Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

Sivasankar, N.; Prins, R.

doi:10.1016/j.cattod.2006.06.027

Cited by 9 publications

(8 citation statements)

References 27 publications

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“…2), indicating that its rate of consumption is higher than its rate of formation. The maximum was lower in the presence of H 2 S. Indeed, trialkylamines were shown to react fast to dialkylamines and alkanethiols, especially in the presence of H 2 S [21,25].…”

Section: Discussionmentioning

confidence: 99%

“…Recent work has demonstrated that the elimination of ammonia from an alkylamine is too difficult under HDN conditions and that C-N bond breaking occurs exclusively by nucleophilic substitution [21][22][23]. It was furthermore demonstrated that this substitution does not occur by a classic nucleophilic substitution, but by addition of H 2 S to an imine C=N or enamine CH 2 =CH 2 -N bond, that is formed by dehydrogenation of an alkylamine [24,25]. Subsequent elimination of ammonia or an amine leads to an alkanethiol.…”

Section: Introductionmentioning

confidence: 99%

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On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

Wang

Prins

2008

Catal Lett

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The hydrodenitrogenation of 2-methylpiperidine and 2-methylpyrrolidine was studied over sulfided NiMo/c-Al 2 O 3 in the presence of dialkylamines, alkylamines, and alkenes to determine why N-pentylpiperidine is formed in the hydrodenitrogenation of pyridine. N-alkylated 2-methylpiperidine and 2-methylpyrrolidine were only formed as primary products by reaction with alkylamines and not by reaction with 2-methylpiperidine and 2-methylpyrrolidine, or by reaction with an alkene. This indicates that, in the hydrodenitrogenation of pyridine, N-pentylpiperidine is formed by the reaction of the secondary intermediate pentylamine with the primary intermediate piperidine, and not by reaction of two primary piperidine intermediates or by reaction of pentene, one of the final products, with piperidine.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

Wang

Prins

2008

Catal Lett

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“…The full mechanism of the formation of N,N-dimethyl- hexylamine is depicted in Scheme 16. Sivasankar and Prins in a further study [89] propose another explanation: according to them, the sought-after intermediate is an iminium cation. Such an interpretation seems to be less probable since it assumes a transfer of a proton on the metal surface in the hydrogenation-dehydrogenation processes.…”

Section: Transfer Of Methyl Groups Between Amines During the Dispropomentioning

confidence: 94%

Nitrile Hydrogenation on Solid Catalysts – New Insights into the Reaction Mechanism

Krupka¹,

Pašek²

2012

COC

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The heterogeneous catalytic hydrogenation of nitriles is an important industrial process for the production of diverse amines. The reaction scheme based on the von Braun and Greenfield proposals has been widely accepted for many years and it remains the most frequently cited reaction sequence for the formation of secondary and tertiary amines via the hydrogenation of nitriles. Over the past decade, there has been a stream of published papers that, using modern scientific techniques, have intensively investigated the detailed mechanism underlying the surface reactions of heterogeneously catalyzed nitrile hydrogenation and the surface intermediates. On the one hand, the results of these studies bring some light to this issue; on the other hand, entirely new, unanswered questions arise from new knowledge. The studies suggest that the mechanism of nitrile hydrogenation on solid catalysts is much more complicated than expected based on the reaction formalism of von Braun and Greenfield. Unfortunately, there are as yet no physicochemical studies available that could confirm in a straightforward manner the intimate details of the reaction mechanism of surface reactions. In this review, the various speculative mechanisms proposed for heterogeneous nitrile hydrogenation are discussed. It seems very likely from current knowledge that aminocarbene complexes and aldimines, coordinated to a metal via the -system of a C=N double bond and/or via the nitrogen lone pair, will prevail among the surface intermediates suggested for nitrile hydrogenation on palladium or platinum, whereas hydrogenation on a cobalt or nickel surface will likely be associated with the formation of nitrene intermediates. This duality provides a satisfactory explanation for the selectivity differences between metal catalysts in nitrile hydrogenation to primary amines.

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“…This reaction, however, does not occur via an elimination reaction but rather by substitution of alkylamines by H 2 S to form an alkanethiol and NH 3 [59,60]. It has been shown that alkylamines and dialkylamines may well react via imine intermediates, whereas the intermediate for trialkylamines can only be an iminium ion [59,60].…”

Section: Surface Chemistry and Reaction Mechanismsmentioning

confidence: 99%

Elimination and Addition Reactions

Kraus

Knözinger

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Scope and Thermodynamics Common Features Mechanism Influence of Reactant Structure on Rate Direction of Elimination and Addition Reactions Elimination Addition Catalysts Surface Chemistry and Reaction Mechanisms Stop Effect Catalyst Poisoning and Deactivation Kinetics Practical Applications of Elimination and Addition Reactions Dehydrochlorination Vinyl Chloride Production Trichloroethene and Tetrachloroethene Production Production of Linear Alkenes Dehydration Hydrochlorination Hydration and Amination Formation of Ethanol Formation of 2‐Propanol Addition of Alcohols and Organic Acids to Alkenes Isopropyl Acetate Methyl tert ‐Butyl Ether Alkylation and Dealkylation

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Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

Cited by 9 publications

References 27 publications

On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

Nitrile Hydrogenation on Solid Catalysts – New Insights into the Reaction Mechanism

Elimination and Addition Reactions

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