Formation of aromatic compounds

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

Formation of aromatic compounds involves either the dehydrogenation (by way of reaction with carbonium ions) of the cyclohexane compounds or, less likely, the cyclization of a triolefinic carbonium ion. 

Formation of Aromatic Compounds A scientific challenge comparable to that of developing oxidation mechanisms for the large hydrocarbon fuels is understanding and describing quantitatively the formation and oxidation of aromatic and polycyclic aromatic compounds (PAH) formed in combustion processes. Aromatic compounds are known to be harmful to the environment, and the emission of these species from a number of combustion systems is a significant concern. Furthermore aromatic species are important pre-... 

J.A. Miller and C.F Melius. Kinetic and Thermodynamic Issues in the Formation of Aromatic Compounds in Flames of Aliphatic Fuels. Combust. Flame, 91 21-39, 1992. 

The use of elemental sulfur itself as a dehydrogenating reagent has found some utility mainly in the formation of aromatic compounds. 

In 2004, excellent yields of hydroperoxides 91 and 92 were obtained (>95%) in the photooxidation of racemic acid 90 (Scheme 11.17) [96]. The diastereoselectivity of the photooxidation favored the trans-configured products due to the anti-directing effect of the protonated carboxylic acid group. Regioselectivity favored the formation of 92 over 91. Pyridine helped to accelerate the deprotonation of the CH next to COOH of 90, affording 92, and also suppressed the formation of aromatic compounds which otherwise would take place in the absence of pyridine. A great many studies of ene reactions have been conducted in organic solvents [97-101] or aqueous media [102-106] one such report appeared which used a fluorous biphasic solution [107]. 

Shaub WM (1982b), Thermochimica Acta 55 59-73.. .Procedure for estimating the heats of formation of aromatic compounds chlorinated benzenes, phenols and dioxins"... 

II. Discovery of the Role of Shikimic Acid in the Formation of Aromatic Compounds. 237... 

Lahaniatis et al. found that a thermal degradation of toxaphene at 400°C to 800°C leads to the formation of aromatic compounds, among them tri- to hexa-chlorobenzenes, low-chlorinated naphthalenes, biphenyls, and even dibenzofu-rans [176]. The major processes of degradation seem to be dechlorination and dehydrochlorination [54]. However, Chandurkar and Matsumura reported that at least some hydroxylated toxaphene metabolites are formed [81]. So far, only very few oxidation products of toxaphene have been identified [177,178,179] which seem to be rather unstable [177]. 

Russell J.M., Miller R.K Molton P. (1983) Formation of Aromatic Compounds from Condensation Reactions of Cellulose Degradation Products. Biomass, 3, 43-57. 

Pyrolysis of polyethylene on catalysts of metal-supported activated carbon changes the composition of pyrolysates with the formation of aromatic compounds. Different metals lead to different yield of aromatic components, the presence of Pt leading to the highest, and Fe and Cu leading to the lowest content of aromatics [63]. 

The formation of aromatic compounds in PVC pyrolysis is schematically exemplified for benzene ... 

By comparing the results for chlorinated polypropylene with those for polypropylene, it can be concluded that the two materials undergo very different pyrolytic reactions. Typical for polypropylene is the formation of fragments of the polymeric backbone with formation of monomer, dimer, etc., or with cleavage of the backbone in random places and formation of compounds with 3n, 3n-1, and 3n+1 carbon atoms (see Section 6.1). Pyrolysis of the chlorinated compound leads to a significant amount of HCI and also char. Very few chlorinated compounds are identified in the pyrolysate, since the elimination of HCI leaves very few chlorine atoms bound to carbons. Some aromatic hydrocarbons are formed by a mechanism similar to that of poly(vinyl chloride) pyrolysis. The elimination of HCI leads to the formation of double bonds, and the breaking of the carbon backbone leads to cyclization and formation of aromatic compounds. The reactions involved in this process are shown below for the case of formation of 1,3-dimethylbenzene ... 

The exact mechanism of propylene glow discharge polymerization is not known. The presence of a terminal acetylene (presumable propyne) in the gaseous products of propylene polymerization was indicated by the interaction of the cold trap gaseous condensates with 1% alcoholic or ammonlacal AgNO sol.(22) after the polymerization was over. An immediate formation of an explosive silver acetyllde was detected. Intermediate formation of propyne is also indicated by the IR spectra of the yellow relatively less volatile liquid left in the cold trap after the polymerization was over. Sharp but weak absorptions at 3310 cm l and 1270 cm are indications of a substituted acetylenic compound. The IR spectra of the yellow liquid also points to the presence of mono, dl- and trl-substituted aromatic compounds in the mixture (i.e. sharp absorption bands at 3080 cm l, 1640 cm l, 920 cm , 810 cm and a multiple band in the 1000-1120 cm l region are observed). The NMR spectra in deuterated acetone indicated the presence of an aromatic nucleus in the yellow liquid obtained from the cold trap. The formation of aromatic compounds can be explained if a propynyllc Intermediate is involved. 

Olsson K., Pernemalm P.A., PopofT T. and Theander O. (1977) Formation of aromatic compounds from carbohydrates. V. Reaction of D-glucose and methylamine in slightly acidic, aqueous solution. Acta Chem. Stand. B31, 469-74. 

The original literature456,463 should be consulted for alkylation by pyrylium salts and the subsequent reactions then observed (formation of aromatic compounds and azulenes). Cyclizations that occur on intramolecular alkylation have been reviewed by Bestmann.456... 

The naturally occurring naphthoquinones such as lawsone and juglone are products of the shikimic acid pathway to aromatic amino-acids but the path which leads to these naphthoquinones branches from the main pathway before the formation of aromatic compounds, probably no later than chorismic acid.It will be most interesting to see whether the biosynthesis of shihunine also follows this route all the other bases of plant origin which arise from products of the shikimic acid pathway derive from aromatic precursors. 

From all the above results, it is inferred that the formation of aromatic compounds from parasite reactions in alkane hydroisomerization play an important role for generation coke precursors, which, during the coke formation, continued their polymerization in the acid sites of the Pd/HM catalyst to be eventually converted into polyaromatic or pseudo-graphitic structures. 

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