Reinvestigation of the activation volume for the base hydrolysis reaction of trans-dichloro [(RSSR)-1,4,8,11-tetraazacyclotetradecane] cobalt(III) cation

The title reaction velocity was studied at 10-40°C under high pressure (up to 200 MPa) using a high-pressure stopped flow apparatus. The resultant activation volume (20-16 cm³ mol^-1) depends on the reaction temperature. It increases with increasing temperature up to 15°C and then decreases with increasing temperature. The latter decrease is consistent with the concept of the mechanistic changeover at high temperature of the title reaction from the rate-determining chloride liberation to the rate-determining conjugate base formation of the reactant complex.