The document describes the preparation and characterization of new dinuclear half-titanocene complexes with ortho- and meta-xylene linkages for use as catalysts in styrene polymerization. Specifically, it details the synthesis of four dinuclear complexes containing either ortho- or meta-xylene bridges and either chloride or aryloxo ligands on the titanium centers. The catalysts were characterized and found to be effective for producing syndiotactic polystyrene when combined with methylaluminoxane. Testing revealed that activity increased with meta-xylene bridges and aryloxo ligands compared to ortho-xylene bridges and chloride ligands, respectively. The activity was also influenced by temperature, aluminum-to
Mechanistic Aspects of Oxidation of P-Bromoacetophen one by Hexacyanoferrate ...IJERA Editor
The kinetics of oxidation of p-bromoacetophenone by hexacyanoferrate (III) has been studied in alkaline
medium. The order of reaction with respect of both acetophenone and hexacynoferrate (III) has been found to be
unity. The rate of reaction increases with increase in the concentration of sodium hydroxide.On addition of
neutral KCl, reaction rate increases. The effects of solvent and temperature have been also studied. The product
p-bromophenyl glyoxal have been characterized by IR studies.
Reaction of aniline with ammonium persulphate and concentrated hydrochloric a...Maciej Przybyłek
In this paper, the reaction of aniline with ammonium persulphate and concentrated HCl was studied. As a result of our experimental studies, 2,4,6-trichlorophenylamine was identified as the main product. This shows that a high concentration of HCl does not favour oxidative polymerisation of phenylamine, even though the ammonium persulphate/HCl system is widely used in polyaniline synthesis. On the basis of the experimental data and density functional theory for reaction path modelling, we proposed a mechanism for oxidative chlorination of aniline. We assumed that this reaction proceeded in three cyclically repeated steps; protonation of aniline, formation of singlet ground state phenylnitrenium cation, and nucleophilic substitution. In order to confirm this mechanism, kinetic, thermochemical, and natural bond orbital population analyses were performed.
Synthesis and characterization of some Chromium(III) complexes of dibasic tri...IJERA Editor
Coordination complexes of Cr(III)with four tridentate Schiff base ligands viz. N-(2-hydroxy-1-naphthaldehyde)- -(4-nitrobenzoyl)hydrazone(HNNH = H2L 1 ), N-(2-hydroxy-4-methoxybenzaldehyde)- -(2-furoyl) hydrazone (HMFH = H2L 2 ), N-(2-hydroxyacetophenone)- -(2-theonyl) hydrazone (HATH = H2L 3 ) and N-(2- hydroxy-5-methylacetophenone)- -(3-toloyl) hydrazone (HMAT = H2L 4 ) have been synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductance, thermogravimetric analysis and spectral (IR, electronic, NMR) measurements. IR spectra indicates that the ligand behave as dibasic tridentate ligand in a chelate coordinating to Cr(III) ion through ketonic oxygen, azomethine nitrogen and by both enolic and phenolic protons (except in H2L 1 by naphtholic oxygen atom) via double deprotonation of ligands. The magnetic and spectral data indicate chelate in octahedral environment and analytical data suggest 1:1 stoichiometries for the complexes
Corrosion Inhibition of Mild Steel in HCl Medium by a Condensation Productijtsrd
A condensation product CP was successfully synthesized from reaction of dimethyl amino benzaldehyde and aniline giving yields of 80 . The compound was characterized by Fourier Transform Infrared FTIR Spectroscopy. The corrosion inhibiting property of the CP on mild steel in HCl solution were investigated by the weight loss measurements, electrochemical impedance spectroscopy EIS and linear polarization resistance LPR . The concentrations of CP were varied from 1 x 10 3 M to 5 x 10 3 M. The inhibition efficiencies obtained from all the methods employed were in good agreement where the percentage of inhibition efficiencies increased with concentration of CP. Results showed that CP was the better inhibitor with inhibition efficiency of 90 at 5 x 10 3 M additive concentration. This is likely due to the effect of its large molecular size, higher number of electroactive heteroatoms and bigger p electron cloud of the conjugated double bond system. Ganesha Achary "Corrosion Inhibition of Mild Steel in HCl Medium by a Condensation Product" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-4 , June 2020, URL: https://www.ijtsrd.com/papers/ijtsrd30869.pdf Paper Url :https://www.ijtsrd.com/chemistry/physical-chemistry/30869/corrosion-inhibition-of-mild-steel-in-hcl-medium-by-a-condensation-product/ganesha-achary
Mechanistic Aspects of Oxidation of P-Bromoacetophen one by Hexacyanoferrate ...IJERA Editor
The kinetics of oxidation of p-bromoacetophenone by hexacyanoferrate (III) has been studied in alkaline
medium. The order of reaction with respect of both acetophenone and hexacynoferrate (III) has been found to be
unity. The rate of reaction increases with increase in the concentration of sodium hydroxide.On addition of
neutral KCl, reaction rate increases. The effects of solvent and temperature have been also studied. The product
p-bromophenyl glyoxal have been characterized by IR studies.
Reaction of aniline with ammonium persulphate and concentrated hydrochloric a...Maciej Przybyłek
In this paper, the reaction of aniline with ammonium persulphate and concentrated HCl was studied. As a result of our experimental studies, 2,4,6-trichlorophenylamine was identified as the main product. This shows that a high concentration of HCl does not favour oxidative polymerisation of phenylamine, even though the ammonium persulphate/HCl system is widely used in polyaniline synthesis. On the basis of the experimental data and density functional theory for reaction path modelling, we proposed a mechanism for oxidative chlorination of aniline. We assumed that this reaction proceeded in three cyclically repeated steps; protonation of aniline, formation of singlet ground state phenylnitrenium cation, and nucleophilic substitution. In order to confirm this mechanism, kinetic, thermochemical, and natural bond orbital population analyses were performed.
