Kinetic and thermodynamic control of pseudobase formation from C-3 substituted 1-methylquinolinium cations

Abstract

. Can. J. Chem. 62, 1301 (1984). The kinetic and thermodynamic control of pseudobase formation from 3-W-1-methylquinolinium cations has been studied for a variety of substituents (W). Spectral data indicate that, in both aqueous and methanolic solution, the C-2 pseudobases predominate at equilibrium for W = H and Br, while the C-4 pseudobases are the thermodynamically preferred species for W = CONH,, C02CH3, CN, and NO2. Stopped-flow studies indicate that in all cases the C-2 pseudobases are the kineticallycontrolled products upon basification of the aqueous solutions of these cations. Equilibrium constants (pKR+) have been measured for pseudobase formation at both C-2 and C-4 for each4W in all cases where they are experimentally accessible.Substituent effecJs upon p~: + correlate with u,, for W, while pKR+ depends upon ul,-. These substituent effects allow the prediction of pKR+ = 15.4 and p~: + = 17.4 for the I-methylquinolinium cation. Rates of C-2 to C-4 pseudobase equilibration have been measured in all cases where the latter species is thermodynamically more stable. These kinetic data allow the evaluation of rate constants for C-4 pseudobase equilibration with each cation. In all cases except W = CN, C-2 pseudobase formation is complete within the mixing time of the stopped-flow instrument. JOHN W. BUNTING et NORMAN P. FITZGERALD. Can. J. Chem. 62, 1301 (1984). On a ttudit le contr8le cinCtique et thermodynamique de la formation de pseudobases h partir de cations W-3 mCthyl-l quinolinium portant plusieurs substituants W. Les donnCes spectrales indiquent que, tant en solution aqueuse que mCthanolique, les pseudobases en C-2 prCdominent h 1'Cquilibre lorsque W = H ou Br alors que les pseudobases en C-4 sont les espkces thermodynamiquement prtfCrCes lorsque W = CONH2, C02CH3, CN et NO2. Des Ctudes par flux stoppC indiquent que, dans tous les cas, les pseudobases en C-2 sont les produits de contr8le cinCtique lorsque les solutions aqueuses de ces cations sont rendues basiques. On a mesurt les constantes dlCquilibre (pKR+) pour la formation de pseudobases tant en C-2 qu'en C-4 pour tous les substituants W dans tous les cas oh ceci Ctait exptrimentalfment possible. On a pu Ctablir une correlation entre les effets des substituants sur les p$+ et les u,,, des W; les valeurs de pKR+ dCpendent de up-. Ces effets de substituants permettent de prtdire des valeurs de pKR+ = I5,4 et p~: + = 17,4 pour le cation methyl-l quinolinium.

Kinetics of the reduction of 1-methylquinolinium cations by 1-benzyl-1,4-dihydronicotinamide

“…This ratio is consistent with the observation that the thermodynamic mixture of pseudobases derived from the 3-cyano-l -methylquinolinium cation favours the C-4 hydroxide adduct over the C-2 adduct in a 26: 1 ratio (17). Studies of pseudobase formation indicate the greater thermodynamic stability of the 1,4-dihydroquinoline over its 1,2-dihydro isomer for 3-Wquinolines having W = NO2, CN, CO?CH3, and CONH,, whereas the 1,2-dihydroquinolines are the thermodynamically more stable pseudobases for W = H and Br (17 of 1 by I-benzyl-1.4-dihydronicotinamide" "Data in 20% CH,CN -80% H 2 0 (v/v), ionic strength 1.0 at 25°C "Combined rate constant for reduction at C-2 and C-4.…”

“…We note that Roberts et al (19) also did not observe such adducts in their studies of the reduction of quinolinium cations, and we can conclude that if such species do exist, they can only be present in insignificant concentrations under the current reaction conditions. This preponderance of C-4 attack in the reduction of 1 by I-benzyl-l,4-dihydronicotinamide contrasts with the somewhat greater rate of attack at C-2 than at C-4 in the borohydride ion reduction of these cations (19), and with the much greater rate of hydroxide ion attack at C-2 than at C-4 in pseudobase formation (17). 4-Cyano-l,4-dihydro-1-methylquinoline is the sole product isolated from reaction of cyanide ion with 1 : W = H (26)(27)(28).…”

“…Most 3-W-I -methylquinolinium cations 1 were available from the accompanying study (17). Salts of the I-methyl-3-nitro-,l,2-dimethyl-, and 1.4-dimethyl-quinolinium cations, which were also available from other work in our laboratories, were recrystallized several times before use.…”

“…tion of 3-W-I-methylquinolinium cations (I) by I-benzyl-1,4-In the light of these observations, we felt that a detailed dihydronicotinamide, since detailed quantitative data are now kinetic study of the 1,4-dihydronicotinamide reduction of quinavailable (17) upon the relative rates of nucleophilic (hydroxide olinium cations would be very appropriate, since these cations ion) attack at C-2 and C-4 of these cations, and also upon the are readily susceptible to attack at either C-2 or C-4 to give relative thermodynamic stabilities of the isomeric dihydro-1,2-dihydro-and 1,4-dihydroquinolines respectively. Our iniquinoline products ( 3 and 4).…”

Kinetics and mechanism of covalent addition of S(IV) species to the acridinium cation

“…In general, 9,lO-dihydroacridines (16) show an intense absorption band with a maximum in the 280 nm region similar to that which we obtained. Pitman and Sternson (1 1) proposed this structure for the acridine-S(IV) adduct and other authors have proposed similar structures for adducts formed with other acridine derivatives (5,6,17).…”