Carbon monoxide saturation effect

The first scheme was ruled out by showing that, at room temperature, a surface formed by very brief exposure of the oxygen-saturated surface to carbon monoxide is stable after removal of the carbon monoxide from the reaction chamber. In other words, no further surface carbide formed by lateral reactions of adsorbed carbon monoxide with surface oxygen atoms. The second scheme was ruled out by showing that exposure of the surface formed in the latter experiment to oxygen had no effect. Consequently the third scheme is believed to represent the mechanism of oxidation of carbon monoxide at the step and kink sites of platinum. 

Low-valent, 18-electron carbene complexes (Fischer-type) are electronically and coordinatively saturated and must usually be activated to become efficient metathesis catalysts. This activation can be effected by thermal or photolytic [781,782] removal of one ligand, e.g. carbon monoxide, or by treatment with a Lewis acid (Table 3.15) [783]. 

Even the precovering with hydrogen is able to block the surface against electronic interaction. In Fig. 27 a nickel surface was precovered with hydrogen at 3 X 10 mm. Hg to saturation (0 = 0.39), causing an irreversible resistance decrease of 1%. After pumping off at B, carbon monoxide of 6 X 10 mm. Hg was added at Aco- At a pure nickel surface the carbon monoxide influence would have effected an increase of the resistance by 0.8%. At the surface precovered with hydrogen, neither a resistance effect nor a carbon monoxide adsorption is to be observed. 

Unsaturated hydrocarbons (alkenes, dienes) react with carbon monoxide and a proton source (H20, alcohols, amines, acids) under strong acidic conditions to form carboxylic acids or carboxylic acid derivatives. Since a carbocationic mechanism is operative, not only alkenes but also other compounds that can serve as the carbocation source (alcohols, saturated hydrocarbons) can be carboxylated. Metal catalysts can also effect the carboxylation of alkenes, dienes, alkynes, and alcohols. 

Fig 5 Effects of carbon monoxide on human beings This chad can be considered only as a general guide because the percent of CO blood saturation will vary with exertion, excitement, fear, depth of respiration, anemia, and general physical condition of the individual... 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

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. 

Hydroformylation of linear olefins in a conventional cobalt oxo process (see Section 5.3) produces increasing linear-to-branched aldehyde ratios as the carbon monoxide ratio in the gas stream is increased up to 5 MPa (50 atm), but there is little further effect if the reaction mixture is saturated with carbon monoxide. An increasing partial pressure of hydrogen also increases this ratio up to a hydrogen pressure of 10 MPa. As the reaction temperature is increased, the linear-to-branched aldehyde ratios decreases. Solvents in conventional cobalt-catalyzed hydroformylation affect the isomer distribution. In propylene... 

The experiments were carried out in small stainless steel autoclaves having an internal volume of 700 mL. The autoclaves, having been charged with a particular catalyst solution and gas mixture of interest, were mounted vertically in electrically heated ovens. The factors affecting the rate of the reaction are partial pressure of carbon monoxide, partial pressure of ethylene, catalyst concentration, temperature, base concentration/pH, and the nature of the base. Carbon monoxide has an inhibitory effect upon the reaction. The rate of reaction increases linearly with ethylene pressure in the low-pressure regime but exhibits saturation at ethylene pressures exceeding 17 atm. The reaction is second order with respect to catalyst concentration. The nature of the base used deter-... 

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