Ruthenium(III) catalysed oxidation of l-leucine by a new oxidant,diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of Ru(III) catalysed oxidation of l-leucine by diperiodatoargentate(III) (DPA) in alkaline medium at 298 K and a constant ionic strength of 0.60 mol dm⁻³ was studied spectrophotometrically. The oxidation products are pentanoic acid and Ag(I). The stoichiometry is [l-leucine]:[DPA] = 1:2. The reaction is of first order in Ru(III) and [DPA] and has less than unit order in both [l-leu] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Ru(III)–l-leucine complex, which further reacts with one molecule of monoperiodatoargentate(III) (MPA) in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectral studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (K_c) was also calculated for the Ru(III) catalysed reaction at different temperatures. From the plots of log K_c versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The active species of catalyst and oxidant have been identified.     

Mechanistic and Spectral Studies of the Ruthenium(III) Catalysed Oxidation of Sulfanilic Acid by Alkaline Hexacyanoferrate(III)

Summary. The kinetics of ruthenium(III) catalysed oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium at a constant ionic strength of 2.5mol·dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 2:8 stoichiometry (SNA:HCF(III)). The reaction showed first order kinetics in [hexacyanoferrate(III)] and [ruthenium(III)] and apparent less than unit order in both sulfanilic acid and alkali concentrations. The reaction rate increases with increasing ionic strength but the relative permittivity (_T) of the medium has a negligible effect on the rate of the reaction. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between sulfanilic acid and hydroxylated species of ruthenium(III) has been proposed. The active species of HCF(III) and ruthenium(III) are understood as [Fe(CN)₆^3–] and [Ru(H₂O)₅OH]²⁺, respectively. The main products were identified by IR, NMR, and mass spectral studies. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

Ruthenium(III) catalyzed oxidation of hexacyanoferrate(II) by periodate in aqueous alkaline medium

Ruthenium(III) catalyzed oxidation of hexacyanoferrate(II) by periodate in alkaline medium is assumed to occurvia substrate-catalyst complex formation followed by the interaction of oxidant and complex in the rate-limiting stage and yield the products with regeneration of catalyst in the subsequent fast step. The reaction exhibits fractional order in hexacyanoferrate(II) and first-order unity each in oxidant and catalyst. The reaction constants involved in the mechanism are derived.     

Ruthenium (III) catalysed and uncatalysed oxidation of torsemide by hexacyanoferrate (III) in aqueous alkaline medium: A kinetic comparative approach

The kinetics approach of oxidation of torsemide (TOR) by hexacyanoferrate (III) [HCF (III)] has been identified spectrophotometrically at 420 ​nm in the alkaline medium in the presence and absence of catalyst ruthenium (III) at 25 ​°C, by keeping ionic strength (1 ​× ​10⁻² ​mol ​dm⁻³) constant. The reaction exhibits at the stoichiometry ratio 1:2 of TOR and HCF (III), for uncatalysed and catalysed reactions. In the absence and presence of the catalyst, the order of the reactions obtained for TOR and HCF (III) was unity. However, the rate of the reactions enhanced by the increase in the concentration of catalyst, as well as the rate increases with an increase in alkaline concentration. The activation parameters for the reaction at the slow step were identified, and the effect of temperature on the rate of the reaction was analysed. A suitable mechanism has been demonstrated by considering the obtained results. The derived rate laws are reliable with analysed experimental kinetics.     

Synthesis of cationic gold(III) complexes using iodine(III)

Abstract

We report the synthesis and characterization of cationic Au(III) complexes supported by nitrogen-based ligands. The syntheses are achieved by reacting Au(I) complexes [Au(N-Me-imidazole)₂]⁺ and [Au(pyridine)(NHC)]⁺ with iodine(III) reagents PhI(OTf)(OAc) and [PhI(pyridine)₂]²⁺ yielding a series of cationic gold(III) complexes. In contrast, reactions of phosphine ligated gold(I) complexes with iodine(III) reagents results in the oxidation of the phosphine ligand.     

