Rate and product studies in the solvolyses of N,N-dimethylsulfamoyl and 2-propanesulfonyl chlorides

Contrary to earlier suggestions of an S(N)1 pathway for solvolyses of N,N-dimethylsulfamoyl chloride (1), an extended Grunwald-Winstein equation treatment of the specific rates of solvolysis in 32 solvents shows an appreciable sensitivity towards changes in both solvent nucleophilicity and solvent ionizing power. The actual values are very similar to those obtained in earlier studies of the solvolyses of sulfonyl and phosphoryl chlorides, solvolyses which are believed to proceed by an S(N)2 pathway. The observation of similar selectivities in aqueous-alcohol solvents further supports this assignment. In a recent report, an addition-elimination (association-dissociation) pathway was proposed for solvolyses of 2-propanesulfonyl chloride (2). A severe multicollinearity problem has been removed by the addition of several specific rates of solvolysis in fluoroalcohol-containing solvents. The new analyses using the extended Grunwald-Winstein equation lead to sensitivities similar to those for and the previously studied related compounds, and these solvolyses are also best described as following an S(N)2 pathway.     

Nucleophilic Participation in the Solvolyses of (Arylthio)methyl Chlorides and Derivatives: Application of Simple and Extended Forms of the Grunwald-Winstein Equations

The specific rates of solvolysis of chloromethyl phenyl sulfide [(phenylthio)methyl chloride] and its p-chloro-derivative have been determined at 0.0 °C in a wide range of hydroxylic solvents, including several containing a fluroalcohol. Treatment in terms of a two-term Grunwald-Winstein equation, incorporating terms based on solvent ionizing power (Y(Cl)) and solvent nucleophilicity (N(T)) suggest a mechanism similar to that for the solvolyses of tert-butyl chloride, involving in the rate-determining step a nucleophilic solvation of the incipient carbocation in an ionization process. A previous suggestion, that a third-term governed by the aromatic ring parameter (I) is required, is shown both for the new and for the previously studied related substrates to be an artifact, resulting from an appreciable degree of multicollinearity between I values and a linear combination of N(T) and Y(Cl) values.     

Rate and product studies with dimethyl phosphorochloridate and phosphorochloridothionate under solvolytic conditions

The specific rates of solvolysis of dimethyl phosphorochloridate and of dimethyl phosphorochloridothionate are very well correlated using the extended Grunwald-Winstein equation, with incorporation of the NT solvent nucleophilicity scale and the YCl solvent ionizing power scale. The sensitivity parameters (l and m) are similar to each other and also similar to previously recorded values for solvolyses of arenesulfonyl chlorides, which were proposed to follow a concerted displacement mechanism. For solvolyses in aqueous ethanol or aqueous methanol the product selectivities (S) are close to unity. For solvolyses in aqueous 2,2,2-trifluoroethanol, the values are too small to accurately measure, showing a very large preference for product formation involving nucleophilic attack by the water component. It is concluded that the chloride and chloridothionate solvolyses, in common with the solvolyses of arenesulfonyl chlorides, follow a concerted displacement mechanism.     

Application of the NT solvent nucleophilicity scale to attack at phosphorus: solvolyses of N,N,N',N'-tetramethyldiamidophosphorochloridate

The specific rates of solvolysis of N,N,N',N'-tetramethyldiamidophosphorochloridate have been measured at 25.0 degrees C in 31 solvents. Analysis with the extended Grunwald-Winstein equation leads to sensitivities toward changes in solvent nucleophilicity (l) of 1.20 +/- 0.07 and toward changes in solvent ionizing power (m) of 0.69 +/- 0.04. The correlation is improved by omission of the four data points for 2,2,2-trifluoroethanol-ethanol mixtures (F-test value from 155 to 320) with very small reductions in both l and m values. Activation parameters are reported for eight of the solvolyses. The l and m values are very similar to those previously reported for solvolyses of several arenesulfonyl chlorides, consistent with a concerted substitution process. This assignment is supported by a large k(Cl)/k(F) ratio for hydrolysis and a corresponding ratio for hydroxide-assisted hydrolysis of 178. The stereochemistry of nucleophilic attack at tetracoordinate phosphorus(V) is discussed.     

