Formation pathway

CO to CO2 (e.g. Finlayson-Pitts and Pitts 1986). The role of HOj in any of these atmospheric cleansing and oxidant formation pathways is a catalytic one, but the generation of ozone is strongly dependent upon the nitric oxide concentration. 

To ascertain that aminomethylphosphonic acid ( ) but not glycine (4) is a photolysis product, the primary amino product was identified by comparison of TLC Rf values. Possible products and their formation pathways from photolytic cleavage of N-nitrosoglyphosate are shown in Figure 1 (5). The TLC Rf values on silica gel for different solvent systems are shown in Table II (5). The data clearly indicate that aminomethylphosphonic acid... 

FIGURE 6.9 Confirmed heterolytic formation pathway for 5a-a-tocopheryl benzoate (11) without involvement of 5a-C-centered radicals and its proof by trapping of ortho-quinone methide 3 with ethyl vinyl ether to pyranochroman 13. Shown are the major products of the reaction of a-tocopherol (1) with dihenzoyl peroxide. 

FIGURE 6.10 Confirmed formation pathway of ethano-dimer 12 by reduction of spiro dimer 9 in different reaction systems. 5a-C-centered radicals 10 are not involved in this process. 

Detailed Formation Pathway and Stabilization of the Tocopherol-Derived o-QM 3 and Other o-QMs... 

The oxidation of a-tocopherol (1) to dimers29,50 and trimers15,51 has been reported already in the early days of vitamin E chemistry, including standard procedures for near-quantitative preparation of these compounds. The formation generally proceeds via orf/zo-quinone methide 3 as the key intermediate. The dimerization of 3 into spiro dimer 9 is one of the most frequently occurring reactions in tocopherol chemistry, being almost ubiquitous as side reaction as soon as the o-QM 3 occurs as reaction intermediate. Early accounts proposed numerous incorrect structures,52 which found entry into review articles and thus survived in the literature until today.22 Also several different proposals as to the formation mechanisms of these compounds existed. Only recently, a consistent model of their formation pathways and interconversions as well as a complete NMR assignment of the different diastereomers was achieved.28... 

Holscher, W., Steinhart, H., Formation pathways for primary roasted coffee aroma compounds, in ACS Symposium Series 543, Thermally Generated Flavors, 1994, 206. (CA120 105189t)... 

Figure 1. Stages of kerogen transformation and hydrocarbon formation pathways in geological situations. Direct inheritange of low molecule weight compounds is indicated by block arrows (from Engel and Macko, 1993).

Klingler and co workers—impact of metal coordination on the formate pathway. Klingler and coworkers114,125 carried out studies on the cation reactivity of formate in solution at 180 °C, 7.8 mol/L of H20 with the solvent triethylene glycol, and the formate concentration was varied. It was noted that formic acid produced from the carbonylation of water is catalyzed by hydroxide anion, and rapidly builds up to close to equilibrium concentration levels under these conditions, so that they had to use gold plated stainless steel autoclaves. They obtained a first order dependency of the water-gas shift reaction rate (i.e., H2 evolution rate) with formate concentration. As a control experiment, they added metal pentacarbonyl iron to the reactor, and observed no additional rate increase, indicating that the water-gas shift... 

PCDD/F and other chlorinated hydrocarbons observed as micropollutants in incineration plants are products of incomplete combustion like other products such as carbon monoxide, polycyclic aromatic hydrocarbons (PAH), and soot. The thermodynamically stable oxidation products of any organic material formed by more than 99% are carbon dioxide, water, and HCl. Traces of PCDD/F are formed in the combustion of any organic material in the presence of small amounts of inorganic and organic chlorine present in the fuel municipal waste contains about 0.8% of chlorine. PCDD/F formation has been called the inherent property of fire. Many investigations have shown that PCDD/Fs are not formed in the hot zones of flames of incinerators at about 1000°C, but in the postcombustion zone in a temperature range between 300 and 400°C. Fly ash particles play an important role in that they act as catalysts for the heterogeneous formation of PCDD/Fs on the surface of this matrix. Two different theories have been deduced from laboratory experiments for the formation pathways of PCCD/F ... 

