Solvolysis Of Chlorides Research Articles

Iodine(III) Derivatives as Halogen Bonding Organocatalysts.

Hypervalent iodine(III) derivatives are known as versatile reagents in organic synthesis, but there is only one previous report on their use as Lewis acidic organocatalysts. Herein, we present first strong indications for the crucial role of halogen bonding in this kind of catalyses. To this end, the solvolysis of benzhydryl chloride and the Diels-Alder reaction of cyclopentadiene with methyl vinyl ketone served as benchmark reactions for halide abstraction and the activation of neutral compounds. Iodolium compounds (cyclic diaryl iodonium species) were used as activators or catalysts, and we were able to markedly reduce or completely switch off their activity by sterically blocking one or two of their electrophilic axes. Compared with previously established bidentate cationic halogen bond donors, the monodentate organoiodine derivatives used herein are at least similarly active (in the Diels-Alder reaction) or even decidedly more active (in benzhydryl chloride solvolysis).

Propanolysis of arenesulfonyl chlorides: Nucleophilic substitution at sulfonyl sulfur

AbstractWe have studied the mechanism of solvolysis of arenesulfonyl chlorides by propan‐1‐ol and propan‐2‐ol at 303‐323 K. Kinetic profiles were appropriately fit by first‐order kinetics. Reactivity increases with electron‐donating substituents. Ortho‐alkyl substituted derivatives of arenesulfonyl chlorides show increased reactivity, but the origin of this “positive” ortho‐effect remains unclear. Likely, ortho‐methyl groups restrict rotation around the C‐S bond, facilitating the attack of the nucleophile. No relevant reactivity changes have been found with propan‐1‐ol and propan‐2‐ol in terms of nucleophile steric effect. The existence of isokinetic relationships for all substrates suggests a single mechanism for the series. Solvolysis reactions of all substrates in both alcohols show isokinetic temperatures (Tiso) close to the working temperature range, which is an evidence of the process being influenced by secondary reactivity factors, likely of steric nature in the TS. Solvation plays a relevant role in this reaction, modulating the reactivity. In some cases, the presence of t‐Bu instead of Me in para‐ position leads to changes in the first solvation shell, increasing the energy of the reaction (ca. 1 kJ·mol−1). The obtained results suggest the same kinetic mechanism of solvolysis of arenesulfonyl chlorides for propan‐1‐ol and propan‐2‐ol, as in MeOH and EtOH, where bimolecular nucleophilic substitution (SN2) takes place with nucleophilic solvent assistance of one alcohol molecule and the participation of the solvent network involving solvent molecules of the first solvation shell.

γ-Cyclodextrin modulates the chemical reactivity by multiple complexation.

Multiple complexation by γ-CD has been studied by self-diffusion coefficients (DOSY) and chemical kinetics experiments in which 4-methoxybenzenesulfonyl chloride (MBSC) solvolysis was used as a chemical probe. The addition of a surfactant as a third component to the reaction mixture induced a very complex reactivity pattern that was explained on the basis of multiple complexation phenomena and surfactant self-assembly to form micelles. A cooperative effect that yielded a ternary complex formed by cyclodextrin-surfactant-MBSC was observed. The larger cavity of γ-CD in comparison with β-CD is responsible for the change from the competitive complexation mechanism predominant with β-CD to a cooperative/competitive mixed mechanism operating for the larger derivative. The cavity size in γ-CD is large enough to bind two surfactant alkyl chains with a cooperative effect. Water molecules released by the formation of 1:1 host-guest complexes made the cavity more hydrophobic and promoted further inclusion. A reduction in the available volume of the cavity should be considered on binding a second guest.

