SOLVENT EXTRACTION OF PALLADIUM FROM CHLORIDE SOLUTIONS BY ALKYLAMMONIUM DI(2-ETHYLHEXYL)DITHIOPHOSPHATES

ABSTRACT

The extraction of palladium (II) from chloride solutions (over a wide region of aqueous acidity) by di(2-ethylhexyl)dithiophosphates of tetraoctylammonium, tri-n-octylammonium and di-n-octylammonium in toluene at the constant chloride concentration has been studied. A synergistic effect was shown to be observed in these systems and it is explained by the formation of unusual complexes with mixed ligands. It has been established the palladium complexes, such as (R₃NH)[PdCl₂A], (R₃NH)[PdCl₂A] and (R₂NH₂)[PdCl₂A], involving both alkylammonium cation and dialkyldithiophosphate anion are extracted under conditions of the loaded organic phase using distribution methods depending on a composition of aqueous and organic phase. At the excess of R₃NHA or R₂NH·HA, PdA₂ is extracted into the organic phase. Table 8 reports the results obtained and indicates the domains of existence of the various species of palladium (II) extracted into the organic phase in the binary ex-tractant systems in comparison with the initial systems     

Antiviral wirksame Koordinationsverbindungen des Palladiums mit Pyrid-2-yl-aminen

Antiviral Active Complexes of Palladium Chloride with 2-Pyridine Amines 2-Pyridine amines (L) form complexes with palladium chloride LPdCl₂OH₂ and L₂PdCl₂, respectively. The synthesis and analytical characterisation, ir-spectra, n.m.r.-spectra of these complexes with L = 2-pyridine amine, 4-methyl-2-pyridine amine and 6-methyl-2-pyridine amine and of π-allyl palladium chloride 4-methyl-2-pyridine amine are described.     

Fatty Imidazolines: A Novel Extractant for the Recovery of Palladium(II) from Hydrochloric Acid Solutions

The extraction of palladium(II) from hydrochloric acid solutions with a novel highly basic extractant, a mixture of homologous 1-[2-(alkanoylamino)ethyl]-2-alkyl-2-imidazolines (AAI) in toluene with 15% (v/v) of n-octanol was studied. Palladium(II) is rapidly and most effectively extracted with AAI hydrochloride at the low hydrochloric acid (chloride ions) concentration (up to 1 M) and can be completely separated from Fe(III), Cu(II), and Co(II). The palladium(II) extraction at the optimum acidity occurs via an anion-exchange mechanism with the formation of ionic associates (LH)₂PdCl₄ (K _ex = (1.5 ± 0.2) · 10⁴ at 0.5 M HCl) and is accompanied by the dimerization of palladium(II) in the organic phase with the formation of ionic associates (LH)₂Pd₂Cl₆ (K _dim = (3.9 ± 0.4) · 10^?4 at 0.5 M HCl). The anion-exchange extraction of palladium(II) at the acidity of 0.5 M HCl is temperature independent in the range 20–49°C. Complete stripping of palladium(II) can be performed using a 5% solution of thiourea in 0.1 M HCl.     

Palladium(II) complexes with polyphosphazene

An allylphenoxy-substituted polyphosphazene has been modified via inorganic chemical concepts. The transition metal salt is bis(acetonitrile)dichloropalladium(II). The coordination complexes have been characterized using acid-base solution chemistry, sol-gel phase transitions, thermomechanical property measurements and infrared spectroscopy. Solid complexes of polyphosphazene and PdCl₂ cannot be dissolved in the original solvent (i.e., tetrahydrofuran) used during sample preparation. These polymeric palladium complexes also cannot be disrupted by a stronger base, like triphenylphosphine. There is a monotonic increase in the glass transition temperature at higher concentrations of palladium chloride. T_g of the pure polymer increases by 21°C in the presence of 10 mol% palladium chloride. The increase in high-strain mechanical properties cannot be explained solely by a “filler effect.” At higher PdCl₂ concentrations, there is a direct correlation between the enhancement in T_g, higher mechanical fracture stress, and increased infrared absorbance @ 1092 cm^?1 because of the formation of a palladium-π-complex with allylic substituents in the phenoxy sidegroup. Palladium chloride relinquishes its acetonitrile ligands after dissolution in THF, and the vacant sites in the first-shell coordination sphere of the transition metal are occupied by these allylic substituents in the sidegroup. This produces interchain coordination crosslinks, which modify the thermomechanical properties of polyphosphazene/ PdCl₂ complexes.     

