Kinetics and Mechanism of Hydrolysis of Tri-2,4,6-Tribromothiophenyl Phosphate via Conjugate Acid species.

Abstract

Hydrolysis of tri–2,4,6–tribromothiophenyl phophate has been made in acid region (0.1–7.0 mol dm^–3 HCl) at 98ºC in 30% aqueous dioxan (v/v) mixtures. Acid log rate profile has a rate maximum at 2.0 mol dm^–3. In general di- and tri-aryl phosphate have been found to give such maxima in the strong acid region. The lowering in rates after 2.0 mol dm^–3 may be due to the negative effect of ionic strength and water activity i.e. reduction in concentration of water which brings about bi-molecular hydrolysis. Ionic strength data up to 3.0 μ requires the participation of conjugate acid species and to determine theoretical rates. Theoretical rates, estimated from second empirical terms of Debye-Hückel equation, have been found in close agreement with the observed rates. Bi-molecular behaviour has been decided by the Arrhenius parameters and by the analysis of molecularity data. The triester involves P–S bond rupture which is strengthened by comparative kinetic data.