Role of water in determining organic reactivity in aqueous binary solvents

Abstract Kinetic data for organic reactions in various binary water-organic solvent mixtures were collected and quantitatively analysed in terms of linear-free-energy relationships by using tert-butyl chloride (2-chloro-2-methylpropane) solvolysis as the reference system. Linear similarity plots for these kinetic data were determined for solvent systems ranging from pure water mixtures up to considerable amount of cosolvent, and 161 similarity coefficients were calculated from slopes of these plots. The existence of these linear plots demonstrated that the solvent effects are of some common nature in all analysed reaction mixtures independent of the reaction type and the cosolvent used. Therefore it was concluded that the observed effects could be connected to the specific solvating properties of water, which govern reactivity even in significant dilution of water by an organic cosolvent. This conclusion was supported by the linear interrelationship between the slopes of similarity plots of different reactions, and hydrophobicity parameters log P of the reacting compounds. The relative solvent effects observed in binary water-organic solvent mixtures were for the first time directly related to the structure of reacting compounds.

Detailed Analysis for the Solvolysis of Isopropenyl Chloroformate.

The specific rates of solvolysis (including those obtained from the literature) of isopropenyl chloroformate (1) are analyzed using the extended Grunwald-Winstein equation, involving the N(T) scale of solvent nucleophilicity (S-methyldibenzothiophenium ion) combined with a Y(Cl) scale based on 1-adamantyl chloride solvolysis. A similarity model approach, using phenyl chloroformate solvolyses for comparison, indicated a dominant bimolecular carbonyl-addition mechanism for the solvolyses of 1 in all solvents except 97% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). An extensive evaluation of the outcomes acquired through the application of the extended Grunwald-Winstein equation resulted in the proposal of an addition-elimination mechanism dominating in most of the solvents, but in 97-70% HFIP, and 97% 2,2,2-trifluoroethanol (TFE), it is proposed that a superimposed unimolecular (S(N)1) type ionization is making a significant contribution.

Supramolecular Catalysis by Cucurbit[7]uril and Cyclodextrins: Similarity and Differences

To understand the analogies and differences between the cucurbituril and cyclodextrin cavities different solvolytic reactions have been studied in the presence of cucurbit[7]uril, CB7, and beta-CD or its methylated derivative, DM-beta-CD. Solvolysis of 1-bromoadamantane has been used as a test to evaluate the ability of the cavities to solvate the Br(-) leaving group. Obtained results show that in both cases the polarity inside the cavity is similar to that of a 70% ethanol:water mixture. Solvolysis of substituted benzoyl chlorides shows a great difference between the CB7 and DM-beta-CD cavity. Solvolysis of electron withdrawing substituted benzoyl chlorides (associative mechanism) is catalyzed by DM-beta-CD and inhibited by CB7. However, solvolysis of electron donating substituted benzoyl chlorides (dissociative mechanism) is catalyzed by CB7 and inhibited by DM-beta-CD. These experimental behaviors have been explained on the basis of different solvolytic mechanisms. Participation of the hydroxyl groups of the cyclodextrin as a nucleophile can explain the catalytic effect observed for solvolysis of benzoyl chlorides reacting by an associative mechanism. Solvolysis of benzoyl chlorides reacting by a dissociative mechanism is catalyzed by CB7 due to the ability of the CB7 cavity to stabilize the acylium ion developed in the transition state by electrostatic interactions.

Ultrasonic detection of hydrophobic interactions: a quantitative approach

AbstractKinetic effects of sonication on ester hydrolysis and tert‐butyl chloride solvolysis, studied in ethanol–water binary solvent, are discussed in terms of quantitative relationships between their magnitude and the hydrophobicity of reagents. A number of conclusions were drawn from the observed linear free‐energy (LFE) relationships. Independent of reaction mechanism, the decrease in reaction rates with increasing ethanol content in the solvent is mainly due to hydrophobic stabilization of the ground state. While hydrophobic species can be hidden in the ethanol clusters present in the region XEtOH > 0.15, at lower ethanol contents hydrophobic reagents are weakly solvated and the hydrophobic stabilization can be easily overcome by sonication. Copyright © 2008 John Wiley & Sons, Ltd.

