The hydrolysis of monodecyl phosphate (C
12MAP) Na and K salts at various degrees of neutralization (DN) in 5.0 wt% aqueous solution was studied by analysis of dodecyl alcohol formed by hydrolysis of C
12 MAP. The hydrolysis rate followed a first-order kinetics and the rate constants (
kobs) showed Λ-shape dependence on DN (Fig.-2) and the maximum
kobs were found at DN=1.08. The extrapolated
kobs at DN=0.18 was zero. Under highly alkaline conditions (at DN=4.0) hydrolysis did not occur. In the pH-DN profile in aqueous solution, there were three equivalent points at DN=0.5, 1.0 and 2.0, indicating MAP to have three dissociation equilibria (Scheme-3,
pK1=2.45,
pK2=5.60,
pK3=7.80) including bimolecular aggregates (
A0,
A1). The Arrhenius activation energy was
Ea-29.7 kcal/mol and did not depend on DN. This value is essentially the same as that for monomethyl phosphate (
Ea=30.6 kcal/mol).
A possible hydrolysis mechanism is proposed and discussed based on the obtained results.
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