SOLVENT EXTRACTION OF PALLADIUM(II) WITH A SULFUR-CONTAINING CARBOXYLIC ACID

The mechanism of solvent extraction of palladium (II) from aqueous ammonium chloride solution with α-butylthiolauric acid( α-BTLA = S) in toluene was investigated in terms of extraction equilibrium and kinetics at 303 K. From the results of extraction equilibrium, it was found that α-BTLA behaves as a solvating extractant for palladium(II) and that the extracted species is a 1:2 metal:reagent complex, PdCl₂S₂ The extraction rate of palladium(II) was measured in a batch-type vigorously stirred cell. The effects of the concentrations of palladium(I I), hydrogen ion, chloride ion and extractant on the extraction rate were quantitatively interpreted by a reaction mechanism where the parallel reactions of α-BTLA with PdCl₃(H₂0)- and PdCl₄ ^2- are the rate-determining steps.     

EQUILIBRIUM OF PALLADIUM(II) EXTRACTION WITH 1-OCTYLTHEOBROMINE

ABSTRACT

1-Octyltheobromine was synthesized to study extraction equiliburium of palladium(II). To evaluate its efficiency as an extractant, the extraction of palladium(II) from acidic chloride media was studied at 303K using toluene. The extraction of palladium(II) from hydrochloric acid media by 1-octyltheobromine exhibited high selectivity for palladium(II) over the platinum group metals. The stoichiometrics of the extraction of palladium(II) with 1-octyltheobromine was elucidated by examining the effects of hydrochloric acid, chloride ion, hydrogen ion, extractant and metal ion concentrations on its extractability. Palladium(II) was found to be extracted as two molecules of 1-octyltheobromine reacted with PdCl₂ as follows: PdCl₂ +{2}¯RN ? ¯PdCl₂(RN)₂. The extraction equilibrium constant was K=2.72?×?10⁸(mol?dm^?3)^?2. The complex of 1-octyltheobromine with PdCl₂ was confirmed by mass spectrometric analysis. The stripping of palladium(II) was performed over 60% by a single batchwise treatment with an aqueous solution of thiourea or ammonia.     

MECHANISTIC STUDIES ON THE EXTRACTION OF PALLADIUM )II) WITH 2-HYDHOXY-5-NONYLBENZOPHENONE OXIME (LIX 65N)

ABSTRACT

Mechanistic studies including equilibrium and kinetic aspects of palladium extraction from acidic chloride media with 2-hydroxy-5-nonylbenzophenone oxime (LIX 65N) in chloroform solution are reported. The extracted species was established to be PdL, and the extraction equilibrium constant K Tor the reaction:

Pd²+2HL(o)2PdL²(o)+2H+ was found to be 10 ^16.30The homogeneous chemical reaction PdCl₃+HLPdCl₂-L^minusH+ Cl^minus was established as The rate-determining step of the overall.reaction having a rate constant of 3.74x10 M-1s.     

Preparation and characterization of the first coordination compounds of tetrazol-2-ylacetic acid

Tetrazol-2-ylacetic acid (2-TzaH) was found to react with CuCl₂, PdCl₂, and K₂PtCl₄ in water giving Cu(2-Tza)₂, PdCl₂(2-TzaH)₂·2H₂O and PtCl₂(2-TzaH)₂, correspondingly. Obtained complexes, being the first reported examples of coordination compounds derived from 2-TzaH, have been characterized by IR spectroscopy, thermal and X-ray diffraction methods. 2-TzaH was found to act as a monodentate ligand coordinated to the metal ion via N4 atom of heteroring in palladium complex and as tridentate bridging ligand coordinated via N4 atom and two oxygen atoms in copper complex. Cu(2-Tza)₂ presents 2D coordination polymer, whereas PdCl₂(2-TzaH)₂·2H₂O is molecular complex.     

SOLVENT EXTRACTION OF PALLADIUM(II) WITH A SCHIFF BASE AND SEPARATION OF PALLADIUM FROM Pd(II)-Pt(VI) MIXTURE

ABSTRACT

A new Schiff base extractant, N,N'-bis[l-phenyl-3-methyl-5-hydroxy-pyrazole-4-benzylidenyl]-l,3-propylene diamine (H₂A) was synthesized and characterized. The extraction mechanism of palladium(II) from HNO₃ or HClO₄ medium with H₂A in chloroform or toluene was investigated. The influences of the Schiff base concentration in the organic phase, the concentration of palladium, the pH and anions (Cl^?, S0₄ ^?, NO₃ ^?, ClO₄ ^?) in the aqueous phase and the temperature on the distribution ratio for palladium (II) have been examined. The extracted complex has been confirmed by chemical analysis, thermoanalyses and IR spectroscopy. It was found that palladium is extracted according to the following extraction reaction:

The extraction equilibrium constants of palladium(II) were 8·4 and 21·3 in chloroform and toluene diluents, respectively. The values for the enthalpy and standard free energy of extraction were also obtained. The separation of Pd(II) from the mixed solution of Pd(II)-Pt(IV) was achieved by adjusting the pH.     

