Formation of cyanogen chloride from the reaction of monochloramine with formaldehyde

Citation
Ej. Pedersen et al., Formation of cyanogen chloride from the reaction of monochloramine with formaldehyde, ENV SCI TEC, 33(23), 1999, pp. 4239-4249
Citations number
38
Categorie Soggetti
Environment/Ecology,"Environmental Engineering & Energy
Journal title
ENVIRONMENTAL SCIENCE & TECHNOLOGY
ISSN journal
0013936X → ACNP
Volume
33
Issue
23
Year of publication
1999
Pages
4239 - 4249
Database
ISI
SICI code
0013-936X(199912)33:23<4239:FOCCFT>2.0.ZU;2-G
Abstract
Methanediol dehydrates to give formaldehyde, which reacts rapidly and rever sibly with monochloramine to form N-chloroaminomethanol. Under drinking wat er conditions, N-chloroaminomethanol undergoes a relatively slow decomposit ion that eventually leads to the formation of cyanogen chloride (CICN) in a pparently stoichiometric amounts. The following reaction sequence is propos ed: CH2(OH)(2) reversible arrow CH2O + H2O; CH2O + NH2Cl reversible arrow C H2(OH)NHCl; CH2(OH)NHCl - CH2NCl + H2O; CH2NCl --> HCl + HCN; CN- + NH2Cl H+ --> ClCN + NH3. These reactions were studied at 25.0 degrees C and an i onic strength of 0.10 M (NaClO4). Stopped-flow photometry was used to monit or rapid, reversible reactions, and photometry was used to study relatively slow decomposition reactions. Equilibrium and rate constants for the addit ion of formaldehyde to manochloramine were (6.6 +/- 1.5) x 10(5) M-1 and (2 .8 +/- 0.1) x 10(4) M-1 s(-1), respectively. The dehydration of N-chloroami nomethanol was catalyzed by both H+ and OH-, with respective rate constants of 277 +/- 7 and 26.9 +/- 5.6 M-1 s(-1). Under characteristic drinking wat er conditions, the decay of N-chloroaminomethanol is the rate-limiting step . N-Chloromethanimine, formed by the dehydration of N-chloroaminomethanol, had a decomposition rate constant of (6.65 +/- 0.06) x 10(-4) s(-1). At the relatively high methanediol concentrations used in this study, the interme diary N-chlorodimethanolamine was formed by the rapid and reversible reacti on of N-chloroaminomethanol with formaldehyde. N-Chlorodimethanolamine then decayed relatively slowly. The following reaction sequence is proposed: CH 2(OH)NHCl + CH2O reversible arrow {CH2(OH)}(2)NCl; {CH2(OH)}(2)NCl --> CH2N Cl + CH2O + H2O. The equilibrium and rate constants for the addition of for maldehyde to N-chloroaminomethanol were (9.5 +/- 2.5) x 10(4) M-1 and (3.6 +/- 0.1) x 10(3) M-1 s-', respectively. The decomposition of N-chlorodimeth anolamine was catalyzed by OH-, with a rate constant of 19.2 +/- 3.7 M-1 s( -1). N-Chlorodimethanolamine would not be present under typical drinking wa ter treatment conditions.