Correlation of the rates of solvolysis of the N,N‐diphenylcarbamoylpyridinium ion

Abstract

Solvolyses of the N,N-diphenylcarbamoylpyridinium ion are subject to specific and/or general base catalysis, which can be eliminated by addition of perchloric acid or increased, especially in fluoroalcohol-containing solvents, by addition of pyridine. The uncatalyzed solvolyses in aqueous methanol and aqueous ethanol involve a weakly nucleophilically assisted (l = 0.22) heterolysis and the solvolyses in the pure alcohols are anomalously slow.

Correlations of the Specific Rates of Solvolysis of Aromatic Carbamoyl Chlorides, Chloroformates, Chlorothionoformates, and Chlorodithioformates Revisited

“…More recently, a study has been made, at 25.0°C, not only of the parent compound but also of the p -chloro- and p -nitro-derivatives [ 36 ]. The value reported for the parent in 80% ethanol of 3.27 × 10 −6 s −1 was in good agreement with a value of 3.37(± 0.14) × 10 −6 s −1 obtained earlier [ 29 ]. Up to three TFE-water solvents were utilized, with the solvents prepared on a volume-volume basis.…”

Kinetic evaluation of the solvolysis of isobutyl chloro- and chlorothioformate esters

“…The l / m ratio of 0.58 obtained for 2 in these 15 solvents is similar in magnitude to the previously observed ratios for methyl- (MeSCOCl) [ 15 ], ethyl- (EtSCOCl) [ 8 ], isopropyl- (iPrSCOCl) [ 16 ], and phenyl- (PhSCOCl) chlorothioformates [ 40 , 46 – 47 ] in solvents where an S N 1 mechanism was said to be operative. The range of the l / m ratios, from 0.53 to 0.93, for these chlorothioformate esters ( Table 3 ) is similar to the l / m ratio of 0.73 obtained for phenyl dithiochloroformate ( 4 ), the recommended standard for understanding ionization mechanisms in acyl containing systems.…”

Solvolytic reactivity of pyridinium ions

“…The solvolysis rates of pyridinium ions slightly decrease as the polarity of the solvent increases, similarly as it has repeatedly been shown for charged substrates, such as dimethylsulfonium [17,18] and thiophenium salts. [19] In more polar solvents, pyridinium ions are more stabilized by solvation in the reactant ground state than in the corresponding TS, because in the latter the charge is delocalized, because of its partial transfer from pyridine to the benzhydryl moiety.…”