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5 Catalysis for Production of Levulinic Esters
Usually, a catalyst is a substance that increases the rate of reaction without being
consumed in the chemical reaction, and the phenomenon occurring when a catalyst
acts is termed as catalysis. The word “catalysis” was first coined by Berzelius in
1836, which originates from two words, the prefix cata-, meaning down, and the
verb lysein, meaning to split or break [63]. He probably used the term “catalysis” to
denote breaking down of the normal forces that are preventing the reaction of molecules. The catalyst primarily influences a chemical reaction, which is already thermodynamically feasible or lowers the reaction temperature at which the reaction
achieves a given rate. Catalyst does not alter the equilibrium constant. The progress
of catalyzed chemical reaction occurs through new and more energetically favored
reaction pathway. Such phenomenon of lowering of activation energy is basic principle of catalysis and applied to all class of catalysis [63].
As far as esterification reaction of levulinic acid with primary alcohols is concerned, the reaction occurs even at room temperature; however, the rate is very slow,
which can be accelerated either by using higher temperature and catalyst to get
equilibrium conversion within reasonable time period. Conventionally, alkyl levulinates can be obtained by levulinic acid esterification in the presence of mineral
acid catalysts such as H 2 SO 4, HCl, or H 3 PO 4 [64]. A variety of catalysts have been
reported for the esterification of levulinic acid to yield levulinate esters that include
homogeneous, heterogenized homogeneous catalysts, heterogeneous catalysts,
enzymatic catalysts, supported catalysts, etc. An overview of several types of catalysts that are reported for synthesis of levulinic esters is provided herein, in the
subsequent text.
In the homogeneous system, it is convenient to manipulate acidic strength by
adding acid/water/native solvent. Varkolu et al. [65] demonstrated synthesis of various levulinates via esterification over environmentally benign bio-glycerol-derived
carbon-sulfonic acid catalyst. Negus et al. [66] prepared ethyl levulinate using ptoluenesulfonic acid (PTSA) and other mineral acid (HCl, H 2 SO 4 , HNO 3 ) homogeneous catalysts. The authors obtained better results with H 2 SO 4 and PTSA due to
their higher acid strength among all studied catalysts.
In the last two decades, ionic liquids (ILs) have emerged as versatile green building blocks and have wide applications in the area of separation, materials, catalysis,
green solvents etc. The use of IL for lignocellulose conversion into value-added
chemicals and fuel products is of great research interest. ILs are molten salts at
room temperature having wide applications in the area of green chemistry due to its
bifunctional role as green solvent and catalyst. Mostly, the IL framework consists of
a combination of cation and anion, wherein, IL cation is organic and IL anion is
inorganic/organic [67]. The salient properties of ILs that are responsible for increasing the popularity of these materials are good thermal stability, broad liquid state
range, non-volatility, better slvation ability, wide electrochemical window, nonflammability, and higher ionic conductivity. They can be a robust reaction medium for
organic synthesis due to their better solubilizing and stabilizing behavior to reactive
Solid Acid-Catalyzed Esterification of Levulinic Acid for Production of Value-Added…
5 Catalysis for Production of Levulinic Esters
Usually, a catalyst is a substance that increases the rate of reaction without being
consumed in the chemical reaction, and the phenomenon occurring when a catalyst
acts is termed as catalysis. The word “catalysis” was first coined by Berzelius in
1836, which originates from two words, the prefix cata-, meaning down, and the
verb lysein, meaning to split or break [63]. He probably used the term “catalysis” to
denote breaking down of the normal forces that are preventing the reaction of molecules. The catalyst primarily influences a chemical reaction, which is already thermodynamically feasible or lowers the reaction temperature at which the reaction
achieves a given rate. Catalyst does not alter the equilibrium constant. The progress
of catalyzed chemical reaction occurs through new and more energetically favored
reaction pathway. Such phenomenon of lowering of activation energy is basic principle of catalysis and applied to all class of catalysis [63].
As far as esterification reaction of levulinic acid with primary alcohols is concerned, the reaction occurs even at room temperature; however, the rate is very slow,
which can be accelerated either by using higher temperature and catalyst to get
equilibrium conversion within reasonable time period. Conventionally, alkyl levulinates can be obtained by levulinic acid esterification in the presence of mineral
acid catalysts such as H 2 SO 4, HCl, or H 3 PO 4 [64]. A variety of catalysts have been
reported for the esterification of levulinic acid to yield levulinate esters that include
homogeneous, heterogenized homogeneous catalysts, heterogeneous catalysts,
enzymatic catalysts, supported catalysts, etc. An overview of several types of catalysts that are reported for synthesis of levulinic esters is provided herein, in the
subsequent text.
In the homogeneous system, it is convenient to manipulate acidic strength by
adding acid/water/native solvent. Varkolu et al. [65] demonstrated synthesis of various levulinates via esterification over environmentally benign bio-glycerol-derived
carbon-sulfonic acid catalyst. Negus et al. [66] prepared ethyl levulinate using ptoluenesulfonic acid (PTSA) and other mineral acid (HCl, H 2 SO 4 , HNO 3 ) homogeneous catalysts. The authors obtained better results with H 2 SO 4 and PTSA due to
their higher acid strength among all studied catalysts.
In the last two decades, ionic liquids (ILs) have emerged as versatile green building blocks and have wide applications in the area of separation, materials, catalysis,
green solvents etc. The use of IL for lignocellulose conversion into value-added
chemicals and fuel products is of great research interest. ILs are molten salts at
room temperature having wide applications in the area of green chemistry due to its
bifunctional role as green solvent and catalyst. Mostly, the IL framework consists of
a combination of cation and anion, wherein, IL cation is organic and IL anion is
inorganic/organic [67]. The salient properties of ILs that are responsible for increasing the popularity of these materials are good thermal stability, broad liquid state
range, non-volatility, better slvation ability, wide electrochemical window, nonflammability, and higher ionic conductivity. They can be a robust reaction medium for
organic synthesis due to their better solubilizing and stabilizing behavior to reactive
Solid Acid-Catalyzed Esterification of Levulinic Acid for Production of Value-Added…