Ethylene-carbon monoxide mechanisms

Activated carbon is an active catalyst for the free radical chlorinations of hydrocarbons. Methane108, in the gas phase, and acetic acid109, in the liquid phase, are both chlorinated in its presence. Surface free radicals are claimed to play a major role in the mechanism of this reaction. A similar mechanism has been established for the active carbon catalyzed chlorination of indane in aqueous solution by quenching methods110. Trimm111 has reviewed the activity of carbon in chlorination of carbon monoxide, ethylene and toluene. 

Quantum, by contrast, converted an ethylene—carbon monoxide polymer into a polyester-containing terpolymer by treatment with acidic hydrogen peroxide, the Baeyer-Villiger reaction (eq. 11). Depending on the degree of conversion to polyester, the polymer is totally or partially degraded by a biological mechanism. 

The mechanism of poisoning automobile exhaust catalysts has been identified (71). Upon combustion in the cylinder tetraethyllead (TEL) produces lead oxide which would accumulate in the combustion chamber except that ethylene dibromide [106-93-4] or other similar haUde compounds were added to the gasoline along with TEL to form volatile lead haUde compounds. Thus lead deposits in the cylinder and on the spark plugs are minimized. Volatile lead hahdes (bromides or chlorides) would then exit the combustion chamber, and such volatile compounds would diffuse to catalyst surfaces by the same mechanisms as do carbon monoxide compounds. When adsorbed on the precious metal catalyst site, lead haUde renders the catalytic site inactive. 

In the ethylene atmosphere, carbon monoxide and ethylenimine copolymerized with a radical initiator to form a terpolymer239. The following radical mechanism may be proposed ... 

Solutions of Ru3(CO)i2 in carboxylic acids are active catalysts for hydrogenation of carbon monoxide at low pressures (below 340 atm). Methanol is the major product (obtained as its ester), and smaller amounts of ethylene glycol diester are also formed. At 340 atm and 260°C a combined rate to these products of 8.3 x 10 3 turnovers s-1 was observed in acetic acid solvent. Similar rates to methanol are obtainable in other polar solvents, but ethylene glycol is not observed under these conditions except in the presence of carboxylic acids. Studies of this reaction, including infrared measurements under reaction conditions, were carried out to determine the nature of the catalyst and the mechanism of glycol formation. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor. 

The kinetics and mechanism for oxygen transfer between 4-cyano-V,V,-dimethylaniline V-oxide and a C2-capped mexo-tetraphenylporphyrinatoiron(III) and mc5 o-tetrakis(pentafiuorophenyl)-porphyrinatoiron(III) have been established. Addition of a copper(II) porphyrin cap to an iron(II)-porphyrin complex has the expected effect of reducing both the affinities and rate constants for addition of dioxygen or carbon monoxide. These systems were studied for tetradecyl-substituted derivatives solubilized by surfactants such as poly(ethylene oxide) octaphenyl ether. ... 

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

A study of the gas phase reactions of sulfur atoms with ethylene and propylene lias been recently carried out by Strausz and Gunning (98). Atomic sulfur, presumably in the (lD) metastable state, was generated by photolysis of carbonyl sulfide in the wavelength region 2550-2290 A., and the study was restricted to 25°C. Pure carbonyl sulfide yields carbon monoxide and sulfur as the main products. When ethylene and propylene are added, the carbon monoxide yield is decreased, tending to a value one half as large as in the absence of the olefins. Cyclic sulfides are simultaneously formed by addition of S atoms to the two olefins. The mechanism which accounts for the main features of the process is... 

The stepwise electron reduction of C02, whether direct or indirect, catalyzed, or by direct transfer on an apparently inert conductive surface, has been the object of considerable attention since the first concise reports of formate anion production. Since then, the list of possible derivatives has grown from formates to carbon monoxide, methane, ethylene, and short-chain saturated hydrocarbons. As noted in Section 12.1, this area of research has been expanded in recent years [8, 80, 83], with information relating to increased yields, to the effect of electrode materials on selectivity, as well as further speculations on possible reaction mechanisms, having been obtained on a continuous basis. Yet, the key to these synthetic processes-an understanding of the relationship between the surface of the electrode and the synthetic behavior of the system-seems no closer to being identified. 

This is probably because 0 atoms produced in primary process (45) react much more rapidly with C2H6 than with N20. Several products are formed including ethylene, butane, carbon monoxide, hydrogen, methane, and probably ethanol and acetaldehyde. More ethylene is formed than one would expect from the amount of butane. It was found that 0 atoms react rapidly with ethylene, which is one of the photolytic products. The reaction-rate constant of O atoms with ethylene is estimated to be about 330 times as rapid as that with ethane.82 Complete elucidation of the mechanism of O-atom reaction with ethane is complicated because of the rapid reaction of O atoms with one or more of the products. 