Correlation of the Rates of Solvolysis of the Benzhydryldimethylsulfonium Ion. Application of the Aromatic Ring Parameter(1)

Values for the specific rates of solvolysis of the benzhydryldimethylsulfonium ion in 34 solvents have been analyzed using various forms of the extended Grunwald-Winstein equation. The specific rates are insensitive toward changes in solvent nucleophilicity (N(T)) values, and they correlate best against a combination of Y(+) values (based on the solvolyses of the 1-adamantyldimethylsulfonium ion) and aromatic ring parameter (I) values. Common-molecule return is observed, being especially powerful in solvents rich in fluoro alcohol; the logarithm of the associated mass law constant correlates inversely with the solvent N(T) values. The product selectivities in ethanol-water mixtures are also consistent with an S(N)1 mechanism for the solvolyses.     

Correlation of the rates of solvolysis of cyclopropylcarbinyl and cyclobutyl bromides using the extended Grunwald-Winstein equation

The reactions of cyclopropylcarbinyl bromide (1) and cyclobutyl bromide (2) in hydroxylic solvents proceed with both solvolysis and rearrangement. Depending on the solvent, the reactions of 1 are 10-120 times faster than those of 2, and both are faster than the previously studied allylcarbinyl bromide (3). Specific rates are reported for the reactions of 2 proceeding to solvolysis products and 3. Reactions of 1 proceed to solvolysis products and both 2 and 3; since 2 slowly undergoes further solvolysis, specific rates are obtained by a modified Guggenheim treatment. The two sets of specific rates are analyzed using the extended Grunwald-Winstein equation to give sensitivities toward changes in solvent nucleophilicity of 0.42 for 1 and 0.53 for 2 and corresponding sensitivities toward changes in solvent ionizing power of 0.75 and 0.94. A mechanism is proposed involving a rate-determining ionization with an appreciable nucleophilic solvation of the incipient carbocation.     

Is the tert-butyl chloride solvolysis the most misunderstood reaction in organic chemistry? Evidence against nucleophilic solvent participation in the tert-butyl chloride transition state and for increased hydrogen bond donation to the 1-adamantyl chloride solvolysis transition state.

Despite theoretical calculations to the contrary, it has been argued that the 1-adamantyl cation is more stable than the tert-butyl cation in media of high dielectric constant. This argument has been utilized to suggest that the higher rate of solvolysis of tert-butyl chloride in aqueous ethanol is evidence for nucleophilic solvent participation in this classic reaction. Further, in "more highly ionizing" solvents, the rate of 1-adamantyl chloride is nearly the same as that of tert-butyl chloride, which is interpreted as a manifestation of the relative stabilities of the cations. However, the evidence cited does not explain the increased sensitivity of the rate of solvolysis of 1-adamantyl chloride over tert-butyl chloride to solvents which are better able to donate hydrogen bonds. The hypothesis developed here is that 1-adamantyl chloride solvolysis is assisted by hydrogen bond donation departing chloride ion to a greater extent than that of tert-butyl chloride solvolysis, most likely due to lessened steric interactions in a developing pyramidal cation. This hypothesis is supported by multiparameter solvent effect factor analyses utilizing the KOMPH2 equation which, in addition, quantifies the important role of ground-state destabilization due to strong solvent-solvent interactions. An important result from the good correlation of free energies of transfer of the tert-butyl chloride solvolysis transition state is that there is no change in mechanism, and, in particular, no nucleophilic participation even in non-hydroxylic basic solvents. The equation is also applied to the case of dimethylsulfonium ion solvolyses where the tert-butyl salt reacts substantially faster than the 1-adamantyl salt in ethanol and the gas phase. The decreased rate of the former in hydrogen bond donating solvents relative to the gas phase is as yet unclear. Solvent N values that were generated to characterize solvent nucleophilicity are shown not to be correlated by measures of solvent basicity but rather by the negative of measures of solvent hydrogen bond donor ability.     

