
%0 Journal Article
%A Brasch, NE 
%A Buckingham, DA 
%A Clark, CR 
%T Nucleophilic Catalysis by HPO<sub>4</sub><sup>2-</sup> in the Hydrolysis of Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup>. Formation and Decay of HO<sub>3</sub>POCrO<sub>3</sub><sup>2-</sup>
%J Australian Journal of Chemistry
%D 1994/12/01
%V 47
%N 12
%P 2283-2289
%K 
%R https://doi.org/10.1071/CH9942283
%U https://www.publish.csiro.au/paper/CH9942283 
%X The initial reaction of Cr2O72- in phosphate buffer (pH 6.03-8.54, 25.0&#176;C, I = 1.0 M NaClO4) follows the rate law kobs = kK [HPO42]/(1+K[HPO42-]). This is interpreted as arising from the reversible and rapid formation of a chromium(VI)- phosphato intermediate of increased coordination number (K = 5.5±1.3M-1), and rate-determining loss of CrO42- from this species (k = 4.4±0.5 s-1) to give HO3POCrO32- ( pKc a= 6.96). This appears to be the first clear demonstration of an addition-elimination (stepwise) mechanism for substitution at chromium (VI). Subsequent equilibration of HO3POCrO32- to give HCrO4- and H2PO4- (K = 5.95±1.90 M-1) is seen as a separate process which is subject to specific H+ and OH-, and general base (HPO42-) catalysis, in addition to a spontaneous reaction. 
