lot higher, indicating that the hydrogen released is reacting with the substrate at other
sites under the reaction conditions.
7 Iridium-Catalyzed Transformations of Fatty Acids
7.1 Vegetable Oil as a Feedstock
Vegetable oils, and to a smaller degree animal fats, are a large source of renewable
chemicals [99]. In contrast to lignocellulose, vegetable oils are also food products,
however currently a lot of oil crops such as rapeseed are grown in large quantities for
the production of biodiesel, so that the conversion of a small fraction of these into
chemicals will not affect the food production. Additionally, oils can be harvested
from algae, which avoids the use of arable land for their production.
For biodiesel production, the triglycerides from vegetable oils are transesterified
with methanol to produce fatty acid methyl esters (FAMEs), leaving large amounts
of glycerol as a side product [100]. Due to this, much research has been done on the
valorization of glycerol, including a range of iridium-catalyzed reactions. These are
discussed in Sect. 2.4. Additionally, as was already discussed in Sect. 5.2, glycerol is
also interesting as a hydrogen donor.
The fatty acids from vegetable oils are mostly unsaturated or polyunsaturated,
although saturated fatty acids also exist, for example in coconut and palm oil.
Animal fat, on the other hand, contains mostly saturated fatty acids, such as
stearic acid.
Oleic acid, a monounsaturated omega-9 fatty acid is the most common fatty acid
in nature. It is present in up to 70% in canola oil, which is made from rapeseed.
7.2 Iridium-Catalyzed Transformations of Fatty Acids
7.2.1 Hydrogenation
A high content of polyunsaturated FAMEs in biodiesel reduces its performance: the
stability and energy density of the fuel are lowered, while viscosity and emission of
hydrocarbons are increased. In the USA the main feedstock for producing biodiesel
are soybean and corn oil, which are high in polyunsaturated fatty acids, unlike in
Europe where high oleic acid content canola oil is most commonly used. Fully
saturated FAMEs, such as those produced from animal fat, on the other hand, have
high melting points and are prone to precipitation in diesel blends [41]. The best
performance is achieved by high oleate content.
Williams and coworkers investigated iridium complex [Ir-9] from their previous
work on the acceptorless dehydrogenation of glycerol to LA (see Sect. 2.4.1) for the
hydrogenation of polyunsaturated FAMEs using glycerol and methanol as hydrogen
Homogenous Iridium Catalysts for Biomass Conversion
383
sites under the reaction conditions.
7 Iridium-Catalyzed Transformations of Fatty Acids
7.1 Vegetable Oil as a Feedstock
Vegetable oils, and to a smaller degree animal fats, are a large source of renewable
chemicals [99]. In contrast to lignocellulose, vegetable oils are also food products,
however currently a lot of oil crops such as rapeseed are grown in large quantities for
the production of biodiesel, so that the conversion of a small fraction of these into
chemicals will not affect the food production. Additionally, oils can be harvested
from algae, which avoids the use of arable land for their production.
For biodiesel production, the triglycerides from vegetable oils are transesterified
with methanol to produce fatty acid methyl esters (FAMEs), leaving large amounts
of glycerol as a side product [100]. Due to this, much research has been done on the
valorization of glycerol, including a range of iridium-catalyzed reactions. These are
discussed in Sect. 2.4. Additionally, as was already discussed in Sect. 5.2, glycerol is
also interesting as a hydrogen donor.
The fatty acids from vegetable oils are mostly unsaturated or polyunsaturated,
although saturated fatty acids also exist, for example in coconut and palm oil.
Animal fat, on the other hand, contains mostly saturated fatty acids, such as
stearic acid.
Oleic acid, a monounsaturated omega-9 fatty acid is the most common fatty acid
in nature. It is present in up to 70% in canola oil, which is made from rapeseed.
7.2 Iridium-Catalyzed Transformations of Fatty Acids
7.2.1 Hydrogenation
A high content of polyunsaturated FAMEs in biodiesel reduces its performance: the
stability and energy density of the fuel are lowered, while viscosity and emission of
hydrocarbons are increased. In the USA the main feedstock for producing biodiesel
are soybean and corn oil, which are high in polyunsaturated fatty acids, unlike in
Europe where high oleic acid content canola oil is most commonly used. Fully
saturated FAMEs, such as those produced from animal fat, on the other hand, have
high melting points and are prone to precipitation in diesel blends [41]. The best
performance is achieved by high oleate content.
Williams and coworkers investigated iridium complex [Ir-9] from their previous
work on the acceptorless dehydrogenation of glycerol to LA (see Sect. 2.4.1) for the
hydrogenation of polyunsaturated FAMEs using glycerol and methanol as hydrogen
Homogenous Iridium Catalysts for Biomass Conversion
383