1785-43-9Relevant academic research and scientific papers
Chemical Reactions Mediated by Heavy Metal Ions. 2. Mercury Ligation Effects on the Hg(II)-Promoted Hydrolyses of Benzaldehyde O-Ethyl S-Ethyl and S-Phenyl Acetals
Jensen, James L.,Maynard, David F.,Shaw, Gregory R.,Smith, Tyrrell W.
, p. 1982 - 1986 (2007/10/02)
The kinetics of the mercury(II)-promoted hydrolyses of acyclic O,S-acetals of benzaldehyde have been measured to establish that (i) mercury(II) is a reagent, not a catalyst, in the hydrolysis reaction, (ii) the rate-limiting step can be any of the three steps in Scheme I (khemi, kHg, or kacetal), depending on the concentration of mercury(II) relative to the acid, and (iii) the state of complexation of mercury(II) is critical to its reactivity.Part 1 of this series established the "standard state" for all further work; this paper utilized the same controls and safeguards.The second-order rate constants for hydrolysis of benzaldehyde O-ethyl S-ethyl acetal promoted by Hg2+, HgCl+, HgBr+, or HgI+ is at the diffusion limit (109 M-1 s-1).Rate constants for HgCl2, HgBr2, HgI2, HgCl3-, and HgI3- are 106, 105, 102, 104, and 50 M-1 s-1, respectively.Rate constants for hydrolysis of benzaldehyde O-ethyl S-phenyl acetal are the same, within experimental error, except for perhaps the least reactive reagents.Thus, although reagents differ in reactivity by 107, the reactivity toward a SEt moiety is equal to the reactivity toward a SPh moiety.A detailed mechanism is presented in which the rate-limiting step does not involve carbon-sulfur bond heterolysis, but rather one of the mercury ligation steps.
