Salt Effects and Ion Pairs in Solvolysis and Related Reactions. VI. Additional Examples of Special Salt Effects in Acetolysis¹

Perchlorate catalysis of the methanolysis of triphenylmethyl chloride in benzene solution and its relation to special salt effects in solvolysis reactions

“…The catalyzed reaction was found to have a kinetic order of one half with respect to the tetra-nbutylammonium perchlorate catalyst, which was interpreted to mean that the catalysis was brought about by single perchlorate ions. On the basis of this result the authors re-interpreted the perchlorate catalysis observed by Winstein and co-workers (10)(11)(12)(13)(14) on the solvolyses of several alkyl sulfonates in acetic acid solvent, as being due to simple perchlorate ions at low concentration and ion-pairs at higher concentration. Winstein prefers to explain this catalysis as an interaction involving the perchlorate ion-pair alone and has carried out a kinetic analysis to prove this (15).…”

“…In contrast to these, the plots in Fig. 6 are straight lines for substrates trans-2-p-anisylcyclopentyl p-bromobenzenesulfonate, trans-2-p-anisylcyclohexyl pbromobenzenesulfonate, and erythro-3-p-anisyl-2-butyl p-bromobenzenesulfonate (13). The slopes of the log-log plots are 0.74,0.82, and 0.56 respectively.…”

Kinetic evidence for the importance of solvent-separated ion pairs during the solvolyses of adamantylideneadamantyl derivatives

“…Therefore, the effect of ionic strength on the rate constant for solvolysis of 1-I was measured in the presence of the common ion ([NaI] = 0.02 mol/L) and these measured rate constants are catalogued in Table S3. 2 Fig. 2 is the kinetic data for solvolysis of 1-I (60:40 v/v, EtOH-H 2 O) measured in the presence and absence of the common ion.…”

“…In 1956, Winstein reported that addition of LiClO 4 to the solvolytic reactions of several structurally diverse arylsulfonates resulted in a nonlinear correlation between the rate constant for acetolysis and the ionic strength of the solution (1)(2)(3)(4). These observations were rationalized within the mechanism shown in Scheme 1.…”

“…In this scheme, a simplified version of Winstein's ion-pair mechanism (5-7), two separate carbenium ion intermediates are incorporated: (i) the solvent-separated ion pair (SSIP); and (ii) the solventequilibrated ion (SEI). Furthermore, the observed nonlinearity is a consequence of SSIP trapping by the added perchlorate with the result that "external" ion-pair return is prevented (1,2).…”