Carbon monoxide , activation assisted

C.l. Carbon monoxide and carbon dioxide activation assisted by... 

The reactions that occur to auto-exhaust emissions when exposed to plasma include oxidation of HCs, carbon monoxide, and partially diesel PM also. Nitric oxide (NO) can be oxidized by plasma to N02. Plasma alone, due to its oxidizing character, is not a viable NO control method. However, combinations of plasma with catalysts, referred to as plasma-assisted catalysts or simply plasma catalysts , have been suggested for NO reduction. The plasma is believed to show potential to improve catalyst selectivity and removal efficiency. Current state-of-the-art plasma catalysts have efficiencies comparable to those of active DeNO systems, removing about 50% of NO at a fuel economy penalty of less than 5% [85],... 

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. 

Colloidal osmium readily undergoes oxidation it catalvtieally assists the oxidation of unsaturated compounds by gaseous hydrogen. In this respect it is stated to be even more effective than the finely divided metal, but less active than either platinum or iridium. Carbon monoxide combines with oxygen, yielding the dioxide, when shaken at ordinary temperatures with the hydrosol of osmium.7... 

Compared in this section are the activation parameters and the relative reactivities toward SO2 of the various types of transition metal alkyl and aryl complexes. As shown in Table IV, the values of AS and AH range from — 63 to — 43 e.u. and from 2.7 to 8.7 kcal/mole, respectively. These entropies of activation are more negative than those for the solvent-assisted carbon monoxide insertion [—33 to —17 e.u. (1J7)] or for the SO2 insertion into the Sn—R (R = Ph and CHaPh)... 

Palladium-assisted carbocarboxylation of enamines with carbon monoxide/methanol and carbanions yields yS-amino acids as /J-lactam precursors14. If the enamine is chirally modified by an optically active carbamate unit, complete diastcrcocontrol is observed15. This method has been used for the synthesis of (+)-thienamycin15. 

Similarly, palladium(II)-assisted carboacylation of optically active vinyl carbamates with mal-onate, carbon monoxide and a trimethylorganostannane leads to optically pure amino oxo esters in good chemical yield and complete diastereocontrol via carbonylative coupling16-38. 

These reactions occur at a very slow rate on pure platinum and this has resulted in a large research effort to discover more active electrocatalysts. At present, platinum—ruthenium offers the best performance. Ruthenium adsorbs water more readily than platinum and the resulting species, Ru—OHads, assists the removal of carbon monoxide from neighbouring platinum sites. Despite this beneficial effect of ruthenium, still more efficient electrocatalysts are required to enhance the power delivered by DMFCs, especially if the system is to compete favourably with hydrogen—air PEMFCs. 

In Scheme 1.2, all of the types of carbonylations that are discussed in the book are depicted. Alcohols, amines, ethers, carboxylic acids and halides can be converted to acids, amides, esters, ketones, alkynones, alkenones, anhydrides and acid halides with the assistance of transition metal catalysts in the presence of a CO source. The CO sources used can be carbon monoxide gas, Mo(CO)6, Co(CO>6, formic acid, aldehyde, etc. If the starting material is alcohols or amines, some additives for activation are needed, such as BuONO, TsCl, AcCl. If the substrate is (Hetero)ArH, additional oxidants will be necessary this is a so-caUed oxidative carbonylation. If an unsaturated compound is to be carbonylated, a nucleophile NuH that carries an acidic hydrogen has to be present. In the case of insertion reactions, this is not necessary. 

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