DKPs are simple and easy to obtain and are quite common by-products of synthetic, spontaneous, and biological formation pathways. DKP formation has been well documented as side reactions of solid-phase and solution-phase peptide synthesis. In addition, DKPs have been shown to be decomposition products of various peptides, proteins, and other commercial pharmaceuticals. Cyclic dipeptides were found to be present in solutions of human growth hormone, bradykinin, histerlin, and solutions of agents within the classes of penicillins and cephalosporins. " DKPs are also enzymatically synthesized in several protists and in members of the plant kingdom. Hydrolysates of proteins and polypeptides often contain these compounds and they are commonly isolated from yeasts, lichens, and fungi. ... 

The relative importance of the heterc eneous and photochemical nitrate formation pathways can be assessed from recently measured aerosol nitrate profiles. " On humid days, a midmoming nitrate... 

Sweetman, J.A., Zielinska, B., Atkinson, R., Ramdahl, T., Winer, A.M., and Pitts, J.N., Jr. A possible formation pathway for the 2-nitroflnoranthene observbed in particnlate organic matter, Atmos. Environ., 20(l) 235-238, 1986. 

Seven of these were found after cyclopropanation of e- and trans-n-Cg2(COOEt)4 (n = 2-4) (4-7) with diethylmalonate (Figure 10.6) [20]. In a few cases, such as the Cj-symmetric adduct 8 (e,e,e-addition pattern), the structure can be assigned based on NMR spectroscopy alone. NMR spectroscopy allows for the determination of the point group of the adduct. The e,e,e-addition pattern is the only one that has Cj-symmetry and as a consequence the assignment is unambiguous. The same is true for the Dj-symmetrical adduct 9. Conversely, C2-, C - or Cj-symmetry of trisadducts can arise from different addition patterns. The structural assignment of such adducts requires the additional analysis of their possible formation pathways. 

Table 10.2 Relative and absolute positional relationships, symmetry and number of possible formation pathways oftrisadducts that can be formed out of e and trans-n [n = 1-4) bisadducts (first row) neglecting cis additions.

Sweetman, J. A., B. Zielinska, R. Atkinson, T. Ramdahl, A. M. Winer, and J. N. Pitts, Jr., A Possible Formation Pathway for the 2-Nitrofluoranthene Observed in Ambient Particulate Organic Matter, Atmos. Environ., 20, 235-238 (1986). 

Prompt NO Formation A second source of NO in gas firing is prompt NO. This formation pathway can be the dominating source of NO under conditions characterized by lower temperatures, fuel-rich conditions, and short residence times. This route, which is also called Fenimore NO, was first proposed by C. P. Fenimore [125]. Prompt NO formation is initiated by attack of CH, radicals on N2, forming cyanide species. The most important initiation step is the reaction... 

CJ. Pope and J.A. Miller. Exploring Old and New Benzene Formation Pathways in Low-Pressure Premixed Flames of Aliphatic Fuels. Proc. Combust. Inst., 28 1519-1527,2000. 

Alternative structures arise that provide parallel formation pathways and consequently slow nucleation kinetics. 

Possible Formation Pathways for the Free Radical Products... 

Among the heterocyclics there is one group which will be thoroughly examined the pyrazines. The compounds belonging to this family play a very important role as contributors of desirable food flavor properties. Structurally, pyrazines are heterocyclic nitrogen compounds and their formation is a quite complicated process. Maga and Sizer (4) present a summary of these formation pathways. 

Figure 2.11. Possible amide formation pathway including the key role of Mn02. Reprinted with permission from Jokic, A., Schulten, H.-R., Cutler, J. N., et al. (2005). Catalysis of the Maillard reaction by 8-Mn02 A significant abiotic sorptive condensation pathway for the formation of refractory N-containing biogeomacromolecules in nature. In Soil Abiotic and Botic Interactions and Impact on the Ecosystem and Human Welfare, Huang, P. M., Violante, A., Bollag, J.-M., and Vityakon, P, eds., Science Publishers, Enfield, NJ, 127-152.

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