Mechanistic aspects of uncatalyzed and ruthenium(III) catalyzed oxidation of dl-ornithine by copper(III) periodate complex in aqueous alkaline medium: A comparative kinetic study

The oxidation of dl-ornithine monohydrochloride (OMH) by diperiodatocuprate(III) (DPC) has been investigated both in the absence and presence of ruthenium(III) catalyst in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm⁻³ spectrophotometrically. The stiochiometry was same in both the cases, i.e., [OMH]/[DPC] = 1:4. In both the catalyzed and uncatalyzed reactions, the order of the reaction with respect to [DPC] was unity while the order with respect to [OMH] was < 1 over the concentration range studied. The rate increased with an increase in [OH⁻] and decreased with an increase in [IO₄⁻] in both cases. The order with respect to [Ru(III)] was unity. The reaction rates revealed that Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. Suitable mechanisms were proposed. The reaction constants involved in the different steps of the reaction mechanisms were calculated for both cases. The catalytic constant (K_C) was also calculated for catalyzed reaction at different temperatures. The activation parameters with respect to slow step of the mechanism and also the thermodynamic quantities were determined. Kinetic experiments suggest that [Cu(H₂IO₆)(H₂O)₂] is the reactive copper(III) species and [Ru(H₂O)₅OH]²⁺ is the reactive Ru(III) species.     

Biphasic oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) by N-bromosuccinimide and the formation of chromium(IV) and chromium(V)

The kinetics of oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) complex, [Cr^III(phen)(H₂O)₂Cl₂]⁺, by N-bromosuccinimide (NBS) is biphasic. The first faster step involves the oxidation of Cr(III) to Cr(IV). The second slower step is due to the oxidation of Cr(IV) to Cr(V). The reaction product is isolated and characterized by electron spin resonance (ESR), IR, and elemental analysis. The chromium(V) product is consistent with the formula [Cr^V(phen)Cl₂(O)]Br. The rate constants k_f and k_s, for the faster and the slower steps respectively, were obtained using an Origin 9.0 software program. Values of both k_f and k_s, varied linearly with [NBS] at constant reaction conditions. The effect of pH on the reaction rate is investigated over the pH (4.11–6.01) range at 25.0°C. The rate constants k_f and k_s increased with increasing pH. This is consistent with hydroxo forms of the chromium species being more reactive than the aqua forms. Chromium(III) complexes, more often than not, are inert. The oxidation of the Cr(III) complex to Cr(IV), most likely, proceeds by an outer sphere mechanism. Since chromium(IV) is labile the mechanism of its oxidation to chromium(V) is not certain.     

The Affinity of Gallium(III) and Indium(III) for Nitrogen Donor Ligands

Abstract

Dedicated to Professor Arthur Martell on the occasion of his seventy fifth birthday.

The complexes of In(III) and Ga(III) with a variety of nitrogen donor ligands were studied in aqueous solution by glass electrode potentiometry at 25°C in 0.1 M NaNO₃. The ligands were 2-aminomethylpyri-dine (AMPY), ethylenediamine (EN), N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (THPED), and N,N-bis(2-hydroxyethyl)glycine (BICIN). A variety of mixed ligand complexes of the MLOH type were detected with many of the above ligands as L. The logK₁ values obtained were with Ga(III) 8.40 (AMPY), 7.94 (THPED) 12.72 (EN), and In(III) 7.6 (AMPY), 8.20 (THPED), and 7.06 (BICIN). These formation constants are discussed in relation to previous predictions that In(III) and Ga(III) would have a substantial chemistry with nitrogen donor ligands. Of particular interest is the Ga(III) system with EN, where a very stable Ga(EN)³⁺ complex is formed, but no higher complexes except for hydrolyzed species such as Ga(EN)OH²⁺ and Ga(EN)(OH)₂ ⁺.     

Calcium Sulfite Solids Activated by Iron for Enhancing As(III) Oxidation in Water

Desulfurized gypsum (DG) as a soil modifier imparts it with bulk solid sulfite. The Fe(III)–sulfite process in the liquid phase has shown great potential for the rapid removal of As(III), but the performance and mechanism of this process using DG as a sulfite source in aqueous solution remains unclear. In this work, employing solid CaSO₃ as a source of SO₃²⁻, we have studied the effects of different conditions (e.g., pH, Fe dosage, sulfite dosage) on As(III) oxidation in the Fe(III)–CaSO₃ system. The results show that 72.1% of As(III) was removed from solution by centrifugal treatment for 60 min at near-neutral pH. Quenching experiments have indicated that oxidation efficiencies of As(III) are due at 67.5% to HO^•, 17.5% to SO₅^•− and 15% to SO₄^•−. This finding may have promising implications in developing a new cost-effective technology for the treatment of arsenic-containing water using DG.     

