Salt Effects and Ion Pairs in Solvolysis and Related Reactions. XVII.<sup>1</sup>Induced Common Ion Rate Depression and the Mechanism of the Special Salt Effect<sup>2-4</sup>

The reaction of the stable thiiranium ion, prepared by the reaction of trifluoromethanesulfonic acid and methyl-3-(4-chlorophenylthio)propene with tetraethylammonium chloride in either 3.5 or 36% v/v methanol/dichloromethane with urea as a buffer, forms 2-methoxy-2-methyl-1-propyl 4-chlorophenyl sulfide, 2-chloro-2-methyl-1-propyl 4-chlorophenyl sulfide, and 1-chloro-2-methyl-2-propyl 4-chlorophenyl sulfide as products. While these same products are formed by the addition of 4-chlorobenzenesulfenyl chloride to methylpropene in the same solvents, their proportions differ. This is one of the rare examples in which there is a difference in the product composition of thiiranium ions formed in different ways and allowed to react under identical conditions. One possible explanation for this difference may be that the two thiiranium ions form products by different paths involving different kinds of ion pairs.

supporting

confidence: 61%

The products of the reaction of thiiranium ions with competing nucleophiles

Sçhmid¹,

Strukelj²,

Dalipi³

1987

“…It is clearly seen from Table 2 that increasing amounts of added NaOAc resulted in lower extents of isotopic scrambling. Similarly, from In a review on ions and ion-pairs in solvolysis reactions, Raber et al (14) have pointed out that since inorganic salts are known to be largely undissociated in glacial acetic acid (15)(16)(17), the free ions are in equilibrium with ion-pairs. Consequently, for salts with univalent cations and anions such as NaOAc, the concentration of the free ions would be proportional to the square root of the concentration of the added salt.…”

Section: Resultsmentioning

confidence: 99%

Rearrangement studies with ¹⁴C. XLVI. Isotopic scrambling studies on the acetolysis of trianisylvinyl bromide labeled with ¹³C and with ¹⁴C

Lee¹,

Obafemi²,

Quail³

et al. 1981

CHOI CHUCK LEE, CRAIG A. OBAFEMI, J. WILSON QUAIL, and ZVI RAPPOPORT. Can. J. Chem. 59,2342Chem. 59, (1981. Acetolyses of a 15mM solution of a doubly labeled trianisylvinyl substrate, 1,2-diani~yl-2-p-[~~C]methoxyphenyl[2-~~C]vin bromide (l-Br-2-'3C-2-methoxy-14C), were carried out in the presence of different amounts of added NaOAc (30-450mM) or NaOAc (30 or 300mM) and Et,. Isotopic scramblings of the 13C or 14C label from C-2 to C-1 were observed in both the reaction product and the recovered unconsumed reactant, indicating the occurrence of cycles of ionization, 1,2-anisyl shift, and return. The extent of scrambling was found to decrease with increasing concentrations of NaOAc, and a further decrease in scrambling was noted with the additional presence of Et,NBr. These findings are attributable to a competition between the 1,2-shift process and capture of the cation by the added nucleophiles. Analysis of the experimental data suggests that the nucleophilic species chiefly involved in the product-forming capture reaction is the acetate ion rather than HOAc or the NaCOAc-ion-pair. Comparisons of the scrambling data, expressed as "%rearrangement", with the assumption that 100% rearrangement corresponds to 33.3% and 50.0% scramblings of the I4C ring label and the I3C chain label, respectively, led to the conclusion that complete equilibration of the labels is achieved in that portion of the molecules that have undergone rearrangement only when the acetolyses are carried out in the presence of high concentrations of added salts. Mechanistic implications of these observations are discussed. . On a observe des melanges isotopiques des marqueurs 13C ou 14C de C-2 a C-1 dans les deux produits de reaction et dans le reactif residue1 indiquant ainsi I'existence de cycles d'ionisation, glissement anisyle-1,2 puis retour a I'etat initial. On a trouve que le taux de melange diminue quand les concentrations en AcONa augmentent et on a note que le melange diminue encore d'avantange lorsque Et,NBr est egalement present. Ces observations sont attribuables a une competition entre le glissement-1.2 et la capture d'un cation par les nucleophiles ajoutes. L'analyse des donnees experimentales suggtre que I'ion acetate plutbt que AcOH ou la paire d'ions Na+AcO-est le nucleophile impliquk principalement dans le compose provenant de la reaction de capture. En comparant les donnees de melange exprimes en "% de transposition" en partant du fait qu'une transposition a 100% correspond a des melanges respectifs de 33,3% et de 50,0% du14C du cycle et du I3C de la chaine conduit a conclure qu'il s'etablit un equilibre complet entre les marqueurs dans cette position des molecules qui se transposent uniquement lors de I'acetolyse en presence de fortes concentrations de sels. On discute Cgalement des implications mkcanistiques de ces observations.[Traduit par le journal]

“…No clear answers have been provided either by those who proposed or by those who have adopted this working hypothesis (27,28,(30)(31)(32). In the absence of such elementary information it remains a convenient working hypothesis.…”

Section: Discussionmentioning

confidence: 99%

Sulfonyl Chloride Kinetics. Part II. Solvolysis of a Series of Benzenesulfonyl Chlorides: An Unexpected Heat Capacity Variation

Robertson¹,

Rossal²

1971

First order rate constants for the solvolysis of a series of 4-X-benzenesulfonyl chlorides (where X = MeO, Me, Br, and NOz) were measured by the conductance method in HzO over the approximate temperature range of 0 to 25". Pseudothermodynamic parameters, AG*, AH*, AS*, and ACp* were derived and the high accuracy of the rate constants enabled an estimation of dACp*/dT.A trigonal bipyramidal transition state is favored for the nucleophilic attack which is probably by an SN2 type mechanism. A novel explanation for the effect of 4-methoxy on ACp* involves a temperature dependent water-solute interaction, which has general applicability to the behavior of 4-methoxy substituents.On a mesurd, par la methode de la conductivite, dans I'eau et a des temperatures entre 0 et 25 "C, les constantes de vitesse du premier ordre pour la solvolyse d'une sirie de chlorures de benzenesulfonyles substituis en position 4. On en a dtrive les parametres pseudothermodynamiques AG*, AH*, AS*, et ACp* et grlce a la grande precision des mesures, on a pu estimer la valeur de dAC,*/dT.On favorise un etat de transition trigonal et bipyramidal pour I'attaque nucleophile qui est probablement un mecanisme SN2. Une nouvelle explication pour l'effet du groupement methoxy en position 4 sur ACp* implique une interaction entre l'eau et le solute qui serait dependante de la temperature; cette explication serait d'application generale chaque fois que des substituants methoxyle en position 4 seraient impliqub.