Abstract
The kinetics of hydrolysis of urea has been studied in 0.5 to 3.0 mol dm(-3) sodium hydroxide solution at different temperatures. Urea hydrolysis follows an in eversible first order consecutive reaction path:
urea (-NH3)-->(k1obs) vyanate (k2obs)--> NH3 + CO2
The variation of k(1obs) with [alkali] is linear at [OH-] = 5.0 to 1.5 mol dm(-3), thereafter a sharp increase in the reaction rate is observed for first step hydrolysis of urea. The second step rate constant (k(2obs)) is found to be independent of [alkali]. Hydrolysis of urea in alkaline medium follows an elemination-addition mechanism. The reaction does not proceed through the formation and decomposition of tetrahedral intermediate. Sodium cyanate hydrolysis obeys an irreversible pseudo-first order kinetics, [OH-] has no significant effect on the rate constants. The following rate equations have been derived for the two step hydrolysis of urea.
k(1obs) = k(0) + k(1)[OH-](k(4) + k(3)[OH-])/k(-1) + k(4) + k(3)[OH-]
k(2obs) = k(2)K(h)
On the basis of observed data, probable mechanisms have been proposed.