Synthesis and characterization of some Chromium(III) complexes of dibasic tri...IJERA Editor
Coordination complexes of Cr(III)with four tridentate Schiff base ligands viz. N-(2-hydroxy-1-naphthaldehyde)- -(4-nitrobenzoyl)hydrazone(HNNH = H2L 1 ), N-(2-hydroxy-4-methoxybenzaldehyde)- -(2-furoyl) hydrazone (HMFH = H2L 2 ), N-(2-hydroxyacetophenone)- -(2-theonyl) hydrazone (HATH = H2L 3 ) and N-(2- hydroxy-5-methylacetophenone)- -(3-toloyl) hydrazone (HMAT = H2L 4 ) have been synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductance, thermogravimetric analysis and spectral (IR, electronic, NMR) measurements. IR spectra indicates that the ligand behave as dibasic tridentate ligand in a chelate coordinating to Cr(III) ion through ketonic oxygen, azomethine nitrogen and by both enolic and phenolic protons (except in H2L 1 by naphtholic oxygen atom) via double deprotonation of ligands. The magnetic and spectral data indicate chelate in octahedral environment and analytical data suggest 1:1 stoichiometries for the complexes
Corrosion Inhibition of Mild Steel in HCl Medium by a Condensation Productijtsrd
A condensation product CP was successfully synthesized from reaction of dimethyl amino benzaldehyde and aniline giving yields of 80 . The compound was characterized by Fourier Transform Infrared FTIR Spectroscopy. The corrosion inhibiting property of the CP on mild steel in HCl solution were investigated by the weight loss measurements, electrochemical impedance spectroscopy EIS and linear polarization resistance LPR . The concentrations of CP were varied from 1 x 10 3 M to 5 x 10 3 M. The inhibition efficiencies obtained from all the methods employed were in good agreement where the percentage of inhibition efficiencies increased with concentration of CP. Results showed that CP was the better inhibitor with inhibition efficiency of 90 at 5 x 10 3 M additive concentration. This is likely due to the effect of its large molecular size, higher number of electroactive heteroatoms and bigger p electron cloud of the conjugated double bond system. Ganesha Achary "Corrosion Inhibition of Mild Steel in HCl Medium by a Condensation Product" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-4 , June 2020, URL: https://www.ijtsrd.com/papers/ijtsrd30869.pdf Paper Url :https://www.ijtsrd.com/chemistry/physical-chemistry/30869/corrosion-inhibition-of-mild-steel-in-hcl-medium-by-a-condensation-product/ganesha-achary
Electrooxidation of methanol on carbon supported pt ru nanocatalysts prepared...suresh899
Carbon Supported PtRu nanocatalysts have been prepared by simple impregnation reduction method in which Pt and Ru precursors are reduced by ethanol under reflux conditions for different reaction times. The prepared nanocatalysts were characterized by means of XRD, EDAX, ICP-AAS, FESEM and TEM. XRD analyses showed that all nanocatalysts exhibited f.c.c crystal structure, the structure characteristic for pure Pt, except for that reduced at prolonged reaction time of 4h which showed the presence of characteristic peak for Ru metal. The lattice constant calculations indicate that all catalysts are present in unalloyed phase and the average particle size as determined by TEM was in the range of 3.7 nm. The electrocatalytic activities and stability for the prepared nanocatalysts methanol electro-oxidation reaction (MOR) were studied by cyclic voltammetry. The catalysts prepared at 2h reduction time showed higher electrocatalytic activity in terms of mass specific activity and good stability over potential sweep for 100 cycles for methanol electro-oxidation. The results showed that the prepared nanocatalysts are considered as promising electrode catalyst (anode catalyst) for electro-oxidation of methanol in direct methanol fuel cells.
Influence of Tetra Alkyl Ammonium Cation and Temperature on Molecular Interac...IOSRJAC
Ultrasonic velocity (u), density (ρ), viscosity (η) and related acoustical parameters such as adiabatic compressibility (β), free energy (∆G), internal pressure (πi), relaxation time (τ) and acoustic impedance (z) have been computed using standard relation for tetra alkyl ammonium cation (Et4N + , Pr4N + , Bu4N + , and Pen4N + ) in binary liquid mixtures of 1, 4 - Dioxane and N, N – Dimethyl Formamide was prepared of 0.14M on different percentage compositions over the temperature range from 303.15K to 323.15K with the interval of 10K under room pressure to investigate inter - ionic interactions. The densities were measured by Magnetic Float Densitometer. Transport properties provide a deep and meaningful insight of various interactions taking place. It has been observed that the influence of small as well as large alkyl chain length of tetra alkyl ammonium cations (R4N + ), in terms of shape and ionic size with the DMF solvent in the presence of Dioxane, is helpful in investigating the molecular interactions, molecular rearrangement, molecular association etc
Thermal properties and size distribution of lignins precipitated with sulphur...Michal Jablonsky
Dissolution and fractionation of lignocellulosic material is a critical step of valorisation of lignins. Precipitated lignin was isolated from black liquor by sulphuric acid at four levels of concentration (5, 25, 50 and 72 % wt). A comparison study was performed through thermal and size properties. Theacid concentration influences of thermal properties of precipitated lignin. The acid concentration has an effect on changes in particle size of precipitated lignin. The results of thermogravimetric analysis indicated that the highest degradation of lignins appeared as an exothermic peak in range 470 - 650°C.The greatest weight loss in this section under an oxidation atmosphere was in the following order lignin 25 % wt (47.3 %), followed by lignin 72 % wt (45.0 %), lignin 5 % wt (43.6 %), and, smallest decline reached by lignin 50 % wt. The lowest temperature at the maximum degradation rate was determined for a sample of lignin 72 % wt at 488°C.
Physicochemical Properties and Proposed Mechanism in the Obtainment of 4-Hidr...IJERA Editor
The mechanism for the poly-condensation event of conjugated polymers with ending 4-hydroxycoumarin has
been proposed. It happened under H2SO4 acidic conditions only using enolic-coumarins without any substituent
at third position. It was studied using Matrix assisted laser desorption/ionization time-of-flight (MALDI-Tof)
mass spectrometry. Besides, some physicochemical properties were analyzed using Thermo-gravimetric (TGA),
X-ray and UV-Vis analysis
Experimental and Quantum Chemical Studies on the Corrosion Inhibition Perform...inventionjournals
Corrosion inhibition nature of a synthesized Schiff’s base was studied on the corrosion of mild steel in 1.0 M HCl using weight loss and electrochemical methods. The results indicated that the synthesized Schiff base is an effective inhibitor in reducing the corrosion of mild steel in 1.0 M HCl solution. The inhibitor efficiency of inhibitor increased with inhibitor concentration and showed maximum inhibition efficiency at 300 ppm concentration. The adsorption of inhibitor molecules on to the metal surface obeyed Langmuir Adsorption isotherm. The adsorption mechanism involved both physical and chemical adsorptions. The potentiodynamic polarization studies showed that the inhibitor is a mixed typed inhibitor with more cathodic nature. Potential of zero charge was also determined and the adsorption mechanism discussed. Quantum mechanical studies showed that the Schiff base molecules have the strong tendency to donate electron pairs to the metallic atoms on the surface
Journal of the Taiwan Institute of Chemical Engineers 0 0 0 (2016) 1–20Al Baha University
Quantum chemical calculations, molecular dynamics simulation and experimental studies of using some azo dyes as corrosion inhibitors for iron. Part 1: Mono-azo dye derivatives
Influence of the alkyl chain length of alkyltriazoles on the corrosion inhibi...Al Baha University
Abstract. Steel is an important material and has been widely used in today's industrial production. Using organic
corrosion inhibitors is an effective means to prevent steel from corrosion. Generally, the molecular structures of
inhibitors can have a major impact on their corrosion inhibition efficiency. In this work, the influence of alkyl chain
length of three alkyltriazoles on the corrosion inhibition of iron has been investigated by density functional based tight
binding (DFTB) approach. Several typical descriptors such as frontier molecular orbital, adsorption energy, density of
states have been discussed in detail. Our findings will contribute to the understanding of the inhibition mechanism and
the designing of novel corrosion inhibitors.
Kinetics and Thermodynamics of Mandelic Acid Oxidation By Tripropylammonium H...inventionjournals
Two new Versatile reagent Tripropylammonium Fluorochromate(TriPAFC) and Tripropylammonium Chlorochromate(TriPACC) has been employed for the oxidation of Mandelic acid. Rate of the réaction is catalysed by surfactant Sodium LaurylEther Sulphate(SLES). The Oxidation has been studied spectrophotometrically at room température in perchloric acid medium. Rate of TriPAFC and TriPACC oxidation of Mandelic acid has been followed under pseudo-first order condition. Rate constants were calculated by the integrated rate equation. The graph of logk versus time was linear and the slope is near to unity, rate constant calculated from graph also agreed with experimental value shows the first order rate dépendance on Mandelic acid. Product formed in this oxidation of Mandelic acid was analysed, polymerization test were carried to confirm that the reaction follows ionic mechanism and stoichiometric data has been accounted.Temperature of the substrate is varried and from the rate constant value, Thermodynamic parameters like Activation energy, Enthalpy change, Entropy change and change in Gibb’s free energy is calculated using Arrhenius and Eyrings plot. All the kinetic runs were repeated and the rate constants were reproducible within ±2% range.
