Formation of aromatics

Formation of aromatic structures such as benzene and its homologues by platforming and other processes. This route is of ever increasing importance in the production of aromatic materials. 

Research is also being conducted in Japan to aromatize propane in presence of carhon dioxide using a Zn-loaded HZSM-5 catalyst/ The effect of CO2 is thought to improve the equilibrium formation of aromatics by the consumption of product hydrogen (from dehydrogenation of propane) through the reverse water gas shift reaction. 

However, it was found that the effect on the equilibrium formation of aromatics is not substantial due to thermodynamic considerations. A more favorable effect was found for the reaction between ethylene (formed via cracking during aromatization of propane) and hydrogen. The reverse shift reaction consumes hydrogen and decreases the chances for the reduction of ethylene to ethane byproduct. 

Other Reactions Involving Formation of Aromatic Diazonium Ions... 

C followed by formation of aromatic hydrocarbons. Minimal residue could be obtained overMO catalysts (Fe,Mg,Al-MO and Ca,Mg,Al-MO). 

The earliest developments in transition metal-assisted formation of aromatic C-P linkages were the result of the efforts of Tavs28 that were concerned with the use of Ni(II) halide salts for the reaction of aryl halides with trialkyl phosphites. These reactions involved conditions reminiscent of the Michaelis-Arbuzov reaction (heating at an elevated temperature) and produced arylphosphonate products in reasonable yield (Figure 6.8). 

Most of the work on the C-N bond-forming crosscoupling reactions has concentrated on the formation of aromatic C-N bonds. Recent studies show that the application of cross-coupling reactions to alkenyl halides or triflates furnished enamines (Scheme 19) (for palladium-catalyzed reaction, see 28,28a-28d, and for copper-catalyzed reaction, see 28e-28g). Brookhart et al. studied the palladium-catalyzed amination of 2-triflatotropone 109 for the synthesis of 2-anilinotropone 110.28 It was found that the reaction of 109 proceeded effectively in the presence of racemic BINAP and a base. As a simple method for the synthesis of enamines, the palladium-catalyzed reactions of alkenyl bromide 111 with secondary amine were achieved under similar conditions.2841 The water-sensitive enamine 112 was isolated as pure compound after dilution with hexane and filtration through Celite. The intramolecular cyclization of /3-lactam 113, having a vinyl bromide moiety, was investigated by Mori s... 

Experiment.—In order to show that this formation of aromatic nitrosamines is reversible, boil a small amount of the pure compound just prepared in xylene and hold a piece of moist potassium iodide-starch paper over the mouth of the tube. 

Except for these studies of their protonation behavior, almost the only other aspect of the chemistry of sulfonic acids that has been investigated to any extent from a mechanistic point of view is the desulfonation of aromatic sulfonic acids or sulfonates. Since this subject has been well reviewed by Cerfontain (1968), and since the reaction is really more of interest as a type of electrophilic aromatic substitution than as sulfur chemistry, we shall not deal with it here. One should note that the mechanism of formation of aromatic sulfonic acids by sulfonation of aromatic hydrocarbons has also been intensively investigated, particularly by Cerfontain and his associates, and several... 

Kamatani, H. and Kuze, K., Formation of aromatic compounds as side reactions in the polycondensation of bishydroxyethyl terephthalate, Polym. J 11, 787-793 (1979). 

Selected examples of the phase-transfer catalysed formation of aromatic esters... 

The detailed modeling of soot formation in the shock tube pyrolysis of acetylene [106] and other fuels [107] provides the central basis for the fuel-independent general mechanisms suggested here. It must be noted, as well, that a large body of work by Howard et al. [108, 109] on premixed flames with regard to formation of aromatic species provides direct tests of the proposed mechanisms and are key to understanding and modeling soot formation. 

E. 1. Shin, M. Nimlos, and R. 1. Evans, The formation of aromatics from the gas-phase pyrolysis of stigmasterol Kinetics, Fuel 80(12 Special Edition SI), 1681-1688 (2001). 

The complex formation of aromatic hydrocarbons with Lewis acids in the presence of hydrogen halide and the colour of the so-called red oils associated with this is the oldest observation which indicates that the interaction is connected with a pronounced effect on the electronic structure of the aromatic hydrocarbons (Gustavson, 1878, 1890, 1903, 1905). 

Brown and Melchiore (1966) have recently determined the temperature-dependence of complex formation of aromatic hydrocarbons with HCl and HRr in n-heptane solution. Dissociation constants and thermodynamic data were calculated. 

Fig. 5. The aromatic cluster of the hydrophobic core of GTD-43, a helrx-loop-helrx dimer, and some of the assigned long-range NOEs that demonstrate the interactions of the aromatic side chains in the folded motif The formation of aromatic clusters has been observed in several designed proteins. Reproduced with permission from J Am Chem Soc (1997) 119 8598. ( 1997 ACS)...

Scheme 4.—Formation of Aromatics from Dihydroxyacetone in Acid Solution.

Aromatic Azo Compounds Reduction of aromatic azo compounds involves a four-electron process that proceeds through a short-lived intermediate, hydrazoben-zene, that ends with complete reductive cleavage of the azo hnkage and formation of aromatic amines. 

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