Extended Grunwald-Winstein Equation Research Articles

Mechanistic studies of the solvolysis of alkanesulfonyl and arenesulfonyl halides.

There have been several studies on the solvolysis mechanisms for alkanesulfonyl chlorides (RSO2Cl) and arenesulfonyl chlorides (ArSO2Cl). The earlier of these studies were reviewed a little over thirty years ago by Gordon, Maskill and Ruasse (Chem. Soc. Rev. 1989, 18, 123–151) in a contribution entitled “Sulfonyl Transfer Reactions”. The present review will emphasize more recent contributions and, in particular, the application of the extended Grunwald–Winstein equation and kinetic solvent isotope effects to the solvolysis reactions. There is also an appreciable number of reports concerning the corresponding anhydrides with the chloride leaving group replaced by the appropriate sulfonate leaving group, concerning sulfamoyl chlorides (ZZ'NSO2Cl) with Z and Z' being alkyl or aryl and concerning the solvolysis of chlorosulfate esters (alkoxy- or aryloxysulfonyl chlorides), with the structures ROSO2Cl or ArOSO2Cl. The solvolyses of these additional types of sulfur(VI) substrates will be the topics of a future review.

The Influence of a Terminal Chlorine Substituent on the Kinetics and the Mechanism of the Solvolyses of n-Alkyl Chloroformates in Hydroxylic Solvents.

A previous study of the effect of a 2-chloro substituent on the rates and the mechanisms of the solvolysis of ethyl chloroformate is extended to the effect of a 3-chloro substituent on the previously studied solvolysis of propyl chloroformate and to the effect of a 4-chloro substituent on the here reported rates of solvolysis of butyl chloroformate. In each comparison, the influence of the chloro substituent is shown to be nicely consistent with the proposal, largely based on the application of the extended Grunwald–Winstein equation, of an addition-elimination mechanism for solvolysis in the solvents of only modest solvent ionizing power, which changes over to an ionization mechanism for solvents of relatively high ionizing power and low nucleophilicity, such as aqueous fluoroalcohols with an appreciable fluoroalcohol content.

확장된 Gruwald-Winstein 식에 의한 Biphenyl-4-carbonyl chloride의 가용매분해 반응대한 연구

The solvolysis rate constants of biphenyl-4-carbonyl chloride (C6H5C6H5COCl, 1) in 19 different solvents are well correlated with the extended Grunwald-Winstein equation, using the NT solvent nucleophilicity scale, YCl solvent ioniz- ing scale, and I aromatic ring parameter with sensitivity values of 0.31±0.10, 0.46±0.05, and 0.96±0.20 for l, m, and h, respec- tively. These l, m, and h values can be considered to support a dissciative SN2 reaction pathway. This interpretation is further supported by the activation parameters, i.e., relatively small positive ΔH ‡ (15.3~16.1 kcal/mol) values and large negative ΔS ‡ (�17.2~�20.0 cal/mol·K) values.

Mechanistic Studies of the Solvolyses of Carbamoyl Chlorides and Related Reactions.

Carbamoyl chlorides are important intermediates, both in the research laboratory and in industrial scale syntheses. The most studied and used are the disubstituted derivatives, incorporating either aryl or alkyl groups (Ar2NCOCl or R2NCOCl). Sometimes, the groups are tied back to give a ring and piperidino- and morpholino-derivatives are commonly encountered. Some studies have been made with two different groups attached. Solvolyses tend to occur at the carbonyl carbon, with replacement of the chloride ion. Studies of both rate and products are reviewed and the solvolysis reactions are usually SN1, although addition of an amine leads to a superimposable bimolecular component. Many of the studies under solvolytic conditions include the application of the extended Grunwald–Winstein equation. The monosubstituted derivatives (ArNHCOCl or RNHCOCl) are less studied. They are readily prepared by the addition of HCl to an isocyanate. In acetonitrile, they decompose to set up and reach equilibrium with the isocyanate (ArNCO or RNCO) and HCl. Considering that the structurally related formyl chloride (HOCOCl) is highly unstable (with formation of HCl + CO2), the unsubstituted carbamoyl chloride (H2NCOCl) is remarkably stable. Recommended synthetic procedures require it to survive reaction temperatures in the 300–400 °C range. There has been very little study of its reactions.