Spectroscopic, Thermal, Magnetic and conductimetric studies on some 7-hydroxy...IOSR Journals
7-hydroxy-4-methyl-8-(p-methylphenylazo)coumarin (L1) and 7-hydroxy-4-methyl-8-(p-methoxyphenylazo)coumarin (L2) have been prepared and characterized by elemental analysis, infrared (IR), proton nuclear magnetic resonance (1H NMR) and mass spectra. The important infrared (IR) spectral bands corresponding to the active groups in the two ligands and the solid complexes under investigation were studied. Also the important fragments in the ligands and complexes were done using mass spectra and the main peaks were corresponding to the molecular weights of the ligands and complexes. The solid complexes have been synthesized and characterized by elemental and thermal analyses (TG and DTA) as well as by IR, 1H NMR, magnetic measurements, electronic transition, molar conductance, mass and electron spin resonance (ESR) spectra. The proposed steriochemical structures for the investigated metal complexes suggest octahedral geometry with respect to Mn, Co, Ni, Cu and Zn divalent metal ions with the investigated ligands 1:1 and 1:2 complexes and all of the formed complexes contain coordinated and hydrated water molecules. All of the prepared solid complexes behave as non-electrolytes in chloroform.
Perkbox isn't just a company, it's a way of life. Happiness isn't just part of our product, it's the core of everything we do. Turn the pages of our Culture Book to discover what it's like to work behind the scenes of the UK's fastest growing employee engagement provider.
Electrooxidation of methanol on carbon supported pt ru nanocatalysts prepared...suresh899
Carbon Supported PtRu nanocatalysts have been prepared by simple impregnation reduction method in which Pt and Ru precursors are reduced by ethanol under reflux conditions for different reaction times. The prepared nanocatalysts were characterized by means of XRD, EDAX, ICP-AAS, FESEM and TEM. XRD analyses showed that all nanocatalysts exhibited f.c.c crystal structure, the structure characteristic for pure Pt, except for that reduced at prolonged reaction time of 4h which showed the presence of characteristic peak for Ru metal. The lattice constant calculations indicate that all catalysts are present in unalloyed phase and the average particle size as determined by TEM was in the range of 3.7 nm. The electrocatalytic activities and stability for the prepared nanocatalysts methanol electro-oxidation reaction (MOR) were studied by cyclic voltammetry. The catalysts prepared at 2h reduction time showed higher electrocatalytic activity in terms of mass specific activity and good stability over potential sweep for 100 cycles for methanol electro-oxidation. The results showed that the prepared nanocatalysts are considered as promising electrode catalyst (anode catalyst) for electro-oxidation of methanol in direct methanol fuel cells.
Influence of Tetra Alkyl Ammonium Cation and Temperature on Molecular Interac...IOSRJAC
Ultrasonic velocity (u), density (ρ), viscosity (η) and related acoustical parameters such as adiabatic compressibility (β), free energy (∆G), internal pressure (πi), relaxation time (τ) and acoustic impedance (z) have been computed using standard relation for tetra alkyl ammonium cation (Et4N + , Pr4N + , Bu4N + , and Pen4N + ) in binary liquid mixtures of 1, 4 - Dioxane and N, N – Dimethyl Formamide was prepared of 0.14M on different percentage compositions over the temperature range from 303.15K to 323.15K with the interval of 10K under room pressure to investigate inter - ionic interactions. The densities were measured by Magnetic Float Densitometer. Transport properties provide a deep and meaningful insight of various interactions taking place. It has been observed that the influence of small as well as large alkyl chain length of tetra alkyl ammonium cations (R4N + ), in terms of shape and ionic size with the DMF solvent in the presence of Dioxane, is helpful in investigating the molecular interactions, molecular rearrangement, molecular association etc
Thermal properties and size distribution of lignins precipitated with sulphur...Michal Jablonsky
Dissolution and fractionation of lignocellulosic material is a critical step of valorisation of lignins. Precipitated lignin was isolated from black liquor by sulphuric acid at four levels of concentration (5, 25, 50 and 72 % wt). A comparison study was performed through thermal and size properties. Theacid concentration influences of thermal properties of precipitated lignin. The acid concentration has an effect on changes in particle size of precipitated lignin. The results of thermogravimetric analysis indicated that the highest degradation of lignins appeared as an exothermic peak in range 470 - 650°C.The greatest weight loss in this section under an oxidation atmosphere was in the following order lignin 25 % wt (47.3 %), followed by lignin 72 % wt (45.0 %), lignin 5 % wt (43.6 %), and, smallest decline reached by lignin 50 % wt. The lowest temperature at the maximum degradation rate was determined for a sample of lignin 72 % wt at 488°C.
Physicochemical Properties and Proposed Mechanism in the Obtainment of 4-Hidr...IJERA Editor
The mechanism for the poly-condensation event of conjugated polymers with ending 4-hydroxycoumarin has
been proposed. It happened under H2SO4 acidic conditions only using enolic-coumarins without any substituent
at third position. It was studied using Matrix assisted laser desorption/ionization time-of-flight (MALDI-Tof)
mass spectrometry. Besides, some physicochemical properties were analyzed using Thermo-gravimetric (TGA),
X-ray and UV-Vis analysis
Experimental and Quantum Chemical Studies on the Corrosion Inhibition Perform...inventionjournals
Corrosion inhibition nature of a synthesized Schiff’s base was studied on the corrosion of mild steel in 1.0 M HCl using weight loss and electrochemical methods. The results indicated that the synthesized Schiff base is an effective inhibitor in reducing the corrosion of mild steel in 1.0 M HCl solution. The inhibitor efficiency of inhibitor increased with inhibitor concentration and showed maximum inhibition efficiency at 300 ppm concentration. The adsorption of inhibitor molecules on to the metal surface obeyed Langmuir Adsorption isotherm. The adsorption mechanism involved both physical and chemical adsorptions. The potentiodynamic polarization studies showed that the inhibitor is a mixed typed inhibitor with more cathodic nature. Potential of zero charge was also determined and the adsorption mechanism discussed. Quantum mechanical studies showed that the Schiff base molecules have the strong tendency to donate electron pairs to the metallic atoms on the surface
Journal of the Taiwan Institute of Chemical Engineers 0 0 0 (2016) 1–20Al Baha University
Quantum chemical calculations, molecular dynamics simulation and experimental studies of using some azo dyes as corrosion inhibitors for iron. Part 1: Mono-azo dye derivatives
Influence of the alkyl chain length of alkyltriazoles on the corrosion inhibi...Al Baha University
Abstract. Steel is an important material and has been widely used in today's industrial production. Using organic
corrosion inhibitors is an effective means to prevent steel from corrosion. Generally, the molecular structures of
inhibitors can have a major impact on their corrosion inhibition efficiency. In this work, the influence of alkyl chain
length of three alkyltriazoles on the corrosion inhibition of iron has been investigated by density functional based tight
binding (DFTB) approach. Several typical descriptors such as frontier molecular orbital, adsorption energy, density of
states have been discussed in detail. Our findings will contribute to the understanding of the inhibition mechanism and
the designing of novel corrosion inhibitors.
Kinetics and Thermodynamics of Mandelic Acid Oxidation By Tripropylammonium H...inventionjournals
Two new Versatile reagent Tripropylammonium Fluorochromate(TriPAFC) and Tripropylammonium Chlorochromate(TriPACC) has been employed for the oxidation of Mandelic acid. Rate of the réaction is catalysed by surfactant Sodium LaurylEther Sulphate(SLES). The Oxidation has been studied spectrophotometrically at room température in perchloric acid medium. Rate of TriPAFC and TriPACC oxidation of Mandelic acid has been followed under pseudo-first order condition. Rate constants were calculated by the integrated rate equation. The graph of logk versus time was linear and the slope is near to unity, rate constant calculated from graph also agreed with experimental value shows the first order rate dépendance on Mandelic acid. Product formed in this oxidation of Mandelic acid was analysed, polymerization test were carried to confirm that the reaction follows ionic mechanism and stoichiometric data has been accounted.Temperature of the substrate is varried and from the rate constant value, Thermodynamic parameters like Activation energy, Enthalpy change, Entropy change and change in Gibb’s free energy is calculated using Arrhenius and Eyrings plot. All the kinetic runs were repeated and the rate constants were reproducible within ±2% range.
