Aromatic hydrocarbons rearrangement

A surpnsing feature of the reactions of hexafluoroacetone, trifluoropyruvates, and their acyl imines is the C-hydroxyalkylation or C-amidoalkylaOon of activated aromatic hydrocarbons or heterocycles even in the presence of unprotected ammo or hydroxyl functions directly attached to the aromatic core Normally, aromatic amines first react reversibly to give N-alkylated products that rearrange thermally to yield C-alkylated products. With aromatic heterocycles, the reaction usually takes place at the site of the maximum n electron density [55] (equaUon 5). 

Whereas the metabolism of aromatic hydrocarbons takes place by dioxygenation, their biotransformation by yeasts and fungi is normally initiated by monooxygenation to the epoxide followed by hydrolysis to the trani-dihydrodiols. Phenols may subsequently be formed either by elimination or by nonenzymatic rearrangement of the epoxide ... 

Hulbert, P. B. Grover, P. L. Chemical rearrangement of phenol-epoxide metabolites of polycyclic aromatic hydrocarbons to quinone-methides. Biochem. Biophys. Res. Commun. 1983, 117, 129-134. 

Dyotropic Rearrangements and Related o--cr Exchange Processes, 16, 33 Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Fast Exchange Reactions of Group I, II, and III Organometallic Compounds, 8, 167 Fischer-Tropsch Reaction, 17, 61 Flurocarbon Derivatives of Metals, 1, 143... 

A comprehensive summary of the theoretical contributions over the past 40 years towards the understanding of the relationship between two-dimensional aromaticity (hydrocarbons) and the electronic structure of three-dimensional deltahedral boranes. Note in particular that rearrangement processes and the isocloso problem in metallaboranes have also been discussed.11... 

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl ethers, the related naphthalene compounds, and even sufficiently reactive aromatic hydrocarbons. Generally, the coupling must be carried out in media which are neutral or slightly basic or which are buffered in the appropriate pH range. The reaction may also be carried out in nonaqueous media. While some primary and secondary aromatic amines initially form an A-azoamine, which may rearrange to the more usual amino-C-azo compound, tertiary amines couple in a normal manner. 

Catalytic reforming92-94 of naphthas occurs by way of carbocationic processes that permit skeletal rearrangement of alkanes and cycloalkanes, a conversion not possible in thermal reforming, which takes place via free radicals. Furthermore, dehydrocyclization of alkanes to aromatic hydrocarbons, the most important transformation in catalytic reforming, also involves carbocations and does not occur thermally. In addition to octane enhancement, catalytic reforming is an important source of aromatics (see BTX processing in Section 2.5.2) and hydrogen. It can also yield isobutane to be used in alkylation. 

Aromatization the conversion of nonaromatic hydrocarbons to aromatic hydrocarbons by (1) rearrangement of aliphatic (noncyclic) hydrocarbons (q.v.) into aromatic ring structures and (2) dehydrogenation of alicyclic hydrocarbons (naphthenes). 

Muller, M., Iyer, V.S., Ktibel, C., Enkelmann, V. and Mullen, K. (1997) Polycyclic aromatic hydrocarbons by cyclodehydrogenation and skeletal rearrangement of oligophenylenes. Angewandte Chemie (International Ed. in English), 36,1607-10. 

Mechanism. The mechanism for the formation of the low molecular weight aromatic hydrocarbons, namely ionene and the dimethylnaphthalene compounds can be explained by the scheme of Edmunds and Johnstone (22), advanced by Vetter et al. (35). The mechanism involves cyclizatlon with twelve electron systems followed by rearrangement to a four-ring intermediate, which leads to the formation of di-methycyclodecapentaene. This leads to the expulsion of ionene and dimethylnaphthalene from the carotene molecule as volatiles and the resulting nonvolatile component has been reported (13). 

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