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2 edition of Mechanistic studies of pyrylium and pyridinium cations. found in the catalog.

Mechanistic studies of pyrylium and pyridinium cations.

David E. Leahy

Mechanistic studies of pyrylium and pyridinium cations.

by David E. Leahy

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Published by University of East Anglia in Norwich .
Written in English


Edition Notes

Thesis (Ph.D.) - University of East Anglia, School of Chemical Sciences 1983.

ID Numbers
Open LibraryOL13809009M

charge on the pyrylium cation is concentrated in the 2-, 4-, and 6-positions, as has been confirmed by quantum-chemical calculations,12)1Λ 4H-pyrans are formed together with 2W-pyrans. The ratios of the products formed (2H-pyrans, cis-dienones, and 4H-pyrans) are determined by the struc-ture of the pyrylium salt, the nature of the nucleophile, and. Mechanistic Studies of Pyridinium Electrochemistry: Alternative Chemical Pathways in the Presence of CO 2 Alex G. Peroff, Eric Weitz, and Richard Van Duyne Northwestern University, Department of Chemistry, Evanston IL, Table of Contents S1 - Experimental and digital simulations of pyridinium .

The complete system for pyrylium-ion-mediated transport of electrons and hydroxide ions is illustrated in Fig. entrifugation studies 4 have established that binding of ZnTPPS 4-to the. Cationic surfactants are being used in various applications industrially and domestically for a long time. Pyridinium salts come under the category of cationic surfactants. These are unsaturated heterocyclic compounds having different functional groups present either on pyridine ring or at nitrogen atom. Initially, they were only considered as effective germicides.

Pyridine is a basic heterocyclic organic compound with the chemical formula C 5 H 5 is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like ne is colorless, but older or impure samples can appear yellow. Pyrylium salts are a very important class of organic molecules containing a trivalent oxygen atom in a six-membered aromatic ring. In this manuscript, we report a theoretical study of pyrylium salts and their thio-, seleno- and telluro- analogues by means of DFT calculations. For this purpose, unsubstituted 2,4,6-trimethyl and 2,4,6-triphenyl cations and anions with different morphologies were.


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Mechanistic studies of pyrylium and pyridinium cations by David E. Leahy Download PDF EPUB FB2

Kinetic rates for cyclisation of divinylogous amides (derived from pyrylium cations and primary amines) into pyridinium cations are measured for CH 2 C 2 solutions and compared with previous results in water and other solvents.

The ring-closure is catalysed by carboxylic acids; a postulated mechanism involves the free acid in catalysis of electrocyclic ring closure. Kinetics and mechanism of the pyrylium to pyridinium cation transformation in dichloromethane Article (PDF Available) in Journal of the Chemical Society Perkin Transactions 2 January with.

Pyrylium cations form pyridines with ammonia and pyridinium salts with primary amines. For example, 2,4,6-triphenylpyrylium cation (; Z = O) yields 2,4,6-triphenylpyridine with ammonia, the corresponding 1-methylpyridinium salt with methylamine, and 1-phenylamino pyridinium with lium ions, where ring opening cannot readily occur, form adducts with.

Pyrylium is a cation (positive ion) with formula C 5 H 5 O +, consisting of a six-membered ring of five carbon atoms, each with one hydrogen atom, and one positively charged oxygen atom.

The bonds in the ring are conjugated as in benzene, giving it an aromatic character. In particular, because of the positive charge, the oxygen atom is um is a mono-cyclic and heterocyclic ChEBI: CHEBI Mechanistic studies of pyrylium and pyridinium cations Author: Leahy, D.

ISNI: Awarding Body: University of East Anglia Current Institution: University of East Anglia Date of Award: Availability of Full Text: Access from EThOS. The initial reaction of primary amines with pyrylium cations to give Mechanistic studies of pyrylium and pyridinium cations.

book ring-opened intermediate is fast for strongly basic amines and is base-catalysed for weak amines. Ring-closure of the intermediate to give the pyridinium derivative is subject to steric and electronic hindrance and is acid-catalysed.

Solvent e. A pyridinium ion with a silane-protected exocyclic hydroxy group can undergo a regio- and stereospecific intramolecular hydride transfer in the presence of fluoride C-2 benzylic alcohol was formed by Grignard addition; after attaching a nucleophilc hydride species to the alcohol in the form of the silyl group, hydride transfer was initiated by treatment with an excess of TBAF.

