Carbon cleavage

The most intense peaks in the mass spectrum of an alcohol correspond to the ton formed according to carbon-carbon cleavage of the type shown ... 

Oxygen donors like peroxy acids, ozone, and pyridine IV-oxides cause carbon-carbon cleavage, perhaps by formation of a perepoxide (43 Scheme 30) (81JCS(P1)1871). Other oxidants have also been reported to react with oxiranes (64HC( 19-1)228). 

Carbon-carbon cleavage induced by chemical attack is rare for oxiranes [cf. thermal and photolytic cleavage (Section 5.05.3.2.1)], but a few examples are known, e.g. Scheme 64 (70TL3025). 

Inoue H, O Takimura, K Kawaguchi, T Nitoda, H Euse, K Murakami, Y Yamaoka (2003) Tin-carbon cleavage of organotin compounds by pyoverdine from Pseudomonas chlororaphis. Appl Environ Microbiol 69 878-883. 

Comparing the product selectivity at low conversion in the hydrogenolysis of 2,2-dimethylbutane for the two catalysts is noteworthy. Zirconium hydride supported on siUca does not produce neopentane, but only isopentane (10%) as a Cs product in agreement with a /1-alkyl transfer as a key step for the carbon-carbon cleavage (no neopentane can be formed through this mechanism, Scheme 25). 

Gross, H. and Keitel, I., a-Substituted phosphonates. 58. A direct phosphorylation of 7,7-bisphosphorylated quinonemethide nucleus with trivalent phosphorus-hydrogen compounds via carbon-carbon cleavage, Phosph., Sulf., Silic. Relat. Elem., 62, 35, 1991. 

Inoue H, Takimura O, Kawaguchi K, Nitoda T, Fuse H, Murakami K, Yamaoka Y (2003) Tin-Carbon Cleavage of Organotin Compounds by Pyoverdine from Pseudomonas chloro-raphis. Appl Environ Microbiol 69 878... 

LiP catalyzes the oxidation of a low-molecular-weight redox mediator, veratryl alcohol, which in mrn mediates one-electron oxidation of lignin to generate aryl cation radicals [100]. The radicals facilitate a wide variety of reactions such as carbon-carbon cleavage, hydroxylation, demethylation, and so on. Dezotti et al. [101] reported enzymatic removal of color from extraction stage effluents using lignin and horseradish peroxidases immobilized on an activated silica gel support. 

Apart from the reactions included in Section IV.A, other processes, including reductive carbon-carbon cleavage with less synthetic importance, will be considered. 

An alternative pathway for entanglement loss is chain scission (Fig. 3.2, process B), in which a covalent bond along the polymer main chain is broken and a stress-bearing, otherwise elastic, chain is lost. Chain scission reactions, for example, homolytic carbon-carbon cleavage, have obviously high activation energies. The stress-free rates of these reactions are therefore typically extremely low. 

Under alkaline conditions isolating lignin degradation products which are essentially of a phenyl.ethyl rather than a phenylpropyl nature is structurally important and requires a lignin structure by which the 7-carbon may be removed as a result of a 0-7 carbon-carbon cleavage reaction, either by direct alkaline hydrolysis or alkali-catalyzed hydrogenolysis. 

Under the initially neutral conditions of hydrogenation, the production of the phenylpropanols as the major products represents a stabilized form of the initially released units. Loss of oxygen from the a- and impositions by a hydrogenolysis reaction may well have occurred. The results of the studies, using initially alkaline conditions whereby phenyl-ethanoid products result, help support the belief that alkali facilitates the 0-7 carbon-carbon cleavage and that oxygen originally was associated with the 0-carbon atom. 

Olah and Hogeveen and co-workers The carbon-carbon cleavage in neopentane (7) yielding methane and the tert-butyl cation 4 occurs by a mechanism different from the /3-scission of carbenium ions [Eq. (5.56)]. 

This reaction is much faster than the carbon-carbon cleavage in neopentane, despite the initial formation of secondary carbenium ions. Norbomane is also cleaved in a fast reaction, yielding substituted cyclopentyl ions. Thus, protonation of alkanes induces cleavage of the molecule by two competitive ways (i) protolysis of a C—H bond followed by /3-scission of the carbenium ions and (ii) direct protolysis of a C—C bond yielding a lower-molecular-weight alkane and a lower-molecular-weight carbenium ion. 

However, most organosilicon compounds are metabolized after ingestion or injection, and their metabolites are eliminated. For example, silameprobamate (27) undergoes to - 1 hydroxylation, following the same pattern as meprobamate itself. The difference in the metabolism of the two compounds is that the silicon compound also undergoes silicon-carbon cleavage to yield a silanol that can be isolated from the urine as a disiloxane (32) see Eq. (1). 

Clawson, P., Lunn, P.M., and Whiting, D.A. (1990) Synthetic studies on O-heterocycles via cycloadditions. Part 1. Photochemical (electron transfer sensitized) carbon-carbon cleavage of diaryloxiranes. Journal of the Chemical Society, Perkin Transactions 1, 153-157. 

Carbon-carbon cleavage has been extensively investigated. Thus bibenzyl derivatives when irradiated in the presence of 1,4-DCB and methanol form the... 

Ozonolysis of the s-alkylmercuric halides and the di-s-alkylmercurials produced the coresponding ketone. Although some carbon-carbon cleavage occurred, it was generally less than with the reaction of the primary organomercurials (see Reactions 13 and 14, Table I). In partial contrast to the results of Bockemuller and Pfeuffer (Reaction II), the ozonation of diisopropylmercury yielded acetic acid in addition to acetone (Reaction 14, Table I). 

Tertiary alkylmercuric halides yielded a considerable amount of the corresponding alcohol upon ozonation (Reaction 17, Table I). Some carbon-carbon cleavage accompanied the main reaction in this case as well. 

Carbon—Carbon Cleavage. As mentioned above, carbon—carbon cleavage usually accompanied the normal carbon-mercury cleavage reaction. While this chain-shortening process was most prominent for the n-alkylmercuric halides which were ozonated at 10°C (Reactions I and 6, Table I), it was reduced to a much lower level when the di-n-alkylmercurials were ozonated at —76°C (Reactions 5 and 10, Table I). Actually even less carbon—carbon scission occurred during the ozonation of the di-s-alkylmercurials halides (Reaction 14, Table I) and during the partial ozonation of the lerl-alkylmercuric halides (not listed). 

By comparison of the n-alkylmercurial results alone, it is possible to generalize that both higher ozonation temperatures and the presence of a halogen ligand on mercury promote carbon-carbon cleavage during the ozonolysis of the carbon-mercury bond. 

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