Aromatics evolution

Figure 2.4 shows species-specific evolution profiles for paraffin, olefin, and alkyl aromatic volatile products formed by heating the PE-HZSM-5 sample. The numbers in parentheses denote the number of isomers detected. The volatile product slates for the PE-HZSM-5 sample reflect that C3-C5 hydrocarbons were the dominant species formed. The temperature corresponding to the maximum paraffin and olefin evolution rates was 280°C, whereas alkyl aromatic evolution maximized at 310°C. Below 200°C, volatile... 

Aromatic products were detected at temperatures above those at which paraffin and olefin evolutions maximized. The shift in alkyl aromatic evolution profiles to higher temperatures relative to paraffins and olefins is consistent with a mechanism in which unsaturated surface ions are precursors for alkyl aromatic formation. Alkyl aromatic yields decrease in the order PE-HZSM-5 > PE-HY > PE-MCM-41, which follows a trend in increasing pore size. Steric restrictions on reaction volume afforded by HY... 

These terroirs have slow and complete maturation conditions. Conversely, excessively hot climates, early harvests and excessive water stress in the summer are unfavorable to the aromatic evolution of white grapes. 

For the selection of descriptors, GA simulated evolution of a population. Each individual of the population represents a subset of descriptors and is defined by a chromosome of binary values. The chromosome has as many genes as there are possible descriptors (92 for the aromatic group, 119 for non-rigid aliphatic,... 

Primary aromatic amides are crystaUine sohds with definite melting points. Upon boiling with 10-20 per cent, sodium or potassium hydroxide solution, they are hydrolysed with the evolution of ammonia (vapour turns red htmus paper blue and mercurous nitrate paper black) and the formation of the alkah metal salt of the acid ... 

Fig. 23. Evolution of the glass transition temperature of polychloroprene-aromatic hydrocarbon resin blends as a function of the resin content. values were obtained from DSC experiments.

Acetophenone.—The Fnedel-Crafts reaction, of which this pieparation is a type, consists in the use of anhydious aluminium chlonde for effecting combination between an aromatic hydrocarbon or its deiivative on the one hand, and a halogen i,Cl 01 Bi) compound on the othei. The leaction 13 always accompanied by the evolution of hydiochloiic or hydio-bromic acid, and the product is a compound with AlCl-j, which decomposes and yields the new substance on the addition of watei. This reaction has been utilised, as in the present case, (r) for the prepaiation of ketones, in which an acid chloiide (aliphatic or aromatic) is employed,... 

It would be expected that a few straightforward steps could accomplish the transformation of alkyl bromide 14 into phosphorus ylide 12 (Scheme 2b). On the other hand, the evolution of 14 from substituted aromatic furan ring 15 may not be obvious. It is, in fact, conceivable that the action of ethylene glycol on substituted furan... 

Concerning the yldiide Ph3P=CH-Li, the question as to whether it could be obtained by direct lithiation of the ylides 23 (Y=H), for a long time in debate between Schlosser and Corey, could have found an answer. Effectively NMR studies seem to show that a directed ortho-metallation occurs on an aromatic ring when 23 is reacted with t-BuLi [65], leading thus to the formation of 24 whose evolution does not afford Ph3P=CH-Li (Scheme 13). 

Most often, these radicals are unstable and can exist only while adsorbed on the electrode, although in the case of polycyclic aromatic compounds (e.g., the derivatives of anthracene), they are more stable and can exist even in the solution. The radicals formed first can undergo a variety of chemical or electrochemical reactions. This reaction type is the analog of hydrogen evolution, where electron transfer as the first step produces an adsorbed hydrogen atom, which is also a radical-type product. 

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