Rate and product studies with benzyl and p-nitrobenzyl chloroformates under solvolytic conditions

The specific rates of solvolysis of p-nitrobenzyl chloroformate are well correlated using the extended Grunwald-Winstein equation, with a high sensitivity (l) to changes in solvent nucleophilicity (N(T)) and a moderate sensitivity (m) to changes in solvent ionizing power (Y(Cl)). The values are consistent with a rate-determining association within an association-dissociation pathway. The selectivity values (S) for the attack at the acyl carbon show a modest preference for ethanol over water and a relatively high preference for ethanol over 2,2,2-trifluoroethanol (TFE). The solvolyses of benzyl chloroformate show similar characteristics in solvents of relatively high nucleophilicity and/or low ionizing power. In solvents with considerable fluoro alcohol content, an ionization mechanism, accompanied by loss of carbon dioxide, leads to benzyl chloride, benzyl alcohol, and benzyl alkyl ether. A new correlation now applies, with a much lower l value and somewhat higher m value. The S values for this pathway are close to unity, even in TFE-ethanol mixtures, consistent with the components of the binary solvent capturing a highly reactive carbocation.     

Nucleophilic Solvent Intervention in Benzylic Solvolyses. The Use of YBnx Scales in Grunwald-Winstein Type Correlation Analysis

New Y_BnX scales of solvent ionizing power are developed and considered superior to Y_x scales for benzylic bromides, chlorides, p-nitrobenzoates and tosylates in Grunwald-Winstein type correlation analysis of solvolytic reactivities. The Y_BnX values, with addition and revision, are summarized. Evidence for nucleophilic solvent intervention in the solvolysis transition state for secondary and tertiary benzylic substrates is given. The advantages of employing this tool to understand solvolysis mechanisms are discussed.     

Correlation of the rates of solvolysis of benzoyl fluoride and a consideration of leaving-group effects

The specific rates of solvolysis of benzoyl fluoride have been determined at 25.0 degrees C in 37 pure and binary solvents. Together with seven values from the literature, these give a satisfactory correlation over the full range of solvents when the extended Grunwald-Winstein equation is applied. The sensitivities to changes in solvent nucleophilicity and solvent ionizing power are very similar to those for octyl fluoroformate, suggesting that the addition step of an addition-elimination mechanism is rate determining. In the solvent-composition region where benzoyl chloride also shows bimolecular solvolysis, the appreciable k(Cl)/k(F) values are proposed as being primarily due to a more efficient ground-state stabilization for the fluoride.     

Thermal and photochemical solvolysis of (E)- and (Z)-2-phenyl-1-propenyl(phenyl)iodonium tetrafluoroborate: benzenium and primary vinylic cation intermediates

The thermal and photochemical solvolysis of the two stereoisomeric 2-phenyl-1-propenyl(phenyl)iodonium tetrafluoroborates has been investigated in alcoholic solvents of varying nucleophilicity. The product profiles and rates of product formation in the thermal reaction are all compatible with a mechanism involving cleavage of the vinylic C-I bond assisted by the group in the trans position (methyl or phenyl), always leading to rearranged products. Depending on the nucleophilicity of the solvent, the primarily formed cations may or may not further rearrange to more stable isomers. The less reactive Z compound also yields some unrearranged vinyl ether product in the more nucleophilic solvents via an in-plane S(N)2 mechanism. The mechanism of the photolysis involves direct, unassisted cleavage of the vinylic, and aromatic, C-I bond in an S(N)1 mechanism. This produces a primary vinyl cation, which is partially trapped prior to rearrangement in methanol. The unrearranged vinyl ethers are mainly formed with retention of configuration via a lambda3-iodonium/solvent complex in an S(N)i mechanism. Thermal and photochemical solvolyses of iodonium salts are complementary techniques for the generation of different cation intermediates from the same substrate.     