A new route to preparation of palladium catalysts for VOC combustion

Methyltheophylline is known to be effective and highly selective extractant for Pd in the solvent extraction process. The high selectivity for Pd extraction might be due to the formation of chelate complex of Pd and methyltheophylline. The chelate complexes made insoluble precipitate in organic solvent when it became a certain condition. Partially-oxidized Pd nanoparticles below 100 nm were obtained by calcination of the precipitate. Pd/γ-Al₂O₃ and Pd/cordierite honeycomb catalysts were prepared by conventional impregnation method using the organic solvent containing Pd extracted from aqueous solution, and their catalytic activities for toluene combustion were compared with that of the Pd catalysts prepared from PdCl₂ aqueous solution. Consequently, the Pd catalyst prepared by using Pd extracted organic solvent showed remarkably higher activity for toluene combustion than that prepared from PdCl₂ aqueous solution.     

Synthesis of Pd(II) coordination complexes of (S)-4-isobutyl-2-methyl-2-oxazoline and (S)-2-(2,2-dimethylpropyl)-4-isopropyl-2-oxazoline

(S)-4-Isobutyl-2-methyl-2-oxazoline (1) was obtained from ethyl acetimidate hydrochloride and l-leucinol in 81% yield. (S)-2-(2,2-Dimethylpropyl)-4-isopropyl-2-oxazoline (2) was synthesized from 3,3-dimethylbutyryl chloride and l-valinol in two steps in a total yield of 44%. Reactions of oxazolines 1 and 2 with Pd(OAc)₂ in AcOH or MeCN at different temperatures followed by treatment with LiCl resulted in the formation of the corresponding coordination complexes PdCl₂(1)₂ and PdCl₂(2)₂ with no traces of cyclopalladated complexes.     

Ligand transfer between hard and soft metal centres. Synthesis and X-ray characterisation of a new trinuclear Pd(II) dithiocarbamate Pd3(Et2NCS2)4Cl2

Reaction between PdCl₂(PhCN)₂ and Nb₂(μ-S₂)₂(Et₂NCS₂)₄ results in a transfer of the dithiocarbamate ligand from Nb(IV) to Pd(II) and allows isolation of the new trinuclear palladium complex Pd₃(Et₂NCS₂)₄Cl₂ for the first time. The crystal structure of the complex has been determined.     

The dissolution of palladium in various electrolytes

The electrochemical dissolution of palladium in a number of aqueous solutions containing ClO₄, Cl^?, I^?, has been investigated using current-potential and impedance-potential measurements. It is concluded that during active dissolution, from Cl^? containing solution, the reaction to form a soluble complex PdCl₂ is inhibited by a PdOH layer and passivated by PdO. Dissolution in I^? containing solutions proceeds by a different mechanism.     

The first carbamoyl–carboxylate complex of transition metals: Synthesis and structure of {(OC4H8NH)[OC4H8NC(O)]Pd}2(μ-CMe3CO2)2

Reactions of palladium(I) carbonyl carboxylate complexes [Pd(μ-CO)(μ-RCO₂)]_n with secondary amines on the example of morpholine were studied. It was found that intramolecular carbonylation of amine in coordination sphere of polynuclear palladium species proceeds and binuclear palladium carbamoyl complex {(OC₄H₈NH)[OC₄H₈NC(O)]Pd}₂(μ-RCO₂)₂ forms as a result. This is the first structurally characterized carbamoyl–carboxylate complex of transition metals. Also it was shown that morpholine itself and carboxylate-anions act as proton acceptors in the reaction of carbonylation of morpholine by coordinated CO.     

EXTRACTION AND CHARACTERIZATION OF PALLADIUM {4-(2-PYRIDYLAZ0) RES0RCIN0L} COMPLEXES

The extraction of palladium complexes with 4-(2-pyridyl-azo)resorcinol (PAR=H₂R) by tetraphenylphosphonium and tetra-phenylarsonium chlorides in chloroform was investigated. The optimum conditions for the extraction and spectrophotometric determination of palladium in the extract were determined and the extracted species studied. The anionic complex {PdRCl}^? was predominantly extracted over a wide pH range (between 3 and 10) forming ion associates with the cation of the extraction agent. The extracted complexes were studied spectrophoto-metrically in solution and by characterization of the ìsolated solid compounds.     

