MECHANISM OF HYDROLYSIS OF (Z)- AND (E)-O-METHYLBENZOHYDROXIMOYL CHLORIDE

The first-order rate constants for the hydrolysis (1:3 dioxane-water, pH = 7) of (E)-O-methylbenzohydroximoyl chloride [C6H5C(Cl)NOCH3, 1Ea] and several 4-substituted derivatives have been measured. A Hammett plot of these rate constants vs σ+ gave a ρ value of −1.4. Molecular orbital calculations (AM1) have been carried out on (Z)-O-methylbenzohydroximoyl chloride (1Za), a hydrazonyl chloride [C6H5C(Cl)NNHCH3], and the corresponding nitrilium ions [C6H5C⋮NOCH3+ and C6H5C⋮NNHCH3+] in an attempt to gain insight into the differences in the reactivities of these two systems. A study of the effect of solvent composition on the rates of hydrolysis of (Z)- and (E)-O-methyl-4-methoxybenzohydroximoyl chloride (1Zb and 1Eb) has been carried out using dioxane/water solutions of various compositions. The Grunwald−Winstein m values were determined to be 1.1 and 0.95 for the Z and E isomers, respectively. The activation parameters for the hydrolysis of 1Zb and 1Eb are as follows:  ΔH‡ = 34 kcal/mol and ΔS⧧ = +2 eu (1Z...