Detailed analysis for the solvolysis of isopropenyl chloroformate

Abstract

The specific rates of solvolysis (including those obtained from the literature) of isopropenyl chloroformate (1) are analyzed using the extended Grunwald-Winstein equation, involving the NT scale of solvent nucleophilicity (S-methyldibenzothiophenium ion) combined with a YCl scale based on 1-adamantyl chloride solvolysis. A similarity model approach, using phenyl chloroformate solvolyses for comparison, indicated a dominant bimolecular carbonyl-addition mechanism for the solvolyses of 1 in all solvents except 97% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). An extensive evaluation of the outcomes acquired through the application of the extended Grunwald-Winstein equation resulted in the proposal of an addition-elimination mechanism dominating in most of the solvents, but in 97-70% HFIP, and 97% 2,2,2-trifluoroethanol (TFE), it is proposed that a superimposed unimolecular (SN1) type ionization is making a significant contribution.

Kinetic Studies that Evaluate the Solvolytic Mechanisms of Allyl and Vinyl Chloroformate Esters

“…The ethanolyses rate of isopropenyl chloroformate (2) at 25.0 °C was reported to be (110 ± 6) × 10 −5 [57]. A comparison of this pure EtOH data point together with the other values listed in Table 1 show, k 4 > k 2 >> k 1 > k 5 ≈ k 3 .…”

“…On the other hand for the alkenyl containing isopropenyl chloroformate ( 2 ), it was proposed [57] that a superimposed unimolecular (S N 1) type ionization process was making a significant contribution in 97%–70% HFIP, and 97% TFE due to the formation of a resonance stabilized intermediate carbocation.…”

“…For 2 in 97% HFIP and 97% TFE at 25.0 °C, values of 3.23 × 10 −7 and 5.94 × 10 −7 are computed from the rates that we reported at different temperatures [57] and the Arrhenius equation. An examination of these calculated rates for 2 together with the rates for 1, 3, and 5 (listed in Table 1) in the highly ionizing and very strongly hydrogen bonding 97% HFIP ( Y Cl value of 5.17), we get k 5 > k 3 > k 2 >> k 1 .…”

“…Isopropenyl chloroformate ( 2 ) was the first alkenyl chloroformate to be exhaustively analyzed using Equation (2) in 51 solvents [57]. A bimolecular tetrahedral addition-elimination pathway was the predominant reaction mechanism observed, and a superimposed ionization pathway was shown to make a significant contribution in the four 97%–70% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and 97% 2,2,2-trifluoroethanol (TFE) mixtures with water.…”

Correlation of the rates of solvolysis of α-bromoisobutyrophenone using both simple and extended forms of the Grunwald-Winstein equation and the application of correlation analysis to related studies

“…The extended Grunwald-Winstein equation [3-6], which has been found to be very useful in its application to the specific rates of solvolysis of a wide variety of substrates, such as phosphorus compounds [34], silicon compounds [35], acid chlorides [36], chloroformate esters [37], chlorothioformate esters [38], and heterocyclic compounds [39], is here applied to the solvolyses of tertiary alpha-substituted ketones, some of which have, contrary to earlier opinions summarized elsewhere [12], been found to be capable of forming carbocations with the charge formally adjacent to the carbonyl group under solvolytic conditions [10-12]. …”