Kinetics of hydride transfer between nitrogen heteroaromatic cations

Bunting, John W.; Luscher, Mark A.

doi:10.1139/v88-396

Cited by 11 publications

(13 citation statements)

References 27 publications

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“…The tropylium salt displayed a clean singlet 6 9.34 (in CF3C02H relative to (CH3),Si), and 9-hydroxyxanthene showed 6 2.25 (br s, OH), 5.68 (s, lH), 6.90-7.60 (m, 8H) (in CDC13). I -Benzyl-l,4-dihydronicotinamide and 10-methyl-9,lOdihydroacridine were synthesized as previously reported (2,22). All compounds were stored in dark bottles in a vacuum desiccator over Drierite.…”

Section: Methodsmentioning

confidence: 99%

“…3 for the reaction of 1 with 4 was fitted to eq. [2], with k2 = 15.1(-+0.6) M-' s-' and pKR+ = 4.82(&0.05). For the other three reactions, log kTP appears to be linear in pH with negative unit slope.…”

Section: -Benzyl-l4-dihydronicotinamidementioning

confidence: 99%

“…These latter three reactions were investigated over pH ranges for which KR+ >> [H+], and under this condition eq. [2] simplifies to k y p = k2[Ht]/KR+; i.e., log k y p = log k2 + pKR+ -pH Thus for each of these reactions, k2 may be readily evaluated from the experimental data in Figs. 3 and 4.…”

Section: -Benzyl-l4-dihydronicotinamidementioning

confidence: 99%

“…More recently, rate-equilibrium correlations of such reactions have been vigorously explored in connection with the application of Marcus theory to the hydride transfer process (1,(13)(14)(15). There is now a significant body of literature relating to the reduction of a variety of pyridinium, quinolinium, isoquinolinium, acridinium, and phenanthridinium cations (2). Various 1,2-and 1,4-dihydropyridine derivatives have been used as the hydride donor species, with 1 ,Cdihydronicotinamides and 9,lO-dihydroacridines being the most commonly investigated hydride donors.…”

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confidence: 99%

“…The choice of 1 -benzyl-1,4-dihydronicotinamide and 10-methyl-9,lO-dihydroacridine as hydride donors was based upon our earlier observations (2) of an approximately constant relative reactivity for these two donors towards several acceptor cations. We wished to explore whether this relative reactivity would also be applicable to two quite different cationic acceptors chosen according to the criteria indicated above.…”

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confidence: 99%

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Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Bunting¹,

Conn²

1990

Can. J. Chem.

