Chemical Reactions Mediated by Heavy Metal Ions. 1. The Mercury(II)-Promoted Hydrolysis of Benzaldehyde O-Ethyl S-Ethyl Acetal

Article abstract of DOI:10.1021/jo00303a013

This is a kinetic study of the hydrolysis of an acyclic O,S-acetal promoted by heavy metal ions.The acyclic structural feature is important because it precludes the potential return of the sulfur moiety at the spectral concentrations at which experiments are conducted, a possiblility which clouds some of the interpretations of earlier work.Results of this study of the hydrolysis of benzaldehyde O-ethyl S-ethyl acetal establish that (1) mercury(II) acts as a reagent, not a catalyst in the hydrolysis reaction, (2) the rate-limiting step can be either of the two steps shown in Scheme I, depending on the concentration of mercury(II) relative to the acid, and (3) the state of complexation of mercury(II) is critical to its reactivity.Experiments are reported defining the rate-limiting step under a wide variety of reaction conditions.The second-order rate constants measured for promotion of the hydrolysis by HgCl⁺, HgCl2, and HgCl3^-1 are 10⁹, 10⁶, and 10⁴ M^-1 s^-1, respectively.The second-order rate constant for the acid-catalyzed breakdown of benzaldehyde ethyl hemiacetal is 660 M^-1s^-1.