M. Buback et al., Pressure and temperature dependence of the decomposition rate of tert-butyl peroxyacetate and of tert-butyl peroxypivalate, Z PHYS CHEM, 210, 1999, pp. 199-221
Citations number
29
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS
The thermal decomposition of tert-butyl peroxyacetate (TBPA) and of tert-t-
butyl peroxy-pivalate (TBPP) in n-heptane solution has been measured up to
2500 bar at temperatures between 120 and 190 degrees C for TBPA and from 11
0 to 145 degrees C for TBPP. Three experimental procedures, two discontinuo
us and one continuous, have been applied. The data from these independent t
echniques are in excellent agreement. The first-order decomposition rate co
efficient, k(obs) at identical p and T is significantly higher for TBPP tha
n for TBPA. The activation energies at 2000 bar are 125.4 +/- 3.9 kJ mol(-1
) and 150.4 +/- 1.7 kJ mol(-1) for TBPP and TBPA, respectively. Significant
differences are also seen in activation volume: Delta V-obs(not equal) of
TBPP decomposition is rather small (3.0 +/- 0.9 cm(3) mol(-1)) and independ
ent of pressure whereas the activation volume of TBPA is relatively large a
nd clearly depends on pressure. Delta V-obs(not equal), (TBPA) at 1000 bar
is close to 18 cm(3) mol(-1). The origin of these differences is discussed.
The experimental material supports the view that TBPA and TBPP are the arc
hetypes of thermal peroxyester decomposition via single-bond and via concer
ted two-bond scission, respectively. Arrhenius-type expressions are present
ed for the pressure range 100 to 2500 bar. They allow to estimate k(obs) of
TBPA between 120 and 190 degrees C and k(obs) of TBPP between 70 and 145 d
egrees C.