Reactivity–selectivity relationship and kinetic solvent isotope effects in nucleophilic substitution reactions

The rate constants of solvolyses of 2,2,2-trichloro-1,1-dimethylethyl chloroformate (I) in 33 solvents can be well correlated using the extended Grunwald-Winstein equation, with incorporation of the NT solvent nucleophilicity scale and the YCl solvent ionizing scale, with sensitivities towards changes in the scale having values of 1.42 ± 0.09 for l and 0.39 ± 0.05 for m, respectively. The activation enthalpies are ∆H ≠ = 12.3 to 14.5 kcal·mol -1 and the activation entropies are -28.2 to -35.5 cal·mol -1 ·K -1 , consistent with the proposed bimolecular reaction mechanism. The kinetic solvent isotope effect of 2.14 in MeOH/MeOD is in accord with a bimolecular mechanism, probably assisted by general-base catalysis.

Section: Resultsmentioning

confidence: 99%

Kinetic Studies of the Solvolyses of 2,2,2-Trichloro-1,1-Dimethylethyl Chloroformate

Koh

Kang²,

Kevill³

2010

“…20 The uncertainty in the k obsd values was estimated to be less than ± 3% from replicate runs. For the solvolyses of 1, the infinity titers could be used to obtain the fractions of reaction proceeding to ester and to acid in water-alcohol mixtures.…”

Section: 18mentioning

confidence: 99%

Rate and Product Studies of 5-Dimethylamino-Naphthalene-1-Sulfonyl Chloride under Solvolytic Conditions

Koh

Kang²

2014

Self Cite

The solvolysis rate constants of 5-dimethylamino-naphthalene-1-sulfonyl chloride ((CH 3 ) 2 NC 10 H 6 SO 2 Cl, 1) in 31 different solvents are well correlated with the extended Grunwald-Winstein equation, using the N T solvent nucleophilicity scale and Y Cl solvent ionizing scale with sensitivity values of 0.96 ± 0.09 and 0.53 ± 0.03 for l and m, respectively; the correlation coefficient value was 0.955. These l and m values can be considered to support an S N 2 reaction pathway having a transition state (TS) structure similar to that of the benzenesulfonyl chloride reaction. This interpretation is further supported by the activation parameters, i.e., relatively small positive ΔH ≠ (12.0 to 15.9 kcal·mol) and large negative ΔS ≠ (−23.1 to −36.3 cal·mol) values, and the solvent kinetic isotope effects (SKIEs, 1.34 to 1.88). Also, the selectivity values (S = 1.2 to 2.9) obtained in binary solvents are consistent with the proposed mechanism.

“…The l/m values from the extended Grunwald-Winstein equation could be classified into two classes of mechanism; l/m values of 1.2 to 3.5 for bimolecular mechanism (S N 2) or an addition-elimination pathway (A-E), and l/m values below 0.7 for an ionization pathway (I.P). 17 For the solvolysis of 1, the l/m value was 1.4 which is similar to those of previous studies investigating the solvolyses of diphenylphosphinyl chloride 22 (l/m = 1.6), N,N-dimethylsulfamoyl chloride 23 (l/m = 1.7), N,N,N',N'-tetramethyldiamidophosphorochloridate 24 (l/m = 1.8), and these similarities suggest the existence of a bimolecular mechanism (S N 2) or an addition-elimination pathway (A-E).…”

Section: Resultsmentioning

confidence: 99%

“…Our analyses are considered to be consistent with such an explanation. 17 The kinetic isotope effect, a change of rate that occurs upon isotopic substitution, is a widely used tool for elucidating reaction mechanism. The most common isotopic substitution is D for H. The solvent kinetic isotope effects (SKIE, k MeOH /k MeOD and k H2O /k D2O ) are frequently observed when reactions are carried out in solvents with O-H (O-D) groups, ordinarily water or alcohols.…”

Section: Resultsmentioning

confidence: 99%

Product-Rate Correlations for Solvolyses of 2,4-Dimethoxybenzenesulfonyl Chloride

Kim¹,

Choi²,

Park³

et al. 2014

Self Cite

The solvolysis rate constants of 2,4-dimethoxybenzenesulfonyl chloride (1) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the NT solvent nucleophilicity scale and YCl solvent ionizing scale, with sensitivity values of 0.93 ± 0.14 and 0.65 ± 0.06 for l and m, respectively. These l and m values can be considered to support a SN2 reaction pathway. The activation enthalpies (H  ) were 12.4 to 14.6 kcal·mol 1 and the activation entropies (S, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effects (SKIE) were 1.74 to 1.86, which is also in accord with the SN2 mechanism and was possibly assisted using a general-base catalysis. The values of product selectivity (S) for solvolyses of 1 in alcohol/water mixtures was 0.57 to 6.5, which is also consistent with the proposed bimolecular reaction mechanism. Third-order rate constants, kww and kaa, were calculated from the rate constants (kobs), together with kaw and kwa calculated from the intercept and slope of the plot of 1/S vs.[water]/[alcohol]. The calculated rate constants, kcalc (kww, kaw, kwa and kaa), are in satisfactory agreement with the experimental values, supporting the stoichiometric solvation effect analysis.