Effect of bromide ions on the UV/H2O2 oxidation of alanine in aqueous solutions

Abstract

This study revealed that Br- had a shielding effect on the α-hydrogen in alanine when it was reacted with OH. The reaction pathways involving OH and alanine were quite different with or without Br-. Decarboxylation and the production of acetic acid from alanine occurred when Br- was present. The main reaction pathway in this system involved the removal of H from the amino groups in alanines by OH, which increased the contribution ratio of this reaction pathway to 70%. In the absence of Br-, OH-mediated removal of a H from the α-carbons in alanine was the dominant reaction pathway and contributed to 86% of the total removed H. In this system, high levels of pyruvic acid and significant degradation of alanine were observed. In experiments involving laser flash photolysis under acidic conditions and in the presence of Br-, transient absorption signals with an absorption range of 260–360nm were produced by H2NĊ(CH3)COO- and HṄCH(CH3)COO-, respectively. The second-order rate constants for the OH-induced H removal from the α-carbons and amino groups in alanine were determined to be (8.9±0.4)×107M−1s−1 and (4.3±0.3)×109M−1s−1, respectively. The second-order rate constants for the reaction between H2O2 and H2NĊ(CH3)COO- or HṄCH(CH3)COO- were also determined. The products produced by the reaction contained double bond between carbon and nitrogen (HNC(CH3)COO- and HNCHCH3) had absorption wavelengths ranging from 260 to 320nm. These results will provide guidance for water treatment plants using advanced oxidation technologies.