Studies of Solvolyses of 1,4‐Benzodioxan‐6‐Sulfonyl Chloride by Extended Grunwald–Winstein Equation

The rate constants of solvolysis of 1,4‐benzodioxan‐6‐sulfonyl chloride (C8H7ClO4Cl, 1) were determined by a conductivity technique. These rate constants of 1 in 28 different solvents correlated well with the extended Grunwald–Winstein equation. The l (1.00) and m (0.59) values support an SN2 reaction pathway having a similar transition state structure to that of the benzenesulfonyl chloride (2, l = 1.10, m = 0.61) reaction. This interpretation is further supported by the activation parameters, i.e., relatively small positive ΔH ≠ (8.9 to 15.5 kcal/mol) and large negative ΔS ≠ (−27.3 to −49.2 cal/mol/K) values, and the solvent kinetic isotope effect (1.62). The Kivinen's n values (n = 0.03 in methanol, 0.04 in ethanol) obtained in binary solvents were consistent with the proposed bimolecular reaction mechanism.

확장된 Grunwald-Winstein 식에 의한 Di-n-butyl Phosphorochloridate의 가용매 분해반응 연구

The solvolysis rate constants of di-n-butyl phosphorochloridate ((CH3CH2CH2CH2O)2POCl, 1) in 28 different solvents are well correlated with the extended Grunwald-Winstein equation, using the NT solvent nucleophilicity scale and YCl solvent ionizing scale, with the sensitivities values of 1.40 and 0.42 for l and m, respectively. These l and m values can be con- sidered to support an SN2 reaction pathway. This interpretation is further supported by the activation parameters, i.e., rela- tively small positive ΔH ≠ (8.0 to 15.9 kcal·mol �1 ) values and large negative ΔS ≠ (�25.8 to �53.1 cal·mol �1 ·K �1 ) values, the Kivinen's n values (0.9~1.7), and the solvent kinetic isotope effect (1.62).

Correlation of the Rates of Solvolysis of 2,1-Benzoxathiol-3-One-1, 1-dioxide (2-Sulfobenzoic Acid Cyclic Anhydride)

Solvolysis of acyclic mixed carboxylic–sulfonic anhydrides in hydroxylic solvents is known to involve displacement at the carbonyl carbon to produce a carboxylic acid (water as the nucleophile) and/or an ester (alcohol as the nucleophile) plus the anion of the sulfonic acid. Parallel solvolyses of the cyclic mixed anhydride 2-sulfobenzoic anhydride (structurally similar to phthalic anhydride but with one carbonyl group replaced by a sulfonyl group) involve expulsion from the carbonyl carbon of a sulfonate anion that remains attached as an ortho-substituent in the benzoic acid and/or benzoate ester produced. This complicates the choice of a solvent-ionising-power scale for use in an extended Grunwald–Winstein equation treatment. The YOTs scale, previously recommended as a good general purpose scale, is chosen and used in conjunction with the NT solvent nucleophilicity scale. An acceptable correlation is obtained, which is improved when the two solvents rich in the highly ionising 1,1,1,3,3,3-hexafluoro-2-propanol are excluded. As the solvent is varied, the sensitivities to the changes induced in the two scales are low, consistent with an early transition state, but their ratio has a value which is typical for a pathway involving addition–elimination, with addition rate-determining. Earlier reports, supporting aspects of the proposed mechanism, are reviewed.

Correlation of Rates of Solvolysis of Diphenylacetyl Chloride Using Extended Grunwald–Winstein Equation

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 SN2 mechanism, and the l/m ratio of 2.2 is also in the range of values found for SN2 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).

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

The solvolysis rate constants of 5-dimethylamino-naphthalene-1-sulfonyl chloride ((CH3)2NC10H6SO2Cl, 1) in 31 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 0.96 ± 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 SN2 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 �1 ) and large negative ΔS ≠ (�23.1 to �36.3 cal·mol �1 ·K �1 ) 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.

Solvolysis Reaction Kinetics, Rates and Mechanism for Phenyl N-Phenyl Phosphoramidochloridate

The rate constants of solvolysis of phenyl N-phenyl phosphoramidochloridate (PhNHPO(Cl)OPh, Target Compound-TC1) have been determined by a conductivity method. The solvolysis rate constants of TC1 are well correlated with the extended Grunwald-Winstein equation, using the <TEX>$N_T$</TEX> solvent nucleophilicity scale and YCl solvent ionizing scale, and sensitivity values of <TEX>$0.85{\pm}0.14$</TEX> and <TEX>$0.53{\pm}0.04$</TEX> for l and m, respectively. These l and m values were similar to those obtained previously for the complex chemical substances dimethyl thiophosphorochloridate; N,N,N',N'-tetramethyldiamidophosphorochloridate; 2-phenyl-2-ketoethyl tosylate; diphenyl thiophosphinyl chloride; and 9-fluorenyl chloroformate. As with the five previously studied solvolyses, an <TEX>$S_N2$</TEX> pathway is proposed for the solvolyses of TC1. For four representative solvents, the rate constants were measured at several temperatures, and activation parameters (<TEX>${\Delta}H^{\neq}$</TEX> and <TEX>${\Delta}S^{\neq}$</TEX>) were estimated. These activation parameters are also in line with the values expected for an <TEX>$S_N2$</TEX> reaction.

