Reactions of ozone with Br(-), SO(3)(2-), HSO(3)(-), I(-), and NO(2)(-), studied by stopped-flow and pulsed-accelerated-flow techniques, are first order in the concentration of O(3)(aq) and first order in the concentration of each anion. The rate constants increase by a factor of 5 x 10(6) as the nucleophilicities of the anions increase from Br(-) to SO(3)(2-). Ozone adducts with the nucleophiles are proposed as steady-state intermediates prior to oxygen atom transfer with release of O(2). Ab initio calculations show possible structures for the intermediates. The reaction between Br(-) and O(3) is accelerated by H(+) but exhibits a kinetic saturation effect as the acidity increases. The kinetics indicate formation of BrOOO(-) as a steady-state intermediate with an acid-assisted step to give BrOH and O(2). Temperature dependencies of the reactions of Br(-) and HSO(3)(-) with O(3) in acidic solutions are determined from 1 to 25 degrees C. These kinetics are important in studies of annual ozone depletion in the Arctic troposphere at polar sunrise.

Bromine chloride in the presence of chloride ion forms the dichlorobromate(1) ion, BrClz-, where K1 = [BrClz-]/ ([BrCl(aq)][Cl-1) = 6.0 M-I. Equilibrium constants (all at 25.0 "C, p = 1.00 M) are also determined for KZ = [Br2Cl-]/([BrCl(aq)][Br-]) = 1.8 x lo4 M-', for K3 = [Br2Cl-]/([Brz(aq)][Cl-]) = 1.3 M-' and for K4 = [Br3-]/ [Brz(aq)][Br-] = 16.1 M-'. UV absorption bands are resolved for BrC12-at 232 nm ( E 32 700 M-l cm-') and 343 nm ( E 312 M-' cm-'), for BrzC1-at 245 nm ( E 24 900 M-' cm-') and 381 nm (6 288 M-' cm-l), and for Br3-at 266 nm ( E 40 900 M-' cm-l). The W spectral properties of Clz(aq), CIS-, Brz(aq), and Br-are examined and compared. The reaction between Cl~(aq) and Br-to form BrC12-occurs at the diffusion-controlled limit; the rate constant, (7.7 f 1.3) x lo9 M-' s-', is measured by the pulsed-accelerated-flow method. The rapid formation of BrClz-can be used as an analytical method for trace bromide ion, where as little as mol % Br-can be detected in aqueous solutions of HCl or chloride salts.

ascribe the difference in reaction enthalpies to a bonding interaction more favorable in CuT than in H[CuT] compared with the change in overall bonding between Cu(EDTA)2' and H [Cu-(EDTA)]". This might result from a reorientation of metal-ligand bonds in the CuT species resulting in either release of strain or more effective metal-ligand interaction. Some internal reorientation is consistent with the more negative AS0 value for H [CuT] acidic dissociation compared with that for H[Cu(EDTA)]'. Both processes restrict internal motion by binding a carboxylate group, but this restriction seems larger in the case of H[CuT]. AS°for the acidic dissociation reactions consists of contributions from several processes: (1) solvent ordering around H+, common to both reactions; (2) increased secondary solvation around the copper complexes, a process that provides a larger negative contribution to H[Cu(EDTA)]" dissociation than to H[CuT] dissociation; (3) positive contributions due to solvent release from the sixth copper coordination; (4) loss of internal freedom. Of these factors the last might account for the more negative AS°value observed for H[CuT] dissociation. That is, differences in solvent binding at the sixth copper coordination site might result in a relatively more negative contribution to AS°for H[CuT] dissociation. However, the sixth coordination position on Cu2+ is known to be only weakly solvated so that differences between weakly solvated sites are not likely to provide for the observed result. Consequently, it appears possible that some distortion of Cu2+ ligation occurs upon CuT formation. This proposition seems supported by the X-ray crystallographic data, which indicate an unusually large trigonal distortion in CuT in which the locus of nitrogen atoms is twisted away from the carboxylate locus by about 30°from the idealized octahedral orientation. A large trigonal distortion of this kind would certainly influence the ligand field near Cu2+ and might profoundly effect the magnitude of the ligand field, thus accounting for the unusual difference between spectral properties of H[CuT] and CuT. As a final comparison we note that Xmax = 660 nm2c for aqueous Cu[9]aneN32+, which we presume exists as a hexacoordinate species. Unfortunately, no crystallographic data is available for this complex. Nevertheless it seems unlikely that large trigonal distortions would be present and that the similar Xmax values of H[CuT] and Cu[9]aneN3(H20)32+ reflect approximately octahedral coordination. Thus, it appears that the large displacement of Xmax from 660 nm for H[GuT] to a value near 750 nm for CuT results from a substantial distortion of the ligand field in CuT, which we connect with a release of strain interactions in H[CuT], The importance of these interactions is consistent with thermodynamic, X-ray crystallographic, and spectral evidence.

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Rate constants of the forward reaction for the reversible hydrolysis of Cl2(aq) at µ = 0.50 M increase from 1.9 s™* 1 at 0.0 °C to 30.5 s™1 at 30.0 °C. The activation parameters at 15.0 °C are AH* = 63 ± 3 kJ mol™1 and AS* = -8 ± 4 J mol™1 K™1 for the forward reaction and AH* = 27 ± 1 kJ mol™1 and AS* = -71 ± 9 J mol™1 K™1 for the reverse reaction. The ® values at µ = 0.50 M decrease markedly with increase in temperature (ACP = -537 ± 7 J mol™1 deg™1), and therefore the AH* and AS* values are not constant over a range of temperatures. The equilibrium constant, K = ([HOCl][H+][Cl™])/[Cl2(aq)], equals 1.04 X 10™3 M2 at 25.0 °C, µ = 0.50 M. The K value depends on the ionic strength as well as the temperature. In the reversible hydrolysis reaction, general bases (A™) assist the hydrolysis rate (the Bronsted ß value is 0.58 ± 0.06) and general acids (HA) assist the reverse reaction (the Brensted a value is 0.40 ± 0.05): Cl2 + H20 + A™ <=* HOC1 + Cl™ + HA (fc2/fc_2).