DIARYLBIS(ACYLAMINO)SPIRO-LAMBDA(4)-SULFANES AND CYCLIC ACYLAMINOSULFONIUM SALTS - A KINETIC-STUDY OF EQUILIBRIUM AND HYDROLYSIS REACTIONS

Kinetics for the hydrolysis of diarylbis(acylamino)spiro-lambda(4)-sul fanes 3a-e and 9 and precursor acylaminosulfonium salts 5a-e and 8 bot h leading to sulfoxides 6a-e and 10, respectively, have been studied u nder pseudo-first-order conditions in dioxane-water mixtures. Medium, substituent (rho(+)-0.44) and solvent isotope effects (k(H2O)/k(D2O)ap proximate to 2) Indicate that the cleavage of one of the S-N bonds and a simultaneous proton-transfer from H2O to the leaving carbamoyl grou p take place in the rate-determining step of the hydrolysis of spiro-l ambda(4)-sulfanes 3a-e. The acylaminosulfonium and OH-ion intermediate s formed together are converted to sulfoxides 6a-e in fast steps. The hydrolysis of acylaminosulfonium salts shows deviation from first-orde r kinetics at the starting period of the reaction, which may be ascrib ed to an equilibrium formation of spiro-lambda(4)-sulfanes. The equili brium between 3a and 5a has been studied by spectroscopic methods, and K-35 5 x 10(-7) mol dm(-3) was obtained in 70:30 (v/v) dioxane-water, at 25 degrees C. The equilibrium is shifted towards the acylaminosulf onium salts as the acidity of the solvent increases with the progress of the hydrolysis, or when acid is added to the mixture. In the case o f hydrolysis of 5a-e and 8 the medium, substituent and deuterium solve nt isotope effects (k(H2O)/K(D2O)approximate to 4.3) as well as the ge neral base catalytic effect of acetate ions suggest that a nucleophili c attack of water on the sulfonium centre occurs in the rate-determini ng step with the cleavage of one of the OH bonds in water and with the formation of a hydroxy(acylamino)-lambda(4)-sulfane. Acylaminosulfoni um salt 12, having a Sterically hindered reaction centre, undergoes hy drolysis only with-more nucleophilic OH-ions. Relative reactivities an d different ring-size effects observed for bis(acyloxy)-, (acyloxy)(ac ylamino)-and bis(acylamino)-spiro-lambda(4)-sulfanes and cyclic acylam inosulfonium salts are compared and interpreted.