Dealkylation simultaneous

Simultaneous measurements of both the amount of butane evolved and the quantity of grafted organometallic fragments at increasing time of reaction allows the stoichiometry of the surface complexes Pts[SnBux] / to be determined (Fig. 7). Furthermore, extrapolation to a low amount of Sn grafted shows that a [BusSnJ Pts species is formed, which then rapidly evolved towards more dealkylated species and finally to Pts[SnBu]jy. 

Other chlorotriazines (simazine, propazine, terbuthylazine) follow the same biotransformation pathway of atrazine therefore, urinary excretion of bi-dealkylated, deisopropylated, and deethylated metabolites is not compound specific. When simultaneous exposure to different chlorotriazines occurs, the unmodified compound measured in urine, even though it represents a minor portion of the absorbed dose, may be useful for a qualitative confirmation of exposure. 

Phenothiazines The phenothiazines (PTZs) undergo extensive metabolism. Metabolic routes include S-oxidation, aromatic hydroxylation, N-dealkylation, N-oxidation, and a combination of these processes. Chlorpromazine, for example, possesses 168 possible metabolites, a large proportion of which are pharmacologically active compounds. The development of an HPLC assay capable of resolving a large number of these metabolites is virtually impossible and assays that permit the simultaneous determination of the parent compound and a selected number of active metabolites must suffice. The PTZ group of compounds includes chlorpromazine, thioridazine, fluphenazine, and perphenazine. 

Table 6.8 shows that the fastest depletion of atrazine occurs under Fenton s reagent. Arnold et al. (1995) demonstrated that OH may react with Ch at low pH to produce HOC1 and Cl2, causing underestimation of Cl concentrations, but the results suggest that Cl- scavenging by OH was minimal. Dechlorination and dealkylation occur simultaneously, and the batch treatment showed that dechlorination occurred more readily with alkylated s-triazines. Chlorinated products accounted for a large part of s-triazines present upon completion of Fenton s reagent. 

Obolentsev (264) has published researches on the conversions of individual hydrocarbons over silica-alumina. Depolymerization of triisobutylene as the temperature was raised from 200 to 365° resulted in a decrease of the liquid products from 45 to 60 % progressively to 24 to 26 % with a corresponding increase in the yield of the gaseous products the dimer was also depolymerized, although other workers reported it to be stable. A mechanism was postulated which involved the intermediate formation of an alkylated cyclobutane (264). Isopropylbenzene was dealkylated with simultaneous disproportionation to diisopropylbenzene at 350-450° (266). Disproportionation may become the principal reaction at the higher temperature (267). 

It is generally admitted that skeletal transformations of hydrocarbons are catalyzed by protonic sites only. Indeed good correlations were obtained between the concentration of Bronsted acid sites and the rate of various reactions, e g. cumene dealkylation, xylene isomerization, toluene and ethylbenzene disproportionation and n-hexane cracking10 12 On the other hand, it was never demonstrated that isolated Lewis acid sites could be active for these reactions. However, it is well known that Lewis acid sites located in the vicinity of protonic sites can increase the strength (hence the activity) of these latter sites, this effect being comparable to the one observed in the formation of superacid solutions. Protonic sites are also active for non skeletal transformations of hydrocarbons e g. cis trans and double bond shift isomerization of alkenes and for many transformations of functional compounds e.g. rearrangement of functionalized saturated systems, of arenes, electrophilic substitution of arenes and heteroarenes (alkylation, acylation, nitration, etc ), hydration and dehydration etc. However, many of these transformations are more complex with simultaneously reactions on the acid and on the base sites of the solid... 

Two explanations have been suggested for this anomalous result83,84. Huffman and coworkers84 have proposed that the 2,2-disubstituted cyclohexanone (38) is derived directly from a 2,6-disubstituted enolate intermediate by simultaneous alkylation at C2 and dealkylation at C6. This is in effect a S 2 mechanism for which there is no precedent in enamine chemistry (Scheme 24). The basis for this suggestion is the anomalous solvent-dependent annulation of 2-substituted cyclohexanone enamines with methyl vinyl ketone (MVK) and the assumption that direct C-alkylation of a tetrasubstituted enamine is improbable for it is known that there is considerably less overlap of the unshared electrons on nitrogen with the n system of the double bond in this isomer relative to the more stable trisubstituted isomer, thereby greatly decreasing the rate of alkylation . 

