Carbon catalyzed

The heterocyclic rings in quinoline (116) and isoquinoline are selectively reduced by Pd on carbon-catalyzed reaction of ammonium formatc[107]. Some benzene rings are also reduced. For example, nitrobenzene is reduced to cyclohexylamine (117) with formic acid. It is important to use a sevenfold excess of formic acid[108]. 

The alkyl azide 118 is reduced to a primary amine by the Pd on carbon-catalyzed reaction of ammonium formate in MeOH at room temperature. No racemization takes place with chiral azides[l 11,112]. 

In a study on the influence of supports on rhodium, the amount of dicyclohexylamine was found to decrease in the order carbon > barium carbonate > alumina > barium sulfate > calcium carbonate. Plain carbon added to rhodium-on-alumina-catalyzed reactions was found to cause an increase in the amount of dicyclohexylamine, suggesting that carbon catalyzes the formation of the intermediate addition product (59). 

The apparent reaction order of carbon-catalyzed methane decomposition reaction was determined to be 0.6 0.1 for AC (lignite) and 0.5 0.1 for CB (BP2000) catalysts. Thus, the rate equation for carbon-catalyzed decomposition of methane can be written as follows ... 

Xu, X. Matsumura, Y. Stenberg, J. Antal, M. J., Carbon-catalyzed gasification of organic feedstocks in supercritical water. Industrial and Engineering Chemistry Research 1996, 35, 2522-2530. 

Intramolecular Michael addition.1 Cesium carbonate catalyzes the intramolecular Michael addition of a cyclic (3-keto ester to an a,(3-ynone to form a cyclic enone after protonation. This reaction proceeds readily when a five- or six-mem-bered ring is formed higher rings can be formed, but in low yield.1... 

Mechanistic studies showed that metalacycle la is competent to be a catalyst in asymmetric allylic substitution reactions. The reaction of benzylamine with methyl ciimamyl carbonate catalyzed by a mixture of LI and [Ir(COD)Cl]2 occurs with an induction period and forms product in 84% yield and 95% ee, whereas the same reaction catalyzed by a mixture of metalacycle la and [Ir(COD)Cl]2 occurs without an induction period in just 2 hours to form the substitution product in 81% yield and 97% ee. The latter reaction was conducted with added [Ir(COD)Cl]2 to trap the -bound LI after dissociation. This ligand must dissociate to provide a site for oxidative addition of the allylic carbonate. 

Scheme 22 Catalytic cycle for the reaction of aniline with methyl cinnamyl carbonate catalyzed by a metalacyclic iridium-phosphoramidite complex...

The use of ethylene adduct lb is particularly important when the species added to activate catalyst la is incompatible with one of the reaction components. Iridium-catalyzed monoallylation of ammonia requires high concentrations of ammonia, but these conditions are not compatible with the additive [Ir(COD)Cl]2 because this complex reacts with ammonia [102]. Thus, a reaction between ammonia and ethyl ciimamyl carbonate catalyzed by ethylene adduct lb produces the monoallylation product in higher yield than the same reaction catalyzed by la and [Ir(COD)Cl]2 (Scheme 27). Ammonia reacts with a range of allylic carbonates in the presence of lb to form branched primary allylic amines in good yield and high enantioselectivity (Scheme 28). Quenching these reactions with acyl chlorides or anhydrides leads to a one-pot synthesis of branched allylic amides that are not yet directly accessible by metal-catalyzed allylation of amides. 

Carreira et al. reported the kinetic resolution of branched allylic carbonates catalyzed by an iridium complex derived from a chiral [2.2.2]-bicyclooctadiene [48]. Reactions of allylic carbonates with phenol were run to 50% conversion of the carbonate, leaving unreacted allylic carbonate in high enantiomeric excess (Scheme 32). The phenyl ether products were also isolated in mid-to-high enantiomeric excess. 

Concurrent with acetic anhydride formation is the reduction of the metal-acyl species selectively to acetaldehyde. Unlike many other soluble metal catalysts (e.g. Co, Ru), no further reduction of the aldehyde to ethanol occurs. The mechanism of acetaldehyde formation in this process is likely identical to the conversion of alkyl halides to aldehydes with one additional carbon catalyzed by palladium (equation 14) (18). This reaction occurs with CO/H2 utilizing Pd(PPh )2Cl2 as a catalyst precursor. The suggested catalytic species is (PPh3)2 Pd(CO) (18). This reaction is likely occurring in the reductive carbonylation of methyl acetate, with methyl iodide (i.e. RX) being continuously generated. 

Feme oxide (3% or more on activated carbon) catalyzes the hydrolytic decomposition of CFC-12 and 1,1,2-tnchlorotrifluoroethane (CFC-113) at450 °C or above... 