Spectroscopic, Thermal, Magnetic and conductimetric studies on some 7-hydroxy...IOSR Journals
7-hydroxy-4-methyl-8-(p-methylphenylazo)coumarin (L1) and 7-hydroxy-4-methyl-8-(p-methoxyphenylazo)coumarin (L2) have been prepared and characterized by elemental analysis, infrared (IR), proton nuclear magnetic resonance (1H NMR) and mass spectra. The important infrared (IR) spectral bands corresponding to the active groups in the two ligands and the solid complexes under investigation were studied. Also the important fragments in the ligands and complexes were done using mass spectra and the main peaks were corresponding to the molecular weights of the ligands and complexes. The solid complexes have been synthesized and characterized by elemental and thermal analyses (TG and DTA) as well as by IR, 1H NMR, magnetic measurements, electronic transition, molar conductance, mass and electron spin resonance (ESR) spectra. The proposed steriochemical structures for the investigated metal complexes suggest octahedral geometry with respect to Mn, Co, Ni, Cu and Zn divalent metal ions with the investigated ligands 1:1 and 1:2 complexes and all of the formed complexes contain coordinated and hydrated water molecules. All of the prepared solid complexes behave as non-electrolytes in chloroform.
Perkbox isn't just a company, it's a way of life. Happiness isn't just part of our product, it's the core of everything we do. Turn the pages of our Culture Book to discover what it's like to work behind the scenes of the UK's fastest growing employee engagement provider.
Deactivation Modeling through Separable Kinetics of Coking On Ni/CZ Catalyst ...IOSR Journals
Abstract : Steam methane reforming (SMR) is a very significant technique to produce hydrogen from fossil fuels. In this particular work, nickel is used as the active metal and ceria-zirconia (CZ) bi-metallic oxide is used as the support. The foremost challenge to this process is sooting or coking over the catalyst surface and blocking the active sites. For the economic viability of the catalyst, it is very significant to make it coke deposition resistant. This is the reason that the kinetic modeling of the deactivation is very important. Therefore, this paper is aimed to model the deactivation and activity of the catalyst. A rate model of the deactivation process is also developed using separable kinetics. A comparison with commercial catalyst is also reported to show that the Ni/CZ catalyst is much more stable towards the coking. Keywords –Coking, Deactivation, Methane, Separable kinetics, Steam reforming.
V mn-mcm-41 catalyst for the vapor phase oxidation of o-xylenesunitha81
The role of V and Mn incorporated mesoporous molecular sieves was
investigated for the vapor phase oxidation of o-xylene. Mesoporous monometallic
V-MCM-41 (Si/V = 25, 50, 75 and 100), Mn-MCM-41 (Si/Mn = 50) and bimetallic
V-Mn-MCM-41 (Si/(V ? Mn) = 100) molecular sieves were synthesized by
a direct hydrothermal (DHT) process and characterized by various techniques such
as X-ray diffraction, DRUV-Vis spectroscopy, EPR, and transmission electron
microscopy (TEM). From the DRUV-Vis and EPR spectral study, it was found that
most of the V species are present as vanadyl ions (VO2?) in the as-synthesized
catalysts and as highly dispersed V5? ions in tetrahedral coordination in the calcined
catalysts. The activity of the catalysts was measured and compared with each other
for the gas phase oxidation of o-xylene in the presence of atmospheric air as an
oxidant at 573 K. Among the various catalysts, V-MCM-41 with Si/V = 50
exhibited high activity towards production of phthalic anhydride under the experimental
condition. The correlation between the phthalic anhydride selectivity and
the physico-chemical characteristics of the catalyst was found. It is concluded that
V5? species present in the MCM-41 silica matrix are the active sites responsible for
the selective formation of phthalic anhydride during the vapor phase oxidation of
o-xylene.
Removal of Coke during Steam Reforming of Ethanol over La-CoOx Catalystinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
Similar to 2009_Nguyen et al._Journal of Organometallic Chemistry (20)
Removal of Coke during Steam Reforming of Ethanol over La-CoOx Catalyst
2009_Nguyen et al._Journal of Organometallic Chemistry
1. Preparation of new dinuclear half-titanocene complexes with ortho-
and meta-xylene linkages and investigation of styrene polymerization
Nguyen Thuy Ba Linh a
, Nguyen Thi Dieu Huyen a
, Seok Kyun Noh a,*, Won Seok Lyoo b
, Dong-Ho Lee c
,
Yongman Kim d
a
School of Display and Chemical Engineering, Yeungnam University, 214-1 Daedong, Gyeongsan, Gyeongbuk 712-749, Republic of Korea
b
School of Textiles, Yeungnam University, 214-1 Daedong, Gyeongsan, Gyeongbuk 712-749, Republic of Korea
c
Department of Polymer Science, Kyungpook National University, Taegu 702-749, Republic of Korea
d
PE Research Center, Hanwha Chemical R&D Center, Daejeon 702-701, Republic of Korea
a r t i c l e i n f o
Article history:
Received 15 May 2009
Received in revised form 20 June 2009
Accepted 23 June 2009
Available online 26 June 2009
Keywords:
Dinuclear metallocene
Half-titanocene
Styrene polymerization
Syndiotactic polystyrene
ortho-Xylene bridge
meta-Xylene bridge
a b s t r a c t
Half-titanocene is well-known as an excellent catalyst for the preparation of SPS (syndiotactic polysty-
rene) when activated with methylaluminoxane (MAO). Dinuclear half-sandwich complexes of titanium
bearing a xylene bridge, (TiCl2L)2{(l-g5
, g5
-C5H4-ortho-(CH2–C6H4–CH2)C5H4}, (4 (L = Cl), 7 (L = O-2,6-
iPr2C6H3)) and (TiCl2L)2{(l-g5
, g5
-C5H4-meta-(CH2–C6H4–CH2)C5H4} (5 (L = Cl), 8(L = O-2,6-iPr2C6H3)), have
been successfully synthesized and introduced for styrene polymerization. The catalysts were character-
ized by 1
H- and 13
C NMR, and elemental analysis. These catalysts were found to be effective in forming
SPS in combination with MAO. The activities of the catalysts with rigid ortho- and meta-xylene bridges
were higher than those of catalysts with flexible pentamethylene bridges. The catalytic activity of four
dinuclear half-titanocenes increased in the order of 4 < 5 < 7 < 8. This result displays that the meta-xylene
bridged catalyst is more active than the ortho-xylene bridged and that the aryloxo group at the titanium
center is more effective at promoting catalyst activity compared to the chloride group at the titanium
center. Temperature and ratio of [Al]:[Ti] had significant effects on catalytic activity. Polymerizations
were conducted at three different temperatures (25, 40, and 70 °C) with variation in the [Al]:[Ti] ratio
from 2000 to 4000. It was observed that activity of the catalysts increased with increasing temperature,
as well as higher [Al]:[Ti]. Different xylene linkage patterns (ortho and meta) were recognized to be a
principal factor leading to the characteristics of the dinuclear catalyst due to its different spatial arrange-
ment, causing dissimilar intramolecular interactions between the two active sites.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Syndiotactic polystyrene (SPS) is a highly crystalline polymer
with a melting temperature (Tm) near 270 °C. The relatively fast
crystallization rate, low specific gravity, low dielectric constant,
high modulus of elasticity, and excellent resistance to chemicals
make SPS a potential material for a large number of applications
in the automotive, electronic, and packaging industries [1,2]. Ishi-
hara succeeded in the synthesis of SPS in 1985 by using homoge-
neous organometallic catalytic systems based on titanium
compounds and methylaluminoxane (MAO) [3]. Since then, a vari-
ety of titanium compounds have been examined for their ability to
produce SPS in the presence of MAO [4–6]. As a result of such re-
search, it turned out that structural characteristics of half-titanoc-
enes based on the electronic and steric effects of Cp´ TiX3
determined not only catalytic activity of the catalyst but also de-
gree of stereoregularity and molecular weight of the SPS. Recently,
the utility of titanium-based half-metallocene with a variety of
substituents at the metal site, such as aryloxo, amide, and ketimide
as an olefin polymerization catalyst, has been investigated exten-
sively [7–9]. These studies demonstrated clearly that the effect of
the substituent on both Cp and titanium plays an essential role
not only regarding catalytic activity, but also for monomer reactiv-
ity in the polymerization of styrene and copolymerization with
ethylene.
