Kinetics and mechanism of alkaline hydrolysis of urea and sodium cyanate

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 irreversible first order consecutive reaction path:<br> <img src='http://www.niscair.res.in/jinfo/equation53.gif' border=0><br>The variation of <i>k</i>_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 (<i>k</i>_2obs) is found to be independent of [alkali]. Hydrolysis of urea in alkaline medium follows an elimination-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.<br><img src='http://www.niscair.res.in/jinfo/equation54.gif' border=0><br> On the basis of observed data, probable mechanisms have been proposed.<br>