Ruthenium(III)-catalyzed oxidation of thallium(i) by 12-tungstocobaltate(III) in hydrochloric acid medium

The reaction between thallium(I) and [Co^IIIW₁₂O₄₀]^5- in the presence of ruthenium(III) as catalyst proceeds viainitial outer-sphere oxidation of the catalyst to ruthenium(VI). The ruthenium(IV) thus generated will oxidize thallium(I) to an unstable thallium(II) which by reacting with oxidant gives the final product, thallium(III). The formation of ruthenium(II) by direct two-electron reduction of the catalyst by thallium(I) is thermodynamically less favorable. The reaction rate is unaffected by the [ H⁺ ], whereas it is catalyzed by chloride ion . The formation of reactive chlorocomplex,TlCl, in a prior equilibrium is the reason for the chloride ion catalysis. Increasing the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the catalyst and oxidant. This revised version was published online in June 2006 with corrections to the Cover Date.     

Oxidative degradation and deamination of atenolol by diperiodatocuprate(III) in aqueous alkaline medium: A mechanistic study

The kinetics of oxidation of atenolol (ATN) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm⁻³ was studied spectrophotometrically. The reaction between DPC and ATN in alkaline medium exhibits 1:2 stoichiometry (ATN:DPC). The reaction is of first order in [DPC] and has less than unit order in both [ATN] and [alkali]. However, the order in [ATN] and [alkali] changes from first order to zero order as their concentration increase. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreases the rate. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate(III)–ATN complex, which decomposes slowly in a rate-determining step followed by other fast steps to give the products. The main oxidative products were identified by spot test, IR, NMR and LC–ESI-MS studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined.     

Complexation studies of Cm(III), Am(III), and Eu(III) with linear and cyclic carboxylates and polyaminocarboxylates

Solvent extraction and potentiometric titration methods have been used to measure the stability constants of Cm(III), Am(III), and Eu(III) with both linear and cyclic carboxylates and polyaminocarboxylates in an ionic strength of 0.1?mol?L^?1 (NaClO₄). Luminescence lifetime measurements of Cm(III) and Eu(III) were used to study the change in hydration upon complexation over a range of concentrations and pH values. Aromatic carboxylates, phthalate (1,2 benzene dicarboxylates, PHA), trimesate (1,3,5 benzene tricarboxylates, TSA), pyromellitate (1,2,4,5 tetracarboxylates, PMA), hemimellitate (1,2,3 benzene tricarboxylates, HMA), and trimellitate (1,2,4 benzene tricarboxylates, TMA) form only 1?:?1 complexes, while both 1?:?1 and 1?:?2 complexes were observed with PHA. Their complexation strength follows the order: PHA～TSA>TMA>PMA>HMA. Carboxylate ligands with adjacent carboxylate groups are bidentate and replace two water molecules upon complexation, while TSA displaces 1.5 water molecules of hydration upon complexation. Only 1?:?1 complexes were observed with the macrocyclic dicarboxylates 1,7-diaza-4,10,13-trioxacyclopentadecane-N,N′-diacetate (K21DA) and 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane-N,N′-diacetate (K22DA); both 1?:?1 and 1?:?2 complexes were observed with methyleneiminodiacetate (MIDA), hydroxyethyleneiminodiacetate (HIDA), benzene-1,2-bis oxyacetate (BDODA), and ethylenediaminediacetate (EDDA), while three complexes (1?:?1, 1?:?2, and 1?:?3) were observed with pyridine 2,6 dicarboxylates (DPA) and chelidamate (CA). The complexes of M-MIDA are tridentate, while that of M-HIDA is tetradentate in both 1?:?1 and 1?:?2 complexes. The M-BDODA and M-EDDA complexes are tetradentate in the 1?:?1 and bidentate in the 1?:?2 complexes. The complexes of M-K22DA are octadentate with one water molecule of hydration, while that of K21DA is heptadentate with two water molecules of hydration. Simple polyaminocarboxylate 1,2 diaminopropanetetraacetate (PDTA) and ethylenediamine N,N′-diacetic-N,N′-dipropionate (ENDADP) like ethylenediaminetetraacetate (EDTA) form only 1?:?1 complexes and their complexes are hexadentate. Polyaminocarboxylates with additional functional groups in the ligand backbone, e.g., ethylenebis(oxyethylenenitrilo) tetraacetate (EGTA), and 1,6 diaminohexanetetraacetate (HDTA) or with additional number of groups in the carboxylate arms diethylenetriamine pentaacetato-monoamide (DTPA-MA), diethylenetriamine pentaacetato-bis-methoxyethylamide (DTPA-BMEA), and diethylenetriamine pentaacetato-bis glucosaamide (DTPA-BGAM) are octadentate with one water molecule of hydration, except N-methyl MS-325 which is heptadentate with two water molecules of hydration and HDTA which is probably dimeric with three water molecules of hydration. Macrocyclic tetraaminocarboxylate, 1,4,7,10-tetraazacyclododecanetetraacetate (DOTA) forms only 1?:?1 complex which is octadentate with one water molecule of hydration. The functionalization of these carboxylates and polycarboxylates affect the complexation ability toward metal cations. The results, in conjunction with previous results on the Eu(III) complexes, provide insight into the relation between ligand steric requirement and the hydration state of the Cm(III) and Eu(III) complexes in solution. The data are discussed in terms of ionic radii of the metal cations, cavity size, basicity, and ligand steric effects upon complexation.     

