643
O 2 in acetonitrile [108]. Yuan et al. disclosed the selective oxidation of HMF catalyzed by reusable cesium-doped manganese dioxide (Cs/MnOx) catalyst with a
DFF yield of 94.7% at 98.4% HMF conversion at 373 K within 12 h under 10 bar
O 2 in N,N-dimethylformamide [112]. The higher catalytic activity of the Cs/MnOx
catalyst was explained by the higher oxidation state of Mn, stronger basicity, larger
amount of defects, larger surface area, and more abundant pores.
2.3 Amination of Furanics
Reductive amination of carbonyl compounds derived from biomass has received
great attention for the synthesis of value-added N-containing compounds, which are
important building blocks for the preparation of synthetic organic intermediates in
pharmaceuticals and agrochemicals. The reductive amination of carbonyl compounds in the presence of amine source (ammonia, primary or secondary amines)
and reducing agent (hydrogen) is one of the most suitable protocols for the synthesis
of the variety of amines. Among them, more valuable primary amines are generated
in two steps: (1) condensation of the carbonyl compound with ammonia, followed
by elimination of water to form an imine over an acid or base catalyst (although this
can also occur without a catalyst), and (2) hydrogenation of the imine to give the
final primary amine catalyzed by a hydrogenation catalyst. However, the selectivity
for primary amines in reductive amination remains difficult to control since primary
amines are more nucleophilic than ammonia and easily react with aldehydes to form
secondary amines. In addition, undesired hydrogenation of the carbonyl groups and
unsaturated bonds also limits selectivity for the corresponding primary amines.
2.3.1 Reductive Amination of Furfural
The reductive amination of FUR over metal catalysts with NH 3 in the presence of
H 2 can convert its carbonyl functionality to an amine such as furfurylamine (FAM).
FAM is one of the primary amines used to prepare drugs, fibers, and pesticides. The
reaction network proposed in the literature for the synthesis of FAM involves
(Fig. 8):
1. Hydrogenation of alcohol.
2. Reaction with ammonia resulting in the formation of reactive intermediates
(including primary imine) or react with FAM to form Schiff base-type
intermediate.
3. Hydrogenation of secondary imine to the secondary amine.
4. It can decompose to the primary amine and primary imine in the presence of
ammonia. From nitrile reduction reactions, it is known that primary imines and
primary amines can couple to form secondary imines and subsequently form
secondary/tertiary amines. A generally accepted mechanistic suggestion conEfficient Nanocomposite Catalysts for Sustainable Production of Biofuels and…
O 2 in acetonitrile [108]. Yuan et al. disclosed the selective oxidation of HMF catalyzed by reusable cesium-doped manganese dioxide (Cs/MnOx) catalyst with a
DFF yield of 94.7% at 98.4% HMF conversion at 373 K within 12 h under 10 bar
O 2 in N,N-dimethylformamide [112]. The higher catalytic activity of the Cs/MnOx
catalyst was explained by the higher oxidation state of Mn, stronger basicity, larger
amount of defects, larger surface area, and more abundant pores.
2.3 Amination of Furanics
Reductive amination of carbonyl compounds derived from biomass has received
great attention for the synthesis of value-added N-containing compounds, which are
important building blocks for the preparation of synthetic organic intermediates in
pharmaceuticals and agrochemicals. The reductive amination of carbonyl compounds in the presence of amine source (ammonia, primary or secondary amines)
and reducing agent (hydrogen) is one of the most suitable protocols for the synthesis
of the variety of amines. Among them, more valuable primary amines are generated
in two steps: (1) condensation of the carbonyl compound with ammonia, followed
by elimination of water to form an imine over an acid or base catalyst (although this
can also occur without a catalyst), and (2) hydrogenation of the imine to give the
final primary amine catalyzed by a hydrogenation catalyst. However, the selectivity
for primary amines in reductive amination remains difficult to control since primary
amines are more nucleophilic than ammonia and easily react with aldehydes to form
secondary amines. In addition, undesired hydrogenation of the carbonyl groups and
unsaturated bonds also limits selectivity for the corresponding primary amines.
2.3.1 Reductive Amination of Furfural
The reductive amination of FUR over metal catalysts with NH 3 in the presence of
H 2 can convert its carbonyl functionality to an amine such as furfurylamine (FAM).
FAM is one of the primary amines used to prepare drugs, fibers, and pesticides. The
reaction network proposed in the literature for the synthesis of FAM involves
(Fig. 8):
1. Hydrogenation of alcohol.
2. Reaction with ammonia resulting in the formation of reactive intermediates
(including primary imine) or react with FAM to form Schiff base-type
intermediate.
3. Hydrogenation of secondary imine to the secondary amine.
4. It can decompose to the primary amine and primary imine in the presence of
ammonia. From nitrile reduction reactions, it is known that primary imines and
primary amines can couple to form secondary imines and subsequently form
secondary/tertiary amines. A generally accepted mechanistic suggestion conEfficient Nanocomposite Catalysts for Sustainable Production of Biofuels and…