GRAFT COPOLYMERIZATION OF VINYL MONOMERS ONTO STARCH INITIATED BY TRANSITION METAL-THIOUREA REDOX SYSTEMS

In this paper, the capabilities of grafting acrylonitrile (AN) onto starch initiatedby Fe(III)-TU, V(V)-TU, Cr(VI)-TU, Mn(VII)-TU redox systems were compared in thepresence of sulfuric acid of different concentrations. It was shown that the grafting capabili-ty of Mn(VII)-TU is the highest in these initiating systems. Using Mn (VII-TU as initia-tor, the effects of various acids (HClO_4, H_2SO_4, HNO_3, HCl) on the graft copolymerizationof acrylonitrile onto starch were discussed, and the capabilities of graft copolymerizationof methyl methacrylate (MMA), acrylamide (AM), acrylic acid (AA) onto starch wereinvestigated. The experimental results show that the order of the influences of differentacids is HClO_4>H_2SO_4>HNO_3>HCl, and the order of grafting capabilities of differentmonomers grafted onto starch is MMA>AN>AM>AA. The structure and morphology ofgraft copolymers were studied with infrared spectroscopy and scanning electron microscopy.The size, shape and roughness of surface of the grafted starch granules are changed aftergrafting.     

三价锰离子引发烯类单体在聚乙烯醇上接枝聚合的研究

<正> 无论是淀粉;纤维素,还是聚乙烯醇(PVA)的接枝反应,Ce(Ⅳ)被认为是一个十分有效的引发剂,已有较详尽的研究。与Ce(Ⅳ)相类似,Mn(Ⅲ)也可以和一些高聚物组成氧化还原引发体系,由此产生自由基,引发烯类单体在高分子主干上进行接枝聚合。Ranby等人,以焦磷酸络合的三价锰离子引发烯类单体在纤维素和淀粉的接枝反应中,获得了高效的接枝产物。有用这种引发体系在淀粉上接枝丙烯腈获得吸水276     

Anodically generated manganese(III) sulphate for the oxidation of dipeptides in aqueous sulphuric acid medium: A kinetic study

The kinetic of oxidation of dipeptides (DP) namely valyl-glycine (Val-Gly), alanyl-glycine (Ala-Gly) and glycyl-glycine (Gly-Gly), by Mn(III) have been studied in the presence of sulphate ions in acid medium at 26°C. The reaction was followed spectrophotometrically at λ_max = 500 nm. A first-order dependence of the rate on both [Mn(III)]_o and [DP]_o was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. The effects of varying the dielectric constant of the medium and addition of anions such as sulphate, chloride and perchlorate were studied. The activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the rate-limiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these dimers, where increased hyphobicity results in increased rate of oxidation     

丙烯腈──苯乙烯/聚丙烯接枝共聚合

丙烯腈（AN）—苯乙烯（St）与聚丙烯（PP）非均相接枝共聚，得杨梅形树脂。研究了AN／St摩尔比对接枝聚合的影响，发现苯乙烯相对含量增大时，非接枝物产量增加，接枝率和接枝效率相应下降。从接枝物的C、H、N分析可计算出聚丙烯、丙烯腈和苯乙烯的组成比例。此外，用二乙烯基苯（DVB）作交联剂，制备了PP－g－（AN－co－St－co－DVB）接枝共聚物—交联型薄壳树脂，交联剂的存在使单体转化率和接枝效率高达100％。     

Graft Copolymerization of Methyl Methacrylate onto Nylon 6 Using Thallium(III) Ions as Initiator

Abstract

Graft copolymerization of methyl methacrylate onto nylon 6 was investigated in aqueous perchloric acid medium using thallium(III) ions as initiator. The rate of grafting was evaluated by varying the concentrations of monomer, initiator, acid, and temperature. The rate of grafting was found to increase with an increase of both monomer and initiator concentrations. The graft yield was found to increase with an increase in the acid concentration up to 0.49 mL^?1, and beyond this concentration of perchloric acid the graft yield was found to decrease. It also increased with an increase of temperature. From the Arrhenius plot the overall activation energy was found to be 3.9 kcal/mol. The effects of inhibitors, various solvents, inorganic salts, and swelling agents on graft yield were studied. A suitable kinetic scheme has been proposed and a rate equation has been derived.     

