Showing papers on "Catalysis published in 1980"

Principles and applications of organotransition metal chemistry

Abstract: A perspective Bonding Survey of organotransition metal complexes according to ligand Ligand substitution processes Oxidative-addition and reductive elimination Intramolecular insertion reactions Nucleophilic attack on ligands coordinated to transition metals Electrophilic attacks on coordinated ligands Metallacycles Homogeneous catalytic hydrogenation, hydrosilation, and hydrocyanation Catalytic polymerization of olefins and acetylenes Catalytic reactions involving carbon monoxide Synthetic applications of transition metal hydrides Synthetic applications of transition metal complexes containing metal carbon bonds Synthetic applications of transition metal carbonyl compounds Synthetic application of transition metal carbenes and metallacycles Synthetic applications of transition metal alkene, diene, and duenyl complexes Synthetic applications of transition metal alkyne complexes Synthetic applications of -allyl transition metal complexes Synthetic applications of transition metal arene complexes.

Enzyme-Catalyzed Phosphoryl Transfer Reactions

Abstract: PERSPECTIVES AND SUMMARY ... 877 Classes of enzyme involving reactions at phosphorus 878 COVALENT REACTION INTERMEDIATES, CRYPTIC AND OTHERWISE 879 Reactions of Phosphoric Monoesters ..... 879 Phosphatoses ..... ..... 879 Phosphokinases • •..•.....• • 881 Phosphomutases 886 Reactions of Phosphoric Diesters 890 REACTION ENERGETICS 892 "Off" Rates 893 Internal Thermodynamics ... .. ... ..... ...... ...... ... 896 THE NATURE OF THE ELEMENTARY STEP ....... ...... 898 Associative versus Diss ociative Pathways 898 Stereochemistry . .. ......... . ... 902 Prochiral substrate ..... prochiral product ... 902 Prochira/ substrate ..... pro-prochira/ product :.... ...... 903 Pro-prochiral substrate ..... pro-prochira/ product .. ........ ...... ........ ...... 905 Metal Ions 907 Cation-dependent diastereoisomer preference 908 Substitution-inert complexes of nucleotides 909 Catalysis ......... 911

Ziegler-Natta Catalysis

Abstract: Publisher Summary This chapter discusses the scope of Ziegler catalysis; stereoselectivity, kinetics, and mechanism of Ziegler catalysis; homogeneous Ziegler–Natta catalysts; and side reactions in homogeneous catalysts. Ziegler catalysis involves rapid polymerization of ethylene and α-ole-fins with the aid of catalysts based on transition-element compounds, normally formed by the reaction of a transition-element halide or alkoxide or alkyl or aryl derivative with a main-group element alkyl or alkyl halide. There are thousands of patents involving every combination of pure or mixed main-group alkyls with transition-element compounds, each claiming advantages. The result of the early work led to the development of “second-generation” Ziegler catalysts. Polymers produced with unmodified Ziegler catalysts showed extremely high molecular weight and broad distribution, and in some cases, there was evidence for “living polymer.” All homogeneous catalyst systems for ethylene polymerization become heterogeneous when polyethylene is formed. On using vanadium-based homogeneous catalysts, polymers consisting of syndiotactic stereo blocks and stereo-irregular blocks are obtained. Very high stereoselectivity is observed for racemic 4-methyl- 1-hexene and racemic 3,7-dimethyl-1-octene, where the asymmetric carbon atom is in the α-position relative to the double bond. Stereoselectivity is caused by the chirality of the catalytically active center, and not by chiral atoms in the growing chain. It must be concluded from the results that reactions take place, which change the number of active sites present, due to the different behavior of the polymers in solution. Study of these new catalysts is intensive. After a short induction period, the activity of polymerization increases as a function of the monomer concentration.

Spectrophotometric determination of hydrogen peroxide using potassium titanium(IV) oxalate

Abstract: A simple and rapid method for the spectrophotometric determination of hydrogen peroxide using potassium titanium(IV) oxalate is described. The method can be used to measure peroxide concentrations down to about 10 µM(0.3 mg kg–1) under the most favourable conditions. A variety of complexing and reducing agents, and catalysts of peroxide decomposition, known to interfere with the alternative iodide method for peroxide determination, had no effect. Fluoride was found to interfere.

