Aromatic reactions, isomerization

Perfluoroalkylation of substituted benzenes and heterocyclic substrates has been accomplished through thermolysis of perfluoroalkyl iodides in the presence of the appropriate aromatic compound Isomeric mixtures are often obtained W-Methylpyrrole [143] and furan [148] yield only the a-substituted products (equation 128) Imidazoles are perfluoroalkylated under LTV irradiation [149] (equation 129). 4-Perfluoroalkylimidazoles are obtained regioselectively by SET reactions of an imidazole anion with fluoroalkyl iodides or bromides under mild conditions [150] (equation 130) (for the SET mechanism, see equation 57)... 

The catalysts generally used in catalytic reforming are dual functional to provide two types of catalytic sites, hydrogenation-dehydrogenation sites and acid sites. The former sites are provided by platinum, which is the best known hydrogenation-dehydrogenation catalyst and the latter (acid sites) promote carbonium ion formation and are provided by an alumina carrier. The two types of sites are necessary for aromatization and isomerization reactions. 

Many reactions occur in the reactor under reforming conditions. These are aromatization reactions, which produce aromatics isomerization reactions, which produce branched paraffins and other reactions. 

During the cracking process, fragmentation of complex polynuclear cyclic compounds may occur, leading to formation of simple cycloparaffins. These compounds can he a source of Ce, C7, and Cg aromatics through isomerization and hydrogen transfer reactions. 

Zwanenburg and Wagenaar148 have reported the rather unusual rearrangement of sulfone 81 to 82, after standing overnight at 0°, and suggested an elimination-addition mechanism, via initial isomerization of A3 to the A2-thiazoline-oxide with subsequent elimination and readdition of sulfmic acid, followed by spontaneous loss of water in a Pummerer-type aromatization reaction. 

Further isomerization reactions may occur with alkyl-substituted aromatic reaction products, and a considerable study has been made of the reactions of this type of molecule. The following are the main types of skeletal reactions involving alkyl substituents on an aromatic ring (a) If the substituent chain is sufficiently large, there may occur within it all of the processes we have already discussed for aliphatic hydrocarbons them-... 

Lipids from marine products have been studied less frequently. The detection of co-(o-alkylphenyl)alkanoic acids with 16,18 and 20 carbon atoms together with isoprenoid fatty acids (4,8,12-trimethyltetradecanoic acid and phytanic acid) and substantial quantities of bones from fish and molluscs has provided evidence for the processing of marine animal products in vessels [58 60]. C16, C18, and C20 co-(o-alkylphenyl)alkanoic acids are presumed to be formed during the heating of tri-unsaturated fatty acids (C16 3, C18 3 and C20 3), fatty acyl components of marine lipids, involving alkali isomerization, pericyclic (intermolecular Diels-Alder reaction) and aromatization reactions. 

Murakami and colleagues132 studied the Diels-Alder reactions of vinylallenes with alkynes catalyzed by a rhodium complex. When a vinylallene lacking substituents at the vinylic terminus was reacted with a terminal alkyne, 1,3,5-trisubstituted benzenes were obtained, the reaction between vinylallene 197 and 1-hexyne (198) being a representative example (equation 55). The reaction was proposed to proceed via a rhodacycle which afforded the primary Diels-Alder adduct via reductive elimination. Aromatization via isomerization of the exocyclic double bond led to the isolation of 199. 

The platforming catalyst was the first example of a reforming catalyst having two functions.43 44 93 100-103 The functions of this bifunctional catalyst consist of platinum-catalyzed reactions (dehydrogenation of cycloalkanes to aromatics, hydrogenation of olefins, and dehydrocyclization) and acid-catalyzed reactions (isomerization of alkanes and cycloalkanes). Hyrocracking is usually an undesirable reaction since it produces gaseous products. However, it may contribute to octane enhancement. n-Decane, for example, can hydrocrack to C3 and C7 hydrocarbons the latter is further transformed to aromatics. 

