SOLVENT EFFECT ON THE ALKALINE HYDROLYSIS OF 2-THIOPHENYL-3,5-DINITROPYRIDINE
165
∗
Thecoefficientofπ parametershowsahighervalue
than α, β, indicating that the rate constant was depen-
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∗
1
1
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2
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is expected, since the transition state of the formation
of the monoanion 2 involves extensive delocalization
of the full negative charge that was consistent with
pathway a in Scheme 1. Furthermore, the coefficient
value of α, Eq. (7), indicated the presence of one charge
in the transition state of intermediate 2, pathway a in
Scheme 1. Also, the coefficient value of parameter β
gave that the more basic solvent, the more rate con-
stant is, i.e., kꢀ values are in harmony with the title
solvent basicities [43] except i-PrOH. Although it is
more basic solvent than t-BuOH, EtOH, and MeOH, it
features the lowest kꢀ value. This is presumably due to
the presence of two electrons donating methyl groups,
which decrease its HBD property, and reflecting a de-
crease in kꢀ value with respect to these two solvents.
In conclusion, these mixed solvent systems affect the
reaction by solvent–solvent interaction and selective
solvation (hydrogen bonding) of the reactant or the
intermediate anion by the water in the solvent
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