Manganese(III) oxidation of L‐serine in aqueous sulfuric acid medium: Kinetics and mechanism

Kinetics and mechanism of oxidation of L‐serine by manganese(III) ions have been studied in aqueous sulfuric acid medium at 323 K. Manganese(III) sulfate was prepared by an electrolytic oxidation of manganous sulfate in aqueous sulfuric acid. The dependencies of the reaction rate are: an unusual one and a half‐order on [Mn(III)], first‐order on [ser], an inverse first‐order on [H⁺], and an inverse fractional‐order on [Mn(II)]. Effects of complexing agents and varying solvent composition were studied. Solvent isotope studies in D₂O medium were made. The dependence of the reaction rate on temperature was studied and activation parameters were computed from Arrhenius‐Eyring plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 525–530, 1999     

Investigations on the conditional kinetic and thermodynamic stability of aquatic humic substance-metal complexes by means of EDTA exchange, ultrafiltration and atomic spectrometry

The conditional metal availability and the kinetic stability of humic substance-metal species in humic-rich waters (e.g. bog water) was characterized by means of EDTA exchange. For this purpose a combined procedure consisting of time-controlled ligand exchange by EDTA, species differentiation by a fast single-stage tangential-flow ultrafiltration (TF-UF) technique (cut-off 1 kDa) and sensitive atomic spectrometry methods (e.g. AAS, ICP-OES, TXRF) was developed. The kinetics and the yield of the EDTA exchange served as operational parameters for assessing the kinetic stability and EDTA availability of HS-metal species, respectively. Considerable fractions of natural HS-metal species studied were shown to be EDTA-inert (e.g. 31% of the total Fe, 44% of the total Al) even after long reaction times (48 h), in contrast to artificial ones formed in solutions of isolated HS. Moreover, the conditional thermodynamic stability of HS-metal complexes formed by successive loading of an aquatic reference HS (HO14) with a number of heavy metal ions (e.g. Cr(III), Cu(II), Fe(III), Mn(II), Zn(II)) was also evaluated discriminating the free metal concentrations by means of TF-UF. In addition, from the loading isotherms obtained conditional complexation capacities could be derived for the studied HS exhibiting the order Fe(III)>Cu(II)>Cr(III)>Co(II)>Mn(II).     

Measured rates of fluoride/metal association correlate with rates of superoxide/metal reactions for Fe(III)EDTA(H2O)- and related complexes

The effects of 10 paramagnetic metal complexes (Fe(III)EDTA(H2O)-, Fe(III)EDTA(OH)2-, Fe(III)PDTA-, Fe(III)DTPA2-, Fe(III)2O(TTHA)2-, Fe(III)(CN)6(3-), Mn(II)EDTA(H2O)2-, Mn(II)PDTA2-, Mn(II)beta-EDDADP2-, and Mn(II)PO4(-)) on F- ion 19F NMR transverse relaxation rates (R2 = 1/T2) were studied in aqueous solutions as a function of temperature. Consistent with efficient relaxation requiring formation of a metal/F- bond, only the substitution inert complexes Fe(III)(CN)6(3-) and Fe(III)EDTA(OH)2- had no measured effect on T2 relaxation of the F- 19F resonance. For the remaining eight complexes, kinetic parameters (apparent second-order rate constants and activation enthalpies) for metal/F- association were determined from the dependence of the observed relaxation enhancements on complex concentration and temperature. Apparent metal/F- association rate constants for these complexes (k(app,F-)) spanned 5 orders of magnitude. In addition, we measured the rates at which O2*- reacts with Fe(III)PDTA-, Mn(II)EDTA(H2O)2-, Mn(II)PDTA2-, and Mn(II)beta-EDDADP2- by pulse radiolysis. Although no intermediate is observed during the reduction of Fe(III)PDTA- by O2*-, each of the Mn(II) complexes reacts with formation of a transient intermediate presumed to form via ligand exchange. These reactivity patterns are consistent with literature precedents for similar complexes. With these data, both k(app,O2-) and k(app,F-) are available for each of the eight reactive complexes. A plot of log(k(app,O2-)) versus log(k(app,F-)) for these eight showed a linear correlation with a slope approximately 1. This correlation suggests that rapid metal/O2*- reactions of these complexes occur via an inner-sphere mechanism whereas formation of an intermediate coordination complex limits the overall rate. This hypothesis is also supported by the very low rates at which the substitution inert complexes (Fe(III)(CN)6(3-) and Fe(III)EDTA(OH)2-) are reduced by O2*-. These results suggest that F- 19F NMR relaxation can be used to predict the reactivities of other Fe(III) complexes toward reduction by O2*-, a key step in the biological production of reactive oxygen species.     