Removal of As(III) and As(V) by natural and synthetic metal oxides

The removal properties of As(III) and As(V) by the several metal oxides having different mineral type and content of metals were investigated in batch and column reactors. The used metal oxides were Fe-oxide loaded sand (ILS), Mn-oxide loaded sand (MLS), activated alumina (AA), sericite (SC) and iron sand (IS). From the pH-edge adsorption experiments with AA and ILS, maximum As(III) adsorption was observed around neutral pH while As(V) adsorption was followed an anionic-type behavior. Among five metal oxides, AA showed the greatest removal capacity for both As(III) and As(V) through adsoption process but it has little oxidation capacity for As(III). Eventhough IS had much greater content of Fe-oxides than ILS, it showed a relatively lower removal capacity for both As(III) and As(V). This result suggests that adsorption of arsenic onto metal oxides is controlled by not only the contents of Fe-oxides but also mineral type of Fe-oxides. Column tests were performed at different combinations of metal oxides in a column reactor to find the best column system, which effectively treat both As(III) and As(V) at the same time. Among several combinations, the column reactors packed with MLS-AA and MLS-ILS showed a near complete oxidation of As(III) by MLS for a long time and the greatest adsorption of total arsenic compared to the column reactor packed with MLS-IS.     

SYNTHESIS AND CHARACTERIZATION OF THE FORMAL Ni(III) AND Cu(III) COORDINATION COMPLEXES OF THE NEW 1,2-DITHIOLENE, 1,4-BUTANEDIYLDITHIOETHYLENE-1,2-DITHIOLATE

Abstract

The new 1,2-dithiolene, 1,4-butanediyldithioethylene-1,2-dithiolate, has been isolated. In addition, new monoanionic bis-complexes with nickel and copper have been prepared and isolated. The formal Ni(III) complex crystallizes in the orthorombic space group, P_bca, with a = 9.762(9), b = 12.53(2), and c = 23.166(3) Å, with 4 molecules in the unit cell. The structure was refined to an R = 9.01% (R_w = 8.95%). The formal Cu(III) complex crystallizes in the monoclinic space group, C_2/c, with a = 25.567(6), b = 8.011(3), c = 14.504(3) Å, and β = 106.17(2)° with 4 molecules in the unit cell. The structure refined to R = 4.2% with R _w = 4.3%. Comparisons to similar 1,2-dithiolenes suggest this ligand produces only modest structural and electronic differences when compared to the 1,3-propanediyldithioethylene-1,2-dithiolate complexes. The oxidation (to a neutral complex) and reduction (to a dianion) for the Ni(III) and Cu(III) complexes show large differences from those of maleonitriledithiolate. Other physical data are presented as well.     

Kinetics and mechanism of the ruthernium(III) catalyzed oxidation of propane-1,3-diol by alkaline hexacyanoferrate(III)

The kinetics of oxidation of propane-1,3-diol by alkaline hexacyanoferrate (III) catalyzed by ruthenium trichloride has been studied spectrophotometrically. A reaction mechanism involving the formation of an intermediate complex between the substrate and the catalyst is proposed. In the rate-determining step this complex is attacked by hexacyanoferate(III) forming a free radical which is further oxidized.     

