Search Results

Now showing 1 - 4 of 4

Some of the metrics are blocked by your
consent settings
Computational Investigation of the Ru-Mediated Preparation of Benzothiazoles From N-Arylthioureas: Elucidation of the Reaction Mechanism and the Origin of Differing Substrate Reactivity
(2024-10-01)
Krawmanee, Pacharaporn
;
Gleeson, M. Paul
;
Gleeson, Duangkamol
Synthesis of novel benzothiazoles via intramolecular CS bond formation reactions is increasingly being explored since they have been found in a wide range of natural products and pharmaceutical agents. Sharma et al. reported the ruthenium-catalyzed preparation of novel benzothiazole derivatives from N-arylthiourea precursors, with a range of reaction yields and selectivity being observed. We have employed a density functional theory-based computational model to investigate the reaction mechanism leading to the benzothiazole product and help uncover the origin of the differing experimental yields and substrate specificities. We proposed a modified mechanistic scheme where the rate-determining step to be the synchronized breaking of the peroxide bond of the oxidizing agent with the concomitant proton-coupled electron transfer from the haloarene urea and a Ru-bound water molecule, not electrophilic RuC bond activation. Evidence for this being the rate-determining step is (a) the barrier is consistent with a lack of kinetic isotope effects associated with the ortho-H atom and (b) the computed rate-determining barriers for 10 N-arylthiourea substrates show good correlation with the observed yield.
Some of the metrics are blocked by your
consent settings
Computational investigation of the radical-mediated mechanism of formation of difluoro methyl oxindoles: Elucidation of the reaction selectivity and yields
(2023-02-15)
Somnarin, Thanachon
;
Krawmanee, Pacharaporn
;
Gleeson, Matthew Paul
;
Gleeson, Duangkamol
Oxindoles are an important class of heterocyclic alkaloids with demonstrated pharmacological activity at multiple biological targets. Preparation of new analogs through novel synthetic routes is therefore highly attractive. In this work, we report a computational study to investigate the synthesis of ethoxycarbonyldifluoromethylated oxindoles from N-arylmethacrylamides. The reaction tolerates a diverse range of acrylamides, shows yields ranging from approximately 38%–96%. We have applied density functional theory (DFT) to explore the reaction mechanism, kinetics and thermodynamics to gain further understanding. We demonstrate that a radical-based ring closure reaction is energetically more favorable than a heterolytic process, that the rate-determining step is the formation of the arylmethacrylamide radical, and that the product yields and selectivities are consistent with experiment. The results demonstrate that theoretical methods can prove useful to understand how such reaction and could be potentially employed to rapidly explore the reaction scope further.
Some of the metrics are blocked by your
consent settings
DFT Investigation of the catalytic conversion of acetic acid to acetone on the zeolite H-ZSM5
(2022-12-01)
Konsue, Adchatawut
;
Gleeson, M. Paul
;
Gleeson, Duangkamol
Biomaterials processing has become increasingly important in the chemical industry. Identification and optimization of processes to facilitate biomass conversion is therefore recognized as being of great importance. Carboxylic acids derived from biomaterials are important building blocks that can be used in a wide variety of industrial applications. As such, methods to process them in an efficient and cost-effective manner are highly desirable. In this study we report the use of theoretical methods to explore the catalytic conversion of acetic acid to acetone on the zeolite H-ZSM5. We have employed a 46T DFT cluster model to explore mechanistic proposals reported in the literature. We investigate the relative energetics associated with the formation of the proposed intermediates, including acyl-zeolite complexes, enols, acylium cations, ketenes, anhydrides, and beta-keto acids, that could potentially connect acetic acid to the desired product, acetone. This assessment would allow us to identify the most probable mechanism connecting the reactant to products. We predict a low energy pathway starting with the generation of a surface acyl, followed by an anhydride, with the rate determining step involving methyl group migration. The reaction is predicted to be bi-molecular and involves C-C bond formation, in line with proposals based on isotopic labelling experiments.
Some of the metrics are blocked by your
consent settings
The skeletal isomerization in ferrierite: A theoretical assessment of the bi-molecular conversion of cis-butene to iso-butene
(2013-03-01)
Gleeson, Duangkamol
It is still not totally clear as to whether the skeletal isomerization of linear butenes to iso-butene in ferrierite occurs via a mono-molecular or bi-molecular process. To try and shed more light on this process, quantum chemical calculations were undertaken on both mechanisms. A large cluster model (H<inf>53</inf>O<inf>52</inf>Si<inf>35</inf>Al) has been employed here to study the bi-molecular process and these results are contrasted to the mono-molecular results previously reported by the author using the same model. The results suggest that a bi-molecular process can indeed result in the formation of iso-butene, as well as longer chained by-products as exemplified by 2,4,4-trimethylpent-2-ene. A rate determining step of 18.6 kcal/mol is found for the bi-molecular process, involving CC bond formation between the two monomers. The barrier is also predicted to be considerably lower than that of the mono-molecular reaction (24.5 kcal/mol). Nevertheless, given that 2,4,4-trimethylpent-2-ene has a considerably lower barrier to reaction, and is more energetically favourable, iso-butene product to might not be expected to form in large quantities via this route. © 2012 Elsevier B.V.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results