The extraction of various metals as their anionic complexes with edta by solutions of aliquat-336 chloride in 1.2-dichloroethane

The extraction of anionic complexes of EDTA with Ca. Mg, V(IV), V(V), Cr(III), Mn(II), Mn(III), Fe(III), Co(II), Co(III), Ni, Cu(II), Zn, Cd, Hg(II), Pd(II), Pb and Bi by solutions of Aliquat-336 chloride in 1,2-dichloroethane has been studied as a function of the pH of the aqueous phase. The order and extent of the extractability varies greatly with the pH and provides a number of new possibilities for separation procedures. Thus iron(III) can be separated from many other metals in strongly alkaline solution while the extraction of V(V), V(IV), Hg(II) and Pd(II) exceeds 99% over wide pH ranges. The complex of Mn(III) with EDTA which is very unstable in aqueous solution can be preserved for up to 5 h when extracted by Aliquat-336.One of us (R. H. A1-J.) wishes to thank the Ministry of Oil of the Republic of Iraq for financial support.     

Reductive nitrosylation and proton-assisted bridge splitting of a (mu-oxo)dimanganese(III) complex derived from a polypyridine ligand with one carboxamide group

Aerobic oxidation of the Mn(II) complex [Mn(Papy3)(H2O)](ClO4) (1, PaPy3- is the anion of the designed ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) in acetonitrile affords the (mu-oxo)dimanganese(III) complex [(Mn(PaPy3))2(mu-O)](ClO4)2 (3) in high yield. The unsupported single oxo bridge between the two high-spin Mn(III) centers in 3 is readily cleaved upon addition of proton sources such as phenol, acetic acid, and benzoic acid, and complexes of the type [Mn(PaPy3)(L)](ClO4) (5, L = PhO-; 6, L = AcO-; 7, L = BzO-) are formed. The basicity of the bridge is evident by the fact that simple addition of methanol to a solution of 3 in acetonitrile affords the methoxide complex [Mn(PaPy3)(OMe)](ClO4) (4). The structures of 3-5 and 7 have been determined. Passage of NO through a solution of 3 in acetonitrile produces the [Mn-NO]6 nitrosyl [Mn(PaPy3)(NO)](ClO4) (2) via reductive nitrosylation. Complexes 4-7 also afford the [Mn-NO]6 nitrosyl 2 upon reaction with NO. In the latter case, the anionic O-based ligands (such as MeO- and PhO-) act as built-in bases and promote reductive nitrosylation of the Mn(III) complexes.     

Synthesis, crystal structures and catalytic abilities of new macrocyclic bis-pyridineamido Mn and Fe complexes

A new macrocyclic ligand H₂L (H₂L = 1,2-[bis(6′-pyridine-2′-carboxamido)-ethane]benzene) has been designed and synthesized by condensation of pyridine-carboxylic acid and diamine. Its Mn(III) and Fe(III) complexes, [Mn(L)Cl (DMF)] and [Fe(L)Cl], were prepared and respectively characterized by IR, UV-Vis, ESI-Mass, elemental analysis and X-ray single crystal diffraction. The catalytic abilities of them were examined, and up to 95% yield was achieved in epoxidation of styrene. The preliminary investigation of catalytic mechanism by manganese complex was carried out, suggesting the involvement of Mn(V) oxo species during catalysis.     

