Development and validation of a second generation pulsed-accelerated-flow spectrophotometer and investigation of the kinetics and mechanism of the reaction of sulfite with hypochlorite and hypochlorous acid in basic solution

Kimber D Fogelman, Purdue University

Abstract

A second generation pulsed-accelerated-flow spectrophotometer (PAF IV) has been fabricated and calibrated against the known rates of reaction of Fe(CIO$\sb4$)$\sb2$ with IrCl$\sb6\sp{2-}$ in 0.5 M HClO$\sb4$ at 25.0$\sp\circ$ C. New features of the PAF IV instrument include extension of observation into the UV region (200-350 nm), a microprocessor based position controller, and a new interface to IBM compatible XT and AT class computers. Pulsed-accelerated-flow spectroscopy is used in the ultraviolet region to measure pseudo-first-order rate constants in the range of 5000 s$\sp{-1}$ to 107,000 s$\sp{-1}$ for the reactions of excess SO$\sb3\sp{2-}$ with HOCl and OCl$\sp{-}$ in the presence of HCO$\sb3\sp{-}$/CO$\sb3\sp{2-}$ buffer. The rate constant for the reaction of HOCl and SO$\sb3\sp{2-}$ is so large (7.6 $\times$ 10$\sp8$ M$\sp{-1}$ s$\sp{-1}$, 25.0$\sp\circ$ C, $\mu$ = 0.5) that the rate of proton transfer from water or from HCO$\sb3\sp{-}$ to OCl$\sp{-}$ can limit the reaction velocity. A mechanism with Cl$\sp{+}$ transfer to sulfur is proposed via a reactive intermediate, HOClSO$\sb3\sp{-}$, that decomposes by itself or with HCO$\sb3\sp{2-}$ assistance to form ClSO$\sb3\sp{-}$. The subsequent hydrolysis of ClSO$\sb3\sp{-}$ to give Cl$\sp{-}$ and SO$\sb4\sp{2-}$ is slow by comparison (270 s$\sp{-1}$). The contribution of the HOCl path is small only above 0.05 M OH$\sp-$, where the rate becomes base independent due to the reaction between OCl$\sp-$ and SO$\sb3\sp{2-}$ (2.3 $\times$ 10$\sp4$ M$\sp{-1}$ s$\sp{-1}$, 25.0 $\sp\circ$C, $\mu$ = 0.5). This reaction may proceed by oxygen atom transfer; the rate constant is a factor of 3.3 $\times$ 10$\sp4$ smaller than the Cl$\sp+$ transfer rate constant for HOCl and SO$\sb3\sp{2-}$.

Degree

Ph.D.

Advisors

Margerum, Purdue University.

Subject Area

Analytical chemistry|Chemistry|Biochemistry

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