Complexation and the laser luminescence studies of Eu(III), Am(III), and Cm(III) with EDTA,CDTA, and PDTA and their ternary complexation with dicarboxylates

Spectroscopy has been used to determine the number of coordinated water molecules bound to Eu(III) and Cm(III) in a series of binary complexes of polyaminocarboxylate and their ternary complexes with dicarboxylates as well as with similar ligands with additional O-, N-, and S-donors. Complexes of Eu(III) and Cm(III) with polyaminocarboxylate alone contain ca. 2.5–3.0 waters of hydration. Increasing the steric requirement of a polyaminocarboxylate by increasing the number of groups in the ligand backbone does not appreciably change the hydration of these cations. The stability constants of the binary and ternary complexes of Cm(III), Am(III), and Eu(III) with these ligands were measured by solvent extraction in a solution of 0.1 M (NaClO₄). The size, basicity, specific M³⁺-second ligand interactions, and steric requirement of the ligands are the factors which affect the ternary complexation. Knowledge of the chemical species formed by actinide cations with organic ligands (carboxylates and aminocarboxylates), which are present in all nuclear waste, is important to understand the behavior of waste forms and the migration behavior of actinides in the environment.     

Chemistry of silver(III) and some of its compounds: A review

Chemistry of Ag(III), as of other transition elements with higher oxidation state(s), is important as its compounds are effectively used as oxidants, catalysts, fluorinating agents, etc. Some basic chemical properties of Ag(III) and up to date report of several Ag(III) compounds are discussed in this present review.     

Spectrophotometry Determination of Arsenic(III) and Antimony(III) by Means of Isonicotinoylhydrazones of 4-Dimethylaminobezaldehyde (4-Dbih) and 2-Hydroxynaphthaldehyde (2-Hnih)

Abstract

4-DBIH and 2-HNIH react with As(III) and Sb(III) respectively, in CH₃COOH medium to form colored complexes stable in presence of EDTA. As(III) and Sb(III) do not react with 2-HNIH and 4-DBIH respectively, and the Sb(III)-2-HNIH complex is extractable into isoamyl alcohol. These behaviours were used for the spectrophotometry determination of As (III) and Sb(III) in presence of several cations.     

Role of oxygen in the degradation of atrazine by UV/Fe(III) process

In this study, the role of oxygen in the regeneration of Fe(III) during the degradation of atrazine in UV/Fe(III) process was studied. The degradations of atrazine in UV/Fe(III) and UV-photolysis processes in the presence and absence of oxygen were compared. The results showed that the degradations of atrazine in these processes followed the pseudo-first-order kinetics well. The process exhibiting the highest rate constant (k) was UV/Fe(III)/air process, because k-value for UV/Fe(III)/air process was about 1.47, 2.23 and 2.56 times of those for UV/Fe(III)/N₂, UV/air and UV/N₂ processes, respectively. The degradation of atrazine was enhanced by oxygen in UV/Fe(III) process and the enhancement was more remarkable at higher initial concentrations of Fe(III). The investigation into the changes of Fe(III) concentrations demonstrated that the presence of oxygen led to the regeneration of Fe(III), which resulted in the enhancement of atrazine degradation. With air bubbling, the ferric ions were 25% more than those with N₂ bubbling. The experimental data showed the regeneration of Fe(III) required the excited organic molecules and oxygen and on the basis of these results, the regeneration mechanism of Fe(III) was proposed. It was also found that due to the oxidation of Fe(II), the degradation of atrazine in UV/Fe(II)/air process was effective at a low Fe(II) concentration of 7 mg/L, similar to that in UV/Fe(III)/air process. This study makes clear the role of oxygen in the regeneration of Fe(III), and thus it provides a guide to reduce the input of Fe(III) and is helpful to the application of UV/Fe(III) process in practice.     

Fe(III)-pyruvate and Fe(III)-citrate induced photodegradation of glyphosate in aqueous solutions

The photolysis of Fe(III)-pyruvate and Fe(III)-citrate complexes in water produces hydroxyl radicals in the presence of dissolved oxygen, and can promote the oxidation of organic compounds. The photodegradation of glyphosate with Fe(III)-pyruvate and Fe(III)-citrate complexes was investigated under irradiation at λ?≥?365?nm. The effect of initial concentration of glyphosate, the initial pH value, and the Fe(III)/carboxylate ratio were examined. Upon irradiation of glyphosate aqueous solution with the complexes in the acidic range of natural waters, the bioavailable orthophosphate could be released from degradation of glyphosate. The amount of orthophosphate increased with increasing Fe(III)/carboxylate ratio.