Phase transfer catalysis

Abstract: Ion Pairs and Ion Pair Extraction Introduction: The Nature of Phase Transfer Catalysis Ion Pairs in Organic Media Extraction of Ion Pairs from Aqueous Solution Crown Ethers, Cryptates, and Other Chelating Agents as Extractants Solid-Liquid Anion Exchange Mechanism of Phase Transfer Catalysis Mechanistic Investigations Empirical Catalyst Evaluations Unusual and Polymer Supported Catalysts Practical Applications of Phase Transfer Catalysis General Experimental Procedures Formation of Halides Preparation of Nitriles Ester Formation Miscellaneous Displacements Thiols and Sulfides Preparation of Ethers N-Alkylations C-Alkylation of Activated CH-Bonds Alkylation of Ambident Anions Isomerizations and H/D Exchange Additions across Multiple CC-Bonds Addition to C=O and C=N Bonds b'-Eliminations Hydrolysis Reactions Generation and Conversion of Phosphonium and Sulfonium Ylides Nucleophilic Aromatic Substitution Miscellaneous Reactions Organometallic PTC Applications a'-Eliminations Reduction Reactions Oxidation Reactions References Subject Index.

Electrode catalysis of the four-electron reduction of oxygen to water by dicobalt face-to-face porphyrins

Abstract: A series of dimeric metalloporphyrin molecules has been synthesized in which the two porphyrin rings are constrained to lie parallel to one another by two amide bridges of varying length that link the rings together. These cofacial metalloporphyrins have been applied to the surface of graphite electrodes and tested for catalytic activity toward the electroreduction of dioxygen to water in aqueous acidic electrolytes. All molecules tested exhibited some catalytic activity, but hydrogen peroxide rather than water was the chief reduction product. However, the dicobalt cofacial porphyrin linked by four-atom bridges produced a catalyzed reduction almost exclusively to water and at exceptionally positive potentials. Rotating ring-disk voltametric measurements were employed to diagnose the electrode reaction pathway and a possible mechanism for the observed catalysis is suggested. The results seem to demonstrate the participation of two metal centers in controlling the course of a multiple-electron process.

A molecular beam study of the catalytic oxidation of CO on a Pt(111) surface

Abstract: The oxidation of carbon monoxide catalyzed by Pt(111) was studied in ultrahigh vacuum using reactive molecular beam–surface scattering. Under all conditions studied, the reaction follows a Langmuir–Hinshelwood mechanism: the combination of a chemisorbed CO molecule and an oxygen adatom. When both reactants are at low coverage, the reaction proceeds with an activation energy E*LH =24.1 kcal/mole and a pre‐exponential υ4 =0.11 cm2 particles−1 sec−1. At very high oxygen coverage, E*LH decreases to about 11.7 kcal/mole and υ4 to about 2×10−6 cm2 particles−1 sec−1. This is largely attributed to the corresponding increase in the energy of the adsorbed reactants. When a CO molecule incident from the gas phase strikes the surface presaturated with oxygen, it enters a weakly held precursor state to chemisorption. Desorption from this state causes a decrease in chemisorption probability with temperature. Once chemisorbed, the CO molecule then has almost unit probability of reacting to produce CO2 below 540 K. The CO2 product angular distribution varies from cosγ to cos4γ depending sensitively upon the adsorbed reactant concentrations.

Electrocatalytic reduction of carbon dioxide by using macrocycles of nickel and cobalt

Abstract: An indirect method for the reduction of CO/sub 2/ in nonaqueous solutions and involving initial reduction of metal complexes and their subsequent reduction with CO/sub 2/ is described. The complexes were tetraazamacrocyclic complexes of Ni and Co. The catalytic reduction process was investigated by means of controlled potential coulometry experiments performed in a gas-tight electrolysis cell under a CO/sub 2/ atmosphere. The effects of water, Ar, and N/sub 2/ on the electrolysis process were investigated. The results indicated that the indirect electrochemical reduction of CO/sub 2/ occurred at a potential between -1.3 and -1.6V vs SCE and that the reduction was indeed catalyzed by the metal complexes. Reaction periods of as long as 24 h did not reduce catalytic activity; and in most cases, the catalyst was isolated in its original form at the end of the run. A protic source was found to be necessary for the reaction to yield CO and H/sub 2/; and in the absence of a protic source, simple stoichiometric reduction of the complex was noted. (BLM)

