31 ppm (s, 3H; C¾C) ; ¹³ C NMR (75 MHz, CDC1 ₃ , 25 °C, TMS) : 5=137.7 (CH ₃ CCH) , 137.2 (CHC ^a S), 132.5

(CHC ^f S), 130.9 (CHCHCS), 129.6 (CCHCS), 127.3 (CCHCH), 71.0 (CH ₂ C¾ ₂ 0) , 70.9 (CH ₂ C¼0) , 58.7 (OC ¹ H ₃ ) , 58.6

(0(^Η ₃ ), 33.2 (SC ^g H ₂ CH ₂ ), 32.5 (3^Η ₂ ΟΗ ₂ ), 21.0 ppm (CH ₃ C); IR (KBr) : ΰ=2980 (C-H), 2924 (C-H), 2876 (C-H), 2823 (C- H) , 2808 (C-H), 1459 (C-C) , 1114 (C-O) , 1095 (C-O) , 1040 cm ^"1 (C-O); UV/Vis (H ₂ 0) : A _(max) (ε)=298 (1927), 248

(10224), 216 nm (18856 mol ^"1 dm ³ cm ^"1 ) ; MS (70 eV) : m/z (%) : 272 (43) [M] ⁺ , 214 (36) [Ci ₀ H ₁₄ OS ₂ ] ⁺ , 167 (100) [C ₉ HnOS] ⁺ , 91 (65) [C ₇ H ₇ ] ; elemental analysis (%) calcd for

C ₁₃ H2 ₀ O2S2: C 57.32, H 7.40, S 23.54; found: C 57.11, H 7.45, S 23.64. 1 , 2-bis (2-hydroxyethylthio) benzene (3)

Yield: 2.19 g (94 %) ; R _f =0.11 (CHC1 ₃ ) ; m.p. 84.5-86.0 °C; ^X H NMR (300 MHz, CDC1 ₃ , 25 °C, TMS) : 5=7.38-7.43 (m, 2H; CHCHCS), 7.18-7.24 (m, 2H; CHCHCH), 3.72 (t, ³ J(H,H)=5.7 Hz, 4H; CH ₂ C¾0 ) , 3.12 (t, ³ J(H,H)=5.7 Hz, 4H; SC¾CH ₂ ) , 2.58 ppm (s, 2H; OH); ¹³ C NMR (75 MHz, CDC1 ₃ , 25 °C, TMS) : 5=136.8 (CHCS), 130.9 (CHCHCS), 127.5 (CHCHCH), 59.9 ( CH2 CH2O ) , 37.8 ppm ( S CH2CH2 ) ; IR (KBr) : ΰ=3329 (O-H) , 3250 (O-H), 2971 (C-H) , 2954 (C-H) , 2923 (C-H) , 2873 (C- H) , 1449 (C-C) , 1057 (C-OH) , 1039 (C-OH) , 1023 (C-OH) , 1008 cm ^"1 (C-OH); UV/Vis (H ₂ 0) : A _(max) (ε)=297 (1535), 246 (10108), 214 nm (16574 ; MS (70 eV) : m/z (%) : 230 (32) [M] ⁺ , 186 (26) [C ₈ H ₁₀ OS ₂ ] ⁺ , 167 (35) [C ₉ HuOS] ⁺ , 153 (100) [C ₈ H ₉ OS] ⁺ ; elemental analysis (%) calcd for CioH ₁₄ 02 S ₂ : C 52.14, H 6.13, S 27.84; found: C 52.10, H 6.10, S 27.75.

