Tellurium(V). A pulse radiolysis study

Four different tellurium(V) oxoradicals, assumed to be H2TeO4-, TeO3-, HTeo (4)(2-), and TeO43-, were detected by the pulse radiolysis technique. H2TeO 4- is the product of the reaction of OH with HTeO3-, whereas HTeo(4)(2-) an d TeO43- arise by reactions of OH and O- with the TeO32-. TeO3- is a second ary product formed by dehydration of H2TeO4-, a process catalyzed by HTeO3- . The same tellurium(V) species except H2TeO4- are formed by reaction of th e hydrated electron with H6TeO6, HSTeO6-, and H4TeO62-. The spectra, kineti cs of the reactions of the tellurium(V) species, the acidity constant of HT eO42- (similar to 10(-13)), and the apparent acidity constant of TeO3- (10( -10)) have been measured. The standard Gibbs energies of formation Delta (f )G(ao)degrees (TeO3-) = -214 kJ/mol, Delta (f)G(ao)degrees (HTeO42-) = -394 kJ/mol, and Delta (f)G(ao)degrees (TeO43-) = -319 kJ/mol were determined f rom the rate constants for the forward and reverse reactions TeO32- + O- re versible arrow Teo(4)(3-) and TeO32- + OH reversible arrow HTeO42-, combine d with the acidity constants of TeO3- and HTeO42- and the standard Gibbs en ergy of formation of OH, O-, and TeO32-. TeO3- is a strong reducing agent ( E-o(red) = -0.40 V), which appears to reduce O-2, as well as a strong oxida nt (E-o(ox) = 1.74 V), oxidizing CO32- to CO3-.