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, 537 (1990). The pH-dependences of the apparent second-order rate constants (k2PP) for the reduction of 2,4,6-cycloheptatrien-1-01 and 9-xanthydrol by each of 1-benzyl-1,4-dihydronicotinamide (BNH) and 10-methyl-9,lO-dihydroacridine (MAH) have been measured in 20% acetonitrile -80% water, at 25OC and ionic strength 1.0. For each of these reactions, the pH-dependence of kyp is only consistent with reduction occurring via the aromatic cation (either tropyliurn or xanthylium) that is present in equilibrium with these alcoholic species. The relative second-order rate constants (k2BNH/kYAH) for reductions by these two reducing agents (1700 for tropylium and 770 for xanthyliurn) are similar for these two cations. These ratios are also similar to those observed for a variety of nitrogen heteroarornatic hydride acceptors, even though the absolute magnitudes of these rate constants vary by 10''-fold. The second-order rate constants for the reductions of the tropyliurn and xanthyliurn cations are predicted reasonably well by their pKR+ values, with the latter cation being (7 x lo5)-fold more reactive than its T-isoelectronic N-methyl acridiniurn cation. The xanthyliurn cation has the greatest k!NH/koH ratio yet observed for any heteroarornatic cation, and this value further extends the known range of this ratio as a function of reactivity.Key words: hydride transfer, kinetics of reduction, 1,4-dihydropyridine derivatives, tropyliurn cation, xanthyliurn cation. 537 (1990). Operant h 25°C et a une force ionique de 1,0, dans des solutions contenant 20% d'acetonitrile et 80% d'eau, on a mesure la relation qui existe entre le pH et les constantes apparentes de vitesse du deuxikrne ordre (kyp) pour la reduction du cyclohepta-2,4,6-trikn-1-01 et du xanthydr-9-01 soit par le I-benzyl-l,4-dihydronicotinamide (BNH) ou par la 10-methyl-9,10-dihydroacridine (MAH). Pour chacune de ces reactions, la relation entre le pH et le kyP ne correspond qu'h celle attendue pour une reduction se produisant par le biais d'un cation aromatique (soit tropyliurn ou xanthylium) qui est present l'equilibre dans ces espkces alcooliques. Les constantes relatives des vitesses de reaction du second ordre (k2BNH/kyAH) pour les reductions par ces deux agents riducteurs (1700 pour le tropyliurn et 770 pour le xanthyliurn) sont sernblables pour ces deux cations. MCme si les valeurs absolues de ces constantes de vitesse varient par des facteurs allant jusqu'h 101°, ces rapports sont aussi similaires h ceux observes pour un grand nornbre de derives hCtCroaromatiques azotks accepteurs d'hydrure. Utilisant les valeurs des pKR+ des cations, on peut aussi predire assez correcternent les constantes de vitesse du deuxikrne ordre pour les reductions des cations tropyliurn et xanthylium; ce dernier cation est environ 7 X lo5 fois plus rkactif que le cation N-methyl acridinium qui lui est T-isoelectronique. La valeur du rapport k!NH/koH du cation xanthyliurn est la plus ClevCe avoir Ct C observee jusqu'h rnaintenant et cette valeur Clargit la plage connue de ce rapport ...

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Section: Methodsmentioning

confidence: 99%

Section: -Benzyl-l4-dihydronicotinamidementioning

confidence: 99%

Section: -Benzyl-l4-dihydronicotinamidementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Bunting¹,

Conn²

1990

Can. J. Chem.

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Kinetik der Hydrid‐Übertragungen von CH‐, SiH‐, GeH‐ und SnH‐Gruppen auf Carbenium‐Ionen

Mayr

Basso

1992

Angewandte Chemie

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Kinetics of Hydride Transfers from CH, SiH, GeH, and SnH Groups to Carbenium Ions

Mayr

Basso

1992

Angew. Chem. Int. Ed. Engl.

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and carbon-centered "multiple warhead" tetraradical 10, a potentially powerful species for DNA damage. In the event, however, none of the products expected to arise from 10 were formed. Instead, the two novel dihydroperoxides 8 and 9 were isolated in 22 and 10% yield, respectively. The same transformations were also effected, although less cleanly, by thermolysis in the presence of hydrogen atom donors. Quite intriguing is the possibility of the intermediacy of a dioxetener'] which is presumed to eject the equivalent of ethenedione,"] perhaps as two carbon monoxide molecules.[91 Compounds2 and 3 caused significant DNA cleavage when incubated with +XI74 supercoiled DNA at pH 8.5 and 50 "C (Fig. 2). Interestingly, dione 4 caused only slight DNA damage under the same conditions, whereas hydroperoxides 8 and 9 showed, as expected, quite strong DNA-cleaving activities. Based on the chemistry of these systems we presume that whereas the ten-membered ring enediynes 2 and 3 may exert their DNA-cleaving power by cyclization to an aromatic diradical, the open-chain enediynes 8 and 9 may operate by an entirely different mechanism involving the generation of oxygen-centered radicals.

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Kinetics of hydride transfer between nitrogen heteroaromatic cations

Cited by 11 publications

References 27 publications

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Kinetik der Hydrid‐Übertragungen von CH‐, SiH‐, GeH‐ und SnH‐Gruppen auf Carbenium‐Ionen

Kinetics of Hydride Transfers from CH, SiH, GeH, and SnH Groups to Carbenium Ions

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