1.2-bis (2-methoxyethylthio) benzene (4)

Yield: 2.34 g (95 %) ; R _f =0.93 (CHCI ₃ ) ; n _D ²⁰ : 1.583;

^X H NMR (300 MHz, CDC1 ₃ , 25 °C, TMS) : 5=7.31-7.36 (m, 2H; CHCHCS), 7.13-7.19 (m, 2H; CHCHCH), 3.59 (t, ³ J(H,H)=6.8 Hz, 4H; CH ₂ C¾0 ) , 3.37 (s, 6H, OC¾) , 3.11 ppm (t,

3J(H,H)=6.8 Hz, 4H; SC¾CH ₂ ) ; ¹³ C NMR (75 MHz, CDC1 ₃ , 25 °C, TMS) : 5=136.9 (CHCS), 129.5 (CHCHCS), 126.6 (CHCHCH), 70.9 (CH ₂ CH ₂ 0 ) , 58.7 ( O CH ₃ ) , 32.7 ppm (SCH ₂ CH ₂ ) ;

IR (KBr) : ΰ=2980 (C-H), 2925 (C-H), 2877 (C-H), 2824 (C- H) , 2808 (C-H), 1446 (C-C), 1114 (C-O) , 1094 (C-O) , 1042 cm ^"1 (C-O); UV/Vis (H ₂ 0) : A _(max) (ε)=300 (1310), 247 (9203), 214 nm (15695 mol ^"1 dm ³ cm ^"1 ) ; MS (70 eV) : m/z (%) : 258 (44) [M]\ 200 (54) [C ₉ H ₁₂ OS ₂ ] ⁺ , 167 (60) [C ₉ HnOS] ⁺ , 153 (100) [C ₈ H ₉ OS] ⁺ ; elemental analysis (%) calcd for CioH ₁₄ 0 ₂ S 2 : C

55.78, H 7.02, S 24.81; found: C 55.68, H 6.99, S 24.92. General procedure for the synthesis of the compounds (5) and (6) :

A suspension of disodium (Z) -dicyanoethene-1 , 2-dithiolate (45 mmol) and a spatula tip of sodium iodide in acetone (80 mL) was heated. Then 2-bromoethanol or 2- chloroethylmethylether (91 mmol) respectively was added. The suspension was heated under reflux and stirred for 20 hours. After that the precipitate was removed and the solvent was evaporated. The residue was dissolved in chloroform and washed with water. The organic layer was dried over anhydrous MgSC^ and evaporated to dryness to yield a yellow solid. This was purified by recrystallisa- tion from diethyl ether to afford (5) as light brownish and (6) as colourless crystals.

(Z) -1,2-bis (2-hydroxyethylthio) -1 , 2-dicyanoethene (5)

Yield: 0.94 g (43 %) ; ¾=0.03 (CHC1 ₃ ) ; m.p. 67.5-68.5 °C; ^X H NMR (300 MHz, CDCI3 , 25 °C, TMS) : 5=3.92 (t,

3J(H,H)=5.7 Hz, 4H; CH ₂ C¾0) , 3.32 ppm (t, ³ J(H,H)=5.7 Hz, 4H; SC¾CH ₂ ) , 2.04 ppm (s, 2H; OH); ¹³ C NMR (75 MHz,

CDCI ₃ , 25 °C, TMS) : 5=121.8 (C=C) , 112.2 (CN) , 61.3

( CH2 CH2O ) , 37.8 ppm ( S CH2CH2 ) ; IR (KBr) : ΰ=3325 (O-H) , 2210 ( C≡N ) , 2001 ( C≡N ) , 1492 (C=C) , 1061 ( C - OH ) , 1014 ( C - OH) , 999 cm ^"1 (C-OH); UV/Vis (H ₂ 0) : A _(max) (ε)=341 (13902), 275 (4450), 216 nm (5896 mol ^"1 dm ³ cm ^"1 ) ; MS (70 eV) : m/z (%) : 230 (20) [M]\ 169 (13) [C ₆ H ₅ N ₂ S ₂ ] ⁺ , 159 (19)

[C ₅ H ₅ NOS ₂ ] ⁺ , 45 (100) [C ₂ H ₅ 0] ⁺ ; elemental analysis (%) calcd for C ₈ H ₁₀ N ₂ O ₂ S ₂ : C 41.72, H 4.38, N 12.16, S 27.84; found: C 41.81, H 4.32, N 12.21, S 27.79.

