An investigation of the oxidation mechanism of abietic acid using two-dimensional infrared correlation spectroscopy

• A novel self-designed gas–solid reactor was used to conducted the oxidation of abietic acid, monitored by FT-IR spectroscopy.
• Molecular mechanism of abietic acid oxidation process in the nature environment was investigated.
• 2D-IR was shown as a suitable measurement to study reaction mechanism and was firstly applied to analyze mechanism of abietic acid oxidation process.

The oxidation behavior of abietic acid was monitored by FT-IR and UV spectroscopy, using a novel, self-designed, gas–solid reactor, and the data was analyzed by 2D-IR. The hetero-spectral two-dimensional correlation of the FTIR data allowed the use of well-established band assignments to interpret less clearly assigned spectral features. Characteristic changes in the conjugated bond and the active methylene in abietic acid were revealed, and a mechanism was proposed. We concluded that the methylene at C7 was first transformed to a hydroxyl, thereby inducing the isomerization of the conjugated band. Meanwhile, the methylene at C12 was converted by an oxygen atom to a hydroxyl intermediate. Hydrogen continued to react with oxygen to form CO and water. Finally, the conjugated band was converted into a peroxide before transforming into an oxidant.