Ultrasonic Evidence of Hydrophobic Interactions. Effect of Ultrasound on Benzoin Condensation and Some Other Reactions in Aqueous Ethanol

The kinetics of KCN-catalyzed benzoin condensation of benzaldehyde in water and ethanol-water binary mixtures was investigated both under ultrasound at 22 kHz and without sonication. Thermodynamic activation parameters were calculated from kinetic data obtained at 35, 50, and 65 degrees C. Evidence that ultrasound can retard reactions is reported and hence a direct proof that sonochemical processes occur in the bulk solution. Former results and literature data for ester hydrolyses and tert-butyl chloride solvolysis are involved in the discussion. A quantitative relationship between sonication effects and the hydrophobicity of reagents is presented for the first time. Ultrasound affects hydrophobic interactions with the solvent, which are not manifested in conventional kinetics. When it suppresses the stabilization of the encounter complexes between reagents, sonication hinders the reaction but accelerates it when it perturbs the hydrophobic stabilization of the ground state of a reagent.

Effects of Zwitterionic Vesicles on the Reactivity of Benzoyl Chlorides

A systematic study on the solvolysis reaction of substituted benzoyl chlorides in the presence of zwitterionic vesicles of dipalmitoyl phosphatidylcholine (DPPC) has been performed. Size, shape, surface charge, and polarity of the interface of the vesicular aggregates were determined using various techniques. The application of the pseudophase formalism allowed us to obtain the thermodynamic and kinetic coefficients characteristic of the reaction. The effects of vesicular aggregates on the solvolysis of benzoyl chlorides, which are known to be sensitive to the physical properties of the medium, depend on the nature of the substrate. For benzoyl chlorides with electron-donating groups, which react predominantly through a dissociative mechanism which is strongly affected by medium properties, the rate constant decreases as the vesicle concentration increases. On the other hand, for benzoyl chlorides with electron-withdrawing groups, which react mainly via an associative pathway, DPPC vesicles catalyze the solvolysis reaction.

Re-examination of the Solvolysis of Acyl Chlorides. Rethinking the Role of Both Carbonyl and Chloride

This letter describes a computational investigation into the hydrolysis mechanism of carbonyl compounds. Hydrolysis has previously been thought to be a very well-understood process. The molecules formaldehyde (CH2O), formyl chloride (HCOCl), and phosgene (COCl2) were used to probe the initial steps of the hydrolysis mechanism. A combination of quantum mechanics calculations and application of Bader's AIM analysis was used to study the mechanism. The results show that the carbon−oxygen double bond is more akin to the polarized bond between phosphorus and oxygen rather than to a true double bond such as that found in ethylene. Further, the results show that the initial step of the reaction is formation of a strongly hydrogen-bonded complex as opposed to direct addition of a nucleophile to the carbonyl center. Finally, the results show that chlorine plays a substantial role in stabilizing the carbocationic center resulting from the initial hydrogen bond formation. These results strongly suggest the mechanism...

Cyclodextrin effect on solvolysis of substituted benzoyl chlorides.

A kinetic study was carried out on the solvolysis of substituted benzoyl chlorides in the presence of alpha-, beta- and gamma-CD. Combination of the substituent dependent mechanism for solvolysis of benzoyl chlorides and the complexation ability of the cyclodextrin yields the following experimental behavior: (i) catalysis by beta- and gamma-CD for solvolysis of electron-attracting substituted benzoyl chlorides due to the reaction with its hydroxyl group C(6); (ii) absence of alpha-CD influence on solvolysis of benzoyl chlorides with electron withdrawing substituents; (iii) inhibition of solvolysis of benzoyl chlorides with electron-donating groups. This behavior is observed for solvolysis of meta/para substituted substrates in the presence of beta-CD, solvolysis of meta-substituted benzoyl chlorides in the presence of alpha-CD and solvolysis of para-substituted benzoyl chlorides in the presence of gamma-CD. This decrease in the rate constant is a consequence of the complexation of the substrate in the cyclodextrin cavity and its low solvation ability, causing the rate of solvolysis in its interior to be negligible. (iv) The solvolysis of meta-substituted benzoyl chlorides in the presence of gamma-CD yields a new behavior where the reaction of the complexed substrate is not negligible in the interior of the cyclodextrin cavity, which has been interpreted as a consequence of incomplete expulsion of hydration water from its cavity when the complexation takes place. (v) The experimental results obtained in the presence of alpha-CD show that meta-substituted benzoyl chlorides give rise to host : guest complexes with 1 : 1 stoichiometries, whereas those which are para-substituted cause a 2 : 1 stoichiometry to be formed. This difference in behavior has been interpreted taking into account the size of the different benzoyl chlorides and their accommodation in the alpha-CD cavity.

