Equilibration of N-(2-cyanoethyl)pyridinium cations with substituted pyridines and acrylonitrile. A change in rate-determining step in an E1cb reaction

Bunting, John W.; Toth, A.; Heo, Christina K. M.; Moors, Rodney G.

doi:10.1021/ja00180a034

Cited by 28 publications

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“…We have observed the elimination reaction of l m (0.046 M) by 'H NMR spectroscopy in basic DzO (pD = 12.5). The decrease in the intensity of the signals from l m is concerted with the appearance of the spectrum of the corresponding N-vinyl pyridinium cation (2m) (6 3.32 (s, 6H), 5.36 (dd, IH), 5.71 (dd, lH), 7.00 (d, 2H), 7.06 (dd, lH), 8. 23 (d, 2H)).…”

Section: Resultsmentioning

confidence: 95%

“…Quantitative comparisons can also be made of the range pKBH = 2-10. These data now allow detailed comreactivities in these systems and in related elimination reparisons of the reactivities of 1 , 3 , and 4 in base-catalyzed actions in which substituted pyridines are the nucleofugic eliminations in aqueous solution, and also demonstrate that leaving groups (8,9).…”

mentioning

confidence: 75%

“…[8]) and a = 0.33 for the deprotonation of N-di(ethoxycarbony1)methyl pyridinium cations (7) (eq. [9]).…”

Section: Discussionmentioning

confidence: 99%

“…[8] and [9] in aqueous solution are linearly correlated with pKBH for the corresponding substituted pyridinium cations: text of the rate-determining bromide ion departure from the carbanionic intermediate that is deduced above from the concave-down Bronsted plot. This result requires that elimination occurs within a solvated (hydrogen-bonded) intermediate in which bromide ion departure occurs more rapidly than exchange of the HOD molecule with bulk D 2 0 (i.e., k, >> k, in Scheme 2).…”

Section: Discussionmentioning

confidence: 99%

“…All data collection and analysis closely followed the methods that we have previously described (8). In most cases, analytical wavelengths were in the vicinity of 250 nm, although wavelengths in the vicinity of 300 nrn were more appropriate for the 3-and 4-aminopyridinium cations.…”

Section: Kinetic Studiesmentioning

confidence: 99%

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Kinetics and mechanism of the formation of N-vinyl pyridinium cations in elimination reactions in aqueous base

Bunting¹,

Toth²,

Kanter³

1992

Can. J. Chem.

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. Can. J. Chem. 70, 1195 (1992). The rates of the elimination reactions of N-(2-bromoethyl) pyridinium cations (1) and N,Nf-ethylene bispyridinium dications (3) to give the corresponding N-vinyl pyridinium cations (2) have been measured spectrophotometrically in basic aqueous solutions (ionic strength 0.1, 25°C) for a variety of substituents in the pyridine rings of each of these classes of pyridinium cation. The reaction kinetics are first order in 1 or 3 and first order in hydroxide ion. Bronsted-type plots of the second-order rate constants (kc,,) as a function of the basicity (as pKBH) of the corresponding substituted pyridine are nonlinear for each of 1 and 3 and can be interpreted in terms of E l c b reaction mechanisms. For 1, the Bronsted-type plot displays two distinct "concave down" linear regions; rate-determining deprotonation for pK,, < 5.16 (slope = -0.30), and a change in rate-determining step to bromide ion departure for pKBH > 5.16 (slope -0.58). For 3, the Bronstedtype plot appears to be smoothly curved for symmetrically disubstituted bispyridinium dications, as a consequence of the multiple substituent effects upon each step of the Elcb reactions of these dications. However, log koH for 3 is a smooth linear function of the previously reported log koH for the E l c b reactions of N-(2-cyanoethyl) pyridinium cations over a range in which a change in rate-determining step has been directly demonstrated for these latter cations. Thus a change in rate-determining step as a function of pyridine basicity is also required within the E l c b mechanism for 3. The E l c b reactions of 1 are approximately lo4-fold faster than the corresponding hydroxide ion catalyzed E2 eliminations from 2-phenylethyl bromides that are isoelectronic with 1. JOHN W. BUNTING, ANDREA TOTH et JAMES P. KANTER. Can. J . Chem. 70, 1 195 (1992). Operant en solutions aqueuses basiques (force ionique de 0,1, a 25°C) et faisant appel des mkthodes spectrophotomktriques, on a mesurt les vitesses des reactions d'elimination des cations N-(2-bromoethy1)pyridinium ( I ) et des dications N,N1-Cthylkne bispyridinium (3) qui portent une variete de substituants sur les pyridines de chacune des classes de cations pyridinium et qui conduisent a la formation des cations N-vinylpyridinium correspondants (2). Les cinetiques des reactions sont du premier ordre en composCs 1 (ou 3) et du premier ordre en ion hydroxyde. Pour chacun des produits 1 et 3 , les courbes de type Bronsted des constantes de vitesse du deuxikme ordre (koH) en fonction de la basicite (exprime en pKBH) de la pyridine substituke correspondante ne sont pas lineaires; on peut interpreter ces resultats en fonction de mecanismes reactionnels Elcb. Pour les composes 1, la courbe de type Brgnsted presente deux regions lineaires aconcaves vers le basn distinctes; une deprotonation qui determine la vitesse se produit un pKBH < 5,15 (pente = -0,30) et un changement dans I'ktape qui determine la vitesse de depart de l'ion bromure a un pKBH > 5,16 (pente = -0,58).Pour les composCs 3 impli...

