Dealkylation, catalyst application

A broad spectrum of chemical reactions can be catalyzed by enzymes Hydrolysis, esterification, isomerization, addition and elimination, alkylation and dealkylation, halogenation and dehalogenation, and oxidation and reduction. The last reactions are catalyzed by redox enzymes, which are classified as oxidoreductases and divided into four categories according to the oxidant they utilize and the reactions they catalyze 1) dehydrogenases (reductases), 2) oxidases, 3) oxygenases (mono- and dioxygenases), and 4) peroxidases. The latter enzymes have received extensive attention in the last years as bio catalysts for synthetic applications. Peroxidases catalyze the oxidation of aromatic compounds, oxidation of heteroatom compounds, epoxidation, and the enantio-selective reduction of racemic hydroperoxides. In this article, a short overview... 

Application of the IR method proved to be also suitable for the measurement of diffusivities in coking porous catalysts. This was deihonstrated by uptake experiments with ethylbenzene where the sorbent catalyst, H-ZSM-5, was intermittently coked in-situ via dealkylation of ethylbenzene at temperatures (465 K) somewhat higher than the sorption temperature (395 K). Coke deposition was monitored in-situ via the IR absorbance... 

The same commercial Bi—Mo—P—O catalyst was used in a study by Van der Wiele [347], which included the oxidation of the xylenes at 400— 500° C. In contrast to the oxidation of toluene, dealkylation cannot be neglected. Table 33 presents an example of the product distribution at a 71—74% conversion level for both the xylenes and toluene. Remarkably, substantial amounts of the dialdehyde are only formed from p-xylene, while an enhanced benzene production is found in the case of o-xylene. The reaction schemes shown on p. 208 are proposed the combustion reactions, applicable to each component in the scheme are left out for simplicity. 

Elguero and Espada29S have used this dealkylation reaction with quaternary salts of heterocyclic compounds. Another application is the preparation of tertiary amines functionalized in the <5 position.296 In these reactions, the ammonium salt 196 is both the catalyst and the reagent. 

Due to the ease of dealkylation of r-alkylbenzenes, such as t-butylbenzene, some interesting applications of this process in both the syndietic and mechanistic areas have resulted. The intermediacy of the r-butyl cation was hinted to account for the observed products. Thus, Knight et al obtained excellent yields of pivalic acid by dealkylating r-butylbenzene and 1,3-dimethyl-S-t-butylbenzene in the presence of carbon monoxide and BFs-HaO as the catalyst (equation 120). They also found that H3PO4, H2SO4 and MeSOsH were ineffective for the dealkylation-carbonylation of t-butylbenzene. 

Not mentioned in the table are the catalysts methanesulphonic acid, xylenesulphonic acid and certain modified zeolites ail of which have found some application. Other alkenes include the pentenes and isomers of the compounds in the table such as non-1-ene. Of importance in industrial reaction conditions are procedures to avoid alkene/alkene side reactions and promote the desired alkene/phenol reaction, with temperature control to avoid dealkylation of the product. 

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