Salt Effects and Ion Pairs in Solvolysis and Related Reactions. V. Special Salt Effect in Acetolysis of 2-Anisylethyl p-Toluenesulfonates

1956 ◽  
Vol 78 (12) ◽  
pp. 2767-2770 ◽  
Author(s):  
Arnold H. Fainberg ◽  
S. Winstein
Keyword(s):  
1989 ◽  
Vol 67 (2) ◽  
pp. 297-304
Author(s):  
Allan R. Stein

No, or at most very small, salt effects have been detected for second-order racemizations of various 1-phenylbromoethanes, confirming that the "mixed kinetics", previously reported for 4-methyl- and 3,4-dimethylphenylbromoethanes with tetrabutylammonium bromide in acetonitrile and nitromethane, did not reflect a salt effect on a unimolecular reaction. Thus the uni- and bimolecular rate components can be evaluated using the equation:[Formula: see text]where k1 = first-order or unimolecular rate constant, the intercept, and [Formula: see text], the latter being the rate constant for the bimolecular substitution. A "special salt effect" was found for the unimolecular component; it was especially pronounced for 3,4-dimethyl substrate in acetonitrile with Bu4NClO4 as the electrolyte. In acetone, where no unimolecular reaction component was detected even with those substrates giving the most stable carbocations, the only salt effect was a common ion, Bu4N+, effect on the incomplete dissociation of Bu4NBr. From an iterative best fit for plots of observed rate versus calculated bromide ion activity for unsubstituted, 4-methyl, and 3,4-dimethyl substrates, Kassoc ~ 15 ± 1 at 40 °C. The results are interpreted as additional support for a progression of mechanism with nucleophilic attack possible at any stage of the series of equilibria: substrate [Formula: see text] contact ion pair [Formula: see text] various solvated ion pairs [Formula: see text] dissociated ions. Keywords: special salt effects, ionic strength effects, racemization of 1-phenylbromoethanes, mechanism of nucleophilic substitution, ion pair mechanism.


2007 ◽  
Vol 32 (2) ◽  
pp. 73-118 ◽  
Author(s):  
Genrih F. Dvorko ◽  
Engelsine A. Ponomareva ◽  
Mykola E. Ponomarev ◽  
Mikhailo V. Stambirsky

Data on the influence of neutral salts on the rates of unimolecular heterolyses of organic substrates, obtained mainly by the verdazyl method, are summarized here. It is assumed that heterolysis takes place with consecutive formation of four ion pairs: contact (CIP), cavity-separated (CSIP), one solvent moleculeseparated (SIP) and solvent-separated (SSIP). [Formula: see text] In the limiting step, the CIP interacts with a solvent cavity and the CSIP is formed, which converts quickly into the SIP and subsequently to the SSIP, which also quickly gives the reaction products. In the transition state, bonds between the molecules solvating the CIP are broken. In the absence of salt, the return from external ion pairs does not have much importance. The verdazyl indicator quickly and quantitatively reacts with the SSIP. The normal salt effect takes place due to the action of salt on the covalent substrate, which catalyses CIP formation. The special salt effect is caused by the association of the salt with the CIP, which prolongs the lifetime of the intermediate and increases the probability of its contact with a solvent cavity. The negative special salt effect is caused by association of the salt with the SIP or SSIP, which prolongs the lifetime of the intermediates and increases the probability of their contact with a solvent cavity to return to the covalent substrate. When the salt reacts with the SIP, the salt effect does not depend on the concentration and nature of verdazyl, but such a dependence takes place when the salt reacts with the SSIP. The site of the action of the salt is determined by the Hard and Soft Acids and Bases (HSAB) principle.


1986 ◽  
Vol 51 (12) ◽  
pp. 2781-2785 ◽  
Author(s):  
M. Martín Herrera ◽  
J. J. Maraver Puig ◽  
F. Sánchez Burgos

A study is made on the kinetic salt effect on the reaction of hydrolysis of several charged esters in alkaline media. The results are interpreted on the basis of the coulombic interaction, the salting in of hydroxide ion and a third component depending on size of the substrate.


RSC Advances ◽  
2015 ◽  
Vol 5 (47) ◽  
pp. 37697-37702 ◽  
Author(s):  
Liuyi Yin ◽  
Yufeng Hu ◽  
Xianming Zhang ◽  
Jianguang Qi ◽  
Weiting Ma

The salt effects and the mechanisms that govern such effects on the sulfuric acid catalyzed synthesis of trioxane are reported.


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