Solvent dependence of diacyl peroxide decomposition kinetics under high pressure

The effect of molecular surrounding on the decomposition kinetics of bis(3,5,5-trimethylhexanoyl) peroxide (BTMBP), dioctanoyl peroxide (DOP) and dibenzoyl peroxide (BPO) has been gauged by measurements in various solvents using time-resolved FTIR spectroscopy. Two complementary on-line methods, one discontinuous the other continuous, were used to study decomposition rates at pressures up to 3 kbar and temperatures up to 155 degrees C. The decomposition of BTMHP, the prime diacyl peroxide of this study, has been monitored in nine solvents. In going from n-pentadecane to acetonitrile the rate increases by a factor of 7 at 80 degrees C and 1500 bar. Both the Kirkwood function and the empirical solvent parameter E-T(N) correlate very well the observed rate of decay. The activation energy of BTMHP decomposition in dichloromethane differs in going from low to high temperatures, whereas a single Arrhenius line is observed in n-heptane. The solvent influence on BTMHP and DOP decomposition is very similar, and distinctly different to that for BPO. The kinetic results for BTMHP and DOP from polarity, viscosity, pressure and temperature variation are not in conflict with two-bond homolysis, although this mechanism can not be proven.