(621ap) Catalytic Oxidation of Kraft Lignin to Chemicals with Substituted N-Hydroxyphthalimide

Keywords:
lignin, oxidation, dicarboxylic
acid, N-hydroxylphthalimide, oxygen

Lignin
as the second most abundant natural biopolymers is well-known for the
difficulty to convert it into value-added chemicals. Most of the researches on
lignin were focused on converting it into liquid hydrocarbons and aromatics via
the thermal depolymerization and subsequent selective
hydrodeoxygenation. However many of the valuable bulk
chemicals are small oxygenate molecules such as aldehydes, diols,
and carboxylic acids. Thus recently the catalytic conversion of lignin into
valuable oxygenates under relatively mild conditions has attracted great
attention. Catalytic oxidation of lignin is one of the most promising way to produce monophenols¹, dicarboxylic
acids², and
aromatic aldehydes³.
However most of these catalytic oxidation processes used the expensive hydrogen
peroxide as the oxidant. It is known that the oxidation occurred in a radical
reaction pathway.² The
activation of oxygen and generation of peroxide radical could be critical for
lignin oxidation. N-hydroxylphthalimide(NHPI) is known to generate phthalimide-N-Oxyl (PINO) and catalyzes the oxidation of liquid
hydrocarbons with oxygen.

In
this work, the lignin oxidation using oxygen as oxidant catalyzed by various
substituted NHPI and certain transition metal cations
were studied. A series of bifunctional metal ion-NHPI
oxidation catalysts were designed and prepared. The synergy effect of the
substituted NHPI and transition metal cations were
examined as well as the effect of solvent, reaction temperature, the ratio of
NHPI to the transition metal cation. The structure
activity relationship between the properties of
metallic ion, spatial proximity of both active centers and the catalytic
activity and selectivity of the catalyst were carefully examined.

References

1.     
Ouyang, X.-p.; Tan, Y.-d.; Qiu, X.-q., Oxidative degradation
of lignin for producing monophenolic compounds. Journal
of Fuel Chemistry and Technology 2014, 42 (6), 677-682.

2.     
Ma, R.; Guo, M.; Zhang, X., Selective Conversion of Biorefinery
Lignin into Dicarboxylic Acids. ChemSusChem
2014, 7 (2), 412-415.

3.     
Zhang, J.; Deng, H.; Lin, L., Wet Aerobic Oxidation of Lignin into Aromatic
Aldehydes Catalysed by a Perovskite-type Oxide: LaFe1-xCuxO3 (x=0, 0.1, 0.2). Molecules
2009, 14 (8), 2747-2757.