Dehalogenation. This combination effects efficient dehalogenation of o- and p-bromo- and iodophenols in CH2CI, at 0°. The corresponding chlorides and fluorides are stable to these conditions. Simultaneous dealkylation can occur when the reaction is applied to halophenolic ethers. ... 

In catalytic cracking many reactions take place simultaneously. Cracking occurs by C-C bond cleavage of paraffins, dealkylation etc. Isomerization and even condensation reactions take place. These reactions occur via positively charged hydrocarbon ions (carbocations). The nature of the carbocations is the subject of debate. For the cracking of paraffinic hydrocarbons it is usually assumed that carbenium ions are the crucial intermediates, which decompose via beta fission into olefins and (smaller) carbenium ions (see Chapter 4, Section 4.4). A typical reaction mechanism for catalytic cracking (and hydrocracking) imder the relatively mild conditions used in FCC is shown overleaf. 

One rather interesting aspect of the Friedel-Crafts reaction is that trialkylation of benzene often leads to a symmetrical 1,3,5-isomer rather than a 1,2,4-derivative as would be expected from the ortho-para orientation of the alkyl group introduced initially. Since alkylation by the Friedel-Crafts method has been shown to be a reversible reaction,68 this anomalous orientation has been explained on the basis that both alkylation and dealkylation occur readily in the ortho and para positions. Simultaneously, however, some alkylation occurs in the meta position but no dealkylation68 If the reaction mixture is allowed to stand in contact with aluminum chloride for some length of time, then principally meta trialkyl derivatives will be formed ... 

C. Aromatic Hydrocarbons, Steam Dealkylation.—Research on steam dealkylation has thrown light on the mechanism of reforming. Rabinovich and other Russian workers, following their earlier research in this area which is summarized by Grenoble, concluded that the toluene reaction with steam over precious metal/alumina catalysts proceeds by simultaneous-consecutive reactions ... 

A further important reaction class refers to the substitutive addition reactions which were already discussed in the pyrolytic mechanism of deposit formation. During PAH formation and growth, there are alkyl substitutions (mainly methyl) on the edge surface too. Active radicals add on the aromatic structures with a simultaneous dealkylation. This results in an increase in the molecular weight and dehydrogenation of the aromatics. 

The compounds with a 2-to7-butylimino or 2-(2,2,4-trimethylpent-4-yl)imino substituent undergo dealkylation to the 3-alkyl-6/M,3,4-thiadiazin-2(3//>imine 0n heating in hydrochloric or hydrobromic acid or simultaneous dealkylation and extrusion of sulfur with reduction of ring size to the l-alkylpyrazol-5-imines.10... 

Vigorous conditions are required and synthetic exploitation has been slight (147,212). Recent detailed studies by Bum and Cadogan (70, 72,73) have shown that substituents on phosphorus enhance the rate in the order RjN > R > RO > RS, and the rate was also increased by the use of solvents of increasing dielectric constant. They suggest that the alkylation of sulfur and dealkylation of oxygen may occur essentially simultaneously. 

A test procedure involving an isomerization reaction of an olefin would obviously be most desirable for testing the activity of the acid function of a dual-function catalyst. Such a test appeared out of question because of the certain interference with this reaction by the platinum activity of the samples under study. Cumene (isopropyl benzene) is known to undergo reaction (dealkylation) on acidic catalysts. We have found the reactivity of cumene to be a useful measure of the activity for other acid-catalyzed reactions (4) of at least certain classes of compositions. Furthermore, we have foimd it to be useful on dual-function class catalysts, i.e., to yield a relative measure of their acidic activity despite the simultaneous presence of platinum. 

Simultaneous Determination of Diso-pyramide and Its Mono-N-dealkylated Metabolite in Plasma by Gas-Liquid Chromatography... 

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