Dealkylation of aromatics

When the temperature of a carbonate reservoir that is saturated with high-viscosity oil and water increases to 200° C or more, chemical reactions occur in the formation, resulting in the formation of considerable amounts of CO2. The generation of CO2 during thermal stimulation of a carbonate reservoir results from the dealkylation of aromatic hydrocarbons in the presence of water vapor, catalytic conversion of hydrocarbons by water vapor, and oxidation of organic materials. Clay material and metals of variable valence (e.g., nickel, cobalt, iron) in the carbonate rock can serve as the catalyst. An optimal amount of CO2 exists for which maximal oil recovery is achieved [1538]. The performance of a steamflooding process can be improved by the addition of CO2 or methane [1216]. 

The cracking of cumene has received considerable attention in recent years as a reaction typical of one class of cracking reactions, namely dealkylation of aromatics. Among the studies of cumene cracking found in the literature there are several attempts to determine the kinetics of... 

Steam Dealkylation. - The steam dealkylation of aromatic hydrocarbons, such as toluene ... 

Under acidic conditions, the alkylation and dealkylation of aromatic compounds are reversible reactions involving several steps in which n- and CT-complexes are formed. However, dealkylation proceeds only under more drastic conditions compared with alkylation. Nevertheless, this is not always the case. For example, if the aromatic compound is of the DPM type, the dealkylation may proceed under mild conditions since the cations formed (Fig. 6.6.5) are resonance-stabilized. This statement is supported by the fact that DPM derivatives may be degraded even at room temperature by aluminum chloride to yield benzene, alkylbenzene, and alkyldiphenylmethane, together with some resinous substances (Tsuge and Tashiro 1962, 1965). 

Dealkylation of tertiary amines. This reagent is preferred over vinyl chloroformate (8, 530) for dealkylation of tertiary amines. The conditions are milder and the yields are somewhat higher. A typical process is outlined in equation (1). Dealkylation of aromatic... 

Even N-dealkylation of aromatic amines occurs cleanly with ACE-CI as it is illustrated in a strigent test by the conversion of N,N-diethyl aniline to 1-chloroethyl N-methyl-N-phenyl carbamate in 87 % yield (Ref. 68). Caubere and Bachelet used this methodology while operating without a solvent for the demethylations as well as for the deethylations of dialkylamino benzofurans in good yields (Ref. 192). 

One trend that stands out from Dinneen s data and from Experiments 113 and 127 is that the naphthalene/2-methyl-naphthalene ratio depends strongly on the temperature at which oil cracking occurs and only weakly on the amount of cracking. This apparently occurs because the activation energy for dealkylation of aromatics is higher than for aromatic formation. Even at very high conversions, this ratio in oils cracked near or below 600°C is not dramatically different than that in assay oil—even though the amount of naphthalene has increased tenfold. 

The reactions of major importance in the octafining process are isomerization of naphthenes and aromatics, hydrogenation of aromatics, dehydrogenation of naphthenes, disproportionation of aromatics, dealkylation of aromatics, and hydrocracking of saturates (Figure 3). The last three reactions, of course, result in loss of product xylenes. These reactions, like the desired isomerization reactions, are carbonium-ion catalyzed. 

Selective dealkylation of aromatic alkoxylated compounds Selective de-ethylation of 2-ethoxyanisole is achieved by use of KO Bu as the reagent in the presence of 18-crown-6 as the phase-transfer agent (PTA). With addition of ethylene glycol (E.G.), the selectivity is reversed and demethylation occurs (Eq. (61), Table 4.18). Although involvement of microwaves is favorable in both examples, the second reaction was shown to be more strongly accelerated than the first [147]. 

Duprez, D., Pereira, P., Miloudi, A., and Maurel, R. (1982) Steam dealkylation of aromatic hydrocarbons II Role of the support and kinetic pathway of oxygenated species in toluene steam dealkylation over group VIII metal catalysts. /. Catal, 75 (1), 151-163. 

Boron Lewis acids have been used routinely in dealkylation of aromatic and alkyl ethers, and as catalysts for Friedel-Crafts type electrophillic aromatic substitution. 

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