Related Experiment Video
Updated: Feb 27, 2026

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
Published on: April 10, 2015
Oxidation of Bromide to Bromine by Ruthenium(II) Bipyridine-Type Complexes Using the Flash-Quench Technique
Kelvin Yun-Da Tsai1, I-Jy Chang1
1Department of Chemistry, National Taiwan Normal University , 88 Tingchow Road, Section 4, Taipei 11677 Taiwan.
Abstract:
Six ruthenium complexes, [Ru(bpy)3]2+ (1), [Ru(bpy)2(deeb)]2+ (2), [Ru(deeb)2(dmbpy)]2+ (3), [Ru(deeb)2(bpy)]2+ (4), [Ru(deeb)3]2+ (5), and [Ru(deeb)2(bpz)] 2+ (6) (bpy: 2,2'-bipyridine; deeb: 4,4'-diethylester-2,2'-bipyridine; dmbpy: 4,4'-dimethyl-2,2'-bipyridine, bpz: 2,2'-bipyrazine), have been employed to sensitize photochemical oxidation of bromide to bromine. The oxidation potential for complexes 1-6 are 1.26, 1.36, 1.42, 1.46, 1.56, and 1.66 V vs SCE, respectively. The bimolecular rate constants for the quenching of complexes 1-6 by ArN2+ (bromobenzenediazonium) are determined as 1.1 × 109, 1.6 × 108, 1.4 × 108, 1.2 × 108, 6.4 × 107, and 8.9 × 106 M-1 s-1, respectively. Transient kinetics indicated that Br- reacted with photogenerated Ru(III) species at different rates. Bimolecular rate constants for the oxidation of Br- by the Ru(III) species derived from complexes 1-5 are observed as 1.2 × 108, 1.3 × 109, 4.0 × 109, 4.8 × 109, and 1.1 × 1010, M-1 s-1, respectively. The last reaction kinetics observed in the three-component system consisting of a Ru sensitizer, quencher, and bromide is shown to be independent of the Ru sensitizer. The final product was identified as bromine by its reaction with hexene. The last reaction kinetics is assigned to the disproportionation reaction of Br2-• ions, for which the rate constant is determined as 5 × 109 M-1 s-1. Though complex 6 has the highest oxidation potential in the Ru(II)/Ru(III) couple, its excited state fails to react with ArN2+ sufficiently for subsequent reactions. The Ru(III) species derived from complex 1 reacts with Br- at the slowest rate. Complexes 2-5 are excellent photosensitizers to drive photooxidation of bromide to bromine.
More Related Videos
Related Concept Videos
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
Radical Substitution: Allylic Bromination
Regioselectivity of Electrophilic Additions-Peroxide Effect
Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.

