Mechanism Of Solvolysis Research Articles

Effects of para-substituents on the mechanisms of solvolysis of styrene oxides

Rate and product studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of styrene oxide and its p-CH 3 O-, p-CH 3 -, p-Cl-, and p-O 2 N-derivatives in water solutions have been carried out. A Hammett correlation of log κ for the acid-catalyzed reactions vs σ + gives a slope p + of -4.2 and only diol products are formed. An intermediate in the hydronium ion-catalyzed hydrolysis of p-methoxystyrene oxide is trapped, subsequent to its rate-limiting formation, by azide ion

Contact ion pairs. Picosecond dynamics of solvent separation, internal return, and special salt effect

Direct observation by time-resolved picosecond spectroscopy of the contact ion pair (CIP) allows the microdynamical rate constants for its (a) annihilation by internal return, (b) relaxation to the solvent-separated ion pair (SSIP), and (c) ionic exchange in the special salt effect to be quantitatively evaluated for the solvolysis mechanism (Scheme I) originally formulated by Winstein and co-workers. The relevant contact ion pair [Ar + ,T - ] is spontaneously generated by the 20-ps laser pulse excitation of the EDA complex from tetranitromethane (TNO 2 ) and anthracene (Ar)

Theoretical and experimental study on the reaction mechanism of photolysis and solvolysis of arylvinyl halides

The reaction mechanisms of solvolysis and photolysis of arylvinyl halides have been studied in terms of ab initio molecular orbital calculations and experiments. The frontier orbital of the p-methoxyphenylvinyl cation requires that nucleophiles attack not only the vinylic carbon but also the ipso position of the p-methoxy group. The experimental results also show the possibility of a mechanism proceeding via the ipso intermediate. The solvolysis affords exclusively the vinyl type products because of the instability of the ipso intermediate. On the other hand, some of the ipso intermediate does not decompose to produce the vinyl cation under the mild conditions of photolysis. Substitution of the p-methoxy group in the anisyl fragment occurs in cases where the nucleophile has the ability to form a bond comparable with or stronger than the original C–O bond.

Solvent effects on the solvolysis of α-t-butylbenzyl tosylate

The solvolysis rates of α-t-butylbenzyl tosylate resulted in a single straight-line correlation with unit slope against 2-adamantyl Y OTs value. The result is compatible with k c solvolysis mechanism without nucleophilic solvent and/or β-methyl participation.

Ion‐Neutral complexes from protonated propyl phenyl ethers. Gas‐phase solvolysis versus elimination‐readdition

AbstractIon‐neutral complexes, well attested as intermediates in the expulsion of alkenes from M+⋅ and MH+ ions from primary alkyl phenyl ethers, are shown to intervene in the decomposition of the MH+ ion of a secondary alkyl phenyl ether, (CD3)2CHOPh. Chemical ionization (CI) (methane reagent gas)‐mass‐analysed ion kinetic energy spectroscopy (MIKES) shows ions of both m/z 96 and 97, indicating that the proton deposited by the CI reagent exchanges with the methyl deuterium atoms. The ratio of daughter ion intensities, as well as the proportions of ions of m/z 95, 96 and 97 from the MH+ of CD3CH2CD2OPh, agree with predictions based on the gas‐phase solvolysis mechanism, in which [i‐Pr+ PhOH] complexes form from the protonated parent via simple bond heterolysis. An alternative mechanism, elimination‐readdition, would proceed via [propene PhOHD+] complexes. This latter mechanism predicts a ratio of daughter ion intensities that is very different from gas‐phase solvolysis and which disagrees with experiment. The elimination‐readdition pathway is effectively ruled out, while the gas‐phase solvolysis mechanism is reinforced.