Surface Science and Catalysis—Studies on the Mechanism of Ammonia Synthesis: The P. H. Emmett Award Address

Abstract: About 5 years ago a Battelle Colloquium on “The Physical Basis of Heterogeneous Catalysis” was held in honor of Professor Emmett where he presented an introductory talk on ″Fifty Years of Progress in the Study of the Catalytic Synthesis of Ammonia″ [1], a field to which he had made significant contributions during this whole period. So why another report on this topic? Justification can perhaps partly be obtained by some of Professor Emmett's concluding remarks which were not completely decisive with respect to the mechanism of this reaction: 'The experimental work of the past 50 years leads to the conclusion that the rate-determining step in ammonia synthesis over iron catalysts is the chemisorption of nitrogen. The question as to whether the nitrogen species involved on the surface is molecular or atomic is still not conclusively resolved. In fact, our own work in this field was mainly induced by this paper, and continuing discussions and correspondence with Professor Emmett were extremely help...

Behavior of metallic iron catalysts during Fischer-Tropsch synthesis studied with Mössbauer spectroscopy, X-ray diffraction, carbon content determination, and reaction kinetic measurements

Abstract: The conversion of unpromoted, unsupported metallic iron catalysts into carbides during Fischer-Tropsch synthesis (CO:H2:He = 1:1:3, 1 atm) was studied with Mossbauer spectroscopy, X-ray diffraction, carbon content analysis, and reaction kinetic measurements. From a comparison between experiments at different temperatures and literature data, it is concluded that both reaction conditions and the nature of the iron catalyst determine the combination of carbides that will be formed. Investigation of single-phase carbides revealed that the X-ray diffraction pattern commonly ascribed to a pseudohexagonal carbide Fe2C actually belongs to the carbide ∈′-Fe2.2C. At synthesis temperatures of 513 K and lower, unknown iron-carbon species were found, referred to as FexC. It is believed that FexC represents poorly defined structures between α-Fe and a crystallographic carbide. The behavior of metallic iron catalysts during Fischer-Tropseh synthesis at 513 K was studied in more detail as a function of time. It was found that the rate of hydrocarbon formation was initially low, passed through a maximum, and decreased thereupon, while the conversion of α-Fe into carbides started at a high rate and decreased rapidly. These results can be understood as the consequence of either a competition between bulk carbidization and hydrocarbon synthesis or a relatively slow activation of α-Fe for the formation of hydrocarbons in which bulk carbidization plays no role. Deactivation is caused by the formation of an excessive amount of inactive carbon at the surface of the catalyst.

Nickel and palladium complex catalyzed cross-coupling reactions of organometallic reagents with organic halides

Abstract: The discovery in 1972 by two research groups that dihalodiphosphinenickel(II) complexes exhibit extremely high catalytic activity for selective cross-coupling of Grignard reagents with sp2-carbon halides has aroused wide-spread interest in application in organic synthesis of this type and related reactions involving other organometallics than Grignard reagents and not only nickel but also palladium complexes as catalysts. In this lecture several aspects of the title subject will be described centering argument on the Grignard coupling using a variety of phosphine-nickel and -palladium complexes of the formula MC12L2 (M = Ni or Pd; L2 = diphosphine) as catalyst precursors.

Biomimetic control of chemical selectivity

Abstract: Enzyme mimics and artificial enzymes have been designed to imitate several different aspects of enzyme catalysis. For instance, mimics have been constructed to imitate an enzymatic mechanism, using the same catalytic groups which the enzyme uses and examining the question of whether a proposed mechanism for the enzymatic process is reasonable or duplicable. Another common goal of enzyme mimics is the imitation of the velocity of enzyme catalyzed reactions. Enzymes can increase the rates of ordinary reactions by factors as large as 1012 using very ordinary catalytic groups to do so. One of the challenges for enzyme mimics is to duplicate not only the mechanism by which the enzyme operates but also the very large rate of the process. The third area of interest is to imitate the selectivity of enzyme-catalyzed reactions.

