Mechanism of bromination of a quaternary pyrimidinium cation. Change of rate determining step with acidity

Tee, Oswald S.; Thackray, David C.; Berks, Charles G.

doi:10.1139/v78-487

Cited by 4 publications

(1 citation statement)

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“…Kinetic and spectral measurements were made on a Unicam SP 1800 spectrophotometer and a Durrum-Gibson stopped-flow spectrophotometer.55 An Aminco DW-2 spectrophotometer with stopped-flow accessory was also used. 24 The output voltage of the DW-2 (proportional to absorbance, (2 V/A) was captured on a Biomation 805 transient recorder (8-bit resolution, 2048 points). The stored trace was viewed on an oscilloscope, and if it was acceptable it was transferred serially at 9600 baud, using a Datos 305 interface to an Apple II microcomputer.…”

Section: Methodsmentioning

confidence: 99%

Observation of a tetrahedral intermediate and its anion in a hydrolysis reaction. Ring opening of a quinazolinium ion

Tee¹,

Trani²,

McClelland³

et al. 1982

J. Am. Chem. Soc.

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The behavior of the 3,4-dihydro-1,3-dimethyl-4-0xoquinazolinium ion (Q') in basic aqueous solution (pH 7-1 4 ) has been studied. Kinetic studies afforded information about four distinct processes: (a) the relatively fast equilibration of Q' with its pseudobase QOH; (b) the slower equilibration of the manifold comprised of Q' , QOH, the pseudobase anion QO-, and the ring-opened form, a formanilide derivative, F (equilibrium is approachable starting from Q' or from F, which exists in solution as a 3:1 mixture of two atropisomers); (c) slower equilibration of the less stable atropisomer of F into the same manifold as above; and (d) hydroxide ion catalyzed hydrolysis of the formanilide moiety to give the benzamide A. The species QOH and QO-, which are observable by UV and NMR spectroscopy, are tetrahedral intermediates at the carboxylic acid level of oxidation. The present work is a rare instance where such intermediates have been observed and where analysis of the kinetic data has provided rate constants for their formation and decomposition starting from different precursors. In strongly basic solutions the equilibrium F s QO-+ H+ is displaced toward QO-; that is, the tetrahedral intermediate anion is thermodynamically stable relative to its acyl precursor. (6) (a) Patchornik, A.; Berger, A,; Katchalski, E.

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Section: Methodsmentioning

confidence: 99%