Mechanistic Studies of Isomerization Reactions of Tetragonal Planar Tertiary Phosphine Complexes of Palladium(II)

1973 ◽  
Vol 51 (10) ◽  
pp. 1634-1644 ◽  
Author(s):  
David G. Cooper ◽  
John Powell
Keyword(s):  
Variable Temperature ◽  
Kinetic Studies ◽  
Ionic Species ◽  
Tertiary Phosphine ◽  
First Order ◽  
Phosphine Complexes ◽  
Trans Isomerization ◽  
Halogen Exchange ◽  
Cis And Trans ◽  
Isomerization Processes

The complexes [PdCl2(Me2RP)2] (R = o-tolyl; α-napthyl) may be isolated in both cis and trans forms. In CHCl3 solution cis-trans isomerization processes for these complexes are slow and this is ascribed to steric hindrance by the bulky R groups. The cis-trans isomerization is catalyzed by a variety of added ligands L. These isomerization processes have been extensively studied for the complexes cis-and trans-[PdCl2(Me2o-tolylP)2] in CHCl3 solution. The results of variable temperature n.m.r. and u.v. kinetic studies are fully consistent with a consecutive displacement mechanism with an ionic species of the type [PdCl(Me2o-tolylP)2L]+Cl− as an intermediate. The kinetic characteristics are determined by the nature and relative stability of this ionic intermediate. For L = Me2o-tolylP the rate of isomerization is zero order in complex and second order in added phosphine concentration. (At 38° kcis→trans = 6.2 × 103 l mol−1 s−1, ktrans→cis = 6.3 × 103 l mol−1 s−1) For L = PPh3 the rate of isomerization is considerably slower and first order in both complex and added PPh3 concentrations (kcis→trans6.3 = × 10 l mol−1 s−1, ktrans→cis = 6.7 × 10 l mol−1 s−1). Isomerization is also effected in neat methanol and the rate is first order in complex concentration. N.m.r. studies of mixtures of trans-[PdI2(Me2o-tolylP)2] and cis-[PdCl2(Me2o-tolylP)2] in CHCl3 solution show halogen exchange to occur more rapidly than isomerization. However a cis-diiodo complex is not observed and instead isomerization to the trans-diiodo complex is observed to occur.

The Stereospecific Synthesis of Neutral and Cationic Tertiary Phosphine Complexes of Platinum(II)

1974 ◽  
Vol 52 (4) ◽  
pp. 692-695 ◽  
Author(s):  
Keith R. Dixon ◽  
Kenneth C. Moss ◽  
Martin A. R. Smith
Keyword(s):  
Synthetic Methods ◽  
Stereospecific Synthesis ◽  
Tertiary Phosphine ◽  
Phosphine Complexes ◽  
Square Planar ◽  
Cleavage Reactions ◽  
Cis And Trans

Stereospecific synthetic methods for the preparation of complexes of the type cis- and trans[PtClL(PEt3)2]+ and cis-[PtClX(PEt3)2] have been developed. Preparations of complexes where L = py, PPh3, PClPh2, or P(OPh)3 and X = SCN, NO2, NO3, N3, NCO, or Br are described and it is shown that bridge cleavage reactions in square planar platinum(II) complexes occur with retention of stereo chemistry.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

scholarly journals N.M.R. studies of ligand exchange on acetylacetonatotrimethylplatinum(IV)

1975 ◽  
Vol 28 (4) ◽  
pp. 759 ◽  
Author(s):  
NS Ham ◽  
JR Hall ◽  
GA Swile
Keyword(s):  
Activation Energy ◽  
Quantitative Analysis ◽  
Ligand Exchange ◽  
Variable Temperature ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Cdcl3 Solution ◽  
Made In

A quantitative analysis of the variable-temperature 1H N.M.R. spectra of acetylacetonatotrimethyl-platinum(IV) has been made. In CDCl3 solution the exchange of acetylacetonate ligands is a first-order reaction and proceeds predominantly by dissociation of the dimer into two separated five-coordinate activated complexes. The activation energy is 61.5 � 0.8 kJ mol-1.

scholarly journals Kinetics of K release from soils of Brazilian coffee regions: effect of organic acids

