Carbon elimination

The mechanism of carbon elimination is similar to those of the earlier open-hearth processes, ie, oxidation of carbon to carbon monoxide and carbon dioxide. The chemical reactions and results are the same in both cases. The progress of the reaction is plotted in Figure 5. 

Mikami M, Hatano M, Akiyama K (2005) Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts. 14 279-322 Minatti A, DOtz KH (2004) Chromium-Templated Benzannulation Reactions. 13 123-156 Miura M, Satoh T (2005) Catalytic Processes Involving b-Carbon Elimination. 14 1-20 Miura M, Satoh T (2005) Arylation Reactions via C-H Bond Cleavage. 14 55-84 Mizobe Y, see Hidai M (1999) 3 227-241... 

Cyclobutanones react with arylboronic acids to afford butyrophenones (Equation (60)). Addition of arylrhodium species to the carbonyl group followed by /3-carbon elimination is proposed. 

A nickel(O) complex catalyzes insertion of alkynes into cyclobutanones (Equation (79)).437 Formation of metalla-cycle 194 via oxidative cyclization of an alkyne with the carbonyl group of a cyclobutanone followed by /3-carbon elimination (formation of metallacycle 195) and reductive elimination are postulated for the mechanism (Scheme 92). 

Carbon-doped silicon carbide, 22 535 Carbon electrodes, 12 305, 752-758 furnaces using, 12 753 grades of, 72 754 in open-arc furnaces, 72 301 production of, 72 755 properties of, 72 755-756 Carbon elimination, in steelmaking, 23 258 Carbon fiber, 77 214-215 Carbon fiber ceramic-matrix composites, 26 773... 

This varies with temperature for the small particles, as at low temperatures the deposited carbon eliminates sites for the reaction while the latter become available at higher temperatures at which surface carbon reacts away with O2. 

An analogous ring contraction-carbon elimination reaction with Ni-etioporphyrin would require loss of a methyl group which is energetically prohibitive. Formation of a methyl carbonium ion, for example, is energetically 50 kcal/mole higher than the corresponding xylyl carbonium ion. 

Metathesis of alkenes has been reviewed in terms of cross-metathesis, ring opening and closing, disproportionation, transmutation, and self-metathesis.34 A review on catalytic processes involving ft -carbon elimination has summarized recent progress on palladium-catalysed C-C bond cleavage in various cyclic and acyclic systems.35... 

Also remember that elimination reactions can accompany berth SX1 and reactions. Elimination occurs when the nucleophile behaves as a base rather than a nucleophile it abstracts a proton rather than attacking a carbon. Elimination reactions always result in a carbon-carbon double bond. El and E2 kinetics are similar to V1 and Ss2 respectively. 

The accelerated carbonation reactions have also been shown to improve the immobilization properties of Portland cements used as radioactive was-teforms. The formation of carbonates eliminates the potential problem of radiolysis while at the same time improving the leaching resistance. The resulting carbonate matrix, which is more thermodynamically stable relative to the untreated cement, would also be preferred for the underground disposal of the wasteforms. Incorportion of fly ash into the cement-type wasteform further enhances the favorable properties of this waste type. 

A nickel-catalysed alkyne insertion between the carbonyl carbon and the -carbon of the cyclobutanone was achieved by combining a ketone-alkyne coupling reaction with a /3-carbon elimination process (Scheme 79).121 The reaction uses cyclobutanones as a four-carbon unit and provides access to substituted cyclohexenones. 

Analogous to the cycloadditions described above, the first step of these ring expansion reactions is believed to involve the initial oxidative coupling between the carbonyl and the alkyne to afford a nickelapentenacycle (12, Scheme 2) [37,38]. Subsequent (3-carbon elimination relieves ring strain and affords a seven-membered nickelacycle 13a that reductively eliminates the... 

When homoallyl alcohols are treated under analogous reaction conditions, the carbonylation reaction does not occur rather, a characteristic carbon-carbon bond cleavage occurs to give ketones and alkenes. During this reaction, /3-carbon elimination occurs to give the products. The CO pressure is cmcial for suppressing deactivation of the catalyst and stabilizing the active species by coordination to the metal center (Eq. 11.27) [69]. 

Fig. 8 (left). Relative catalytic activity as a function of carbon elimination from the commercially coked catalyst. , benzene hydrogenation. , n-pentane isomerization... 

Thus there are two different types of catalyst pellet failure. The first takes place during elongation produced by carbon deposition. The second takes place during contraction produced by carbon elimination. 

Keywords Activation, C-C bond, Transition metal, Cleavage, Oxidative addition, P-carbon elimination, Directionality, Homogeneous... 

As described in Sect. 2.1, oxidative addition provides a direct approach to C-C bond cleavage. An alternative method for breaking C-C bonds employs a alkyl-metal complexes. The bond between the (3- and y-carbon atoms in these complexes can be cleaved via (3-carbon elimination. Examples of C-C bond cleavage via this process are quite rare. 

Watson et al. reported a leading example of (3-carbon elimination observed with a well-defined metal complex [67]. Thermal decomposition of a lutetium-isobutyl complex having a vacant coordination site leads to the formation of a lutetium-methyl complex and propene by way of (3-methyl elimination, the microscopic reverse of olefin insertion. A concerted four-center transition state is proposed. This study demonstrated that (3-carbon elimination is an energetically accessible process, and provided a model for the chain transfer that occurs during propene oligomerization. 

Migration of more complex alkyl groups was recently reported [70]. Reversible migratory insertion/(3-carbon elimination occurs between the coordinated alkyne and the bound alkyl group of alkyl-niobium(alkyne) complex 52. 

For examples of P-carbon elimination in late transition metal systems, Bergman et al. identified P-methyl transfer with four-membered ruthenacycles, which is driven by the formation of Ji-allyl and Ji-oxallyl complexes. Warming the solution of oxaruthenacycle 58 to 45°C led to formation of methane and cyclic enolate complex 60 [76]. ji-Oxallyl complex 59 initially arises from P-methyl... 

A o,jt-bonded alkyl-palladium complex undergoes P-carbon elimination on protonation of the cyclopentadiene ring [79]. 

A cyclobutylmethyl-metal system provides another opportunity to observe 13-carbon elimination. The ring opening process harnesses the release of the least necessitating ring strain of a four-membered ring. Scandocene hydride 63 reacts with 3-methyl-l,4-pentadiene to afford the linear Ji-allyl complex 65 [80]. The intermediacy of cyclobutylmethyl complex 64 which undergoes P-carbon elimination accommodates the observed rearrangement. 

Yttrium hydride reacts with methylenecyclobutane to form pentenyl chelate complex 67 [81]. P-Carbon elimination occurs to open the ring of cyclobutylmethyl intermediate 66. 

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