Silver-containing catalyst system

The catalyst systems employed are based on molybdenum and phosphorus. They also contain Various additives (oxides of bismuth, antimony, thorium, chromium, copper, zirconium, etc.) and occur in the form of complex phosphomolybdates, or preferably heteropolyacids deposited on an inert support (silicon carbide, a-alumina, diatomaceous earths, titanium dioxide, etc.). This makes them quite different from the catalysts used to produce acrylic acid, which do not offer sufficient activity in this case. With residence times of 2 to 5 s, once-through conversion is better than 90 to 95 per cent, and the molar yield of methacrylic acid is up to 85 to 90 per cent The main by-products formed are acetic add, acetone, acrylic add, CO, C02, etc. The major developments in this area were conducted by Asahi Glass, Daicel, Japan Catalytic Chemical, Japanese Gem, Mitsubishi Rayon, Nippon Kayaku, Standard Oil, Sumitomo Chemical, Toyo Soda, Ube, etc. A number of liquid phase processes, operating at about 30°C, in die presence of a catalyst based on silver or cobalt in alkaline medium, have been developed by ARCO (Atlantic Richfield Co,), Asahi, Sumitomo, Union Carbide, etc. 

In 2014 several reports described the use of inverse-electron-demand Diels-Alder reactions to furnish naphthalene-based compounds from phthalazine-containing ring systems. Employing nonprecious metal complexes, copper(l) and nickel(O) complexes, instead of silver salts to catalyze formal [4+ 2] cycloadditions of 1,2-diazines and siloxyalkynes, Rawal and his group developed an environmentally friendlier and more economical method for preparing siloxy derivatives of naphthalene, anthracene, and phenanthrene (Scheme 16) (140L3236). In addition, the copper catalyst could also be employed for the synthesis of the corresponding quinolines and isoquinolines. This method provided the respective products in... 

Despite the considerable synthetic potential of this reaction, only two NHC-containing catalysts have been reported to date. The in situ generated complex from the reaction between [RhCl(COD)]2 and the NHC-silver ligand transfer reagent 20 was found to be active in the arylation of an At-phosphi-noyl aldimine with phenylboronic acid but unfortunately only one catalytic test was performed [eqn (8.9)]. In a more systematic study, Suzuki and Sato screened various azolium salts, among which the system [RhCl(COD)]2/ lAd-HCl proved to be the most active catalyst for the arylation of a series of A -sulfonyl and A -phosphinoyl arylimines. ... 

Similarly, numerous other oligocyclic ring systems containing cyclopropane units have been obtained according to this method.The reaction is mechanistically interpreted as occurring via edge attack of the silver ion followed by a cationic rearrangement. Softer metal catalysts, such as rhodium, nickel and palladium, mostly lead to alternative products (e.g. [2-F2] cycloreversion). ... 

There is a bewildering amount of information on the kinetics of ethylene oxidation over silver. Static, flow, differential, and recycle systems have been used with various catalysts, feed ratios, and additives. From this work two conclusions are clear (1) it is not possible to cover all conditions with a simple rate law and (2) attempts to determine mechanisms by means of kinetics are quite risky. Earlier studies have been reviewed by Margolis (f), Sampson and Shooter (2), and Dixon and Longfield (S7). The classic paper was that of Twigg (34), who used mainly a static system. By now it is evident that, although Twigg s results contain much of value, they are not directly applicable to flow systems using modem catalysts. Under practical conditions the... 

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