Carbenium ion formation by fragmentation of electrochemically generated oxonium ions

2018 ◽  
Vol 16 (28) ◽  
pp. 5094-5096 ◽  
Author(s):  
Anna Lielpetere ◽  
Aigars Jirgensons
Keyword(s):  
Oxidation Potential ◽  
Carbenium Ions ◽  
Ion Formation ◽  
Oxonium Ions ◽  
Carbenium Ion

Fragmentation of electrochemically generated oxonium ions can be exploited to form carbenium ions at a low oxidation potential in the presence of a nucleophile such as allylsilane.

Aromatization of C2-C6 Aliphatic Hydrocarbons on Copper-Containing ZSM-5 Zeolites

1992 ◽  
Vol 57 (12) ◽  
pp. 2553-2560
Author(s):  
Zdravka Popova ◽  
Katia Aristirova ◽  
Christo Dimitrov
Keyword(s):  
Copper Content ◽  
Acid Strength ◽  
The State ◽  
Aliphatic Hydrocarbons ◽  
Bronsted Acid ◽  
Ion Formation ◽  
Brönsted Acid ◽  
Wide Range ◽  
Carbenium Ion ◽  
Acid Centers

The aromatization of a wide range of model aliphatic and cycloaliphatic hydrocarbons (ethene, ethane, propene, n-hexane, 1-hexene, methylcyclopentane, cyclohexane, cyclohexene) on copper-containing NaZSM-5 and HZSM-5 zeolites has been investigated. It was established that the degree of aromatization is related to carbenium ion formation and depends on the acid strength and copper content of zeolite. Experiments with copper-containing samples reduced prior to use indicated the possibility to enhance the selectivity to aromatization. The change of the state of Cu2+ ions during catalytic experiments confirmed the assumption about participation of Cu0 simultaneously with the Bronsted acid centers in the dehydrogenation/hydrogenation steps.

Catalyzed β scission of a carbenium ion III — Scission observed in ab initio molecular dynamics simulations

2009 ◽  
Vol 87 (10) ◽  
pp. 1512-1520 ◽  
Author(s):  
Greg M. Berner ◽  
Allan L. L. East
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Density Functional ◽  
Time Windows ◽  
Three Dimensional ◽  
Ab Initio Molecular Dynamics ◽  
Catalytic Systems ◽  
Carbenium Ions ◽  
Carbenium Ion ◽  
Dynamics Simulations

The β scission (cracking) of branched carbenium ions have been observed in molecular dynamics simulations, possibly for the first time. Simulations were performed with molecular dynamics based on PW91 density functional theory, and which included three-dimensional periodic boundary replication of the unit cell to mimic long-range bulk effects. A rising-temperature algorithm was used to encourage reaction within the narrow time windows (∼10 ps) of the simulations. Twenty-eight simulations were performed, featuring alkyl ions in three different catalytic systems: the ionic liquid, [(C5H5NH+)5(Al2Cl7−)6]−, the chabazite zeolite, [AlSi23O48]−, and the chabazite zeolite, [Al4Si20O45(OH)3]−. Twenty-four runs began with unbranched sec-n-alkyl ions, but only one exhibited β scission, and only after branching to a tertiary ion and under extreme heating. In contrast, the four simulations that began with branched alkyl ions were all successful in demonstrating β scission at lower temperatures: 2,4,4-trimethyl-2-pentyl ion and 2,4-dimethyl-2-hexyl ion in each of the first two catalysts. The lifetimes of desorbed alkyl ions in the chabazite models were < 5 ps at 1000–1500 K. The β scission results support the classical Weitkamp et al. ( Appl. Catal. 1983, 8, 123 ) mechanism over the nonclassical Sie ( Ind. Eng. Chem. Res. 1992, 31, 1881 ) and the chemisorping Kazansky et al. ( J. Catal. 1989, 119, 108 ) mechanisms.

Reactions of some substituted phenols with chromyl and vanadyl chlorides

1980 ◽  
Vol 58 (7) ◽  
pp. 686-693 ◽  
Author(s):  
John F. Harrod ◽  
Asha Pathak
Keyword(s):  
Metal Complexes ◽  
Oxidation Potential ◽  
Lewis Acidity ◽  
Substituted Phenols ◽  
Phenoxyl Radicals ◽  
Organic Group ◽  
Product Distributions ◽  
Carbenium Ion ◽  
Electron Withdrawal ◽  
Ligand Transfer

The oxidation of 2,4,6-tritertbutylphenol and several other alkyl and halophenols by CrO2Cl2 and VOCl3 was studied. The products of CrO2Cl2 oxidation are mostly quinones and diphenoquinones, whilst those of VOCL3 oxidation also include major amounts of dealkylated phenols and C—C coupled dimers. The product distributions are interpreted in terms of a mechanism involving phenoxyl radicals, ligand transfer from metal to radical, and either phenoxonium ions or metallate esters where there is sufficient electron withdrawal from the organic group for it to exhibit carbenium ion properties. The differences in behaviour between CrO2Cl2, VOCl3, and CuCl2 are attributed to different balances between the oxidation potential and Lewis acidity of the metal complexes. It is concluded that CrO2Cl2 is not a good model for proposed ferryl intermediate in heme oxidase systems since it induces 1 → 3 rather than 1 → 2 halogen shifts and an NIH shift that is best explained by carbenium ion-like intermediates.

An Investigation of Gaseous α-Halogenated Carbocations and Isomeric Halonium, Halenium, and Allylhalonium Ions

2003 ◽  
Vol 56 (5) ◽  
pp. 437 ◽  
Author(s):  
Robert W. Holman ◽  
Jennifer Davis ◽  
Amy Walstrom ◽  
Michelle McCombs ◽  
Gina Jackson ◽  
...  
Keyword(s):  
Gas Phase ◽  
Halogen Atom ◽  
Mass Spectrometric ◽  
Recent Theory ◽  
Tandem Mass ◽  
Carbenium Ions ◽  
Ion Formation ◽  
Tandem Mass Spectrometric ◽  
Ion Species ◽  
Halonium Ion

We investigated with tandem mass spectrometric methods (MS/MS) the nature and extent of stabilization of gas-phase alkyl, vinyl and 2-allyl carbenium ions caused by halogen participation of neighboring chlorine and bromine atoms. The extent of halogen atom stabilization is greatest for alkyl ions, followed closely by that for vinyl ions, and is significantly less for the 2-halosubstituted allyl ions. The data is consistent with bridged halonium ion formation in alkyl systems and bridged halenium ion formation in vinyl systems. Our results for the 2-chloro allyl system are in accord with an earlier NMR interpretation rather than with recent theory, indicating that a bridged allyl halonium ion species is involved.

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