[en] Solvolyses of isobutyl chloroformate (4) in 43 binary solvent mixtures including highly aqueous media, water, D₂O, CH₃OD, 2,2,2-trifluoroethanol (TFE) as well as aqueous 1,1,1,3,3,3-hexafluoro-isopropanol (HFIP) solvents were performed at 45 .deg. C, in order to further investigate the recent results of D'Souza, M. J¹. et al.; solvolyses of 4 are found to be consistent with the proposed mechanism (Ad_E). The variety of solvent systems was extended to comprise highly ionizing power solvent media (Y_Cl > 2.7 excepted for aqueous fluorinated solvents and pure TFE solvent) to investigate whether a mechanistic change occurs as solvent compositions are varied. However, in case of 18-solvent ranges having aqueous fluorinated solvent systems (TFE-H₂O and HFIP-H₂O) and/or having Y_CI > 2.7 solvent systems, the solvent effect on reactivity for those of 4 are evaluated by the multiple regression analysis as competition with SN₂ - type mechanism. And in pure TFE and 97 w/w % HFIP solvents with high Y_Cl and weak N_T, these solvolyses are understood as reactions which proceed through an ionization (S_N1) pathway

[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] Our research have conducted to obtain further information on the possible effect of adjacent group including S-atom to reaction center [ie; S-CH₃ or S-Ph group]. Consequently, the change from a unit of mechanism indicating S_N2 type [SCH₃], involving solvent nucleophilic participation by a molecule of the solvent from the rear side in TS of ionization, to the dual reaction channel [S-Ph] with SN1- SN2 type by means of a specific solvent effect has shown in solvolyses of 2-chloro-2-thioacetophenone. Such phenomenon can be explained as a difference in the solvation between CH₃- and Ph-group, considering previous the result reported as a quite different solvation between alkyl groups (CH₃-) and aromatic rings (Ph-) in solvolyses of substituted acetyl chloride in fluorinated alcohol systems

[en] The solvolysis mechanism of 4-methylthiobenzoyl chloride (1) was studied by kinetic methods, and these results were compared with 4-methoxy (2) and 3,4,5-trimethoxybenzoyl chlorides (3) reported previously. The analysis of kinetic data was carried out using both the simple and extended Grunwald-Winstein(G-W) equations, thermodynamic parameters, and kinetic solvent isotope effects (KSIE). In fact, 4-methylthiobenzoyl chloride (1) has a sulfur atom which is bigger in size and has more electrons than oxygen in the para-position. The results were obtained and showed typical dispersed plots from the simple (R = 0.939) and extended G-W equations (l/m = 0.33, R = 0.952) for all data, and when the data from some of the most dispersed points were removed, the correlation coefficients were improved remarkably. Thermodynamic parameters revealed that the change of enthalpies were 16.2 ⁓ 17.6 kJ/mol and the change of entropies were -16.5 ⁓ -8.6 J/K-mol. The KSIE of MeOH/MeOD was 1.42. The above results for 4-methylthiobenzoyl chloride supported a unimolecular pathway, or more precisely, a dissociated S_N2 mechanism classified by l/m ratio.

[en] The solvolysis rate constants of piperonyloyl chloride (1) in 27 different solvents are well correlated with the extended Grunwald-Winstein equation, using the N_T solvent nucleophilicity scale, Y_Cl solvent ionizing scale, and I aromatic ring parameter with sensitivity values of 0.30 ± 0.05, 0.71 ± 0.02, and 0.60 ± 0.04 for l, m, and h, respectively. The solvent kinetic isotope effect values (SKIE, k_MeOH/k_MeOD and k_{50%MeOD-50%D2O}) of 1.16 and 1.12 were also in accord with the values for the S_N1 mechanism and/or the dissociative S_N2 mechanism. The product selectivity values (S) for solvolysis of 1 in alcohol/water mixtures were in the range of 0.5 to 1.9, which is also consistent with the proposed unimolecular ionization mechanism