Geminal systems. 50. Solvolysis of 1-tosyloxy-?2-1,2,3-triazoline-5,5-dicarboxylate esters and the structure of the solvolysis product, O-tosyl-N-?,?-bis(ethoxycarbonyl)-?-methoxyethylhydroxylamine

Solvolysis of 1-tosyloxy-Δ2-1,2,3-triazoline-5,5-dicarboxylic acid esters (1) occurs via elimination of N2 and leads predominantly to N-β-hydroxylethyl-O-tosylhydroxylamines (II), whose structure was determined unequivocally by x-ray structural analysis. The mechanism of solvolysis of triazolines (I) is discussed, along with the structural characteristics and stabilization factors of the O-tosylhydroxylamine products (II).

THE SYNTHESIS, SOLVOLYSIS AND REARRANGEMENT OF BENZYL TRIFLUOROMETHANESULFINATES

Abstract The synthesis and reactivity of benzyl trifluoromethanesulfinates have been investigated. These esters are easily and almost quantitatively obtained by selective oxidation of the corresponding sulfenates. A study of their behavior has revealed some unique features. In sharp contrast to benzyl arenesulfinates, which undergo ethanolysis with complete sulfur-oxygen bond fission, the corresponding trifluorornethanesulfinates undergo ethanolysis with exclusive carbon-oxygen bond fission, and with a rate enhancement by a factor of 6 powers of ten. The unusual high reactivity of these esters, comparable to that of the corresponding tosylates, is discussed. A kinetic study of the solvent and substituent effects on the rate of solvolysis has been performed. Also in contrast with benzyl arenesulfinates, these esters undergo facile rearrangement to sulfone on heating in polar nonhydroxylic solvents such as acetonitrile, in high yields. The mechanisms of solvolysis and rearrangement are discussed.

Solvolysis of highly reactive phosphorus‐sulphonic anhydrides. Stereochemical and chemical arguments for phosphathiacylium cation formation

AbstractThe stereochemistry and mechanism of solvolysis of optically active tert‐butylphenylphosphinothioic‐O‐trifluoromethanesulphonate (1) in solvents of different ionizing power were studied. It was found that in solvents of high ionizing power and low nucleophilicity 1 ionizes with the formation of a phosphathiacylium cation (2) as the reaction intermediate. Product resulting from the reaction of 2 with anisole was isolated and characterized.

Kinetics and mechanism of solvolysis of N-aryl sulfuric diamides

The methanolysis and hydrolysis kinetics have been studied with the following sulfuric diamide derivatives: N-methyl-N-phenyl- (IIIa), N-methyl-N-(4-methoxycarbonylphenyl)- (IIIb), N-(4-methoxycarbonylphenyl)- (IIIc), N-methyl-N-(2-methoxycarbonylphenyl)- (IIId), N-(2-methoxycarbonylphenyl)- (IIIe), and N-methyl-N-(2,4-dibromophenyl)- (IIIf). The solvolyses of the neutral substrates IIIa and IIIb proceed by the addition-elimination mechanism. In the presence of the solvent lyate ions the solvolyses go by the E1cb mechanism. The solvolyses of the conjugated bases of compounds IIIa and IIIb are subject to general acid catalysis, the effects of the ring substituents being opposite to those in the addition-elimination mechanism. The solvolyses of compounds IIId and IIIf exhibit a distinct catalytic effect of neighbouring group; the reaction goes via a reactive intermediate, the transformation of the intermediate into the solvolysis product being subject to general acid and base catalysis.

Mechanism of solvolysis of substituted benzoyl halides

Mechanism of solvolysis of substituted benzoyl halides

Methanolyses of para-substituted benzoyl chlorides in isodielectric binary mixtures

The kinetics and mechanism of solvolysis of p-substituted benzoyl chlorides have been investigated in three isodielectric systems: methanol–acetonitrile, methanol–nitrobenzene, and methanol–nitromethane mixtures. Only SN1–SN2 processes are favoured by electron-donating substituents in all binary systems, but carbonyl addition processes become dominant in the low basicity (β) region of binary mixtures, especially in methanol–nitromethane for compounds with electron-withdrawing substituents. The rates for unsubstituted substrates as well as those substitutes with electron-withdrawing groups are higher than those for p-methyl substituted substrates, suggesting the contribution of a combined SN1–SN2 and carbonyl addition pathway, rather than the involvement of a concerted displacement with variable transition state.