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.

The Grunwald–Winstein relationship in the solvolysis of crowded tertiary alkyl chlorides. Hindered hydration and hydrophobic effect

The Grunwald–Winstein relationship in the solvolysis of crowded tertiary alkyl chlorides. Hindered hydration and hydrophobic effect

Ab initio molecular dynamics simulations on the hydrolysis of methyl chloride with explicit consideration of three water molecules

Ab initio molecular dynamics (MD) simulations were performed on the hydrolysis of methyl chloride (CH3Cl) with explicit consideration of three water molecules to understand the dynamics of the reaction and the role of solvent molecules in SN2 reactions in solution. The simulations clearly showed the existence and dynamical characteristics of two nearly concerted proton transfers involving the attacking water molecule and the solvent water molecules on the way to formation of the products. Observation of these proton transfers points clearly to the need for an explicit quantum chemical treatment of at least a few solvent water molecules to describe methyl chloride solvolysis.

Solvolysis of benzylic chlorides with extended charge delocalization. ?-tert-butyl(2-naphthyl)methyl, 9-fluorenyl and monosubstituted benzhydryl chlorides

Rate constants of solvolysis of α-tert-butyl(2-naphthyl)methyl chloride (1), 9-fluorenyl chloride (2) and a series of monosubstituted benzhydryl chlorides (3) in a wide range of solvents were measured. Grunwald–Winstein-type correlation analysis of log k for 2 and 3 against YBnCl, with or without nucleophilicity N, yielded less satisfactory linear correlations than that against log k(1). A new scale of solvent ionizing power, YxBnCl, for the correlation of solvolytic reactivities of benzylic chlorides with extended charge delocalization based on log k(1) was developed. Application to the mechanistic study suggested the solvolysis of 2 and 4-nitrobenzhydryl chloride were non-limiting. Hammett plots against σ+ constants exhibited more negative ρ values in less nucleophilic solvents. In a benzhydryl chloride containing a strong deactivating substituent, such as 4-nitro, the positive charge delocalizes mainly over the unsubstituted ring in the cationic transition state. The uneven charge distribution was also confirmed by Mulliken population analysis at the level of the RHF/6–31G*//RHF/3–21G(*) basis set for cations. Comparison of the results of correlation analysis using the equation log(k/k0) = mY vs the equation log(k/k0) = mY+hI, and using the equation log(k/k0) = mY+lN vs the equation log(k/k0) = mY+lN+hI indicated the use of YBnCl or YxBnCl could give a better understanding of solvolytic mechanisms than the combinatorial use of YCl and I. © 1998 John Wiley & Sons, Ltd.

Chlorophosphate solvolyses. Evaluation of third-order rate laws and rate–product correlations for diphenyl phosphorochloridate in aqueous alcohols †

Rate constants and product selectivities for solvolyses of diphenyl phosphorochloridate in aqueous ethanol and methanol have been determined, along with additional kinetic data for solvolyses in acetone–water, D2O, MeOD, 2,2,2-trifluoroethanol–water, and CF3CH2OH–EtOH. Kinetic data for solvolyses of bis(4-chlorophenyl) phosphorochloridate in the above solvents have also been obtained. The results show that these solvolyses have the following features: (i) no evidence for mechanistic changes over the solvent range ethanol to water; (ii) the largest kinetic solvent isotope effect (KSIE in MeOH/MeOD) yet reported for a chloride solvolysis; (iii) large rate decreases in CF3CH2OH-rich solvents, indicating a very high sensitivity to solvent nucleophilicity. The large KSIE and the product selectivities are well explained by the accepted SN2(P) mechanism, extended to incorporate two solvent molecules in the rate-determining step; i.e. reactions are third-order, with one molecule of solvent acting as nucleophile and the other acting as general base. This relatively simple theory accounts well for several important features of these solvolyses (including solvolyses in trifluoroethanol–water and –ethanol), but the third-order rate constants derived from product selectivities lead to calculated first-order rate constants which are not always in agreement with experimental values. The unexpected failure of the rate–product correlation may be due to initial-state effects, reducing values of third-order rate constants as alcohol is added to water.