[en] The specific rates of solvolysis of 1- naphthyl chloroformate (1-NaphOCOCl, 1) and 2-naphthyl chloroformate (2-NaphOCOCl, 2) have been determined in a wide range of solvents at 2.0 and 10.0 .deg. C. These give a satisfactory correlation over the full range of solvents when the extended (two-term) Grunwald-Winstein equation is applied. The sensitivities (l and m-values) to changes in solvent nucleophilicity (N_T) and solvent ionizing power (Y_Cl) are similar to those reported previously for solvolysis of phenyl chloroformate, which has been suggested to proceed through an addition-elimination mechanism with the addition step being rate determining. For four representative solvents, studies were made at several temperatures and activation parameters determined. These observations were also compared with those previously reported for phenyl chloroformates and naphthoyl chlorides

[en] The specific rates of solvolysis of isopropyl fluoroformate are well correlated using the extended Grunwald- Winstein equation, with a sensitivity (l ) to changes in solvent nucleophilicity (N_T) and a sensitivity (m) to changes in solvent ionizing power (Y_Cl). The sensitivities (l = 1.59 ± 0.16 and m = 0.80 ± 0.06) toward changes in solvent nucleophilicity and solvent ionizing power, and the k_F/k_Cl values are very similar to those for solvolyses of n-octyl fluoroformate, suggesting that the addition step of an addition-elimination mechanism is rate-determining. For methanolysis, a solvent deuterium isotope effect of 2.53 is compatible with the incorporation of general-base catalysis into the substitution process. The large negative values for the entropies of activation are consistent with the bimolecular nature of the proposed rate-determining step. These observations are also compared with those previously reported for the corresponding chloroformate and fluoroformate esters

[en] The photoreaction of 2 in a deaerated benzene provided 4 and 5 via a photo-Fries rearrangement reaction but the expected photoproduct from the intramolecular reaction between the C=Si moiety and ortho-substituent, C=O group was not obtained. The photolysis of 2 in a deaerated methanol gave a photoproduct 7 via β silicon atom attack of pentamethyldisilanyl group by methanol and the photo-Fries rearrangement and compounds 1 and 8 but the expected photoproducts from the silene intermediate was also not obtained in this photoreaction. It is well known that the photoreactions of aryldisilanes show four reaction patterns since the first report on the photolysis of phenylpentamethyldisilane and (p-tolyl)penta-methyldisilane by Ishikawa et al. in 1975 : (path a) formation of a silene compound via elimination of a trimethylsilane, (path b) formation of a silene compound arising from 1,3-shift of trimethylsilyl radical, which is formed via homolytic cleavage of silicon-silicon bond, (path c) formation of a trimethylsilyl compound via elimination of a silylene, (path d) formation of a direct solvolysis compound via elimination of a trimethylalkoxysilane or pentamethylalkoxydisilane. Silenes having the C=Si moiety are regarded as highly interesting intermediates. Consequently the synthesis and reactions of silenes as useful intermediates have been extensively investigated. The intermolecular reactions between highly unstable silenes and the compounds containing functional groups such as OH, C=O, and C=C bonds resulted in the formation of the addition products

[en] The specific rates of sovolysis of 4-methylthiophene-2-carbonyl chloride (1) have been determined in 26 pure and binary solvents at 25.0 .deg. C. Product selectivities are reported for solvolyses of 1 in aqueous ethanol and methanol binary mixtures. Comparison of the specific rates of solvolyses of 1 with those for p-methoxybenzoyl chloride (2) in terms of linear free energy relationships (LFER) are helpful in mechanistic considerations, as is also treatment in terms of the extended Grunwald-Winstein equation. It is proposed that the solvolyses of 1 in binary aqueous solvent mixtures proceed through an S_N1 and/or ionization (I) pathway rather than through an associative S_N2 and/or addition-elimination (A-E) pathway

[en] A method for the correlation of the magnitude of kinetic secondary β-deuterium isotope effects in solvolytic reactions with the conformation of the reaction transition states is proposed. An empirical angular correlation was developed and several secondary and tertiary carbocation species were analyzed. Good agreement between the observed and calculated isotope effects was found for all cases where the secondary substrate reacts by the same mechanism as the corresponding tertiary α-Me derivative. This makes the described method a convenient probe for the geometry of solvolytic transition states. The possibility of making deductions about the involvement of anchimeric and/or nucleophilic participation in the solvolysis of secondary substrates is discussed. The absence of hyperconjugative stabilization of secondary cations appears to be the major factor responsible for high (greater than 10⁶) CH₃/H rate ratios