ChemInform Abstract: Kinetics and Mechanism of Solvolysis of Precocene I 3,4‐Oxide (I): Change in Rate‐Determining Step and Trapping of an Intermediate in an Epoxide Solvolysis Reaction

ChemInform Abstract: Kinetics and Mechanism of Solvolysis of Precocene I 3,4‐Oxide (I): Change in Rate‐Determining Step and Trapping of an Intermediate in an Epoxide Solvolysis Reaction

Kinetics and mechanism of solvolysis of Precocene I 3,4-oxide: change in rate-determining step and trapping of an intermediate in an epoxide solvolysis reaction

Kinetics and mechanism of solvolysis of Precocene I 3,4-oxide: change in rate-determining step and trapping of an intermediate in an epoxide solvolysis reaction

Mécanisme de solvolyse des cis‐ et trans‐(p‐toluénesulfonates) d' aryl‐2‐cyclopentyle III. Etude des étapes ultérieures à I'ionisation lors de lasolvolyse du trans‐ (p‐toluènesulfonate) de phényl‐2‐cyclopentyle

Solvolysis Mechanism of cis‐and trans‐2‐Arylcycyclopentyl p‐ Toluenesulfonate. Subsequent Steps in trans‐2‐Phenylcyclopenthyl p‐Toluenesulfonate SolvolysisThe solvolysis of the 1‐deuteriated, 2‐deuteriated, and undeuteriated trans‐2‐phenylcyclopentyl p‐toluenesulfonate in HCOOH, AcOH, and EtOH has studied. We have shown that the classical secondary carbocation arising from substrate ionisation undergoes three concurent processes, namely kc (direct product formation),kip (hydrogenium bridged ion formation as tertiary carbocation or products precursor) and kΔph (phenonium‐ion formation as retained product precursor.) The kΔph process contribution increases with solvent ionising power. The kinetic iotope effect of DC(1) show, that the steps following ionisation have a preponderant effect on the total solvolysis rate.

Mécanisme de solvolyse des cis‐ et trans‐(p‐toluènesulfonates) d'aryl‐2‐cyclopentyle I. Etude de la première étape de la solvolyse: effets isotopiques de l' atone de deutérium en position 2, effets de sel basique et effet spécial de sel

Solvolysis Mechanism of cis ‐ and trans‐2‐Arylcylopentyl p‐Toluenesulfonates. The Step: 1‐Deuterium Isotope Effects, Basic Salt Effects, and Special Salt EffectWe have studied the first step of the solvolysis of cis and trans‐2‐arylcyclopentyl p‐toluenesulfonates in HCOOH, AcOH, and EtOh. All substrates show a high kinetic 1‐deuterium isotope effect (kH/kD(1) >1.15). This fact indicates that first step leads to classical intimate ion‐pair Which dissociates to a solvet‐separated ion‐pair, without participation either of solvent, the 2‐aryl group, or a H‐atom at C(2). The slight influence of added basic ions on reaction rate allows us to exclude any direct solvent attack on the covalent substrate even in the most favorable case, i.e. ethanolysis of 2‐(p‐nitrophenyl)cylopentyl‐p‐toluenesulfonates. Furthermore, solvent‐separated ion pair formation is indicated by the special salt effect induced by LiClO4.

Mécanisme de solvolyse des cis ‐ et trans‐(p‐toluénesulfonates) d'aryl1‐2‐cyclopentyle II. Etude des étapes ultérieures à l'ionisation lors de la solvolyse des cis‐(p‐toluénesulfonates) d'aryl‐2‐cyclopentyle