Investigation of the properties of dinuclear metallocenes has
been a topic of this lab’s research since these metallocenes may of-
fer cooperative effects between two active sites that could provide
an effective tool for the discovery of a new class of catalysts for ole-
fin polymerization [10,11]. In fact, the dinuclear metallocene sys-
tems display not only the defining characteristics of well-defined
mononuclear metallocenes, but also a strong dependence upon
the nature of the bridging ligand [12–18]. The initial attempts to
exploit dinuclear half-titanocenes were performed by Royo et al.
and Flores et al. [19–21]. It was found that the activity for the dinu-
clear half-titanocenes is one order of magnitude lower than that of
the mononuclear half-titanocene [18,21]. Osakada reported also
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.06.033
* Corresponding author. Tel.: +82 53 810 2526; fax: +82 53 810 4651.
E-mail address: sknoh@ynu.ac.kr (S.K. Noh).
Journal of Organometallic Chemistry 694 (2009) 3438–3443
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
2. the higher activity of dinuclear zirconium metallocene catalyst
comparing to the corresponding normal metallocene due to the
bridge effect [25]. To the contrary, Do and coworkers reported that
the activity of dinuclear half-titanocene with two phenyl spacers
was, in actuality, similar to the mononuclear half-titanocene, dem-
onstrating that the nature of the bridging unit in dinuclear metal-
locenes exerted a significant influence on determining the
characteristics of the catalysts [22]. We have also reported that
para-xylene bridged dinuclear half-titanocene exhibited greater
activity than the polymethylene bridged, demonstrating the effect
of the bridge rigidity on the catalyst [14,15].
Much work has been performed to establish the effect of the
bridge nature in dinuclear metallocenes; however, the topics re-
lated to the geometric effect of the bridging ligand on dinuclear
metallocenes have not been well established. Herein, it is the in-
tent of the authors to describe an efficient preparative route to
make four novel dinuclear half-titanocenes with meta- and ortho-
xylene bridges as new metallocenes in order to understand the
influence of the geometric arrangement of dinuclear metallocenes
on catalytic behavior as shown in Scheme 1. The results of styrene
polymerization using these catalysts have exhibited some mean-
ingful aspects to point out the effect of space orientation of the
two active sites.
2. Experimental
2.1. General considerations
All manipulations were performed either under a dry, oxygen-
free atmosphere using standard Schlenk techniques or under a
double manifold vacuum line. Nitrogen gas was purified by pas-
sage through a column of molecular sieve (4 Å) and Drierite
(8 mesh). Tetrahydrofuran (THF), diethyl ether, hexane, and tolu-
ene were distilled from sodium/benzophenone ketyl prior to use.
Methylene chloride and trimethylsilyl chloride (97%, Aldrich Co.,
City, State, Country) were distilled from calcium hydride prior to
use. a,a0
-Dibromo-o-xylene (96%, Aldrich Co.), a,a0
-dibromo-m-xy-
lene (97%, Aldrich Co.), sodium cyclopentadienylide (2.0 M solution
in THF, Aldrich Co.), sodium hydride (as a 60% dispersion in mineral
oil, Aldrich Co.), n-BuLi (2.5 M solution in hexane, Aldrich Co.), tita-
nium chloride (Aldrich Co.), and modified methylaluminoxane
(MMAO, 5.9 wt.% Al, Akzo, City, State, USA) were used without fur-
ther purification. 1
H NMR (300 MHz) and 13
C NMR (75.46 MHz)
spectra were recorded using a Bruker VNS-300 FT-NMR spectrom-
eter. Elemental analysis was conducted on an EA 1108 elemental
analyzer (FISONS Instrument, City, Italy).
Molecular weight and molecular weight distribution were mea-
sured by a Waters GPC (Alliance GPC 2000, City, State, Country)
with a polystyrene gel column (Styragel HT 3, 4, 5) at 140 °C using
1,2,4-trichlorobenzene. The molecular weight was calculated by a
standard procedure based on calibration with standard polysty-
rene samples. Differential scanning calorimetric (DSC) data were
recorded with a Pyris 6 DSC (Perkin Elmer, City, State, Country) un-
der a nitrogen atmosphere [conditions: heating from 25 to 300 °C
(20 °C/min); cooling from 300 to À55 °C (10 °C/min)].
Catalysts 6 and 9 having pentamethylene bridge were prepared
by the literature method [12,15].
2.2. Synthesis
2.2.1. Synthesis of (TiCl3)2{(l-g5
, g5
-C5H4-ortho-(CH2–C6H4–CH2)
C5H4}, 4
a,a0
-Bis(trimethylsilyl)cyclopentadienyl-ortho-xylene (3o) was
synthesized according to literature methods [23]. A solution of
3o (3.0 g, 7.93 mmol) in methylene chloride (50 mL) was added
dropwise to 1.74 mL (15.86 mmol, 2.0 eq) of TiCl4 at -78 °C; an
C
H2
C
H2
Ti Ti
L LCl Cl
Cl Cl
H2CCH2
Ti Ti
L LCl Cl
Cl Cl
Ti Ti
L L
Cl Cl
Cl Cl
Ortho - Xylene Bridge Catalyst
4 (L= Cl), 7 (L= )
Meta - Xylene Bridge Catalyst
5 (L= Cl), 8 (L= )
Pentamethylene Bridge Catalyst
6 (L= Cl), 9 (L= )
O O
O
Scheme 1. Structure of dinuclear half-titanocenes.
N.T.B. Linh et al. / Journal of Organometallic Chemistry 694 (2009) 3438–3443 3439
3. immediate solution color change from clear to greenish black was
observed. After the addition (%10 min), the solution was allowed
to warm to room temperature and stirred overnight. Methylene
chloride was removed under vacuum and the residue extracted
with ether. The final solid was obtained as a greenish yellow prod-
uct after washing with hexane.
Compound 4: Yield: 2.77 g (65%). 1
H NMR (300 MHz, CDCl3): d
7.20 (s, 4H, C6H4), 6.86 (t, 4H, C5H4), 6.68 (t, 4H, C5H4), 4.14 (s,
4H, CH2); 13
C NMR (CDCl3): d 141.9, 136.1, 130.6, 128.2, 123.4,
34.8. Anal. Calc. for C18H16Cl6Ti2: C, 39.98; H, 2.98. Found: C,
40.26; H, 3.20%.
