The hydration of 1-aryl-3,3,3-trifluoropropynes and some other phenylacetylenes in sulfuric acid. An excess acidity analysis

1990 ◽  
Vol 68 (10) ◽  
pp. 1876-1881 ◽  
Author(s):  
Robin A. Cox ◽  
Ewart Grant ◽  
Todd Whitaker ◽  
Thomas T. Tidwell
Keyword(s):  
Sulfuric Acid ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Linear Free Energy Relationship ◽  
Hydration Kinetics ◽  
Hydration Mechanism ◽  
Linear Free Energy ◽  
Vinyl Cation ◽  
Solvent Isotope ◽  
Kinetics Of

The excess acidity method has been used to analyse the hydration kinetics of the phenylacetylenes Y-C6H4-C≡C-Z in aqueous sulfuric acid mixtures; Z = CF3 (1), H (2), COC6H4-X (3), and CO2H (4). All substrates gave acetophenone-type products consistent with the normal hydration mechanism involving rate-determining vinyl cation formation. Standard-state log k0 intercepts, and m≠m* slopes, were both used in linear free energy relationship plots against the substituent σ+ values. Solvent isotope effects and activation parameters were obtained in some cases. The deactivating Z substituents in 1, 3, and 4 all cause reaction to be some 100 times slower than that of the parent phenylacetylene 2. Compounds 2,3, and 4 all have ρ+ values of about −3.8, but 1 is more substituent sensitive, with a ρ+ of −5.3. A σ+ value of 0.38 is calculated for the CF3C≡C substituent. The ρ+ values were found to be acidity independent for 1 and 2, and probably for 3, but not for 4. Proton transfer at the transition state was found to be most advanced for the fastest reaction, that of 2, contrary to intuition. Keywords: alkyne hydration, excess acidity, phenylacetylenes, vinyl cations, deactivated carbocations.

Oxidation of secondary alcohols by sodium N-chlorobenzenesulphonamide in aqueous solution. A kinetic study

1991 ◽  
Vol 56 (8) ◽  
pp. 1671-1679 ◽  
Author(s):  
Chirchingi K. Mythily ◽  
Dandinasivara S. Mahadevappa ◽  
Kanchugarakoppal S. Rangappa
Keyword(s):  
Isotope Effects ◽  
Activation Parameters ◽  
Secondary Alcohols ◽  
Energy Relation ◽  
Linear Free Energy ◽  
Rate Limiting Step ◽  
Different Temperatures ◽  
Entropy Of Activation ◽  
Free Energy Relation ◽  
Solvent Isotope

The kinetics of oxidation of five secondary alcohols by sodium N-chlorobenzenesulphonamide (chloramine-B) has been studied in acid medium at 40°C. The reaction is first order with respect to the oxidant and alcohol and fractional order in [H+]. The influence of added halide ions and of reaction product and the effects of varying ionic strength and dielectric constant of the medium have also been studied. The solvent isotope effects k’(H2O)/k’(D2O) were determined. The rates were studied at four different temperatures and the activation parameters were evaluated. Attempts have been made to arrive at a linear free energy relation through the Taft treatment. An isokinetic relation is observed with β = 248 K, indicating the entropy of activation as the rate controlling factor. Protonated chloramine-T (monochloramine-T) has been postulated as the reactive oxidizing species, the main product of oxidation being the corresponding ketone. A mechanism involving the interaction of protonated haloamine species and the alcohol in a rate limiting step has been proposed.

Kinetics and mechanism of bromination of styrenes

1967 ◽  
Vol 45 (2) ◽  
pp. 167-173 ◽  
Author(s):  
Keith Yates ◽  
W. V. Wright
Keyword(s):  
Activation Parameters ◽  
Second Order ◽  
Linear Free Energy Relationship ◽  
Reaction Products ◽  
Order Process ◽  
Third Order ◽  
Linear Free Energy ◽  
Reaction Constant ◽  
Relationship Of ◽  
Kinetics Of

The kinetics of bromination of six substituted styrènes (3-fluoro-, 3-chloro-, 3-bromo-, 3,4-dichloro-, 3-nitro-, and 4-nitro-) in anhydrous acetic acid have been investigated at several temperatures. At 25.3 °C the reactions follow the rate expression [Formula: see text]The rate constants for the second order process show a good linear free energy relationship of the log k versus σ type with ρ = − 2.24. (The value obtained at 35.3 °C is − 1.93.) No simple rate-substituent dependence is obtained for the more complex third order process. Activation parameters have been obtained for the second order brominations, the ΔS≠ values being large and negative. Bromination of styrene in the presence of a large excess of acetate or nitrate gives only two products in each case, the α,β-dibromide and the α –acetoxy β-bromide or α -nitrato- β -bromide respectively.The magnitude of the reaction constant ρ, the values of ΔS≠, and the reaction products all support a mechanism involving a highly unsymmetrical bromonium ion intermediate.

scholarly journals Deuterium Isotope Effects on Acid-Base Equilibrium of Organic Compounds

