Annihilation of aromatic cation radicals by ion-pair and radical pair collapse. Unusual solvent and salt effects in the competition for aromatic substitution

Sankararaman, S.; Haney, William A.; Kochi, J. K.

doi:10.1021/ja00259a035

Cited by 78 publications

(42 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[49][50][51][52][53][54][55][56][57] Concentrated H 2 SO 4 and HNO 3 in the usual ratio of 2:1, as well as 1:1, were mixed and left to cool to ar oom temperature (around 25 8 8C). Such bands,h owever,h ave been observed for processes in which alternative nitrating agents were applied.…”

Section: Methodsmentioning

confidence: 99%

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

et al. 2015

View full text Add to dashboard Cite

Experimental evidence is reported for the first intermediate in the classic S E Ar reaction of benzene nitration with mixed acid. The UV/Vis spectroscopic investigation of the reaction showed an intense absorption at 320 nm (appearing as ab and shoulder) arising from ar eaction intermediate.O ur theoretical modeling shows that the interaction between the two principal reactants with solvent (H 2 SO 4 )m olecules significantly affects the structure of the initial complex. In this complex, al arger distance between the aromatic ring and nitronium ion precludes the possibility for electronic charge transfer from the benzene p-system to the electrophile.T he computational modeling of the potential energy surface reveals that the reaction favors astepwise mechanism with intermediate formation of p-a nd s-( arenium ion) complexes.

show abstract

Section: Methodsmentioning

confidence: 99%

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

et al. 2015

View full text Add to dashboard Cite

show abstract

“…In all of these cases, the special salt effect is manifest kinetically as a marked rate acceleration at low ionic strengths. Recently special salt effects that manifest themselves as a marked rate deceleration have been reported for photolysis or pulsed radiolysis generated ion pairs (9). Thus time-resolved or picosecond spectroscopy of photogenerated charge-transfer ion pairs, from aromatic hydrocarbons and tetranitromethane (9a), and from benzophenones and dialkylanilines (9b), show special salt effects that markedly extend the lifetime of the ion pairs.…”

Section: Special Salt Effectsmentioning

confidence: 99%

“…Without added nucleophile (salt) there can be no substitution. Unimolecular processes or the unimolecular portion of reactions showing mixed kinetics should be more amenable to scrutiny and might show special salt effects (1,8,9).…”

mentioning

confidence: 99%

The ion-pair mechanism and bimolecular displacement at saturated carbon. VII. Racemization of substituted 1-phenylbromoethanes; ionic strength effects

Stein¹

1989

Can. J. Chem.

View full text Add to dashboard Cite

ALLAN R. STEIN. Can. J. Chem. 67,297 (1989). No, or at most very small, salt effects have been detected for second-order racemizations of various 1-phenylbromoethanes, confirming that the "mixed kinetics", previously reported for 4-methyl-and 3,4-dimethylphenylbromoethanes with tetrabutylammonium bromide in acetonitrile and nitromethane, did not reflect a salt effect on a unimolecular reaction. Thus the uni-and bimolecular rate components can be evaluated using the equation:where kl = first-order or unimolecular rate constant, the intercept, and k; = 2k2, the latter being the rate constant for the bimolecular substitution. A "special salt effect" was found for the unimolecular component; it was especially pronounced for 3,4-dimethyl substrate in acetonitrile with Bu4NC104 as the electrolyte. In acetone, where no unimolecular reaction component was detected even with those substrates giving the most stable carbocations, theonly salt effect was a common ion, Bu4N+, effect on the incomplete dissociation of Bu4NBr. From an iterative best fit for plots of observed rate versus calculated bromide ion activity for unsubstituted, 4-methyl, and 3,4-dimethyl substrates, K,,so, -15 * 1 at 40°C. The results are interpreted as additional support for a progression of mechanism with nucleophilic attack possible at any stage of the series of equilibria:substrate S contact ion pair = various solvated ion pairs e dissociated ions.Key words: special salt effects, ionic strength effects, racemization of 1-phenylbromoethanes, mechanism of nucleophilic substitution, ion pair mechanism. ALLAN R. STEIN. Can. J. Chem. 67, 297 (1989). Pour les rackmisations du deuxieme ordre de divers phenyl-1 bromokthanes, on n'a dttecti aucun, ou tout au plus de tres faibles, effet de sels; ces resultats confirment que les (< cinCtiques mixtes >> qui ont t t t observCes anttrieurement lors des reactions des mCthyl-4 et dimtthyl-3,4 phCnylbromotthanes avec le bromure de tttrabutylammonium dans l'acktonitrile et le nitromethane, ne sont pas le reflet d'un effet de sel sur une rtaction unimol6culaire. On peut donc Cvaluer les composantes uni-et bi-molCculaires de la vitesse en utilisant 1'Cquationdans laquelle kl = constante de vitesse du premier ordre ou unimoltculaire, l'ordonde a l'origine, et k; = 2k2 oh k2 est la constante de vitesse de la substitution bimolCculaire. On a observC un << effet de sel spCcial,, sur la composante unimoltculaire; cet effet Ctait particulierement prononcC pour le substrat dimCthyle-3,4, dans l'acetonitrile, avec le Bu2NC104 comme tlectrolyte. Dans l'acCtone, on n'a detect6 aucune composante relite a une reaction unimoltculaire (mCme pas avec les substrats qui donnent les carbocations les plus stables) et le seul effet de sel qui a pu Ctre observe est celui d'un ion commun, B u~N ' , d i a une dissociation incomplete du Bu4NBr. En se basant sur des ittrations des courbes des vitesses observtes versus l'activitt calculCe de I'ion bromure pour les reactions des substrats mtthyle-4, dimkthyl-3,4 ou non-substituts, on a tvalue q...

show abstract

“…Moreover, it was shown that the nitration with 40% HNO 3 in the presence of some nitrous acid yielded 2,4-dintrophenol as a main product. Olah et al [5] also nitrated by charged-transfer mechanism in the presence of tetranitromethane in acetonitrile [7]. Apart from different nitrating mixtures, application of solid acid catalysts in anisole nitration were also described.…”

Section: Introductionmentioning

confidence: 99%

Controlled nitration of anisole over HNO3/PO4/MoO3/SiO2/solvent systems

Adamiak

2015

Journal of Molecular Catalysis A: Chemical

View full text Add to dashboard Cite

Annihilation of aromatic cation radicals by ion-pair and radical pair collapse. Unusual solvent and salt effects in the competition for aromatic substitution

Cited by 78 publications

References 1 publication

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

The ion-pair mechanism and bimolecular displacement at saturated carbon. VII. Racemization of substituted 1-phenylbromoethanes; ionic strength effects

Controlled nitration of anisole over HNO3/PO4/MoO3/SiO2/solvent systems

Contact Info

Product

Resources

About