2.2.2. Synthesis of (TiCl3)2{(l-g5
, g5
-C5H4-meta-(CH2–C6H4–CH2)
C5H4}, 5
This reaction proceeded in an analogous fashion to the above
reaction with the following exceptions: a,a0
-Bis(trimethyl-
silyl)cyclopentadienyl-meta-xylene (3m) was used in place of 3o.
a,a0
-Bis(trimethylsilyl)cyclopentadienyl-meta-xylene (3m) was
synthesized according to literature methods [22]. Purification re-
sulted in a greenish yellow solid of 5.
Compound 5: Yield: 2.81 g (66%). 1
H NMR (300 MHz, CDCl3): d
7.15 (s, 4H, C6H4), 6.93 (t, 4H, C5H4), 6.78 (t, 4H, C5H4), 4.16 (s,
4H, CH2); 13
C NMR (CDCl3): d 142.8, 138.3, 129.5, 127.8, 123.7,
37.6. Anal. Calc. for C18H16Cl6Ti2: C, 39.98; H, 2.98. Found: C,
40.18; H, 3.41%.
2.2.3. Synthesis of {Ti(O-2,6-iPr2C6H3)Cl2}2{(l-g5
, g5
-C5H4-ortho-(CH2
-C6H4-CH2)C5H4}, 7
To a solution of 4 (1.0 g, 1.8 mmol) in methylene chloride was
added Li(O-2,6-iPr2C6H3) (0.72 g, 3.6 mmol) at À30 °C. The solution
was warmed to RT slowly and stirred overnight. The solvent was
then removed in vacuo to leave a dark orange residue that was ex-
tracted into hexane, separated, and recrystallized from hexane at
À30 °C to give the final product as a light orange solid.
Compound 7: Yield: 0.62 g (42%). 1
H NMR (300 MHz, CDCl3): d
7.12 (s, 4H, C6H4), 7.09 (m, 6H, C6H3), 6.44 (t, 4H, C5H4), 6.37 (t,
4H, C5H4), 4.22 (s, 4H, CH2), 3.24 (m, 4H, CH), 1.25 (d, 24H, CH3);
13
C NMR (CDCl3): d 164.2, 138.9, 138.3, 137.0, 130.3, 127.6,
124.6, 123.4, 120.9, 120.0, 34.1, 26.9, 23.6. Anal. Calc. for
C42H50Cl4Ti2O2: C, 61.19; H, 6.11%. Found: C, 61.04; H, 6.04%.
2.2.4. Synthesis of {Ti(O-2,6-iPr2C6H3)Cl2}2{(l-g5
, g5
-C5H4-meta-(CH2
–C6H4–CH2)C5H4}, 8
A method similar to those used to make 7 was also applied. The
only exception was introduction of 5 in place of 4. The final product
8 was separated in 45% yield as a pale orange solid.
Br
Br
Cp
Cp
CpNa
CpNa
C
H2
C
H2SiMe3 SiMe3
+ 2NaCp
THF
-780
C
+ 2NaH
THF
+ 2SiMe3Cl
1o
1m
2o
2m
3o, 3m
C
H2
C
H2
Ti
O Cl
Cl
Ti
O Cl
Cl
H2CCH2
Ti Ti
OO Cl Cl
Cl Cl
H2CCH2
Ti Ti
Cl ClCl Cl
Cl Cl
C
H2
C
H2
Ti Ti
Cl ClCl Cl
Cl Cl
+ 2 TiCl4
7
8
O+ 2Li+ O+ 2Li+
Scheme 2. Synthesis of dinuclear half-titanocenes.
3440 N.T.B. Linh et al. / Journal of Organometallic Chemistry 694 (2009) 3438–3443
4. Compound 8: Yield: 0.66 g (45%). 1
H NMR (300 MHz, CDCl3): d
7.14 (s, 4H, C6H4), 7.08 (m, 6H, C6H3), 6.45 (t, 4H, C5H4), 6.37 (t,
4H, C5H4), 4.22 (s, 4H, CH2), 3.24 (m, 4H, CH), 1.25 (d, 24H, CH3);
13
C NMR (CDCl3): d 164.2, 138.9, 138.3, 137.1, 130.4, 127.7,
124.6, 123.4, 121.0, 120.0, 34.1, 27.0, 23.6. Anal. Calc. for
C42H50Cl4Ti2O2: C, 61.19; H, 6.11. Found: C, 61.50; H, 6.55%.
2.3. Styrene polymerization
Polymerizations were carried out in a 300-mL Schlenk flask. The
reactor was filled with the proper amount of toluene, MMAO, and
styrene. Polymerization was initiated by injection of the catalyst.
After 1 h, polymerization was stopped by adding 10% acidified
methanol. Polymers were filtered and washed with methanol and
dried under vacuum to a constant weight. The SPS was separated
by removing atactic PS via extraction using refluxing MEK for
24 h and the ratio of the separated SPS to the total polystyrene
was defined as syndiotactic index (SI). The insoluble portions after
the extraction were dried under vacuum and analyzed by the
instrument.
3. Results and discussion
3.1. Synthesis and characterization
Dinuclear half-titanocenes with ortho- and meta-xylene bridges,
(TiCl2L)2{(l-g5
, g5
-C5H4-ortho-(CH2–C6H4–CH2)C5H4} (4 (L = Cl), 7
(L = O-2,6-iPr2C6H3)) and (TiCl2L)2{(l-g5
, g5
-C5H4-meta-
(CH2–C6H4–CH2)C5H4} (5 (L = Cl), 8(L = O-2,6-iPr2C6H3)), were con-
veniently prepared in modest yields (40–70%) by treating the
respective trimethylsilyl derivatives of the ligands with 2.0 eq of
TiCl4 in methylene chloride as shown in Scheme 2. The preparative
route to obtain new compounds was different from the synthetic
procedure to make the corresponding catalyst with a para-xylene
bridge [14]. It was found that biscyclopentadienyls connected
through ortho- or meta-xylene 1o and 1m gave rise to the formation
of polymeric structure which was difficult to be separated as a sta-
ble compound. The best way to overcome these complications was
to conduct a one-pot reaction from the first step to the third step to
form trimethylsilyl derivatives 3o and 3m without separation of
any intermediate compound [23,24]. In situ reaction of 1o and 1m
with excess sodium hydride readily produced the dianion species
2o and 2m, respectively, conveniently recognizable due to the vig-
orous evolution of hydrogen gas. Reaction of the corresponding
disodium salts with SiMe3Cl yielded 3o and 3m, stable enough to
be separated for identification. Methylene chloride was an effective
solvent for the reaction between ditrimethylsilyl derivatives 3 and
TiCl4. At À78 °C in methylene chloride, catalysts 4 and 5 were
formed by the reaction of the trimethylsilyl derivatives of
complexes 3o and 3m with 2.0 eq of TiCl4 in about 65% yield [24].
Preparation of aryloxo-substituted, xylene-bridged, dinuclear half-
titanocenes 7 and 8 were achieved in 50% yield by treating catalysts
4 and 5 with 2.0 eq of the corresponding aryloxo lithium salts for
15 h at RT. For reactivity comparison, the dinuclear half-titanocenes
6 and 9 with pentamethylene bridges were also synthesized. Cata-
lysts 4, 5, 7, and 8 were characterized by 1
H- and 13
C NMR, and
elemental analysis.
