The oxidation of 5-O-caffeoylquinic acid (5-CQA) was investigated in the temperature range from 161 to 188 °C. The kinetic experiments were carried out in small batch reactors made of glass, where a very thin (1.1 μm) fixed bed of powder 5-CQA was in contact with air at approximately 91.4 kPa. Aqueous 5-CQA solutions were prepared with the solid found in the reactors at different reaction times and used to measure the decrease of 5-CQA concentrations with a spectrophotometer operated at 323 nm. A shrinking core model was applied to describe the non-catalytic heterogeneous reaction between 5-CQA and oxygen. It basically assumes mass transfer of O2 from bulk air to the outer surface of nonporous particles of solid 5-CQA, where an irreversible reaction with no formation of solid products takes place. The proposed model correctly reproduced the obtained kinetic results in all the investigated operating conditions when an exponential reduction of external area of solid with reaction time was taken into account. Arrhenius-type expressions successfully described the dependence of the calculated global reaction and shrinking rate constants on temperature. An activation energy close to 77046 J mol−1 was found for the slow combustion reaction of 5-CQA.
Feng, R, Lu, Y, Bowman, LL, Qian, Y, Castranova, V, Ding, M (2005) J Biol Chem280:27888–27895.