Oxidation of 3‐(3,4‐dihydroxy phenyl)‐l‐alanine (levodopa) and 3‐(3,4‐dihydroxy phenyl)‐2‐methyl‐l‐alanine (methyl dopa) by manganese(III) in pyrophosphate media: Kinetic and mechanistic study

Manganese(III) (Mn(III)) has been stabilized in weakly acidic solution by means of pyrophosphate and the nature of the complex was elucidated spectrophotometrically. Stoichiometry of Mn(III)‐oxidation of levodopa and methyl dopa in pyrophosphate medium was established in the pH range 2.5–4.0 by iodometric and spectrophotometric methods. The reaction shows a distinct variation in kinetic order with respect to [Mn(III)], a first‐order dependence in the pH range 1.9–2.6, decreasing to fractional order above pH 3. Other common features include first‐order dependence on [dopa], positive fractional order dependence on [H⁺], and inverse first‐order dependence on [Mn(III)] in the pH range studied. The effects of varying ionic strength and solvent composition were studied. Added ions such as SO₄^2? and ClO₄^? alter the reaction rate, probably due to the change in the formal redox potential of Mn(III)–Mn(II) couple because of the changes in coordination environment of the oxidizing species. Evidence for the transient existence of the free radical intermediate is given. Cyclic voltametric sensing of levodopa and methyl dopa has ruled out the formation of dopaquinones as oxidation products in the pH range studied. Activation parameters have been evaluated using the Arrhenius and Erying plots. Mechanisms consistent with the kinetic data have been proposed and discussed. These studies are expected to throw some light on dopa metabolism. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 449–457, 2001     

Effect of Toluene on the Kinetics of Ce(IV)-Ion-Initiated Grafting of Methyl Methacrylate onto Chemically Modified Jute Fibers

A study of the graft copolymerization of methyl methacrylate onto jute fiber using Ce(IV) and toluene has been carried out. The effects of concentration of monomer, Ce(IV), and toluene on graft yield have been studied. The effects of time, temperature, acid, amount of jute fiber, and some inorganic salts and organic solvents on graft yield have also been investigated. The investigation includes characterization of the grafted fiber by infrared and thermo-gravimetric studies. Grafting improves the thermal stability of jute fibers. More than 200% graft yield was achieved in the present investigation.     

甘蔗髓与丙烯腈的接枝共聚

本文研究了以Fe~(2+)—H_2O_2为引发剂引发甘蔗髓与丙烯腈的接枝共聚反应。研究了亚铁含量,H_2O_2浓度,单体量,反应液比、温度和时间对接枝反应的影响;探讨了接枝共聚物碱水解条件,如碱浓度和用量、水解温度和时间、接枝增量等因素对水解产物吸水性能的影响。结果表明,在一定的条件下可获得较高接枝增量的接枝共聚物,降低反应液比或增加单体量均可明显提高接枝增量,接枝增量对水解产物吸水性能的影响不大。     

二过碘酸合铜(Ⅲ)钾引发丙烯腈在聚丙烯酰胺上接枝共聚合反应的研究

本文以二过碘酸合铜(Ⅲ)钾为氧化剂,聚丙烯酰胺(PAAM)自身为还原剂组成的氧化还原引发体系,在PAAM上引发丙烯腈接枝共聚合反应,获得了高接枝效率和高接枝百分比的产物,由红外光谱、扫描电镜及X射线衍射分析对接枝反应进行了表征,测定了各种条件对接枝参数的影响,并对引发机理进行了探讨。     

Oxidation of L-aspartic acid and L-glutamic acid by manganese(III) ions in aqueous sulphuric acid,acetic acid,and pyrophosphate media: A kinetic study

Kinetics of oxidation of L-aspartic acid and L-glutamic acid by manganese(III) ions have been studied in aqueous sulphuric acid, acetic acid, and pyrophosphate media. Manganese(III) solutions were prepared by known electrolytic/chemical methods in the three media. The nature of the oxidizing species present in manganese(III) solutions was determined by spectrophotometric and redox potential measurements. The reaction shows a variable order in [manganese(III)]_o: the order changes from two to one as the reactive oxidizing species changes from an aquo ionic form to a complex form. There is a first-order dependence of the rate on [amino acid]_o in all the three media while the other common features include an inverse dependence each on [H⁺] and on [manganese(II)]. Effects of varying ionic strength and solvent composition were studied. Added anions such as pyrophosphate, fluoride, or chloride alter the reaction rate and mechanism by changing the formal redox potential of Mn(III)-Mn(II) couple. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the kinetic data have been proposed and discussed. © 1995 John Wiley & Sons, Inc.     