LFER Studies Evaluating Solvent Effects on an α-Chloro-and two β,β,β-Trichloro-Ethyl Chloroformate Esters.

To provide insight and to identify the occurrence of mechanistic changes in relation to variance in solvent-type, the solvent effects on the rates of solvolysis of three substrates, 2,2,2-trichloro-1,1-dimethylethyl chloroformate, 2,2,2-trichloroethyl chloroformate, and 1-chloroethyl chloroformate, are analyzed using linear free energy relationships (LFERs) such as the extended Grunwald-Winstein equation, and a similarity-based LFER model approach that is based on the solvolysis of phenyl chloroformate. At 25.0 °C, in four common solvents, the α-chloroethyl chloroformate was found to react considerably faster than the two β,β,β-trichloro-substituted analogs. This immense rate enhancement can be directly related to the proximity of the electron-withdrawing α-chlorine atom to the carbonyl carbon reaction center. In the thirteen solvents studied, 1-chloroethyl chloroformate was found to strictly follow a carbonyl addition process, with the addition-step being rate-determining. For the two β,β,β-trichloro-substrates, in aqueous mixtures that are very rich in a fluoroalcohol component, there is compelling evidence for the occurrence of side-by-side addition-elimination and ionization mechanisms, with the ionization pathway being predominant. The presence of the two methyl groups on the α-carbon of 2,2,2-trichloro-1,1-dimethylethyl chloroformate has additive steric and stereoelectronic implications, causing its rate of reaction to be significantly slower than that of 2,2,2-trichloroethyl chloroformate.

Correlation of the Rates of Solvolysis of Electron-Rich Benzoyl Chloride Using the Extended Grunwald-Wistein Equation

for many years.However, the mechanismsof most of these reactions remain not well established,especially for electron-rich acyl transfer reactions. In order to obtain further understanding of the electron-rich acyl transfer mechanism, a kinetic study of the solvo-lysis of piperonyloyl chloride (1) (Eq. 1) in a variety of pureand binary solvents at 25.0 ??C was undertaken. Furthermore,the l, m, and h values were determined using the extendedGrunwald-Winstein equations [Eqs. (2) and (3)];

Extent of Nucleophilic Participation in the Solvolyses of an Aryl Chloromethyl Ether, α,p-Dichloroanisole

The specific rates of solvolysis of α, p-dichloroanisole (chloromethyl p-chlorophenyl ether, 1) have been measured conductimetrically in a variety of hydroxylic solvents. In three typical solvents, at 25.0 °C, the rate is 20–45 times greater than for the corresponding sulfide. In a comparison with the solvolysis of a substrate with an alkyl group replacing the aryl group, chloromethyl ethyl ether (2), at −10.0 °C in four typical solvents, 1 reacted considerably more slowly than 2, by a little over four orders of magnitude. An extended Grunwald–Winstein equation treatment of the specific rates of solvolyses in 24 solvents at 25.0 °C leads to an l value of 0.68 ± 0.04 and an m value of 0.59 ± 0.03 ( l/ m = 1.15). Appreciable nucleophilic assistance in the progress to the transition state is indicated and either nucleophilic solvation to an ionisation process or a loose SN2 transition state with extensive bond-breaking accompanied by a smaller degree of bond-making lead to an appropriate transition state.