The NMR spectrum of catalyst 4 indicates the predicted reso-
nances for the bridging meta-xylene-biscyclopentadienyl ligand
that appears as: two sets of pseudotriplets at 6.86 and 6.68 ppm
due to the AA0
BB0
system of cyclopentadienyl protons; a singlet
at 4.14 ppm for methylene protons; a multiplet between 7.00
and 7.20 ppm for phenyl protons. The 1
H NMR spectrum of catalyst
5 exhibited a slight difference from catalyst 4 (Experimental sec-
tion). Formation of aryloxo compounds 7 and 8 was quite easily
identified by 1
H- and 13
C NMR spectra. Resonances of the isobutyl
group of 7 and 8 appeared at 3.24 ppm (septet) and 1.25 ppm (dou-
blet), assigned to CH and two CH3, respectively. The most distinc-
tive change in the proton NMR spectrum due to aryloxo
substitution at titanium was represented by the chemical shift
change of protons at the cyclopentadienyl ring, as well as the value
of dd = [dd À dp], the chemical shift difference between the distal
and proximal protons in the cyclopentadienyl ring. Chemical shifts
of the cyclopentadienyl protons of catalyst 7 were moved to 6.44
and 6.37 ppm from 6.86 and 6.68 ppm of those of catalyst 4, indi-
cating that aryloxo substitution caused a 0.42 and 0.31 ppm up-
field shift of cyclopentadienyl protons. This may be understood
by the electron density increase around the metal center due to
the superb electron pushing power of the aryloxo group. The value
of dd = [dd À dp] of catalyst 4 was 0.18 ppm, much larger than
0.07 ppm of catalyst 7. This kind of trend was seeing between cat-
alysts 5 and 8 as well. A detailed correlation of the values of dd with
the geometric characteristics of dinuclear metallocene may not be
simply overviewed, but one point was noted. The large dd value for
the dinuclear metallocene displayed the relatively small steric
interactions around the metal center due to the enlarged separa-
tion between the connected cyclopentadienyl rings [20]. It is not
so unreasonable that the reduced dd value of compounds 7 and 8
were merely the reflection of the aryloxo group, larger than the
chloride, leading to more substantial steric interactions around
the titanium.
3.2. Polymerization
In order to probe the catalytic properties of the prepared cata-
lysts, styrene polymerization was conducted in the presence of
MMAO with pentamethylene bridged dinuclear half-titanocenes
6 and 9, and simultaneously examined for comparison. In a series
of experiments, the catalysts were used in toluene at 25, 40, and
70 °C, at two ratios of [Al]:[Ti]; the results are summarized in Table
1. Table 1 reveals that the catalytic activity of the six catalysts in-
creased in the order of 6 (232) < 9 (376) < 4 (398) < 5 (450) < 7
(501) < 8 (603) at 70 °C, [Al]:[Ti] = 4000 (activity unit = kg of poly-
mer/(mol of Ti-h). At 40 °C, this tendency remained unchanged;
however, abnormal activity data came from the experiment at
25 °C, probably due to an irregular initiation rate of the catalysts.
This result exhibited a very meaningful implication that the geo-
metric characteristics might play a significant role in directing
the catalytic activity of the dinuclear half-titanocenes with the iso-
meric xylene bridge. Firstly, four xylene bridged catalysts dis-
played much higher activity than the two pentamethylenes.
Activities of catalysts 4, 5, 7, and 8 with a xylene bridge were at
least 1.5 times larger than those of catalysts 6 and 9 with pentam-
ethylene bridges, at a [Al]:[Ti] ratio of 4000 at 40 and 70 °C. Sec-
ondly, meta-xylene bridged catalysts exhibited much higher
activities than the corresponding ortho-xylene bridged catalysts.
For instance, activity of 5 with a [Al]:[Ti] ratio of 4,000 and a
70 °C polymerization temperature was 450 kg of polymer/(mol of
Ti-h), larger than the activity of 4, 398 kg of polymer/(mol of Ti-
h). Thirdly, regardless of the bridge nature of the catalysts, having
an aryloxo substituent at the titanium represented much larger
activities than those having chloride at the titanium. Catalysts 7,
8, and 9 with an aryloxo group showed 20–60% higher activity than
catalysts 4, 5, and 6 with chloride.
The different activity trend between the xylene and pentameth-
ylene linkages may be understood both by steric and electronic
factors. It is not surprising that the presence of a xylene bridge
can deliver more electrons to the metal center than the linear pen-
tamethylene bridge [14,15]. Electron density increase to the active
site should lead to an increase in activity. In terms of steric circum-
stances, the most principal difference of xylene from pentamethyl-
N.T.B. Linh et al. / Journal of Organometallic Chemistry 694 (2009) 3438–3443 3441
5. ene is rigidity. The xylene bridge is stiff enough to prohibit any
possible intramolecular approach between the two titanium cen-
ters. Conversely, pentamethylene would have no problem allowing
the approach of two titanium centers given the flexibility inherent
to a carbon single bond. As a consequence, the larger activity of the
catalysts bearing the xylene bridge compared to those with the
pentamethylene bridge can be attribute to the increased electron
density at the titanium center and less steric disturbance between
the two titanium centers. It is worthwhile to point out an effect of
the geometric differences between the ortho and meta linkages of
the xylene on catalytic activity. It was found that meta-xylene
bridge catalysts 5 and 8 displayed activities larger than the
ortho-xylene bridged 4 and 7. The range in activity differences of
5 from 4 was actually larger than those of 8 from 7, suggesting that
aryloxo substitution attenuated the geometric effect. It is not
unreasonable that a widened angle of meta geometry, compared
to ortho geometry, would be the reason for a faster rate of polymer-
ization given a bigger active site. From previous work of this lab
with the para-xylene catalyst, it was confirmed that the dinuclear
half-titanocene with the para-xylene bridge represented the great-
est activity among the three isomers, followed by the catalyst with
meta-xylene bridge. Substituent effects of the half-titanocene on
polymerization properties have been demonstrated by Nomura
as well [7–9]. By substitution of chloride with the aryloxo group
at the titanium of the half-titanocene, copolymerization ability
was improved considerably in terms of activity as well as comono-
mer reactivity. Catalysts 7, 8, and 9 may be able to effectively delo-
calize the cationic charge of the active site through the phenyl ring
that delivers the resonance stabilization to the active species,
inducing overall activity enhancement.
It was observed that the activity of the dinuclear half-titanoc-
enes is sensitively affected by polymerization temperature and
the [Al]:[Ti] ratio. All the catalysts, irrespective of type, displayed
a maximum activity at 70 °C that decreased upon lowering of poly-
merization temperature. Activities of catalysts 7, 8, and 9 at 70 °C
were 2.7 times larger than those at 25 °C. Activity differences
according to polymerization temperature among the catalysts with
two chlorides at the titanium were much smaller than those
among the catalysts with the aryloxo group. In all cases, the activ-
ities at [Al]:[Ti] = 4000 were much greater than those at 2000. With
catalyst 7, the activity at [Al]:[Ti] = 4,000 was more than three
times larger than those at 2000. It should be noted that the higher
activity at the higher reaction temperature with the higher amount
of cocatalyst is not unusual at all.
The variation in molecular weight and molecular weight distri-
bution does not seem to be very sensitive to catalyst structure.
Among catalysts 7, 8, and 9, the ortho-xylene bridged 7 gave rise
to the formation of the highest molecular weight SPS, while SPS
formed by the catalyst with the pentamethylene bridge exhibited
the lowest molecular weight. Nearly identical molecular weights
were found from the polymers produced by respective catalysts
with the aryloxo group and chloride. Molecular weight distribu-
tions of polymers by catalysts bearing either ortho- or meta-xylene
bridges ranged from 1.7 to 3.6 and were relatively wider than those
Table 1
Results of styrene polymerization using the new dinuclear half-titanocene catalysts.