S(N)2 Mechanism for Alcoholysis, Aminolysis, and Hydrolysis of Acetyl Chloride

First-order solvolysis rate constants are reported for solvolyses of acetyl chloride in methanol and MeOD, and in binary aqueous mixtures with acetone, acetonitrile, ethanol, methanol, and trifluoroethanol at 0 degrees C. Product selectivities (S = [MeCOOR]/[MeCOOH] x [water]/[alcohol]) are reported for solvolyses in ethanol/ and methanol/water at 0 degrees C. Solvolyses of acetyl chloride show a high sensitivity to changes in solvent ionizing power, consistent with C-Cl bond cleavage. As the solvent is varied from pure ethanol (or methanol) to water, S values and rate-rate profiles show no evidence for the change in reaction channel observed for solvolyses of benzoyl and trimethylacetyl chlorides. However, using rate ratios in 40% ethanol/water and 97% trifluoroethanol/water (solvents of similar ionizing power but different nucleophilicities) to compare sensitivities to nucleophilic attack, solvolyses of acetyl chloride are over 20-fold more sensitive to nucleophilic attack than benzoyl chloride. The solvent isotope effect of 1.29 (MeOH/MeOD) for acetyl chloride is similar to that for p-methoxybenzoyl chloride (1.22) and is lower than for benzoyl chloride (1.55). Second-order rate constants for aminolyses of acetyl chloride with m-nitroaniline in methanol at 0 degrees C show that acetyl chloride behaves similarly to p-methoxybenzoyl chloride, whereas benzoyl chloride is 40-fold more sensitive to the added amine. The results indicate mechanistic differences between solvolyses of acetyl and benzoyl chlorides, and an S(N)2 mechanism is proposed for solvolyses and aminolyses by m-nitroaniline of acetyl chloride (i.e. these reactions are probably not carbonyl additions, but a strong sensitivity to nucleophilic attack accounts for their high rates).     

Alkylation on graphite in the absence of Lewis acids

Graphite is introduced as a convenient catalyst for alkylation of aromatic compounds and alcohols by benzyl, tertiary alkyl, and secondary alkyl halides in the absence of strong Lewis acids. Primary alkyl halides are not active under the reaction conditions.     

Hydroxylation of alkyl halides with water in ionic liquid: significantly enhanced nucleophilicity of water

A facile method for the nucleophilic hydroxylation of alkyl halides and mesylates with water has been developed in which the use of ionic liquid as an alternative reaction medium not only enhanced the nucleophilicity of water but also reduced the formation of elimination products predominantly formed under the conventional basic reaction conditions. For example, hydroxylation of model compound 2-(3-bromopropyl)naphthalene (1) to 2-(3-hydroxypropyl)naphthalene (2) with water in 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) and 1,4-dioxane proceeded selectively in high yield (94%). The reactivity of other nucleophilic oxygen sources such as alcohol, phenol, and acetic acid in an ionic liquid was also investigated.     

Correlation of the rates of solvolysis of the S-Ethyldibenzothiophenium Ion

The specific rates of solvolysis of S-ethyldibenzothiophenium trifluoromethanesulfonate have been found to give a good linear correlation with the previously determined specific rates of solvolysis of the triethyloxonium ion, and hence with the solvent nucleophilicity scale established from the triethyloxonium ion study. A value for the sensitivity to changes in solvent nucleophilicity ( 1 ) of greater than unity (1.15) is in accord with reactivity-selectivity considerations.     

有机磷化合物的研究 X:五价膦(磷)酸酯与卤代烷在卤化钠存在下的酯烷基交换反应

A detailed study on the ester alkyl exchange reaction of various types of quinique-valent phosphorus esters with alkyl halide in the presence of sodium bromides was reported. This ester alkyl exchange reaction was evidently influenced by the structure of phosphorus esters and alkyl halides as well as by the nature of the halides of metal ions. In contrast with the reaction without sodium hadlide, the alkyl phosphinmate is more reactive than phosphonate and phosphate by treatment with alkyl halide in the presence of sodium halide. This is consistent with the high nucleophilicity of >P(CO)O- as leaving group. The reactivity of butyl halides was decreased in the following order: n-BuBr>i-BuBr=s-BuBr>t-BuBr. Alkyl iodide was proved to be more reactive than the corresponding bromide and chloride. However, the use of iodioe is limited by the formation of alkene resulted from the elimination of HI. These structural effects show the general characteristics of a nucleophilic substitution reaction. A reaction mechanism involving the formation of sodium salt intermecutiate was proposed based on the concept of HSAB principle. This reaction may, however, be used as a convenient method for the preparation of mixed esters of quinque-valent phosphorus acids.     

