A large fraction of the dissolved amino-N in natural waters and wastewaters
is contained in amide groups, for example, in proteins. Whether this N poo
l reacts with and modifies the chemical behavior of chlorine during water d
isinfection is unclear. To investigate this issue, water-suppressed, proton
NMR spectra have been obtained for aqueous, acetylated glycine, alanine, a
nd alanylalanylalanine before and after treatment with NaOCl at near-neutra
l pH. N-Chlorination of N-acetylglycine (aceturic acid) induced cis-trans r
otation about the amide bond at ambient temperature. N-Bound Cl+ induced a
measurable downfield chemical shift in the acetyl methyl resonance in N-ace
tylglycine, partial derivative delta = 0.15 ppm (cis) and partial derivativ
e delta = 0.3 ppm (trans), and in N-acetylalanine methyl resonances, acetyl
methyl partial derivative delta = 0.3 ppm (trans) and side chain methyl pa
rtial derivative delta = 0.2 ppm. Chlorination of N-acetylalanylalanylalani
ne produced partial derivative delta values similar to N-acetylalanine. The
spectral effects were reversible, the original spectra being regenerated u
pon dechlorination with sulfite. Negligible substrate decomposition was obs
erved. Rate constants for chlorination of N-acetylalanine near neutral pH a
re k(f) = 1.58 x 10(-3) M-1 s(-1) and k(b) = 7.57 x 10(-7) s(-1) where K-eq
= 2.1 x 10(3). Because of both sluggish formation kinetics and an unfavora
ble equilibrium constant, N-chloramides are predicted to be unimportant und
er typical disinfection conditions.