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The kinetics of the hydrolysis of p-nitrophenyl esters of straight chain carboxylic acidswith various chain lengths,viz.,acetate (C2),octanoate (C8) dodecanoate (C12) and hexadecanoate(C16) was investigated in ten aquiorgano binary solvent systems.In the Φ=0.50 (50% v/v) sol-vent mixtures,aggregation and coiling-up of C 16 occur only in HOCH_2CH_2OH-H_2O and Me_2SO-H_2O,in which k_(C8)/k_(C16)1,whereas the hydrolytic behaviors of C 16 and C 8 are similar inall other solvents.But at Φ=0.30,C 16 aggregates and coils-up in all solvent mixtures except thet-BuOH-H_2O system.If the k_(C8)/k_(C16),values in the Φ=0.30 media are taken as an arbitrarystandard,the order of decreasing hydrophobic-lipophilic interactions between the solvent and sub-strate molecules for the various solvents are as follows:HOCH_2CH_2OH>Me_2SO>CH_3OCH_2-CH_2OH>DMF～CH_3OCH_2CH_2OCH_3>dioxane>ethanol～acetone～acetonitrile>t-BuOH.When k_(C8)/k_(C16)1,there is a large difference in the activation parameters betweenC 16 and its shorter counterparts.No simple correlation can be found between log (k_(C8)/k_(C16))and various solvent polarity parameters,but log (k_(C8)/k_(C16)) correlates with Rekker’s hydrophobicfragmental constants (f) of the organic components of these solvent systems (r=0.976),indicatingthat the major factor which controls the hydrolysis of long-chain esters here is the hydrophobic-lipophilic interactions.Apparently,this is the first example of an application of Rekker’s f con-stants to a correlation between solvent property and chemical reactivity in terms of rate constants.
The kinetics of the hydrolysis of p-nitrophenyl esters of straight chain carboxylic acids with various chain lengths, viz., Acetate (C2), octanoate (C8) dodecanoate (C12) and hexadecanoate (C16) was investigated in ten aquiorgano binary solvent systems. the Φ = 0.50 (50% v / v) sol-vent mixtures, aggregation and coiling-up of C 16 occur only in HOCH_2CH_2OH-H_2O and Me_2SO-H_2O, in which k_ (C8) / k_ (C16) The hydrolytic behaviors of C 16 and C 8 are similar in all other solvents.But at φ = 0.30, C 16 aggregates and coils-up in all solvent mixtures except the t-BuOH-H 2 O system.If the k_ (C8) / k_ (C16) , values in the Φ = 0.30 media are taken as an arbitrarystandard, the order of decreasing hydrophobic-lipophilic interactions between the solvent and sub-strate molecules for the various solvents are as follows: HOCH_2CH_2OH> Me_2SO> CH_3OCH_2-CH_2OH> DMF ~ CH_3OCH_2CH_2OCH_3> dioxane> ethanol ~ acetone ~ acetonitrile> t-BuOH.When k_ (C8) / k_ (C16) 1, there is a large difference in the activation parameters betwe enC 16 and its shorter counterparts.No simple correlation can be found between log (k_ (C8) / k_ (C16)) and various solvent polarity parameters, but log (k_ (C8) / k_ (C16)) correlates with Rekker’s hydrophobic structural constants (f) of the organic components of these solvent systems (r = 0.976), indicating that the major factor which controls the hydrolysis of long-chain ester here is the hydrophobic-lipophilic interactions. Apparently, this is the first example of an application of Rekker’s f con-stants to a correlation between solvent property and chemical reactivity in terms of rate constants.