Kinetics of a Diels-Alder reaction of maleic anhydride and isoprene in supercritical CO2

The kinetics of the reaction of maleic anhydride and isoprene in supercriti cal carbon dioxide was studied over an extended concentration range, from 5 x 10(-5) to 1.3 x 10(-2) mote fractions of both maleic anhydride and isopr ene at 60 degreesC and pressure 100 atm. The apparent rate constant of the reaction was found to be concentration dependent, in contradiction with the literature data. The results are interpreted in terms of limited solubilit y of maleic anhydride in supercritical CO2. The solubility of maleic anhydr ide in supercritical carbon dioxide was directly measured by sampling and a nalyzing the supercritical phase. The observed sharp increase in the appare nt rate constant of the reaction between maleic anhydride and isoprene corr elates with the solubility of maleic anhydride in supercritical carbon diox ide. The interpretation was confirmed using visual observations of the phas e behavior. The rate constant of the reaction measured under the true super critical, single phase, conditions is k(x) = (17.0 +/- 1.3) hr(-1) (mole fr action units, 60 degreesC, pressure 100 atm).