Molecules ◽  
2021 ◽  
Vol 26 (24) ◽  
pp. 7687
Author(s):  
Meiyi Liu ◽  
Jiali Gao
Keyword(s):  
Free Energy ◽  
Isotope Effects ◽  
Linear Free Energy Relationship ◽  
Acid Base ◽  
Exchange Effect ◽  
Linear Free Energy ◽  
Acid Base Equilibrium ◽  
Deuterium Isotope Effects ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Deuterium isotope effects on acid–base equilibrium have been investigated using a combined path integral and free-energy perturbation simulation method. To understand the origin of the linear free-energy relationship of ΔpKa=pKaD2O−pKaH2O versus pKaH2O, we examined two theoretical models for computing the deuterium isotope effects. In Model 1, only the intrinsic isotope exchange effect of the acid itself in water was included by replacing the titratable protons with deuterons. Here, the dominant contribution is due to the difference in zero-point energy between the two isotopologues. In Model 2, the medium isotope effects are considered, in which the free energy change as a result of replacing H2O by D2O in solute–solvent hydrogen-bonding complexes is determined. Although the average ΔpKa change from Model 1 was found to be in reasonable agreement with the experimental average result, the pKaH2O dependence of the solvent isotope effects is absent. A linear free-energy relationship is obtained by including the medium effect in Model 2, and the main factor is due to solvent isotope effects in the anion–water complexes. The present study highlights the significant roles of both the intrinsic isotope exchange effect and the medium solvent isotope effect.

scholarly journals Rate and Product Studies with 1-Adamantyl Chlorothioformate under Solvolytic Conditions

2021 ◽  
Vol 22 (14) ◽  
pp. 7394
Author(s):  
Kyoung Ho Park ◽  
Mi Hye Seong ◽  
Jin Burm Kyong ◽  
Dennis N. Kevill
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Carbonyl Sulfide ◽  
Activation Parameters ◽  
Chloride Ions ◽  
Reaction Channels ◽  
Decomposition Pathway ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

A study was carried out on the solvolysis of 1-adamantyl chlorothioformate (1-AdSCOCl, 1) in hydroxylic solvents. The rate constants of the solvolysis of 1 were well correlated using the Grunwald–Winstein equation in all of the 20 solvents (R = 0.985). The solvolyses of 1 were analyzed as the following two competing reactions: the solvolysis ionization pathway through the intermediate (1-AdSCO)+ (carboxylium ion) stabilized by the loss of chloride ions due to nucleophilic solvation and the solvolysis–decomposition pathway through the intermediate 1-Ad+Cl− ion pairs (carbocation) with the loss of carbonyl sulfide. In addition, the rate constants (kexp) for the solvolysis of 1 were separated into k1-Ad+Cl− and k1-AdSCO+Cl− through a product study and applied to the Grunwald–Winstein equation to obtain the sensitivity (m-value) to change in solvent ionizing power. For binary hydroxylic solvents, the selectivities (S) for the formation of solvolysis products were very similar to those of the 1-adamantyl derivatives discussed previously. The kinetic solvent isotope effects (KSIEs), salt effects and activation parameters for the solvolyses of 1 were also determined. These observations are compared with those previously reported for the solvolyses of 1-adamantyl chloroformate (1-AdOCOCl, 2). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions calculated using Gaussian 03.

scholarly journals Kinetics of alkoxysilanes hydrolysis: An empirical approach

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Ahmed A. Issa ◽  
Marwa El-Azazy ◽  
Adriaan S. Luyt
Keyword(s):  
Reaction Mechanisms ◽  
Hydrolysis Reaction ◽  
Hydrolysis Rate ◽  
Coupling Agents ◽  
Linear Free Energy Relationship ◽  
Acidic Media ◽  
Linear Free Energy ◽  
Primary Materials ◽  
Kinetics Of ◽  
Hydrolysis Of

AbstractAlkoxysilanes and organoalkoxysilanes are primary materials in several industries, e.g. coating, anti-corrosion treatment, fabrication of stationary phase for chromatography, and coupling agents. The hydrolytic polycondensation reactions and final product can be controlled by adjusting the hydrolysis reaction, which was investigated under a variety of conditions, such as different alkoxysilanes, solvents, and catalysts by using gas chromatography. The hydrolysis rate of alkoxysilanes shows a dependence on the alkoxysilane structure (especially the organic attachments), solvent properties, and the catalyst dissociation constant and solubility. Some of the alkoxysilanes exhibit intramolecular catalysis. Hydrogen bonding plays an important role in the enhancement of the hydrolysis reaction, as well as the dipole moment of the alkoxysilanes, especially in acetonitrile. There is a relationship between the experimentally calculated polarity by the Taft equation and the reactivity, but it shows different responses depending on the solvent. It was found that negative and positive charges are respectively accumulated in the transition state in alkaline and acidic media. The reaction mechanisms are somewhat different from those previously suggested. Finally, it was found that enthalpy–entropy compensation (EEC) effect and isokinetic relationships (IKR) are exhibited during the hydrolysis of CTES in different solvents and catalysts; therefore, the reaction has a linear free energy relationship (LFER).

