Non-metal redox reactions of chloramines with bromide ion and with bromine and the development and testing of a mixing cell for a new pulsed-accelerated-flow spectrophotometer with position-resolved observation

Michael Gazda, Purdue University

Abstract

The reactions of NH$\sb2$Cl, NHCl$\sb2$, and NCl$\sb3$ with bromide ion have been examined (pH 0-7, 0.50 M ionic strength, 25.0$\sp\circ$C). The rate determining step in each case is a Cl$\sp{+}$-transfer from the chloramine to Br$\sp{-}$ to give BrCl, which rapidly equilibrates to HOBr, Br$\sp2$, and Br$\sb3\sp{-}$. These initial products are shown to brominate the chloramines to give the mixed haloamines NHBrCl, NBrCl$\sb2$, and NBr$\sb2$Cl. Relative reactivities at pH from pH 5-7 are NH$\sb2$Cl $>$ $>$ NHCl$\sb2$ $>$ NCl$\sb3$ for the reactions with Br$\sp{-}$ and NH$\sb2$Cl $>$ NHCl$\sb2$ for the reactions with HOBr and Br$\sb2$. Kinetic and UV-vis data are presented to characterize the bromochloramines; NHBrCl is identified by membrane introduction mass spectrometry. These compounds have maximum UV absorption bands at 220 nm (NHBrCl), 228 nm (NBrCl$\sb2$), and 241 nm (NBr$\sb2$Cl). The bromochloramines can also react with bromide ion by both Cl$\sp{+}$- and Br$\sp{+}$-transfer mechanisms with some reversibility. The results presented here are significant both in the area of non-metal redox chemistry and in water treatment chemistry, where bromide ion and chloramines can both be present. A new pulsed-accelerated-flow spectrophotometer with position-resolved observation (PAF-PRO) has been constructed in the Margerum lab. Details of the design and characterization of the ball-type mixing/observation cell are given for the PAF-PRO instrument. In this mixer, two solutions meet in a narrow channel built around a spherical surface. A turbulent wake develops behind the sphere as the solutions pass around the sphere. The narrow channel provides high localized solution velocities, while the spherical geometry creates a zone of high turbulence, thus providing efficient mixing in short periods of time.

Degree

Ph.D.

Advisors

Margerum, Purdue University.

Subject Area

Analytical chemistry|Chemistry

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