Chlorination and monochloramination of 3-aminophenol: kinetics and formation of first by-products

Abstract

<div><p>Aminophenols (AP) are synthetic intermediates in pharmaceutical, photographic and chemical dye industry. They can be released into the environment from wastewater and can react during water treatment processes. Therefore, it was interesting to study the oxidation of AP with chlorine and monochloramine in aqueous solution. In particular, the chlorination and monochloramination of 3-aminophenol (3AP) were investigated, and the formation of first by-products and kinetic rates were determined. The chlorination rate was 3.6 × 10⁵ times greater than the monochloramination rate at pH 8.6. Two reaction pathways can explain the variation of the monochloramination apparent rate constant with pH. The first one was an electrophilic substitution of Cl⁺ on the aromatic ring of the non-ionized 3AP, leading to the formation of chloroaminophenol, with an individual rate constant of 6.7 × 10² M⁻¹ h⁻¹. The second reaction pathway was a monochloramine attack on the amino group of 3AP catalyzed at acidic pH with an individual rate constant of 9.2 × 10⁹ × M⁻² × h⁻¹.</p></div