Triazoline aromatization to triazoles can be achieved by oxidation, isomerization reactions, and elimination of stable molecular fragments, all of which require the presence of a free hydrogen at position 4 and/or 5 of the triazoline ring. The aromatization reaction affords a selective, synthetic route for the preparation of triazoles of definitive structure, inasmuch as azide addition to acetylenes is not regioselective.33... 

The rate of fluorine displacement from fluorotoluenes by H-atoms has been measured in single-pulse shock tubes at 988-114 K.158 The addition of CF3 to CgFsCl has been studied.159 The intermediate adduct radical (CF3C6F5C1) was shown to react with an additional CF3 to give CF3CI and C6F5CF3. A range of fluorinated biphenyls can be produced by the reaction of pentafluorobenzene radicals with both electron-rich and -poor aromatics. The isomeric ratios of biphenyls produced indicated an efficient homolytic chain process.160... 

Skeletal rearrangement reactions over Pt single crystals have been studied for methyl cyclopentane, 2- and 3-methylpentane350 and for n-hexane.3sl One conclusion351 is that whereas aromatization reactions are very sensitive to surface structure [Pt(l 11)> Pt(100)], isomerization, Cs-cyclization, and hydrogenolysis reactions display little dependence on structure. Temperature and H2 pressure are more important in affecting the selectivity. 

Scheme 1 summarizes the characteristics of the reactions, processes, and mechanistic aspects of this group of important chemical transformations, which form the basis of a large fraction of the current chemical industry. The reactions can be classified as intentional C-H transformations, carried out in aromatization reactions and in olefin synthesis, or as unintentional C-H transformations, for example isomerization reactions and all heteroatom functionalization such as oxidation or amination. 

In practice the primary F-T hydrocarbon products then go on to react further in secondary processes. These include isomerization (both by H-migra-tion and skeletal isomerization), hydrogenation and dehydrogenation, and aromatization reactions, as well as in the incorporation of CO, of other oxygenates, and even nitrogenous compounds. A typical F-T product... 

The most widely studied aspect of arene-oxide chemistry is the aromatization reaction to yield phenols. The acid-catalyzed, spontaneous, and thermal rearrangements of epoxides to ketones have a parallel in the isomerization of arene oxides to dienone intermediates with subsequent aromatization to phenols. Prior to their availability by chemical synthesis, arene oxides were postulated as initial inter-... 

Isomerization of n-paraffin, especially normal pentane to iso-pentane is essential for making high octane gasoline with low aromatics content. Isomerization of lower paraffins has been conducted in the solid catalyzed gas-phase reaction system by using noble metal-supported solid acid under hydrogen atmosphere. The most predominant reaction mechanism for the isomerization of alkane is as follows (1) the dehydrogenation of alkane to alkene on the supported metal (2) proton addition to the alkene to form carbenium ion on the acidic component (3) skeletal isomerization of the carbenium ion on the acidic component (4) deprotonation of the isoraerized carbenium ion to form alkene on the acidic component (5) hydrogenation of the alkene to alkane on the metal [1]. 

The expert system we are developing concerns several aromatic reactions of great industrial interest [12-23], e.g., alkylation and isomerization of aromatics such as benzene, toluene, and xylene, catalyzed by ZSM-5, mordenite, and Y... 

Cyclo-olefins are subject to structural isomerization in contact with acidic catalysts, as Bloch and Thomas (27) and Greensfelder and Voge (21) have shown. Therefore, such catalytic activity when intimately coupled to the aromatization reaction may direct the reaction path to products having five-carbon ring structures which cannot aromatize ... 

Cycloaddition, Diels-Alder reactions, epoxidation of aromatic aldehydes, isomerization of aryl-substituted epoxides, and aziridination catalyzed by the iron Lewis acid [(j 5-C5H5)Fe(CO)2(THF)] 03ACA3. 

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