[en] The solvolysis rate constants of 2,2,2-trichloroethyl chloroformate (Cl_3CCH_2OCOCl, 3) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the N_T solvent nucleophilicity scale and the Y_C_l solvent ionizing scale, with sensitivity values of 1.28 ± 0.06 and 0.46 ± 0.03 for l and m, respectively. The activation enthalpies (ΔH"≠) are 10.1 to 12.8 kcal·mol"-"1 and the activation entropies (ΔS"≠) are -27.8 to -36.8 cal·mol"-"1·K"-"1, which is consistent with the proposed bimolecular reaction mechanism. The kinetic solvent isotope effect (k_M_e_O_H/k_M_e_O_D) of 2.39 is also in accord with S_N2 mechanism probably assisted by general-base catalysis

[en] The solvolyses of the isopropenyl chloroformate proceeded rather rapidly at 35.0 .deg. C and the progress of the reaction as a function of time can be conveniently monitored using a rapid-response conductivity technique. For five typical solvents, the activation parameters were determined and the large negative entropies of activation were consistent with a bimolecular process. Application of the extended Grunwald-Winstein equation (equation 2) in 33 solvents led to an l value of 1.42 and an m value of 0.46 (correlation coefficient of 0.949). These values are shown to be similar to the previously determined values for a mechanism involving rate-limiting addition in an addition-elimination pathway. The kinetic solvent isotope effect is also very close to the literature values for the solvolyses of other chloroformate esters and it is consistent with general-base catalysis being super imposed upon a bimolecular process. The mechanism of acyl-transfer reactions have been investigated intensively for many years both experimentally and theoretically. The mechanisms of most of these reactions are, however, still not well established. The bimolecular solvolysis of acyl halides (RCOX) is believed to proceed either through a direct displacement mechanism (S_N2) or through an associative addition-elimination mechanism involving a tetrahedral intermediate. For acyl halides with a strong electron donating group, a dissociative mechanism involving an acylium ion intermediate has also been invoked. The two types of mechanism, S_N2 and stepwise addition-elimination, are also common for the bimolecular aminolysis of acyl halides. The aminolyses of acetyl chloride, MeCOCl, and methyl chloroformate, MeOCOCl, have been proposed to proceed by rate-limiting breakdown of a zwitterionic tetrahedral intermediate, T^±, for weakly basic amines with a change to rate-limiting attack for more basic amines

[en] Initial-state stabilization through π-electron resonance has been suggested to be responsible for the decreased reactivity of since such resonance interaction is not possible for RCOCl. This resonance effect would be more significant as the R in 1 becomes a stronger electron donating group but be insignificant when R is a strong electron withdrawing group. The electronic nature of the R group would also cause a change in the reaction mechanism, i. e., from rate limiting breakdown of a tetrahedral intermediate to rate-limiting formation an intermediate upon introducing a strong electron donating group, R. The activation parameters, ΔH^≠ and ΔS^≠, calculated from the k values at 4-different temperatures for solvolysis of 3 in pure EtOH and MeOH, and in 80% EtOH and 50% TFE are shown in Table 2. One can find relatively low ΔH^≠ (11.2 to 13.1 kcal·mol^--1) and large negative ΔS^≠ values (-31.1 to -38.6 cal·mol^-1K^-1), which are within the ranges of those reported previously for a normal S_N2 reaction. In deuterated methanol (MeOD), a kinetic solvent isotope effect (k_MeOH/k_MeOD) of 2.20 ± 0.03 is observed. This is within the KIE values of 1.58-2.31 reported for the corresponding methanolyses of n-propyl chloroformate and a series of benzenesulfonyl chlorides at 25.0 .deg. C, in which the reactions are believed to be S_N2 in character

