Reaction Mechanism for Chlorination of Urea

Experiments were conducted to elucidate the mechanism of the reaction between free chlorine and urea. In combination with findings of previous investigations, the results of these experiments indicate a process by which urea undergoes multiple N-chlorination steps. The first of these steps results in the formation of N-chlorourea; this step appears to require Cl(2) to proceed and is the overall rate-limiting step in the reaction for conditions that correspond to most swimming pools. N-Chlorourea then appears to undergo further chlorine substitution; the fully N-chlorinated urea molecule is hypothesized to undergo hydrolysis and additional chlorination to yield NCl(3) as an intermediate. NCl(3) is hydrolyzed to yield NH(2)Cl and NHCl(2), with subsequent decay to stable end products, including N(2) and NO(3)(-). Conversion of urea-N to nitrate is pH-dependent The pattern of nitrate yield is believed to be attributable to the fact that when urea serves as the source of reduced-N, entry into the reactions that describe chlorination of ammoniacal nitrogen is through NCl(3), whereas when NH(3) is the source of reduced-N, entry to these reactions is through NH(2)Cl.