(Z) -1.2-bis (2-methoxyethylthio) -1 , 2-dicyanoethene (6)

Yield: 0.76 g (31 %) ; R _f =0.660 (CHCI ₃ ) ; m.p. 36.3-37.2 °C; ^X H NMR (300 MHz, CDC1 ₃ , 25 °C, TMS) : 5=3.66 (t,

3J(H,H)=5.9 Hz, 4H; CH ₂ C¾0) , 3.39 (s, 6H, OC¾) , 3.32 ppm (t, ³ J(H,H)=5.9 Hz, 4H; SC¾CH ₂ ) ; ¹³ C NMR (75 MHz, CDC1 ₃ ,

25 °C, TMS) : 5=121.1 (C=C) , 112.1 (CN) , 70.6 (CH ₂ CH ₂ 0) , 59.0 (OCH ₃ ), 34.8 ppm (SCH ₂ CH ₂ ) ; IR (KBr) : ΰ=2212 (C≡N) , 2002 (C≡N) , 1504 (C=C) , 1109 (C-O) , 1040 cm ^"1 (C-O);

UV/Vis (H ₂ 0) : A _(max) (ε)=340 (13902), 276 (4255), 215 nm (5803 mol ^' m ³ ™ ^-1 ); MS (70 eV) : m/z (%) : 258 (21) [M] ⁺ , 199 (4) [C ₇ H ₇ N ₂ OS ₂ ] ⁺ , 59 (54) [C ₃ H ₇ 0] ⁺ , 45 (100) [C ₂ H ₅ 0] ⁺ ; elemental analysis ( % ) calcd for Ci ₀ H ₁₄ N ₂ O ₂ S ₂ : C 46.49, H 5.46, N 10.84, S 24.82; found: C 46.55, H 5.49, N 10.93, S 24.85. Synthesis of the oligomeric compounds (7) -(9)

General

The MALDI-TOF MS spectra were recorded with a Bruker Mi- croflex LRF spectrometer using trihydroxyacetophenone (THAP) as matrix for the samples. Calibration was done with angiotensin II in -cyano-4- hydroxy cinnamic acid. The ESI-MS spectrum was recorded using a Micromass Q- TOFmicro mass spectrometer in positive electrospray mode. Elemental analyses of (7) -(9) and the SIRs (C, H, N, S) were performed with an Elementar Vario EL elemental ana- lyser.

Reagents and solutions

Unless otherwise stated all chemicals used have been pur ^¬ chased from Merck.

Oligomeric mixture (7) :

Disodium (Z) -dicyanoethene-1 , 2-dithiolate [26] (16 mmol) and 1, ll-dichloro-3, 6, 9-trioxaundecane [29] (16 mmol) were dissolved in ethanol (20 mL) and water (2 mL) under an argon atmosphere. The solution was heated to 60 °C (using a reflux condenser) and stirred for 7 days. The solvents were evaporated and the residue was dissolved in chloroform and washed with water. The organic layer was dried with anhydrous sodium sulfate and the solvent evaporated to dryness to yield a dark red, viscous oil. Yield: 5.6 g; MALDI-TOF-MS : m/z: 553.13 + n-300.06

[C1C ₈ H ₁₆ 0 ₃ (Ci ₂ H _{16 2} 0 ₃ S ₂ ) _n ClNa] ⁺ (n=l-12), 569, 00 + n-300.06 [C1C ₈ H ₁₆ 0 ₃ (Ci ₂ H _{16 2} 0 ₃ S ₂ ) _n ClK] ⁺ (n=l-12); elemental analysis (%) found: C 43.11, H 5.66, N 4.88, S 11.28.