The Synthesis and Characterization of s-Triazine-Cored and [Fe(III)Salen]-Capped Polymer Complexes

2,4,6-Trichloro-1,3,5-triazine (cyanuric chloride, C₃N₃Cl₃, 1) was used as the starting material. 2-(4-Carboxyphenylamino)-4,6-dichloro-1,3,5-triazine (2) was obtained from the reaction of cyanuric chloride with 4-aminobenzoic acid in the presence of sodium bicarbonate in acetone. A mononuclear complex (4) was obtained by reacting 2 and [FeSalen]₂O (3). A series of polymeric compounds was obtained by reacting 4 with a series of diamines. The polymeric complexes were characterized by elemental analysis, AAS, FT-IR, ¹H NMR, TGA and magnetic susceptibility measurements. The complexes are low-spin, distorted octahedral Fe(III) species that are bridged by carboxylic acids. The [FeSalen]-containing compounds may have the electronic structure t_2g⁵e_g⁰. All the complexes have six coordination and are polymeric.     

Synthesis and structural study of tri- and dinuclear palladium complexes of 2,6-bis(diphenylphosphino)pyridine

The bridging ligand 2,6-bis(diphenylphosphino)pyridine, L, was used to synthesize two palladium complexes: Pd₃Cl₆(μ-L)₃ has a C₂ axis passing through an 18-membered macrocyclic ring, in which two cis- and one trans-coordinated palladium(II) atoms are alternately bridged by three L ligands; [Pd₂(μ-L)₂]²⁺ exhibits a rare coordination mode in which two metal–metal bonded palladium(I) atoms (Pd–Pd = 2.5525(7) Å) are each P, N-chelated by one ligand and connected to the bridging phosphorus atom of the other ligand.     

PALLADIUM WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE SOLVENT EXTRACTION OF PALLADIUM(II) WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE

Equilibrium distribution of palladium(II) was investigated in the solvent extraction with tri-octylmethylammonium chloride (QC1) in toluene from hydrochloric acid solutions at 303 K. The title extracting reagent extracted hydrochloric acid as the species of the types, QC1(HC1) (_n(n= 1,2), according to the similar extraction reactions as observed in the extraction of organic acids such as acetic acid and phenol with high-molecular-weight amines in the previous works. From the concentration dependencies of the reactant species on the distribution ratio and from the result of loading test, it was elucidated that palladium(II) is extracted as a mononuclear ion pair complex of the type, Q⁺;[PdCl]₃ (HCl)] in the very high concentration region of hydrochloric acid. The equilibrium constant of the extraction reaction was evaluated.     

Effect of Br− on the Adsorption Rate of Palladium(II) Ions onto Condensed-Tannin Gel in Chloride Media

Abstract

In chloride media, chloropalladium(II) species are adsorbed onto tannin gel particles through an inner-sphere redox reaction mechanism containing the intermediate step, formation of a ligand-substituted Pd(II)-tannin complex. In this Pd(II) adsorption process, it was observed that the adsorption rate can be increased by introducing Br^?, a softer ligand than Cl^?, into the aqueous chloride solution. The formation of mixed-ligand palladium(II) complexes accelerates the rate of ligand-substitution reactions with the hydroxyl groups of tannin gel by the trans effect. The adsorption condition can be optimized by controlling the [Br_tot]/[Cl_tot] ratio, in which the predominant Pd(II) species are bromo-chloro palladium(II) complexes, the favorable species for the trans effect.     

Studies on the hydrogenation of olefins using polymer-bound palladium (II) species

bis-Benzonitriledichloropalladium(II) [(PhCN)₂PdCl₂] has been supported on two copolymers containing carboxyl and pyridyl groups and has been employed as a catalyst for the hydrogenation of olefins under mild conditions. The coordination environment and the nature of the metal species on the polymer have been studied by IR, ESCA, X-ray and a chemical test based on KCN treatment. Based on experimental evidence it is proposed that the polymer-palladium complexes initially contain palladium atoms with chlorine atom bridges which are cleaved in the activation. The catalysts were found to be active towards the hydrogenation of olefins under ambient conditions (room temperature and 1 atmosphere total pressure). The kinetic and mechanistic aspects of the hydrogenation of styrene and acrylonitrile and recycling capacity data using one catalyst (Cat-I) are reported.