Solvolysis Mechanism of cis‐ and trans‐2‐Arylylopentylp‐ Toluenesulfonates, Subsequent Step in cis‐2‐Arylcyclopentyl p‐Toluenesulfonate SolvolysisThe solvolysis of a series of 1‐deuteriated, 2‐deuteriated, and undeuteriated cis‐2‐arylcyclopentyl p‐toluenesulfonates in HCOOH, AcOH, and EtOH has been studied. We have shown that classical secondary carbocation arising from substrate ionisation undergoes two concurrent processes, namely kc (direct products formation) and kip (hydrogenium bridged ion formation as tertiary carbocation or products precursor). The intrinsic properties of solvent and the aryl substitutant electronic effects the total solvolysis rate and the respective contributions of k c and k ip processes. Comparing the observed and calculated kinetic isotope of D–C(2) allows one to conclude that no step can called ‘rate‐determining step’ but that the steps following ionisation have a preponderent effect on the total solovolysis rate.

Chemical evidence in favor of a stabilized oxocarbonium-ion intermediate in the NAD + glycohydrolase-catalyzed reactions

The mechanism of the spontaneous solvolysis (hydrolysis and methanolysis) of the nicotinamide-ribose bond of NAD +, studied under unimolecular rate conditions, was compared to the mechanism of the reactions catalyzed by NAD + glycohydrolase. Experimental arguments—i.e., sensitivity of the observed solvolytic rates to the medium effects, stereochemical course of the methanolysis of α- and β-NAD +, partitioning ratio of the ADP-ribosyl intermediate, and entropy of activation—are presented, suggesting that the nonenzymatic solvolysis of β-NAD + proceeds through an enforced preassociation mechanism in which the acceptor molecules, methanol or (and) water, stabilize the developing ADP-ribosyl oxocarbonium ion generated by the bond cleavage. In aqueous solution this intermediate seems too unstable to exist as a fully developed solvent-equilibrated species. In contrast to the spontaneous solvolysis, the ADP-ribosyl intermediate generated in the active site of NAD + glycohydrolase shows a high selectivity when reacting with competing acceptor nucleophiles. This suggests that the enzyme provides a substantial stabilization of the intermediary ADP-ribosyl oxocarbonium ion. We conclude that catalysis of the nicotinamide-ribose bond cleavage by NAD + glycohydrolase would be due, in part, to the ability of the enzyme to effectively stabilize an oxocarbonium ion-like structure in the transition state.

Kinetics and mechanism of solvolysis of substituted phenyl N-phenylbenzimidoesters

Kinetics of hydrochloric acid-catalyzed solvolysis of substituted phenyl and methyl N-phenylbenzimidoesters have been studied in methanol, 50 vol. % aqueous methanol, and 50 vol. % aqueous tetrahydrofurane, and the composition of the reaction products has been determined. The rate-limiting step consists in addition of water or methanol to the protonated substrate. The reaction of methyl N-phenylbenzimidoester with both water and methanol and that of substituted phenyl N-phenylbenzimidoesters with methanol produce aniline, the ester (or orthoester) and the corresponding phenol. The reaction of substituted phenyl N-phenylbenzimidoesters with water gives both the neutral tetrahedral intermediate (which is decomposed into phenol and anilide) and the protonated intermediate (which produces aniline and the ester). At the same proton concentration the phenol content increases with increasing value of the σ constant of the substituent.

Identification of the products of solvolysis of N-benzylpyridinium cations in the absence of nucleophiles

Mono-, tri-, and penta-cyclic N-benzylpyridinium tetrafluoroborates undergo thermolysis in chlorobenzene as solvent to give products of benzylation both of the solvent and of the pyridine leaving group. Thermolysis alone, and in nitrobenzene as solvent, yielded mainly products of benzylation of the leaving group. The results support the previously postulated mechanism of unimolecular solvolysis of compounds of these types in non-polar solvents.

Kinetics of the reduction of manganese(III) porphyrins by hexaammineruthenium(II): a reductive acid solvolysis mechanism

Cinetique de reduction de plusieurs porphyrines de manganese(III) par Ru(NH 3 ) 6 2+ . Le mecanisme met en jeu un processus de demetallation et les resultats sont compares avec des reactions de transfert d'electron apparentees et des reactions de solvolyse acide