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Acid Zeolite Catalysis
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
The major transformations of hydrocarbons catalyzed by zeolites are condensations, rearrangements, and cleavages of olefins, alkyl aromatics, and paraffins singly or in combination. The reactive intermediate strongly implicated in most of these reactions is the carbonium ion. Manifestation of such activity requires ion exchange of at least part of the alkali metal cations by polyvalent main group cations or ammonium ions followed by thermal activation. The formation of the carbonium ion on the zeolite surface has been studied by direct spectroscopic observations. For the alkali metal ion-containing zeolites, there are a smaller number of reported reactions for which parallel behavior can be found in thermal gas-phase reactions and therefore analogies are best sought in the behavior of free radicals.
Hydrolysis
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
In aqueous systems, formation of the highly reactive carbonium ion by the SN1 mechanism is usually followed by reaction with water, resulting in the formation of an alcohol (2.11); however, prior to reaction with water, rearrangement may occur through migration of substituents, usually protons or alkyl groups, resulting in formation of a more stable carbonium ion (2.12). Also, elimination of a proton on the carbon adjacent to the carbocation, which results in the formation of alkenes, may occur (2.13). The observation of reaction products resulting from these processes can serve as evidence for the intermediacy of a carbonium ion. () () ()
Production of Low-Cost Aliphatic Isocyanates
Published in John R. Kosak, Thomas A. Johnson, Catalysis of Organic Reactions, 2020
P. L. Brusky, J. H. Kyung, R. A. Grimm
A two-step reaction process for diisocyanate was demonstrated using a solution process with strong acid catalysts (see Figure 1). Toluene was selected in the first reaction because it gave the best yield. Highly polar solvents were selected for the second reaction to promote the proposed carbonium ion reaction. In addition, the interaction between nitromethane and isocyanic acid is still unclear at this time and may be beneficial in stabilizing the isocyanic acid.
Study on the influence of low-carbon alcohol on non-hydrodewaxing reaction of hydrocracking tail oil
Published in Petroleum Science and Technology, 2020
Yuying Yang, Jing Zhu, Wentao Wu
From Figure 2, it can be seen the pour point of lubricating oil base oil declines with the extension of reaction time when low-carbon alcohol is added into the raw oil. It shows that the addition of low-carbon alcohol is easier to produce carbonium ion, which accelerates the cracking reaction of n-alkane. So the content of macromolecular n-alkane and the pour point of lubricating oil base oil decrease. The carbonium ion stability is: tertiary > secondary > primary. It is easier to generate stable carbonium ion because tert-butyl alcohol contains tertiary carbon ions, which further initiates the cracking reaction of n-paraffin.