Structure and Property of Hydroperoxide in Solution

Abstract

Structure and property of hydroperoxide in solution were studied in connection with the epoxidation of olefins. The pKa values of n-, sec- and tert-butyl hydroperoxide and that of benzyl-, ethylbenzene- and cumene-hydroperoxide were measured by UV spectrophotometric method and the pKa values were plotted against Taft polar substituent constants. A linear relation was obtained and ρ^* value was +4.1 for the aliphatic series, but the line for aromatic series was different from that for aliphatic series even though having almost the same slope. In the case of aromatic hydroperoxides, intramolecular π-H bonding between peroxy H and π-electron of aromatic ring was observed by IR spectrum and the fact well explains why a different line from that of aliphatic series is obtained. The abilities of association and solvation of six hydroperoxides examined in this study were evaluated in terms of the shift of νOH and the relation with pKa is discussed. Equilibrium constants of the dimeric association and the intra molecular. π-H bonding of hydroperoxide is also estimated. The rates of epoxidation of 1-octene by the six hydroperoxides were measured in the presence of a solvent-soluble molybdenum catalyst and a possible configuration of the transition state complex is suggested.