Oligomeric mixture (8) :

The reaction was carried out under an argon atmosphere. Benzene-1 , 2-dithiol [28] (28 mmol) was added to a solu ^¬ tion of sodium (56 mmol) in dry ethanol (18 mL) and stirred for 2 hours. 1, ll-dichloro-3, 6, 9-trioxaundecane [29] (28 mmol) in dry ethanol (2 mL) was added and the solution was heated to 60 °C (using a reflux condenser) and stirred for 7 days. The solvents were evaporated and the residue was dissolved in chloroform and washed with water. The organic layer was dried with anhydrous sodium sulfate and the solvent evaporated to dryness to yield a yellow, viscous oil.

Yield: 6.5 g; MALDI-TOF-MS: m/z: 465,12 + n · 300.09

[C ₆ H ₅ S ₂ (C ₁₄ H ₂₀ O ₃ S ₂ ) _n HNa] ⁺ (n=l-6), 553, 23 + n · 300.09

[C1C ₈ H ₁₆ 0 ₃ ( C14H20O3 S 2 ) _n ClNa] ⁺ (n=l-5), 359, 05 + n · 300.09 [CI ( C14H20O3 S 2 ) _n HNa] ⁺ (n=l-7); elemental analysis (%) found: C 51.54, H 6.23, S 19.41. Oligomeric mixture (9) :

The reaction was carried out under an argon atmosphere. Sodium methoxide (95 mmol) in dry methanol (18 mL) was added to benzene-1 , 2-dithiol [28] (47 mmol) and cooled to 0 °C. 1 , 3-dibromopropane (47 mmol) was added dropwise un- der stirring. Afterwards the solution was heated to 60 °C (using a reflux condenser) and stirred for 7 days. The solvent was evaporated and the residue was dissolved in chloroform and washed with water. The organic layer was dried with anhydrous sodium sulfate and the solvent evaporated to dryness to yield an orange, viscous oil. Yield: 7.2 g; ESI-MS: m/z: 262 + n · 182 [Br (C ₉ H ₁₀ S ₂ ) _n H] ⁺ (n=l-3), 384 + n · 182 [BrC ₃ H ₆ (C ₉ H ₁₀ S ₂ ) _n Br ] ⁺ (n=l-2), 324 [C ₆ H ₅ S ₂ (C ₉ H ₁₀ S ₂ ) _n H] ⁺ ; MALDI -TOF-MS : m/z: 286.98 + n · 182.02 [Br (C ₉ H ₁₀ S ₂ ) _n HNa] ⁺ (n=2-7), 406, 99 + n · 182.02

[BrC ₃ H ₆ (C ₉ H ₁₀ S ₂ ) _n BrNa] ⁺ (n=l-6), 347.00 + n · 182.02

[C ₆ H ₅ S ₂ (C ₉ HioS ₂ ) _n H] ⁺ (n=2-5) ; elemental analysis (%) found: C 51.39, H 4.85, S 28.49.

Preparation of the solvent impregnated resins (SIRs) and investigation procedure

Immobilisation of the extractants on solid supports

Silica gel 60 (0.04-0.063 mm) and silica gel (0.2-1 mm) from Merck as well as Amberlite XAD-2 from Supelco were used .

According to the data sheet provided by Sigma Aldrich (Supelco) the utilized Amberlite XAD-2 has the following characteristics:

Amberlite® XAD®-2 polymeric adsorbent is a hydrophobic crosslinked polystyrene copolymer resin, supplied as 20- 60 mesh size white insoluble beads.

The typical physical properties of Amberlite® XAD®-2 are Appearance: hard, spherical opaque beads

Solids: 55%

Porosity: 0.41mL pore/mL bead

Surface Area (Min.) : 300m2/g

Mean Pore Diameter: 90A

True Wet Density: 1.02g/mL

Skeletal Density: 1.08g/mL

Bulk Density: 640g/L

The silica gel used was purchased from Merck and charac- terized by its paricle size range, "silica gel 60" has a particle size range from 0.04-0.063 mm and "silica gel" has a particle size range from 0.2-1 mm. According to the product data sheet both products have a bulk density of 200-800 kg/m ³ . Before impregnating the silica gels were washed in the following sequence: 20% HNO ₃ , deionised ¾0, 5 M NaCl so ^¬ lution, deionised ¾0, acetone, diethyl ether. The XAD 2 was washed with: toluene, acetone, ethanol, deionised H ₂ O. Afterwards the solid supports were dried under vac- uum at 105 °C.