Dehalogenation of chlorinated arenes.3 Palladium (10%) on carbon catalyzes the rapid transfer of hydrogen from ammonium formate to aryl chlorides to provide the parent arene. Dehalogenation of 2,4,6-trichlorophenol proceeds through di-chloro- and chlorophenol and is complete within 10 minutes at ambient temperature and pressure. 

This reaction was first observed by Plate, Erivanskaya, and Khalima-Mansur over platinum-on-carbon and platinum-on-alumina catalysts (43-48). Platinum-on-carbon catalyzes this reaction between 310°C and 390°C (above which the catalyst is poisoned) (44). Over an acidic platinum-alumina catalyst containing 0.5 wt% platinum and 0.1 wt% sodium, 16.7% acenaphthenes and 1.5% acenaphthylene are obtained at 460°C and at 0.4 liquid hourly space velocity in hydrogen diluent. Conversions are considerably lower in helium. 

There was a good agreement oft such an interpretation with kinetic measurements of sodium carbonate catalyzed polymerization (84,87,91). This idea of a simple anionic interchange reaction between an amide group and an amide anion was very attractive, because it allowed to extrapolate the possibility of macroring formation by a simple building-in of caprolactam units into the amide bond. However, basic endgroups... 

Diene-A-ynes. Propargylic carbonates in reactions catalyzed by Pd(0) can react as allenyl complexes. Thus carbonylation of 2-alkynyl carbonates catalyzed by Pd(0) results in 2,3-dienylcarboxylates as the major or only product (equation I). Similarly, coupling of 2-alkynyl carbonates with terminal acetylenes in the presence of Cul and LiCl and catalyzed by Pd(0) provides l,2-diene-4-ynes in 60-83% yield (equation II). 

Scheme 5.3 Synthesis of various carbonates catalyzed by PEG6000- supported hexaalkylguanidinium bromide [13]...

Xie H, Duan H, Li S et al (2005) The effective synthesis of propylene carbonate catalyzed by silica-supported hexaalkylguanidinium chloride. New J Chem 29(9) 1199-1203... 

Tian J-S, Wang J-Q, Chen J-Y et al (2006) One-pot synthesis of dimethyl carbonate catalyzed by n-Bu4NBr/n-Bu3N from methanol, epoxides, and supercritical C02. Appl Catal A-Gen 301(2) 215-221... 

Scheme 62 Palladium on carbon-catalyzed synthesis of COX-inhibitors...

Palladium-carbon-catalyzed hydrogenation of (16) gave (24), and NaBH4 reduction of (22) gave (25), both receptors now containing a saturated linkage between the aza crown system and the ferrocenyl redox center. This methylene-ferrocene linkage was found to serve as an insulator both compounds (24) and (25) are totally electrochemically insensitive to the presence of any alkali metal cation. 

Sigmatropic rearrangements catalyzed by silver salts have been used in total synthesis. The synthesis of three monoterpene compounds that comprise the pheromone of male boll weevil Anthonomus grandis has been achieved using the silver-carbonate catalyzed rearrangement of an acetoxycyclohexyl acetylene as the key step (Scheme 3.35).56... 

The rate of the reaction (86-90) is about two orders of magnitude slower than the O2/C reaction, consistent with the greater strength of the NO bond than that in O2. The CO/CO2 ratio in the products of the reaction increases with increasing temperature (86, 87). At low temperatures (850 K), a stable chemisorbed oxygen compled (86) forms and inhibits the reaction. At AFBC temperatures, however, it has been observed that the reaction is accelerated in the presence of oxygen (91). This latter result may be a consequence of the increase in the CO concentration within a char particle as the 0 concentration is raised. Because the O2/C reaction is so much faster than the NO/C or the carbon catalyzed CO/NO reaction (86, 91), the situation exists in which the effectiveness factor for the O2/C reaction is small and little O2 penetration into char occurs at a time when the effectiveness factor for the NO reduction reactions are near unity. Additional NO reduction reactions that may occur are the CO/NO reaction catalyzed by bed solids (90 - 92) and the reduction of NO by sulfite-containing, partially sulfated limestone (93). 

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. 

A practical application of activated carbon catalyzed chlorination is the synthesis of para nitrobenzotrichloride via chlorination at 150-200 °C112. At even higher temperature (250 °C) large-pore carbon, in presence of water vapors, is an effective catalyst for chlorodemethylation of para xylene (equation 6)113. 

Figure 3 describes reaction schemes for naphthalene carbonization catalyzed by metallic potassium or by aluminum chloride (13,14) these catalysts produce contrasting isotropic and anisotropic carbons, respectively. The intermediate structures are similar except for more naphthenic structure induced in the AlCl -catalyzed carbonization. The role of naphthenic structures leading to optical anisotropy has been recognized in many examples, and their introduction can improve the anisotropic development, as described later. Higher fusibility, lower melting temperature, and higher solubility of the intermediate molecules may be obtained by the formation of partially naphthenic structures (15). 

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