Nucleophilic substitution reactions of cinnamoyl chlorides with anilines in acetonitrile and acetonitrile–methanol mixtures

Kinetic studies on the solvolysis (in McOH–MeCN mixtures) and aminolysis (with anilines in McCN) of cinnamoyl chlorides have been carried out at 25.0 °C. The relatively large negative values of ρY+=–0.9 ∼–1.5 for the methanolysis are consistent with a dissociative SN2-like mechanism. For the aminolysis, the ρY values are positive (ρY= 0.52 ∼ 1.64) and ρX values range from –1.68 to –2.51 in acetonitrile. The positive values of βX= 0.6–0.9 and ρXY= 0.88 in acetonitrile, and isotope effect data suggest that the aminolysis proceeds by a stepwise mechanism with rate-limiting breakdown of the tetrahedral intermediate, T±. It is noted that in the acyl-transfer reactions proceeding by rate-limiting departure of the leaving group from the tetrahedral intermediate the signs of both ρY and ρXY are positive and the reactivity–selectivity principle (RSP) is valid in general.

Sulphonyl transfer reactions: solvolysis of arenesulphonyl chlorides in aqueous trifluoroethanol

Activation parameters for the solvolysis in aqueous trifluoroethanol of arenesulphonyl chlorides with electron-supplying substituents have been determined; the results are not in accord with earlier proposals that such compounds react by an SN1 mechanism.

Substituent Effects. 22. The Solvolysis of α-t-Butylbenzyl Tosylates

Abstract The rates of solvolysis of α-t-butylbenzyl tosylates were determined in 80% aqueous acetone (80A) and 80% aqueous ethanol (80E) for an extended series of substituents. The substituent effect can be linearly correlated in terms of the Yukawa–Tsuno LArSR relationship, with a ρ value of −5.542 and an r value of 1.093 in 80A, and −5.650 and 1.106 in 80E, respectively. The large negative ρ and exalted r values suggest the operation of the kc mechanism in this solvolysis without nucleophilic solvent assistance and methyl participation. From a comparison of the substituent effects, the exalted r value of 1.15 observed in the solvolysis of α-methylbenzyl chlorides can be attributed to the enhanced resonance demand characteristic of secondary benzylic system rather than to a correlational artifact arising from nonlinearity due to SN1–SN2 mechanistic change. The solvolysis of this system can be utilized as an appropriate reference system for the accurate estimation of σ+ constants in various solvents.

Linear solvation energy relationships. Part 37. An analysis of contributions of dipolarity–polarisability, nucleophilic assistance, electrophilic assistance, and cavity terms to solvent effects on t-butyl halide solvolysis rates

Solvolysis/dehydrohalogenation rates of t-butyl chloride in 21 hydrogen bond donor (HBD) and non-HBD solvents are well correlated (r= 0.9973, s.d. = 0.24) by the equation: log k=–14.60 + 0.48λH2/100 + 5.10π*+ 4.17α+ 0.73β where δH2 is the solvent cohesive energy density, and π*, α, and β are the solvatochromic parameters that scale solvent diplority–polarizability, HBD acidity (electrophilicity), and hydrogen-bond acceptor basicity (nucleophilicity). In the corresponding equation over the same solvent set for t-butyl bromide, the terms in δH2 and α are smaller still, and the terms in δH2 and β are not statistically significant. It is shown that a trifluoroethanol (TFE)–ethanol plot, wherein ButCl and 1-adamantyl chloride (1-AdCl) solvolysis rates are compared, can be interpreted as evidence for electrophilic assistance of 1-AdCl in TFE rather than the more usual interpretation of nucleophilic assistance to ButCl in EtOH–H2O.