2008 ◽  
Vol 32 (2) ◽  
pp. 533-540 ◽  
Author(s):  
Vladimir Antônio Silva ◽  
Giuliano Marchi ◽  
Luiz Roberto Guimarães Guilherme ◽  
José Maria de Lima ◽  
Francisco Dias Nogueira ◽  
...  
Keyword(s):  
Release Kinetics ◽  
Kinetic Studies ◽  
Release Rates ◽  
First Order ◽  
Potassium Release ◽  
Minas Gerais State ◽  
Soil Clay ◽  
Extractant Solution ◽  
Kinetics Of ◽  
K Release

Kinetic studies on soil potassium release can contribute to a better understanding of K availability to plants. This study was conducted to evaluate K release rates from the whole soil, clay, silt, and sand fractions of B-horizon samples of a basalt-derived Oxisol and a sienite-derived Ultisol, both representative soils from coffee regions of Minas Gerais State, Brazil. Potassium was extracted from each fraction after eight different shaking time periods (0-665 h) with either 0.001 mol L-1 citrate or oxalate at a 1:10 solid:solution ratio. First-order, Elovich, zero-order, and parabolic diffusion equations were used to parameterize the time dependence of K release. For the Oxisol, the first-order equation fitted best to the experimental data of K release, with similar rates for all fractions and independent of the presence of citrate or oxalate in the extractant solution. For all studied Ultisol fractions, in which K release rates increased when extractions were performed with citrate solution, the Elovich model described K release kinetics most adequately. The highest potassium release rate of the Ultisol silt fraction was probably due to the transference of "non-exchangeable" K to the extractant solution, whereas in the Oxisol exchangeable potassium represented the main K source in all studied fractions.

scholarly journals Reuse of Newspaper As An Adsorbent For Cu (II) Removal By Citric Acid Modification

2018 ◽  
Vol 156 ◽  
pp. 02012 ◽  
Author(s):  
Mardiah ◽  
Rif’an Fathoni ◽  
Pratiwi Pudyaningtyas ◽  
Hamdania Gamu ◽  
Rinaldy
Keyword(s):  
Citric Acid ◽  
Adsorption Process ◽  
Kinetic Studies ◽  
Order Reaction ◽  
Acid Modification ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo Second Order ◽  
Heavy Metal Adsorbent ◽  
The Impact

High Consumption of paper, bring the impact of the waste paper itself. And the utilization of the paper is limited to recycled products and crafts, whereas paper such as newspaper still contains cellulose that can be potential to be used as a heavy metal adsorbent. In this study, newspaper was dissolved in sodium bicarbonate to reduce various impurities and then was reacted with citric acid (CA). The modified adsorbent was characterized by FTIR and was tested for adsorb Cu(II) in artificial solution. After adsorption process, the solution was filtered and analysed using Atomic Absorption Spectrophotometer (AAS). The adsorption experimental data was fitted to Langmuir, Freundlich, Tempkin, and Dubinin-Radushkevich for equilibrium model and was fitted to pseudo first order reaction and pseudo second order reaction for kinetic studies. The result showed that CA-modification newspaper able to remove heavy metals Cu(II) in solution.

scholarly journals Degradation of the pharmaceuticals lamivudine and zidovudine using advanced oxidation processes

2020 ◽  
Vol 42 ◽  
pp. e9
Author(s):  
Alex Leandro Andrade de Lucena ◽  
Daniella Carla Napoleão ◽  
Hélder Vinícius Carneiro da Silva ◽  
Rayany Magali da Rocha Santana ◽  
Beatriz Galdino Ribeiro ◽  
...  
Keyword(s):  
Lactuca Sativa ◽  
Advanced Oxidation Processes ◽  
Advanced Oxidation ◽  
Kinetic Studies ◽  
Degradation Process ◽  
Oxidation Processes ◽  
First Order ◽  
Input Variables ◽  
Pharmaceutical Degradation ◽  
Uv C

