Abstract
The specific rates of solvolysis of 2-butyn-1-yl-chloroformate (1) and 2-methoxyphenyl chloroformate (2) are studied at 25.0 °C in a series of binary aqueousorganic mixtures. The rates of reaction obtained are then analyzed using the extended Grunwald-Winstein (G-W) equation and the results are compared to previously published G-W analyses for phenyl chloroformate (3), propargyl chloroformate (4), p-methoxyphenyl choroformate (5), and p-nitrophenyl chloroformate (6). For 1, the results indicate that dual side-by-side addition-elimination and ionization pathways are occurring in some highly ionizing solvents due to the presence of the electron-donating γ-methyl group. For 2, the analyses indicate that the dominant mechanism is a bimolecular one where the formation of a tetrahedral intermediate is rate-determining.
Highlights
Introduction γMethyl-β-alkynyl and mono substituted phenyl chloroformate esters such as 2-butyn-1-ylchloroformate (1) and 2-methoxyphenyl chloroformate (2) shown in Figure 1, have found use in the preparation of symmetrical urea’s that have patented herbicidal control applications [1,2] against certain weeds, fungi, and bacteria
To commemorate the sixtieth anniversary of the original Grunwald-Winstein equation (Equation 1) [9] we documented [12] the utility of these G-W Linear free energy relationships (LFERs) (Equations 1 and 2) in the analysis of a variety of organic compounds including a collection of chloroformate esters
In the Grunwald-Winstein Equations 1 and 2, k and ko are the specific rates of solvolysis of a substrate in a given solvent and in the standard solvent (80% ethanol), respectively, m represents the sensitivity to changes in the solvent ionizing power YX [13,14,15,16,17], l is the sensitivity to changes in solvent nucleophilicity NT [18,19,20], and c is a constant term
Summary
Introduction γMethyl-β-alkynyl and mono substituted phenyl chloroformate esters such as 2-butyn-1-ylchloroformate (1) and 2-methoxyphenyl chloroformate (2) shown in Figure 1, have found use in the preparation of symmetrical urea’s that have patented herbicidal control applications [1,2] against certain weeds, fungi, and bacteria. Linear free energy relationships (LFERs) [6,7,8] such as the Grunwald-Winstein (G-W) equations (Equations 1 and 2) [9,10] are often used to correlate [11,12] the specific rates of solvolysis of organic substrates to the solvent ionizing power [13,14,15,16,17] and solvent nucleophilicity values [18,19,20].
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