The Palladium Catalyzed Nucleophilic Substitution of Aryl Halides by Thiolate Anions

Abstract: In the presence of a catalytic amount of tetrakis(triphenylphosphine) palladium, phenyl and methyl or methoxyphenyl iodides and bromides were found to react with thiolate anions in alcoholic solven...

Homogeneous Catalysis: The Applications and Chemistry of Catalysis by Soluble Transition Metal Complexes

Abstract: Trends in Homogeneous Catalysis in Industry. Isomerization of Olefins. Reactions of Olefins and Dienes--Hydrogenation and HY Additions. Polymerization and Oligomerization of Olefins and Dienes. Reactions of Carbon Monoxide. Oxidation of Olefins and Dienes. Arene Reactions. Reactions of Acetylenes. Carbene Complexes in Olefin Metathesis and Ring-Forming Reactions. Oxidation of Hydrocarbons by Oxygen. Esterification, Polycondensation, and Related Processes. Homogeneous Catalysis in Halocarbon Chemistry. Appendix. Index.

A Mechanistic Study of O 2 Reduction on Water Soluble Phthalocyanines Adsorbed on Graphite Electrodes

Abstract: : Co and Fe tetrasulfonate phthalocyanines (M-TSP), adsorbed at monolayer levels on graphite surfaces, have been found to have a pronounced catalytic effect on the O2 reduction process in both acid and alkaline solutions. The kinetics have been examined with the rotating ring-disk electrode technique. Co-TSP promotes the O2 reduction process via 2-electrons to give peroxide whereas Fe-TSP promotes a 4-electron reduction to give water. (Author)

Synthesis of solid superacid catalyst with acid strength of H0⩽–16.04

Abstract: A solid superacid catalyst with an acid strength of H0⩽–16·04, which was active for reactions of propane and butane, was obtained by exposing Zr(OH)4, prepared by the hydrolyses of ZrOCl2 and ZrO(NO3)2, to 1 N H2SO4 and then calcining in air at 575–650 °C.

Interaction of ribulosebisphosphate carboxylase/oxygenase with transition-state analogues.

Abstract: 2-C-Carboxy-D-ribitol 1,5-bisphosphate and 2-C-carboxy-D-arabinitol 1,5-bisphosphate have been synthesized, purified, and characterized. In the presence of Mg2+, 2-C-carboxy-D-arabinitol 1,5-bisphosphate binds to ribulose-1,5-bisphosphate carboxylase/oxygenase by a two-step mechanism. The first, rapid step is similar to the binding of ribulose 1,5-bisphosphate or its structural analogues. The second step is a slower process (k = 0.04 s-1) and accounts for the tighter binding of 2-C-carboxy-D-arabinitol 1,5-bisphosphate (Kd less than or approximately to 10(-11) M) than of 2-C-carboxy-D-ribitol 1,5-bisphosphate (Kd = 1.5 X 10(6) M). Both carboxypentitol bisphosphates exhibit competitive inhibition with respect to ribulose 1,5-bisphosphate. 2-C-(Hydroxymethyl)-D-ribitol 1,5-bisphosphate and 2-C-(hydroxymethyl)-D-arabinitol 1,5-bisphosphate were also synthesized; both are competitive inhibitors with respect to ribulose 1,5-bisphosphate with Ki = 8.0 X 10(-5) M and Ki = 5.0 X 10(-6) M, respectively. Thus, the carboxyl group of 2-C-carboxy-D-arabinitol 1,5-bisphosphate is necessary for maximal interaction with the enzyme. Additionally, Mg2+ is essential for the tight binding of 2-C-carboxy-D-arabinitol 1,5-bisophsphate. A model for catalysis of ribulose 1,5-bisphosphate carboxylation is discussed which includes a functional role for Mg2+ in the stabilization of the intermediate 2-C-carboxy-3-keto-D-arabinitol 1,5-bisphosphate. Mechanistic implications that arise from the stereochemistry of this intermediate are also discussed.