For the loading the "dry" impregnation method [18] was used . The extractants have been diluted in chloroform (about 25 mL per gram extractant) and contacted with the sup ^¬ porting material. The solvent was evaporated using a ro ^¬ tary evaporator giving the SIRs. These have been washed with deionised water and dried under high vacuum.

Solutions

All aqueous solutions were diluted with deionised water (Elga, Purelab ultra) . In order to prepare the 10 ^~4 M Pd(II) model solutions, a 1000 ppm palladium absorption standard solution in 5% (w/w) HC1 from Sigma-Aldrich was used. The solution of the automotive catalyst was ob ^¬ tained by leaching the monolith (1 kg) with heating with aqua regia (2 L) until the evolution of the gas was fin ^¬ ished. Afterwards this was diluted with the same volume of deionised water. This leach liquor had an oxidation potential of 1.09 V vs. SHE and the approximate concen ^¬ tration of free chloride ions was 2 M. The eluent was prepared with thiourea (purissimum, Germed) and 30% (w/w) hydrochloric acid (suprapur, Merck) . Procedure

All experiments were carried out at room temperature. For batch experiments, 15 mg ± 1 mg of the dry SIR was mixed with 3 mL of the respective feed (10 ^~4 M Pd) or eluent (0.5 M thiourea in 0.1 M HC1) using a Heidolph Multi Reax vibrating shaker (1700 rpm) . Afterwards the mixture was centrifuged and the aqueous sample separated. In order to determine the capacities the loading (and stripping) was done in several subsequent steps until palladium was not extracted (or re-extracted, respectively) any longer. For the column tests, 100 mg ± 1 mg of the dry SIR was filled into a bond elut reservoir column from Varian (20 ym frits, dimension: 5 mm x 55 mm, capacity: 1 mL) . The feed, the wash and the stripping liquids were pumped up- stream through the column via a Gilson Minipuls Evolution peristaltic pump with a constant flow rate and the eluate samples were collected using a Gilson Prep FC fraction collector. The determination of the metal concentration of the samples was done with a Perkim Elmer Optima 7300 DV ICP OES (with cyclonic spray chamber and Mira Mist nebuliser) , which was coupled to the oneFAST sample introduction system from ESI. Correlating the Pd(II) content in the aqueous phases before [Pd]o and after the ex ^¬ traction [Pd]* gave the extraction yield E _Pd as follows: rpdi ₀ - rpdi*

E _Pd = - -° - - -100%

L"uj0

In the column tests the capillary and the column material were washed with 0.5 L of deionised water after each elu- tion step. While the flow rate of the column extraction experiments varied, the elution and wash was generally done at a flow rate of 1 mL/min.

One problem of the present invention was to provide com ^¬ pounds that are suitable as complex forming agents for the extraction of Pd(II) at different pH values from a wide range of secondary raw materials.

The problem of the present invention is solved by provid ^¬ ing novel monomeric and oligomeric unsaturated vicinal dithioethers according to general formula I .

The compounds of the present invention proved to be use ^¬ ful in the selective separation of Pd(II) in the solvent extraction and solid phase extractions using SIRs. In the present invention examples are disclosed for extraction procedures wherein the compounds of the invention are utilized.

It was exemplarily shown that the disclosed novel dithio- ethers can be used successfully in different environ ^¬ ments .

The disclosed embodiments are only exemplary given for media with different pH ranges. With simple tests a per- son skilled in the art can easily find out which of the disclosed compounds of the invention can be utilized in different application and media that differ from the in ^¬ vestigated reaction media.

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