Mechanism of triarylchloroallene solvolysis

Abstract

A detailed study of the solvolysis of triarylchloroallenes is reported. The rate of disappearance of haloallene was found to equal the rate of appearance of HC1. An increase in solvent polarity results in a marked increase in the rate constant for solvolysis. The m value for triphenylchloroallene in aqueous acetone solutions is found to be 0.69 ± 0.06. No change in rate is observed with a 1250-fold excess of triethylamine added. Addition of 0.10 M LiCl results in a 29 % rate depression while the addition of 0.10 M LiBr results in a slight rate enhancement. The exclusive product of solvolysis of triphenylchloroallene is 1,1,3-triphenylprop-2-yn-l -ol. Substituent effect data yield p = -2.0 against +. The temperature dependence of the rate yields AH* = 20.2 kcal mol-1 and AS* = -10.7 eu. These data are interpreted in terms of a unimolecular reaction proceeding via a chargedelocalized allenyl cation.

The Rubrenic Synthesis: The Delicate Equilibrium between Tetracene and Cyclobutene

“…[8] The solvolysis (at room temp.) of chloro-triphenylallene occurs by the formation of a carbocation, which is stabilized by resonance and affords either the enone or the starting propargyl alcohol, [18] but the formation of cyclobutenes or acenes has never been reported under solvolytic conditions. A clearer picture of the mechanism was available only after the reactions of chloroand polyphenylallenes had been thoroughly studied.…”

Steric factors in the solvolysis of haloallenes

“…l-(terf-Butylchlorovinylidene)-2,2-dimethylindan (2) was prepared according to the general procedure for the preparation of chloroallenes by Jacobs and Fenton.7 After three successive distillations from a small amount of sodium borohydride to remove unreacted alcohol, the desired chloroallene was obtained in 23% yield: bp 96-100°at 0.3 mm; ir (neat) 1945 cm-1 (C= C=C); nmr (CC14) S 1.22 (s, 9), 1.29 (s, 6), 2.86 (s, 2), 7.08 (m, 4).…”

“…In connection with current studies of transition metal complexes of strained cyclic olefins, we required a supply of benzocyclobutene. The preparations of benzocyclobutene (2) previously reported in the literature are inconvenient for large-scale synthesis. Hydrogenation of 1,2-diiodobenzocycl obutene with palladium on carbon3 requires a specially aged sodium ethoxide catalyst and involves lengthy purifications.…”

“…2 and tri(n-butyl)tin halide (which can be reduced to the hydride), only a limited amount of tri(n-butyl)tin chloride is needed. Thus this route is convenient for a large-scale synthesis since the reaction is carried out in one reaction vessel with no special apparatus required, the course of the reaction is readily monitored by nmr spectroscopy, and the purification procedures are straightforward.…”

Vinylic cations from solvolysis. XX. Ion pairs and free ions in the solvolysis and isomerization of 1,2-dianisyl-2-phenylvinyl halides and mesylates. Use of cis-trans isomerization as a mechanistic tool

“…Sion ~kt -Siaom = S7iaom + &8iaom (11) Table IV summarizes three first-order isomerization runs, where k ¡som values are based on the observed ("equilibrium") infinities. At these high Brconcentrations 106 kt = 4 sec-1, and k \on values were calculated by eq 11.…”