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Section: Resultsmentioning

confidence: 95%

mentioning

confidence: 75%

“…[8]) and a = 0.33 for the deprotonation of N-di(ethoxycarbony1)methyl pyridinium cations (7) (eq. [9]).…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Kinetic Studiesmentioning

confidence: 99%

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Kinetics and mechanism of the formation of N-vinyl pyridinium cations in elimination reactions in aqueous base

Bunting¹,

Toth²,

Kanter³

1992

Can. J. Chem.

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Deprotonation of 1-(carbethoxyalkyl)pyridinium halides with strong N-bases

Dega‐Szafran

Schroeder

Szafran

1999

J. Phys. Org. Chem.

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The rate constants were measured for deprotonation of 1-(carbethoxymethyl)pyridinium chloride and 1-(2-carbethoxyethyl)pyridinium bromide with strong bases (DBU, MTBD, TBD and P2-Et) in acetonitrile. The UV spectra and semiempirical calculations are consistent with an ylide structure of the deprotonated species. The ylides obtained slowly decompose, and the reaction products were identified by 1 H NMR spectroscopy; 1-(carbethoxymethyl)pyridinium chloride gives N-methylpyridinium cation and ethanol and 1-(2-carbethoxyethyl)pyridinium bromide converts to pyridine and ethyl acrylate.

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Nucleophilicities and Carbon Basicities of Pyridines

Brotzel

Kempf

Singer

et al. 2006

Chemistry A European J

136

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Rate and equilibrium constants for the reactions of pyridines with donor‐substituted benzhydrylium ions have been determined spectrophotometrically. The correlation equation log k(20 °C)=s(N+E), in which s and N are nucleophile‐specific parameters and E is an electrophile‐specific parameter, has been used to determine the nucleophilicity parameters of various pyridines in CH2Cl2 and aqueous solution and to compare them with N of other nucleophiles. It is found that the nucleophilic organocatalyst 4‐(dimethylamino)pyridine (DMAP) and tertiary phosphanes have comparable nucleophilicities and carbon basicities despite widely differing Brønsted basicities. For that reason, these reactivity parameters are suggested as guidelines for the development of novel organocatalysts. The Marcus equation is employed for the determination of the intrinsic barriers of these reactions.

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Equilibration of N-(2-cyanoethyl)pyridinium cations with substituted pyridines and acrylonitrile. A change in rate-determining step in an E1cb reaction

Cited by 28 publications

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Kinetics and mechanism of the formation of N-vinyl pyridinium cations in elimination reactions in aqueous base

Kinetics and mechanism of the formation of N-vinyl pyridinium cations in elimination reactions in aqueous base

Deprotonation of 1-(carbethoxyalkyl)pyridinium halides with strong N-bases

Nucleophilicities and Carbon Basicities of Pyridines

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