We have used highly substituted pyrylium salts for the two‐step conversion of the amino group in alkylamines RNH 2 into numerous other functionalities. In the first step, the pyrylium salts are converted with the amines into N ‐substituted pyridinium salts, which, in the second step, react with Nu ⊖ to give the desired products RNu.

General Procedure for synthesis of Pyridinium salts 6, 7 To a solution of chitosan ( mg) in aqueous acetic solution (25 mL), a solution of pyrylium tetrafluoroborate salt ( mmol) in MeOH. Synthesis of pyrylium salts from (A) chalcone and (B) directly from aldehydes and ketones Following the later approach, symmetric compounds were synthesized with intrinsic fluorescence in acceptable yields.

For this kind of structures singlets for H-3 and H-5 at 9 ppm approximately that confirm the presence of pyrylium cation were.

Mechanism of the Pyrylium/Pyridinium Ring Interconversion. Mild Preparative Conditions for Conversion of Amines into Pyridinium Ions. Successive base and acid catalysis in the transformation of pyrylium (1) into pyridinium ions (2) permits drastic reduction of reaction time (depending upon R) and/or of the temperature.

Citing Literature. Pyridines and Pyridinium Salts. JV-Oxides The most typical example of the reactions of pyrylium salts is their interaction with ammonia and its derivatives leading to the formation of pyridine and other heterocyclic nitrogen-containing bases.

In an early study Baeyer 1 established that pyrylium salts are readily converted into. In this mini-review authors focused mostly on bioactive properties of pyridinium salts, and main preparations of these compounds such, synthesis pyridinium salts from pyrylium salts via nucleophilic substitution SN (ANRORC), obtaining pyridinium salts via directs arylation, and via Addition at Nitrogen atom, and the last method is synthesis of pyridinium salts via ring opening and re-cyclisation.

Pyridinium cations are aromatic ion, as determined through Hückel's rule. It is isoelectronic to benzene. N-Alkylpyridinium cations. Nicotinamide adenine dinucleotide is a N-alkylpyridinium cation that occurs widely in life.

When the acidic proton is replaced by alkyl, the compounds are called N-alkylpyridinium. Mechanistic studies of pyridinium electrochemistry: alternative chemical pathways in the presence of CO 2† A. Peroff, E. Weitz and R. Van Duyne* Protonated heterocyclic amines, such as pyridinium, have been utilized as catalysts in the electrocatalytic reduction of carbon dioxide.

We employ quantum chemical calculations to investigate the mechanism of homogeneous CO2 reduction by pyridine (Py) in the Py/p-GaP system. We find that CO2 reduction by Py commences with PyCOOH0 formation where: (a) protonated Py (PyH+) is reduced to PyH0, (b) PyH0 then reduces CO2 by one electron transfer (ET) via nucleophilic attack by its N lone pair on the C of.

In solution, the pyrylium and amine reaction is reported to proceed via a 2H-pyran intermediate (3, Scheme 2), which has been identified in this study as the m/z ion (MS/MS analysis indicate it is ethanolamine adduct of the parent pyrylium cation, Figure 4a).Product pyridinium cation is formed by gradual loss of water from the ring-opened 2H-pyran intermediate 4.

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in this book the mechanism is explained with coloured arrow notation. Pyrylium Salts: Syntheses, Reactions, and Physical Properties leading Md H Md Md Md Md methyl methylene nucleophilic obtained oxidation Ph H phenyl primary amines protons pseudobase pyran pyridine pyridinium salts pyrylium cation pyrylium ring pyrylium salts qd H react reaction reagents ring opening ring transformation S.

Baranov S. On the basis of the measured basicity constants of pyrylium and pyridinium salts containing p-aminophenyl substituents it is shown that the positive charge in the pyrylium cation is considerably higher than in the pyridinium cation.

The σ constants of the pyrylium and pyridinium substituents, which show that the magnitude of the electronic. Pyridinium definition is - a univalent ion [C5H5NH]+ or radical C5H6N that is analogous to ammonium and is derived from pyridine.Mechanistic studies of pyridinium electrochemistry: alternative chemical pathways in the presence of CO2.

SER spectroelectrochemistry of pyridinium solutions shows no evidence for a pyridinium radical or a pyridinium ion.

Increased cathodic current in the presence of CO2 is only detected at scan rates less than 10 mV s(-1) in aqueous.The synthesis of pyridinium salts was achieved by adapting the procedure of Studer2 as follows: A round-bottom flask equip with a stir bar and a side arm inlet adapter was heat dried under vacuum, allowed to cool to room temperature, and refilled with N2.

The flask was charged with the pyrylium salt (1 eq) and was then evacuated and refilled.