Correlation of the rates of solvolysis of acetic p‐toluenesulfonic anhydride (acetyl p‐toluenesulfonate) and a comparison with acetyl halides

The specific rates of solvolysis of acetyl p‐toluenesulfonate have been measured by a rapid‐response conductivity technique at temperatures in the temperature range of −10 to −55 °C. For 13 solvents at −39.6 °C, an extended Grunwald–Winstein equation correlation led to sensitivities to changes in solvent nucleophilicity of 0.56 and to changes in solvent ionizing power of 0.61. In 89.1% acetone at −20 °C, the comparison with acetyl bromide solvolysis led to a kOTs/kBr ratio of 1.4. In methanol and methanol‐d at −39.6 °C, the solvent deuterium isotope effect kMeOH/kMeOD is 0.99. These results are consistent with an SNl reaction with appreciable nucleophilic solvation or an SN2 reaction with a loose transition state. These two approaches lead to similar structures for the transition state. A solution of the acetyl p‐toluenesulfonate was conveniently prepared by the rapid reaction of acetyl chloride with silver p‐toluenesulfonate in acetonitrile. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Extent of Nucleophilic Participation in the Solvolyses of Alkyl Chloromethyl Ethers and Sulfides

The specific rates of solvolysis have been determined for chloromethyl ethyl ether (3) and chloromethyl octyl ether (4) at −10.0 °C and for chloromethyl methyl sulfide (5) at 25.0 °C in a variety of pure and binary solvents. These values were used for a correlation analysis treatment using the extended Grunwald–Winstein equation incorporating literature values for solvent nucleophilicity ( NT) and solvent ionising power ( YCl). Appreciable values were found for the sensitivities towards changes in both NT and YCl values. Using a literature specific rate of hydrolysis at 25.0 °C for fluoromethyl methyl ether (2), the required value for chloromethyl methyl ether (1) was obtained from use of NT and YCl values and the sensitivities for 3 to changes in their values, to adjust an experimental specific rate value for 1 in 100% ethanol to the corresponding value in 100% water. In this way, an estimated kCl/ kF of 1.2 × 105 was obtained, essentially identical to values for the solvolyses of tert-butyl halides. A unimolecular mechanism for the solvolyses, with appreciable nucleophilic solvation of the developing carbocation, is proposed. Electronic supplementary information provides, for several solvents, specific rates of solvolysis for 3, 4, and 5 at additional temperatures and the calculated activation parameters.

Rate-Product Correlations for the Solvolysis of 5-Nitro-2-Furoyl Chloride

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 NT solvent nucleophilicity scale and YCl 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, kMeOH/kMeOD) of 2.65 was also in accord with the SN2 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.

Correlation of the rates of solvolysis of tert-butyl chlorothioformate and observations concerning the reaction mechanism.

The "parent" tertiary alkyl chloroformate, tert-butyl chloroformate, is unstable, but the tert-butyl chlorothioformate (1) is of increased stability and a kinetic investigation of the solvolyses is presented. Analyses in terms of the simple and extended Grunwald-Winstein equations are carried out. The original one-term equation satisfactorily correlates the data with a sensitivity towards changes in solvent ionizing power of 0.73 ±0.03. When the two-term equation is applied, the sensitivity towards changes in solvent nucleophilicity of 0.13 ± 0.09 is associated with a high (0.17) probability that the term that it governs is not statistically significant.

Correlation of the Rates on Solvolysis of 2,2,2-Trichloroethyl Chloroformate Using the Extended Grunwald-Winstein Equation

ents are well correlated with the extended Grunwald-Winstein equation, using the NT solvent nucleophilicity scale and the YCl 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 (kMeOH/kMeOD) of 2.39 is also in accord with SN2 mechanism probably assisted by general-base catalysis.

Correlation of the Rates of Solvolyses of 4-Methylthiophene-2-carbonyl Chloride Using the Extended Grunwald-Winstein Equation

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 SN1 and/or ionization (I) pathway rather than through an associative SN2 and/or addition-elimination (A-E) pathway.

Correlation of the Rates of Solvolysis of 3,4,5-trimethoxy- and 2,4,6-trichlorobenzoyl chlorides

The introduction of methoxy groups into the 3- and 5-positions of 4-methoxybenzoyl chloride leads to a reduction in specific rates of solvolysis. An extended Grunwald–Winstein equation correlation for the specific rates of solvolysis of 3,4,5-trimethoxybenzoyl chloride gives sensitivities towards changes in solvent nucleophilicity (/ value) of 0.29 and towards changes in solvent ionising power ( m value) of 0.54. The low m value allows specific rates to be determined in highly ionising fluoroalcohol-H2O mixtures. A parallel correlation of the specific rates of solvolysis of 2,4,6-trichlorobenzoyl chloride reveals that solvolyses in 100% and 90% ethanol or methanol do not appreciably follow the ionisation pathway indicated for solvolyses in the other solvents and it is proposed that, despite the two ortho-substituents, the addition–elimination pathway has become dominant.