The existence of pharmaceuticals in nature is a growing environmental problem, turning necessary the use of efficient treatments for the degradation of these substances, as the advanced oxidation processes (AOPs). In this work the AOPs UV/H2O2 and photo-Fenton were applied to degrade the pharmaceuticals lamivudine and zidovudine in an aqueous solution using a bench reactor, composed of three UV-C lamps. It was verified that the UV/H2O2 process presented a degradation of 97.33 ± 0.14% for lamivudine and 93.90 ± 0.33% for zidovudine, after 180 min of treatment and for an initial concentratin of each pharmaceutical of  5 mg.L-1 and [H2O2] of 600 mg.L-1.  A methodology by artificial neural networks (ANNs) was used to model the photocatalytic process, with the MLP 7-23-2 ANN representing it well, and determining the relative importance (%) of each of the input variables for the pharmaceutical’s degradation process. Kinetic studies for the pharmaceutical degradation and the conversion of organic matter showed good adjustments to the pseudo first-order models with R2 raging from 0.9705 to 0.9980. Toxicity assays for the before treatment solution indicated that the seeds Lactuca sativa and Portulaca grandiflora showed growth inhibition whereas the post-treatment solution inhibited only the growth of Lactuca sativa.

Solution Studies of the Dynamic Stereochemistry of Palladium(II) Carboxylate Complexes

1975 ◽  
Vol 53 (17) ◽  
pp. 2558-2574 ◽  
Author(s):  
Thomas R. Jack ◽  
John Powell
Keyword(s):  
Ring Opening ◽  
Variable Temperature ◽  
Equilibrium Constants ◽  
Quantitative Measure ◽  
Intermediate Species ◽  
Tertiary Phosphine ◽  
Crystalline Complex ◽  
Carboxylate Complexes ◽  
Solution Studies ◽  
Dynamic Stereochemistry

A series of dimeric tertiary phosphine carboxylate complexes of palladium(II) of the general types [(PR3)Pd(O2CR)2]2 and [(PR3)Pd(O2CR)(O2CR)]2 have been synthesized and struc-turally characterized. The dynamic stereochemistry of the complexes where PR3 = Me2PhP has been investigated using variable temperature n.m.r. techniques. Exchange of the stereochemically nonequivalent methyl groups of the coordinated Me2PhP ligand occurs via a solvent assisted process involving ring opening of the "Pd2(OCO)2" bridged structure. For the trifluoroacetate complexes solution equilibria between monomer and dimer are readily apparent at low temperatures in the 19F n.m.r. The observed equilibrium constants are a function of the solvent and the size of the PR3 ligand. The reaction of [(PMe2Ph)Pd(O2CCF3)2]2 with excess AgO2CCF3 gives an unusual crystalline complex of stoichiometry Ag[(PMe2Ph)Pd(O2CCF3)3]. A quantitative measure of the ability of a coordinated carboxylate to stabilize intermediate species via chelation has been obtained from a variable temperature n.m.r. study of [(Π-2-methylallyl)Pd(O2CR)(Me2PhP)] (R=CH3, CH2Cl, CHCl2, CCl3, CF3, CMe3, CPh3, CH2Ph).

Snowpack Ion Accumulation and Loss in a Basin Draining to Lake Superior

1987 ◽  
Vol 44 (11) ◽  
pp. 1812-1819 ◽  
Author(s):  
Robert Stottlemyer
Keyword(s):  
Lake Superior ◽  
Ionic Species ◽  
Winter Precipitation ◽  
Stream Chemistry ◽  
Order Stream ◽  
Freezing Soil ◽  
First Order ◽  
Stream Discharge ◽  
Biological Uptake ◽  
Thaw Period

The objective of this study was to relate winter precipitation ionic inputs, snowpack retention, and change in first-order stream chemistry with spring snowpack melt. During winter 1982–83, measurement of precipitation inputs, snowpack concentration and loading, and streamwater concentration and discharge of Ca2+, K+, H+, NO3−, and SO42− from a 176-ha watershed reveals that only H+ might be lost from the snowpack before first thaw. Above-freezing soil temperature beneath the snowpack may be a factor in H+ loss. An initial 1-d thaw resulted in loss of over one third (6 eq∙ha−1) of the snowpack Ca2+. Over one half the snowpack load of K+, H+, NO3−, and SO42−, was lost in a subsequent midwinter freeze–thaw period. Snowpack loading of ionic species was reduced by 70–90% before peak spring melting and stream discharge. Ecosystem H+ retention and biological uptake of NO3− further mitigate ionic "pulses" in streamwater. Sulfate discharge exceeds bulk inputs, which suggests significant dry deposition input and little forest soil retention of this anion. The snowpack was relatively small, which limits wider application of these results to the region.

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