Phenoxenium ions identical intermediates in the acid-catalyzed solvolysis of n-tosyl-O-Arylhydroxylamines and in the thermolysis of N-Aryloxypyridinium salts

The acid-catalyzed solvolysis of N-tosyl-O-arylhydroxylamines in aromatic solvents and the thermolysis of N-arylqxypyridinium salts involve common intermediates, phenoxenium ions, for the formation of hydroxybiphenyl derivatives. Diphenylethers are formed when the hydrolysis of the N—O bonds is slow and the aromatic solvent has high nucleophilicity.     

Nucleophilic participation in the solvolysis of the t-butyldimethylsulfonium ion

Studies with the $\text{t}$-butyldimethylsulfonium ion give evidence for nucleophilic participation in the solvolyses of $\text{t}$-butyl compounds but electrophilic assistance would be the dominant factor for $\text{t}$-butyl chloride solvolysis.     

Influence of alkyl substitution on the gas-phase stability of 1-adamantyl cation and on the solvent effects in the solvolysis of 1-bromoadamantane

1-Adamantyl cations having three methyl groups or one, two, or three isopropyl groups on the 3-, 5-, and 7-positions were found by FT ICR to be more stable than the 1-adamantyl cation and that the stability increases with the number of isopropyl group. The relative stabilities calculated by PM3 were in good agreement with the experimental results. In contrast, the sequence of the rates for the solvolysis in nonaqueous solvents are 3,5,7-(Me)(3)-1-AdBr < 1-bromoadamantane (1-AdBr) < 3,5,7-(n-Pr)(3)-1-AdBr < 3,5,7-(i-Pr)(3)-1-AdBr. The rates of solvolysis of 3,5,7-(i-Pr)(3)-1-AdBr and 3,5,7-(n-Pr)(3)-1-AdBr relative to 1-AdBr at 25 degrees C are 15 and 3.8 in EtOH, respectively, but markedly decreases with the increase in the amount of added water, reaching 0.84 and 0.15, respectively, in 60% EtOH. Reflecting these effects of water, the Grunwald-Winstein (GW) relationship for 3,5,7-(i-Pr)(3)-1-AdBr and 3,5,7-(n-Pr)(3)-1-AdBr against Y(Br) is linear for nonaqueous alcohols (EtOH, MeOH, TFE-EtOH, TFE, 97% HFIP), but marked downward deviations are observed for aqueous organic solvents, in particular, aqueous ethanol and aqueous acetone. The effect of the alkyl substituents to diminish relative solvolytic reactivity in EtOH-H(2)O mixtures may be ascribed to a blend of steric hindrance to Betarphinsted base-type hydration to the beta-hydrogens and hydrophobic interaction of the alkyl groups with ethanol to make the primary solvation shell less ionizing. The introduction of one nonyl group to the 3-position showed much smaller deviations in the GW relationship than the case of 3,5,7-(n-Pr)(3)-1-AdBr. The markedly decelerated solvolysis of alkylated 1-bromoadamantanes in aqueous organic solvents is a kinetic version of anomalously diminished dissociation of alkylbenzoic acids in aqueous ethanol and aqueous tert-butyl alcohol that was demonstrated by Wepster and co-workers a decade ago and ascribed to hydrophobic effects.     

The Barbier-Grignard-type carbonyl alkylation using unactivated alkyl halides in water

The aqueous Barbier-Grignard-type alkylation of aldehydes with unactivated alkyl iodides and bromides was developed. By using a combination of zinc and cuprous iodide, catalyzed by indium(I) chloride, we successfully added tertiary, secondary, and primary alkyl halides to various aromatic aldehydes in 0.07 M aqueous Na2C2O4. A mechanistic rationale for the success of the reaction has been proposed.