Catalyst Tp
a
(°C) [Al]/[Ti] Activityb
Tm (°C) S.I.c
Mw  10À3
Mw/Mn
4 25 2000 75 267.6 92.8 105 2.8
25 4000 186 267.3 94.7 101 2.5
40 2000 123 267.1 90.4 70 1.8
40 4000 286 264.8 91.1 55 1.7
70 2000 139 262.8 90.3 50 3.6
70 4000 398 267.1 91.6 44 3.3
5 25 2000 180 266.7 91.1 116 3.6
25 4000 335 271.3 98.9 106 2.9
40 2000 220 271.4 94.8 71 3.2
40 4000 392 271.5 97.3 64 2.1
70 2000 252 262.2 92.2 33 2.4
70 4000 450 267.5 94.8 30 2.2
6 25 2000 102 267.9 93.4 98 2.2
25 4000 172 264.6 96.5 86 1.9
40 2000 112 268.3 95.5 85 1.6
40 4000 186 262.7 97.8 76 1.8
70 2000 137 262.1 92.3 40 1.9
70 4000 232 263.3 94.4 37 1.8
7 25 2000 84 269.1 96.2 128 3.4
25 4000 187 269.9 98.7 114 3.1
40 2000 155 262.8 91.6 73 1.9
40 4000 492 266.7 94.1 68 2.1
70 2000 150 268.6 89.4 41 2.1
70 4000 501 264.9 96.6 38 2.4
8 25 2000 108 270.8 97.6 114 2.4
25 4000 223 268.9 98.6 109 3.1
40 2000 200 263.6 92.7 83 2.1
40 4000 582 267.5 98.8 62 2.5
70 2000 246 269.1 93.9 38 3.3
70 4000 603 264.9 98.9 33 2.5
9 25 2000 56 264.1 94.2 92 2.4
25 4000 132 265.3 95.6 87 1.8
40 2000 140 262.9 92.3 91 2.1
40 4000 231 262.8 96.7 82 1.8
70 2000 245 266.6 91.1 41 2
70 4000 376 265.7 96.8 36 1.7
Reaction conditions: styrene concentration, 1.32 mol/l; [Ti] = 0.83 Â 10À6
mol/l.
a
Tp = Polymerization temperature.
b
Activity = kg-polymer/mol-Ti-h-atm.
c
S.I. = Syndiotactic index.
3442 N.T.B. Linh et al. / Journal of Organometallic Chemistry 694 (2009) 3438–3443
6. (1.8–2.4) by the catalyst bearing the pentamethylene bridge.
Dependence of the molecular weights of SPS upon polymerization
temperature follows the general tendency that polymerization at
lower temperatures produces larger molecular weights regardless
of the catalyst structure. Molecular weight of SPS generated by
the xylene bridged catalysts at 25 °C ranged between 100 000
and 128 000. However, molecular weights of polymers at 70 °C
ranged from 30 000 to 50 000. Effects of cocatalyst amount on
molecular weight was found not to be significant, although SPS
from [Al]:[Ti] = 2000 represented lower molecular weights com-
pared to those from [Al]:[Ti] = 4000. This result illustrates that
the polymerization temperature is the major element to adjust
molecular weight of SPS using the catalysts in this study.
The dinuclear catalysts mentioned herein were very efficient in
preparing syndiotactic polystyrene (SPS) with high stereoregular-
ity. All the SPS possessed a syndiotactic index (SI) from 90% to
99%. When comparing SI0
s of the polystyrenes, it was interesting
that the catalysts with the aryloxo group (7, 8, 9) seemed to form
polymers with slightly higher SI values than those with the corre-
sponding chloride group (4, 5, 6). The polymers generated by
catalysts 4 and 7, having an ortho-xylene bridge, exhibited syndio-
tacticity relatively lower than those made by catalysts bearing a
meta-xylene bridge, as well as pentamethylene bridge. Generally
speaking, the structure of the bridging ligand of the dinuclear
half-titanocenes does not seem to have a crucial effect upon differ-
entiating the stereochemical process of polymerization despite the
abovementioned difference. This result can be attributed to the
mechanistic property of styrene polymerization via half-titano-
cene. It is accepted that a perfect regioselective insertion of a coor-
dinated styrene monomer to the metal-carbon bond via a
secondary 2,1-insertion mode led to the generation of syndiotactic
stereoregularity due to p-bonding of the terminal styrene unit of
the growing chain to the metal center. This indicates that the ste-
reoregular configuration is induced by a repulsing interaction be-
tween the phenyl ring of the last unit of the growing chain and
the phenyl ring of the incoming monomer and accounts for the
finding that in the case of syndiospecific styrene polymerization,
variation of the catalyst ligand sphere has only a minor effect on
polymer structure. Many homogenous metallocene catalysts were
able to produce SPS with a decrease in syndiotacticity and melting
temperature as polymerization temperature increased [7,8,14].
This general trend has also been demonstrated in this experiment.
4. Summary
Preparation of dinuclear half-titanocenes with ortho- and meta-
xylene bridges [{Ti(g5
-cyclopentadienyl)Cl2L}2-ortho, meta-(CH2–
C6H4–CH2)] (L = Cl (4, 5), L = O-2,6-iPr2C6H3 (7, 8)) has been
achieved by the reaction of the respective trimethylsilyl deriva-
tives of the ligands with 2.0 eq of TiCl4 in methylene chloride.
The preparative route to obtain new compounds was the improved
synthetic procedure to make the corresponding catalyst with the
para-xylene bridge. Catalysts 4, 5, 7, and 8 were characterized by
1
H and 13
C NMR, and elemental analysis. The 1
H NMR spectrum
of catalyst 4 indicated the predicted resonances for the bridging
meta-xylene-biscyclopentadienyl ligand that appears as: two sets
of pseudotriplets at 6.86 and 6.68 ppm due to the AA0
BB0
system
of the cyclopentadienyl protons; a singlet at 4.14 ppm for the
methylene protons; a multiplet between 7 and 7.20 ppm for the
phenyl protons. Chemical shifts of the cyclopentadienyl protons
of catalyst 7 moved to 6.44 and 6.37 ppm from 6.86 and
6.68 ppm of those of catalyst 4, indicating that aryloxo substitution
caused a 0.42 and 0.31 ppm upfield shift of the cyclopentadienyl
protons. It is suggested that the reduced value of d of compounds
7 and 8 likely reflects the larger size of the aryloxo group over
the chloride that lead to greater steric interaction around the tita-
nium. The catalytic activity of the six catalysts increased in the or-
der of 6 < 9 < 4 < 5 < 7 < 8, at 40 and 70 °C, [Al]:[Ti] = 4000 (activity
unit = kg of polymer/(mol of Ti-h). This result was understood as
the geometric characteristics of the catalysts due to the presence
of the ortho- and meta-xylene bridge. The different activity trend
between the xylene and pentamethylene linkage may be under-
stood both by steric and electronic factors. The variation in molec-
ular weight and molecular weight distribution does not seem to be
very sensitive to catalyst structure. The ortho-xylene bridged 7
gave rise to the formation of the highest molecular weight SPS
while the SPS formed by the catalyst with the pentamethylene
bridge exhibited the lowest molecular weight. All the SPS gener-
ated in this study possessed a syndiotactic index (SI) from 90% to
99%. It was found that the polymers generated by catalysts 4 and
7 having the ortho-xylene bridge exhibited relatively lower syndio-
tacticity than the others made by the catalysts with the meta-xy-
lene bridge, as well as the pentamethylene bridge. Generally
speaking, the structure of the bridging ligand of the dinuclear
half-titanocenes does not seem to have a crucial effect upon differ-
entiating the stereochemical process of polymerization.
Acknowledgements
We are grateful for the support of the Korean Ministry of
Knowledge and Economy (Grant 10016450).
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