Acid-Catalyzed Hydration of Prop-2-en-1-ol and 2-Methylprop-2-en-1-ol: Correlation of Reactivity

1989 ◽  
Vol 42 (8) ◽  
pp. 1345 ◽  
Author(s):  
KP Herlihy
Keyword(s):  
Activation Parameters ◽  
Relative Reactivity ◽  
Nucleophilic Attack ◽  
Alternative Mechanism ◽  
Catalysed Reaction ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Kinetics Of

The kinetics of the acid-catalysed reaction of prop-2-en-1-ol and 2-methylprop-2-en-1-ol have been measured. The relative reactivity, solvent isotope ( kH+/kD +) and change in acidity effects, and activation parameters, have been determined and found to be similar to those of other alkenes. While this correlation of results for the hydration of both these alkenols can be interpreted in terms of the conventional Ad-E2 mechanism, computed values for the lifetime of possible carbocation intermediates suggest that an alternative mechanism for the reaction of prop-2-en-1-ol, in which nucleophilic attack by the solvent is concerted with protonation, is feasible.

A comparison of the mechanisms of hydrolysis of benzimidates, esters, and amides in sulfuric acid media

2005 ◽  
Vol 83 (9) ◽  
pp. 1391-1399 ◽  
Author(s):  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Isotope Effects ◽  
Ester Hydrolysis ◽  
Water Molecules ◽  
Acid Media ◽  
Tetrahedral Intermediate ◽  
Amide Hydrolysis ◽  
Solvent Isotope ◽  
Reaction Media ◽  
Hydrolysis Of

The mechanisms given in textbooks for both ester and amide hydrolysis in acid media are in need of revision. To illustrate this, benzimidates were chosen as model compounds for oxygen protonated benzamides. In aqueous sulfuric acid media they hydrolyze either by a mechanism involving attack of two water molecules at the carbonyl carbon to give a neutral tetrahedral intermediate directly, as in ester hydrolysis, or by an SN2 attack of two water molecules at the alkyl group of the alkoxy oxygen to form the corresponding amide, or by both mechanisms, depending on the structure of the benzimidate. The major line of evidence leading to these conclusions is the behavior of the excess acidity plots resulting from the rate constants obtained for the hydrolyses as functions of acid concentration and temperature. The first of these mechanisms is in fact very similar to one found for the hydrolysis of benzamides, as inferred from: (1) similar excess acidity plot behaviour; and (2) the observed solvent isotope effects for amide hydrolysis, which are fully consistent with the involvement of two water molecules, but not with one or with three (or more). This mechanism starts out as essentially the same one as that found for ester hydrolysis under the same conditions. Differences arise because the neutral tetrahedral intermediate, formed directly as a result of the protonated substrate being attacked by two water molecules (not one), possesses an easily protonated nitrogen in the amide and benzimidate cases, explaining both the lack of 18O exchange observed for amide hydrolysis and the irreversibility of the reaction. Protonated tetrahedral intermediates are too unstable to exist in the reaction media; in fact, protonation of an sp3 hybridized oxygen to put a full positive charge on it is extremely difficult. (This means that individual protonated alcohol or ether species are unlikely to exist in these media either.) Thus, the reaction of the intermediate going to product or exchanged reactant is a general-acid-catalyzed process for esters. For amide hydrolysis, the situation is complicated by the fact that another, different, mechanism takes over in more strongly acidic media, according to the excess acidity plots. Some possibilities for this are given.Key words: esters, amides, benzimidates, hydrolysis, excess acidity, mechanism, acid media.

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

2015 ◽  
Vol 87 (4) ◽  
pp. 341-351 ◽  
Author(s):  
Armin R. Ofial
Keyword(s):  
Free Energy ◽  
Rate Constants ◽  
The Other ◽  
Steric Effects ◽  
Linear Free Energy Relationship ◽  
Reliable Tool ◽  
Linear Free Energy ◽  
Sensitivity Parameter ◽  
Meldrum's Acids ◽  
Kinetics Of

AbstractThe linear free energy relationship log k = sN(N + E) (eq. 1), in which E is an electrophilicity, N is a nucleophilicity, and sN is a nucleophile-dependent sensitivity parameter, is a reliable tool for predicting rate constants of bimolecular electrophile-nucleophile combinations. Nucleophilicity scales that are based on eq. (1) rely on a set of structurally similar benzhydrylium ions (Ar2CH+) as reference electrophiles. As steric effects are not explicitely considered, eq. (1) cannot unrestrictedly be employed for reactions of bulky substrates. Since, on the other hand, the reactions of tritylium ions (Ar3C+) with hydride donors, alcohols, and amines were found to follow eq. (1), tritylium ions turned out to be complementary tools for probing organic reactivity. Kinetics of the reactions of Ar3C+ with π-nucleophiles (olefins), n-nucleophiles (amines, alcohols, water), hydride donors and ambident nucleophiles, such as the anions of 5-substituted Meldrum’s acids, are discussed to analyze the applicability of tritylium ions as reference electrophiles.

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