[en] Rate constants for solvolysis involving the displacement of chloride from the carbonyl carbon of diphenylacetyl chloride ((C₆H₅₎2CHCOCl, 1) in ethanol, methanol, aqueous binary mixtures incorporating ethanol, methanol, acetone, 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoro-2-propanol, and binary mixtures of TFE with ethanol are reported. The kinetic data obtained from the reactions in 34 different solvents and solvent mixtures gave an extended Grunwald–Winstein correlation with the l value of 0.76 ± 0.06, the m value of 0.34 ± 0.04, and the correlation coefficient (R²) of 0.932. The appreciable values for both l and m suggest that the bond formation is ahead of the bond breaking with an S_N2 mechanism, and the l/m ratio of 2.2 is also in the range of values found for S_N2 reaction. This interpretation is further supported by the activation parameters, i.e., relatively small positive ΔH^≠ (7.7–16.3 kcal/mol) values and large negative ΔS^≠ (−24.6 to −53.4 cal/mol/K) values, and the solvent kinetic isotope effect (1.62)

[en] 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 N_T solvent nucleophilicity scale and Y_Cl 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 S_N2 reaction pathway. The activation enthalpies (ΔH^≠) were 12.4 to 14.6 kcal·mol^-1 and the activation entropies (ΔS^≠) were -15.5 to -32.3 cal·mol^-1·K^-1, 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, k_ww and k_aa, were calculated from the rate constants (k_obs), together with k_aw and k_wa calculated from the intercept and slope of the plot of 1/S vs. [water]/[alcohol]. The calculated rate constants, k_calc (k_ww, k_aw, k_wa and k_aa), are in satisfactory agreement with the experimental values, supporting the stoichiometric solvation effect analysis

[en] 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 N_T solvent nucleophilicity scale and the Y_Cl 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 ΔH≠ = 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

[en] Rates of solvolyses of diphenyl thiophosphorochloridate ((PhO)₂PSCl, 1) in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone and 2,2,2-trifluoroethanol (TFE) are reported. For four representative solvents, studies were made at several temperatures and activation parameters were determined. The 30 solvents gave a reasonably precise extended Grunwald-Winstein plot, correlation coefficient (R) of 0.989. The sensitivity values (l = 1.29 and m = 0.64) of diphenyl thiophosphorochloridate ((PhO)₂PSCl, 1) were similar to those obtained for diphenyl phosphorochloridate ((PhO)₂POCl, 2), diphenylphosphinyl chloride (Ph₂POCl, 3) and diphenylthiophosphinyl chloride (Ph₂PSCl, 4). As with the previously studied of 3∼4 solvolyses, an S_N2 pathway is proposed for the solvolyses of diphenyl thiophosphorochloridate. The activation parameters, ΔH^≠ (= 11.6∼13.9 kcal·mol^-1) and ΔS^≠ (= -32.1 ∼ -42.7 cal·mol^-1·K^-1), were determined, and they were in line with values expected for an S_N2 reaction. The large kinetic solvent isotope effects (KSIE, 2.44 in MeOH/MeOD and 3.46 in H₂O/D₂O) are also well explained by the proposed S_N2 mechanism

[en] The kinetic isotipe effects(KIE) are determinid for the reactions of benzyly benzenesulfonates (BBS), ethyl benzenesulfonates (EBS) and phenacyl benzensulfonates (PAB) with deuterated benzylamine nuclrophiles. The inverse secondary α-deuterium KIE observed were somewhat smaller than those for the corresponding reactions with aniline nucleophilis. The promary KIE, obtained with PAB were slightly greater than those for the corresponding reactions with anilines, which suggested that the inverse sevondary KIE is decreased due to a relatively earlier transition state for bond-making with little change in the hydrogen bonding strength to the carbonyl oxygen.(Author)

[en] The solvolysis rate constants of 5-nitro-2-furoyl chloride (5-NO₂(C₄H₂O)-2-COCl, 1) in 27 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 1.20 ± 0.05 and 0.37 ± 0.02 for l and m, respectively. The activation enthalpies (ΔH^≠) were 5.63 to 13.0 kcal·mol^-1 and the activation entropies (ΔS^≠) were -25.9 to -43.4 cal·mol^-1·K^-1, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effect (SKIE, k_MeOH/k_MeOD) of 2.65 was also in accord with the S_N2 mechanism and was possibly assisted using a general-base catalysis. The product selectivity (S) for solvolysis of 1 in alcohol/water mixtures was 1.2 to 11, which is also consistent with the proposed bimolecular reaction mechanism