Kinetics and mechanism for addition of amines to formyl-1-methylpyridinium ions

Journal of Chemical Research

Mejias

2015

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Oxime formation from 4-pyridine carboxaldehyde N-oxide is shown to occur with rate-determining carbinolamine dehydration under acidic and neutral conditions. First, saturation effects observed at pH~ 7 are strongly suggestive of carbinolamine accumulation, requiring that dehydration of the intermediate be the rate-determining step. Second, this reaction occurs exclusively with general acid catalysis in the pH range investigated; the value of the Brønsted exponent, α=0.66, is suggestive of rate-determining carbinolamine dehydration, not amine attack. Third, no evidence was found for the usual pH-independent reaction typical of addition of weakly basic amines to the carbonyl function. Finally the break observed in the pH-rate plot at pH near 0.5 can be interpreted in terms of protolytic equilibrium of the substrate.

Section: Methodsmentioning

confidence: 99%

Kinetics and Mechanism for Oxime Formation from 4-Pyridinecarboxaldehyde N-Oxide

Journal of Chemical Research

Mejias

2015

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“…On the other hand, a comparison between equilibrium constants in Table I and the same constants in oxime formation from pyridine-4-carboxaldehyde [4] and its N-methyl derivative [3] (Table 2) indicates that pyridinecarboxaldehydes have more affinity for the amine than 4-dimethylaminobenzaldehyde and its Nmethyl derivative. Note that in respect to 4-formyl-1-methylpyridinium ion, 4-trimethylammoniobenzaldehyde iodide has a 547-fold reduction in the equilibrium constant and an increment of 181-fold in the dehydration rate constant.…”

Section: (S )(H )/(S )mentioning

confidence: 99%

“…These include the addition of several amines to Nmethylpyridinecarboxaldehyde ions [3]; the addition of hydroxylamine to pyridine-2-, -3-, and 4-carboxaldehydes [4]; and to 2-quinolinecarboxaldehyde [5]. In the work described herein, attention is directed to oxime formation from 4-trimethylammoniobenzaldehyde iodide and 4-dimethylaminobenzaldehyde.…”

Section: Introductionmentioning

confidence: 99%

“…The cationic nature of 4-trimethylammoniobenzaldehyde iodide makes it similar in some ways to the conjugate acids of 4-dimethylaminobenzaldehyde, pyridine-2-, -3-, and 4-carboxaldehydes, 2-quinolinecarboxaldehyde and to N-methylpyridinecarboxaldehyde ions. For N-methylpyridinecarboxaldehyde ions, oxime, semicarbazone, and phenylhydrazone formation occurs with rate-determining acid-catalyzed carbinolamine dehydration under acidic, neutral and basic conditions, therefore the pH-rate profiles do not exhibit breaks [3]. This behavior is attributed to i) strong destabilization of the substrate, and ii) to the fact that the possession of the cationic center may not increase the rate of carbinolamine dehydration: that is, the increased equilibrium constant for formation of carbinolamine may be offset or overridden by the effect of the cationic center on the rate of expulsion of water.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Kinetics and mechanism for oxime formation from 4-dimethylaminobenzaldehyde and 4-trimethylammoniobenzaldehyde iodide

Córdova

et al. 1999

Int. J. Chem. Kinet.

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The following lines of evidence establish that oxime formation from 4-dimethylaminobenzaldehyde and 4-trimethylammoniobenzaldehyde iodide occurs with a simple twostep mechanism. The pH-rate profile for the reaction of 4-trimethylammoniobenzaldehyde iodide exhibits, in order of decreasing pH, a negative deviation at pH near 2.0, corresponding to a transition from rate-determining step carbinolamine dehydration with acid catalysis to the uncatalyzed carbinolamine formation. In the case of the reaction of 4-dimethylaminobenzaldehyde, the pH-profile exhibits, in order of decreasing pH, a positive deviation at pH near 3.5 and then a negative deviation at pH near 2.0. These deviations have been interpreted in terms of i) transition of the rate-determining step, and ii) protolytic equilibrium of the substrate.

“…[1][2][3] The justification for this behavior was basically attributed to two factors: (i) very activated substrates to addition and (ii) the difficulty of the acidcatalyzed dehydration of the carbinolamines due to an unfavorable electrostatic situation. Depending on the pH, pyruvic acid exists as an acid, an anion or a mixture of both species, and there are different affinities to water between the acid and its anion.…”

Section: Introductionmentioning

confidence: 99%

Kinetics and mechanism of oxime formation from pyruvic acid

Córdova

2000

J. Phys. Org. Chem.

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The following lines of evidence establish that oxime formation from pyruvic acid occurs with ratedetermining carbinolamine dehydration under acidic and neutral conditions. First, saturation effects observed at pH 7 are strongly suggestive of carbinolamine accumulation, requiring that dehydration of the intermediate be the ratedetermining step. Second, the reaction occurs exclusively with general acid catalysis in the entire range investigated.The pH-rate plot shows a break at pH near 2, which can be interpreted in terms of protolytic equilibrium of the substrate.