The compatibility of blends of poly (vinyl chloride) (PVC) and a terpolymer (TP) of ethylene, vinyl acetate, and carbon monoxide was investigated by dynamic mechanical, dielectric, and calorimetric studies. Each technique showed a single glass transition and that transition temperature, as defined by the initial rise in E" at 110 Hz, c" at 100 Hz, and Cp at 20°C/min, agreed to within 5°C. PVC acted as a polymeric diluent which lowered the crystallization temperature, Tc, of the terpolymer such that Tc decreased with increasing PVC content while Tg increased. In this manner, terpolymer crystallization is inhibited in blends whose value of (Tc — Tg) was negative. Thus, all blends which contained 60% or more PVC showed little or no crystallinity unless solvent was added. 

Such a mechanism of carbon monoxide interaction with active centers is compatible with the data on the slow copolymerization of CO with ethylene found for the ethylene polymerization by some one-component catalysts This copolymerization may proceed also in the case of two-component catalysts resulting in an increase of the number of radioactive tags in the polymer with time (see Fig. 1). Arguments have been given that the rapid increase of polymer radioactivity in the initial period (5-10 min) is due to the insertion of the first CO molecule into the active metal-carbon bond. 

After activation, the catalyst is intrcxiuced into the polymerization reactor as slurry in a saturated hydrocarbon such as isobutane. The precise mechanism of initiation is not known, but is believed to involve oxidation-reduction reactions between ethylene and chromium, resulting in formation of chromium (II) which is the precursor for the active center. Polymerization is initially slow, possibly because oxidation products coordinate with (and block) active centers. Consequently, standard Phillips catalysts typically exhibit an induction period. The typical kinetic profile for a Phillips catalyst is shown in curve C of Figure 3.1. If the catalyst is pre-reduced by carbon monoxide, the induction period is not observed. Unlike Ziegler-Natta and most single site catalysts, no cocatalyst is required for standard Phillips catalysts. Molecular weight distribution of the polymer is broad because of the variety of active centers. 

The pyrolysate components of both copolymers show similar mechanisms of the reaction. Both C(0)-CH2 and CH2-CH2 bonds can be cleaved. For example, in the case of poly(ethylene-co-carbon monoxide), the reactions taking place with C(0)-CH2 cleavage are shown schematically below ... 

Many catalytic reactions described in this book depend on carbon monoxide and hydrogen as feedstock chemicals. Hydroformylation (CO + H2) and simple hydrogenation (H2) are typical examples. In many cases carbon monoxide undergoes side reactions, among which the water-gas shift reaction is well studied in terms of the mechanism. This explains why carbon monoxide in the presence of water (e. g., aqueous media) can be used to hydrogenate substrates such as olefins, nitroaromatics, and other unsaturated organic compounds. In a number of industrial processes (e. g., the hydrocarboxylation of ethylene), however, this is an unwanted side reaction. 

Incineration is a rapid, exothermic reaction between a fuel (waste) and oxygen (O2). Incineration produces the same end products and by-products, whether the material burned is municipal solid waste, hazardous waste, or medical waste. This is because of the fact that complex fuel molecules first undergo thermal decompositions upon being preheated by the preceding flame, forming smaller molecules such as methane, acetylene, ethylene, carbon monoxide, hydrogen, and alike, and it is the combustion of these smaller molecules that primarily influence the nature of combustion products and pollutants formed. This aspect of combustion chemistry has significantly helped in the development of detailed kinetic mechanisms of combustion for all types of hydrocarbon fuels. Solid decomposition... 

Under certain conditions, such as exposure/to particular catalytic materials, each of these reactions may give yields asjiigh as SO per cent or more of theoretical. Each of these reactions are Reversible, practically completely so, under certain conditions where side reactions and decompositions are largely eliminated. Secondary decomposition of acetaldehyde to methane and carbon monoxide, reduction of the ethylene by hydrogen to ethane, break down of ether to lower molecular weight compounds, polymerizations, etc., so involve any equilibrium relations that the relative rates of the different reactions as well as the equilibria are difficult to obtain experimentally. Even where specific and directive catalysts are used, side reactions are present and complicate any precise analysis of the decomposition mechanism. 

By a similar mechanism to that proposed for the formation of ethyl ether by dehydration of ethanol, it is possible that the reaction occurs stepwise with the intermediate dehydration of one ethanol molecule to form ethylene which then reacts with another ethanol molecule to form butanol. It is thus possible that higher alcohols may be built up by the reaction of olefins with the lower alcohols. Mixed oxide type of catalysts are used in the process of a nature similar to those which have been found effective in alcohol synthesis from hydrogen and carbon monoxide. It should lie noted here that catalysts which promote the union of carbon atoms must be used, and since potassium oxide promoted catalysts composed of mixtures of zinc, copper, or chromium oxides have been found to be effective in the syuthesis of higher alcohols, such catalysts should be useful in promoting the addition of olefins to alcohols or other oxygenated organic molecules.77... 

On irradiation with ultraviolet light, the activated ketone groups present can take part in two different types of free radical, bond-breaking reactions. In organic photochemistry, these two reactions are referred to as Norrish I and Norrish II Reactions, and their mechanisms are shown below for the degradation of copolymers of ethylene and carbon monoxide [46, 47] ... 

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