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

This study revealed that Br- had a shielding effect on the alpha-hydrogen in alanine when it was reacted with (OH)-O-center dot. The reaction pathways involving (OH)-O-center dot 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)-O-center dot, which increased the contribution ratio of this reaction pathway to 70%. In the absence of Br, (OH)-O-center dot-mediated removal of a H from the alpha-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 BC, transient absorption signals with an absorption range of 260-360 nm were produced by H2NC(CH3)COO- and HNCH(CH3)COO-, respectively. The second-order rate constants for the (OH)-O-center dot-induced H removal from the alpha-carbons and amino groups in alanine were determined to be (8.9 +/- 0.4) x 10(7) M-1 s(-1) and (4.3 +/- 0.3) x 109 M-1 s(-1), respectively. The second-order rate constants for the reaction between H2O2 and H2NC(CH3)COO- or H&CH(CH3)COO- were also determined. The products produced by the reaction contained double bond between carbon and nitrogen (HN=C(CH3)-COO- and HN=CH-CH3) had absorption wavelengths ranging from 260 to 320 nm. These results will provide guidance for water treatment plants using advanced oxidation technologies. (C) 2015 Elsevier B.V. All rights reserved.