A novel polyurethane macroinitiator for free radical polymerization

Polyurethane macroinitiator (PUMI) has been prepared from toluene diisocyanate and benzopinacol and successfully used to polymerize acrylonitrile (AN). The effects of PUMI and AN concentrations and polymerization time on the yield, number average molecular weight and intrinsic viscosity of the resulting Polyacrylonitrile have been studied.     

Complexation and Thermal Studies of Uric Acid with Some Divalent and Trivalent Metal Ions of Biological Interest in the Solid State

Nine new [metal uric acid] complexes [M(Ua) n ]°·XH 2 O have been synthesized. These complexes have been characterized by elemental analysis, X-ray diffraction (XRD), magnetic susceptibility ( w eff. ), FTIR spectra, thermal analysis (TG & DTA), and electronic spectra (UV/visible). Uric acid (HUa) coordinates as a bidentate ligand to Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Al(III), Cr(III) and Fe(III) through the protonated N-7 within the imidazole ring and O-6 within the pyrimidine ring. Uric acid forms neutral metal urate complexes with all the above metal ions. The quantitative compositions were determined as [M(Ua) 2 ·(H 2 O) 2 ]°·XH 2 O where M(II)=Mn, Fe, Co, Ni, Cu, Zn and X=2, 4, 2, 4, 2, 2, respectively. The M(II) complexes exhibit an isostructural octahedral coordination with N-7, O-6 of two uric acid ligand molecules, and O of two water molecules. Compositions were also determined as [M(Ua) 3 ]°·YH 2 O where M(III)=Al, Cr, Fe and Y=6, 3, 3 respectively. All the M(III) complexes form an isostructural octahedral coordination with N-7 and O-6 of three uric acid ligand molecules. Iron(III) complexes prepared with N 1 , N 3 and N 9 -methyl uric acid yielded brown complexes with a metal ligand ratio of 1 3, while N 7 -methyl uric acid did not yield a complex due to blockage of N-7 with a methyl group.     

Biologically active thiosemicarbazone Fe chelators and their reactions with ferrioxamine B and ferric EDTA; a kinetic study

The Fe(III) abstraction from Fe(III)/DFO and Fe(III)/EDTA complex systems by thiosemicarbazone ligands derived from 2-acetylpyridine has been studied from a kinetico-mechanistic perspective at relevant pH conditions and at varying temperatures and buffer solutions. The reactions have been found to be extremely dependent on the dominant E/Z isomeric form of the TSC ligands present in the reaction medium. Consequently the isomerisation processes occurring on the free ligands have also been monitored under equivalent conditions. The isomerisation process is found to be acid dependent, despite the absence of protonation under the conditions used, and presumably proceeds via an azo-type tautomer of the ligand. In all cases the existence of outer-sphere interaction processes has been established, both promoting the reactions and producing dead-end complexes. The better oriented forms of the ligands (EZ thiolate) have been found to react faster with the [Fe(HDFO)](+) complex, although for mono-N(4) substituted thiosemicarbazones the process is retarded by the formation of a dead-end outer-sphere complex. A comparison with the abstraction of Fe(III) from [Fe(EDTA)(H(2)O)](-) has also been conducted with significant differences in the kinetic features that implicate keystone outer-sphere interactions which dominate reactivity, even with isomeric forms that are not the best suited for direct complexation.     

Thermometric studies on the Fe(III)-EDTA chelate

A DeltaH of -11.5 +/- 0.5 kJ/mole has been determined for the formation of the Fe(III)-EDTA chelate at 25.0 degrees and mu = 0.1(= [HClO(4)] + [NaClO(4)]) by a direct thermometric titration procedure. The entropy change, DeltaS, has been calculated to be 440 J.mole(-1) .deg(-1) by combining the result of the heat measurements with the free energy change obtained from the stability constant previously determined. A relationship between the DeltaS values and the standard partial molal entropies of the tervalent metal ions is discussed. In addition, conditions for the thermometric titration of Fe(III) with NA(4)EDTA at room temperature have been investigated. Iron(III) can be determined in the presence of fairly large amounts of phosphate, Cr(III), Mn(II) and Al(III).