Issue 23, 2000
From the journal:

Journal of the Chemical Society, Dalton Transactions

Bromination of phenol red mediated by vanadium(V) peroxo complexes at pH 6.5

Roxana M. Tótaro,ab   Patricia A. M. Williams,c   María C. Apella,*ab   Miguel A. Blesade  and  Enrique J. Baranc  

* Corresponding authors

a Centro de Referencia para Lactobacilos (CERELA-CONICET), Chacabuco 145, San Miguel de Tucumán, Argentina
E-mail: mapella@cerela.org.ar

b Universidad Nacional de Tucumán, Miguel Lillo 205, San Miguel de Tucumán, Argentina

c Centro de Química Inorgánica (CEQUINOR-CONICET,UNLP), Facultad de Ciencias Exactas, UNLP, C. Correo 962, La Plata, Argentina

d Unidad de Actividad Química, Comisión Nacional de Energía Atómica, Avenida del Libertador 8250, Buenos Aires, Argentina

e Escuela de Posgrado, Universidad Nacional de San Martín, Avenida General Paz y Constituyentes (Iado Provincia), Buenos Aires, Argentina

Abstract

The kinetics of bromination of phenol red (HPhR) to yield bromophenol blue (BrPhB) was studied at pH 6.5, in the presence of peroxovanadium(V) species generated by acid decomposition of [VO(O2)2(NH3)]− and of [O{VO(O2)2}2]4−. In the concentration ranges 10−6–10−7 (HPhR), (1.5–8.0) × 10−4 (vanadium complexes) and 0.004–0.12 mol dm−3 (bromide), the rate law is R = k[V]T [Br−][HS], where HS is the substrate undergoing bromination in the rate determining step, with k = 2.49 × 105 dm6 mol−2 s−1. Acid treatment of the precursor complexes yields a mixture of [VO(O2)L]n complexes, with L = H2O, [VO(O2)(H2O)]+, or O22−, [VO(O2)2]−. Alkalinization leads to active species that react with bromide to yield a brominated vanadium complex (e.g. [VO(O2)Br]), which is postulated to be the active bromination agent. Kinetic data rule out the mediation of hypobromous acid. The results support the idea that five-co-ordinated vanadium species are required in the bromination reaction.

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Article information

DOI
https://doi.org/10.1039/B005733I
Article type
Paper
Submitted
17 Jul 2000
Accepted
09 Oct 2000
First published
16 Nov 2000

J. Chem. Soc., Dalton Trans., 2000, 4403-4406

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Bromination of phenol red mediated by vanadium(V) peroxo complexes at pH 6.5

R. M. Tótaro, P. A. M. Williams, M. C. Apella, M. A. Blesa and E. J. Baran, J. Chem. Soc., Dalton Trans., 2000, 4403 DOI: 10.1039/B005733I

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