Kinetic Studies of the Decarboxylation of Some N-Substituted Pyridinecarboxylic Acids

Haake, Paul; Mantecon, Joaquin

doi:10.1021/ja01077a038

Cited by 45 publications

(31 citation statements)

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“…Accordingly, it may be assumed, at least as a first approximation, that, in the p H range studied, the only species present in significant concentration are H,At and HA, that the only important ionization constant is K,, and that k, is negligible. These assumptions are expressed in [3], [4], and [5] which may be combined to give [6].…”

Section: Discussionmentioning

confidence: 99%

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Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

Dunn¹,

Lawler²,

Yamashita³

1977

Can. J. Chem.

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Can. J. Chem. 55,2478(1977.Pseudo-first-order rate constants for the decarboxylation of pyrimidine-2-carboxylic acid have been determined at 65'C in aqueous solution over the acidity range p H = 2 to HO = -9.5.Rate constants increase rapidly from p H = 2 to Ho = -3, then remain constant. This behaviour can be accounted for by a Hammick-type mechanism in which monoprotonated pyrimidine-2-carboxylic acid loses carbon dioxide to form an ylide (stabilized by the adjacent positively charged nitrogens) which rapidly converts to pyrimidine.

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Section: Discussionmentioning

confidence: 99%

“…Thus quaternization of the nitrogen increases the rate of decarboxylation by factors of about 100 in aqueous solution (I) and 700 in ethylene glycol (4). Substituents in the 3-position have a much larger effect on the rate than in the 4-, 5-, or 6-positions (1) and appear to exert their influence by a mixture of electronic and steric effects.…”

Section: Methodsmentioning

confidence: 99%

Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

Dunn¹,

Lawler²,

Yamashita³

1977

Can. J. Chem.

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“…First-order rate constants for the decarboxylation of 3-methylpicolinic acid at 150-C, y = 1.0. Circles represent experimental points and the solid line is calculated from [6].…”

Section: -Metlzylpicolinic Acidmentioning

confidence: 99%

“…Combination of [2]- [5] gives [6], the dependence of the stoichiometric rate constant, k, on hydrogen-ion concentration :…”

Section: Ha--'h+mentioning

confidence: 99%

Kinetics and mechanism of decarboxylation of some pyridinecarboxylic acids in aqueous solution. II

Dunn¹,

Thimm²

1977

Can. J. Chem.

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Six 3-substituted picolinic acids were synthesized and decarboxylated in buffered aqueous solutions of ionic strength 1.0 at 150 and/or 95°C. 3-Amino-and 3-hydroxypicolinic acids appear to decarboxylate by initial protonation, but the others fit the requirements of the Hammick mechanism for picolinic acid decarboxylation. Both electron-withdrawing and electron-releasing 3-substituents accelerate decarboxylation in picolinic acids but inhibit decarboxylation in their anions. Acceleration in the acids is considered to be the result of interference by 3-substituents with coplanarity of the carboxyl group and the aromatic nucleus. This reduces the order of the bond between the carboxyl group and the ring, thus facilitating bond breaking. In decarboxylation of the anions water appears to play a critical role, since picolinate ions have not been observed to decarboxylate in any other solvent, including ethylene glycol. It is proposed that water forms a hydrogen-bonded bridge between carboxylate oxygen and aromatic nitrogen, so that as the carbon-carbon bond breaks a nitrogen-hydrogen bond is formed. This may provide a lower energy path through an ylide intermediate than would be required if the picolinate ion were to decarboxylate to a 2-pyridyl carbanion. Chem. 55, 1342Chem. 55, (1977. On a synthetise six acides picoliniques substitues en position 3 et on les a dCcarboxyles dans des solutions aqueuses tamponnes de force ionique 1 .O, a 150 et/ou 95'C. I1 semble que les acides amino-3 et hydroxy-3 picoliniques se decarboxylent par une protonation initiale; toutefois les autres presentent les caracteristiques necessaires pour le mecanisme propose par Hammick pour la dCcarboxylation de I'acide picolinique. Les substituants en position 3 qui attirent les electrons ainsi que ceux qui repoussent les electrons accelerent la decarboxylation des acides picoliniques mais inhibent la decarboxylation de leurs anions. On considere que I'accelCration dans les acides provient d'une interference, par les substituants en position 3, sur la coplanarite du groupe carboxyle et du noyau aromatique. Cet effet reduit l'ordre de la liaison entre le groupement carboxyle et le cycle et facilite ainsi le bris du lien. Dans le cas de la decarboxylation des anions, il sernble que l'eau joue un r6le critique puisque l'on n'a jarnais observe la decarboxylation des ions picolinates dans d'autres solvants, m&me i'ethylene glycol. On suggere que l'eau forme des ponts hydrogene entre I'oxygkne du carboxylate et I'azote du cycle arornatique provoquant la formation d'un lien azote-hydrogene au moment oh le lien carbone-carbone se brise. Ce processus pourrait fournir une voie requtrant une energie plus basse, via un ylide intermediaire, que celle qui serait requise si l'ion picolinate se decarboxylait par I'intermidiaire d'un carbanion pyridyle-2.[Traduit par le journal]

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“…14 It was subsequently found 15,16 that N-alkylated pyridinium 2-carboxylates release CO 2 more than 700 times faster than 2-picolinic acid (Scheme 1). Since the resulting carbene intermediates can be trapped by electrophiles and may be used for the low temperature synthesis (60-80 1C) of pyridinium salts, 17 we reasoned that betaines of this kind could be employed as precursors for transition metal carbenes.…”

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confidence: 99%

A simple, general route to 2-pyridylidene transition metal complexes

2010

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Pyridinium 2-carboxylates decompose thermally in the presence of a variety of late transition metal precursors to yield the corresponding 2-pyridylidene-like complexes. The mild reaction conditions and structural diversity that can be generated in the heterocyclic ring make this method an attractive alternative for the synthesis of 2-pyridylidene complexes. IR spectra of the Ir(I) carbonyl compounds [IrCl(NHC)(CO) 2 ] indicate that these N-heterocyclic carbene ligands are among the strongest r-electron donors.The importance of N-heterocyclic carbenes (NHCs) as ligands for transition metal complexes and catalysis is nowadays well established.

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Kinetic Studies of the Decarboxylation of Some N-Substituted Pyridinecarboxylic Acids

Cited by 45 publications

References 0 publications

Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

Kinetics and mechanism of decarboxylation of some pyridinecarboxylic acids in aqueous solution. II

A simple, general route to 2-pyridylidene transition metal complexes

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