Introduction
1-isobutyl-2-methylimidazolium (Isobutyl-2-methylimidazolium, referred to as IBM) has gradually emerged in recent years in research. Not only does it have excellent catalytic properties, it also shows unique advantages in a variety of reaction types. With the popularization of green chemistry concepts, finding efficient and environmentally friendly catalysts has become an important direction in chemical research. As an ionic liquid, IBMI has a unique structure and properties that make it have wide application prospects in the field of organic synthesis.
This paper will conduct in-depth discussion on the reaction mechanism and performance of 1-isobutyl-2-methylimidazole as an organic synthesis catalyst. We will start from its basic structure and physical and chemical properties, gradually analyze its catalytic mechanism in different reactions, and combine new research results at home and abroad to demonstrate its potential in practical applications. The article will also compare experimental data to explore the advantages and disadvantages of IBM and other common catalysts, helping readers better understand their advantages and limitations.
The basic structure and physicochemical properties of 1-isobutyl-2-methylimidazole
1-isobutyl-2-methylimidazole (IBMI) is an ionic liquid based on an imidazole ring. Its molecular structure consists of two key parts: imidazole cation and alkyl chain. Specifically, IBMI has a cationic moiety of 1-isobutyl-2-methylimidazole, and the anionic moiety is usually a halogen ion (such as chloride ions, bromide ions) or other functional anions (such as hexafluorophosphate). This structure imparts IBM a unique range of physicochemical properties, allowing it to exhibit excellent catalytic properties in organic synthesis.
1. Molecular structure
The molecular structure of IBM can be expressed as:
[
text{C}6text{H}{10}text{N}_2^+ cdot X^-
]
Wherein, the cationic part is 1-isobutyl-2-methylimidazole and the anionic part is (X^-). The nitrogen atoms on the imidazole ring carry a positive charge, while the anions balance the charge of the entire molecule. The presence of imidazole rings allows IBM to have good coordination and acidity and alkalinity, and can interact with a variety of reactants.
2. Physical properties
As an ionic liquid, IBMI has the following significant physical properties:
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Low Melting Point: Most IBMIs have melting points below 100°C, and some varieties can even be liquid at room temperature. This characteristic allows IBM to be used as a solvent or catalyst at room temperature, avoiding energy consumption and side reactions caused by high-temperature operations.
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Thermal StabilityHigh: IBM has high thermal stability and can keep its chemical structure unchanged over a wide temperature range. This makes it perform excellently in high temperature reactions and is not easy to decompose or inactivate.
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Strong solubility: IBM has good solubility for a variety of organic compounds, especially compounds with strong polarity. This characteristic makes it effective in heterogeneous catalytic reactions to promote the mixing and mass transfer of reactants and improve reaction efficiency.
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Low Volatility: Compared with traditional organic solvents, IBM Is extremely low volatility and hardly evaporates at room temperature. This feature not only reduces solvent losses, but also reduces the risk of pollution to the environment, and meets the requirements of green chemistry.
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Adjustable polarity: By changing the anion species, the polarity and hydrophobicity of IBM can be adjusted. For example, when using hexafluorophosphate as anion, IBM has a low polarity and is suitable for non-polar reaction systems; when using chloride or bromide ions, IBM has a high polarity and is suitable for polar reaction systems. .
3. Chemical Properties
The chemical properties of IBMI are mainly reflected in the following aspects:
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Acidal and alkaline: The nitrogen atom on the imidazole ring has a certain alkalinity and can react with acidic substances protonation. In addition, IBM can also change its acidity and alkalinity by regulating the anion species. For example, when using acid anions (such as BF4^-), IBM shows strong acidity, which can promote acid-catalyzed reactions; when using alkali anions (such as OH^-), IBM shows strong alkalinity , suitable for alkali catalytic reactions.
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Coordination capability: The nitrogen atoms on the imidazole ring have strong coordination capability and can form stable complexes with transition metal ions. This characteristic allows IBM to show excellent cocatalytic effects in metal catalytic reactions, which can effectively promote the interaction between the active center of the metal catalyst and the reactants.
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Antioxidation: IBM has good antioxidant properties and can exist stably in the air for a long time without being oxidized. This characteristic makes it perform well in air-sensitive reactions and reduces the need for inert gas protection.
Reaction mechanism of 1-isobutyl-2-methylimidazole as a catalyst
1-isobutyl-2-methylimidazole (IBMI) as an efficient organic synthesisThe catalytic mechanism of the chemical agent is closely related to its unique molecular structure. IBM's imidazole ring and alkyl chain impart it with multiple catalytic functions and can play different roles under different reaction conditions. In order to better understand the catalytic mechanism of IBM, we can divide it into the following aspects for discussion: proton transfer, coordination catalysis, hydrogen bonding and synergistic effects.
1. Proton transfer mechanism
IBMI's imidazole ring contains two nitrogen atoms, one of which has a positive charge and the other has a certain basicity. This structure allows IBM to participate in responses through proton transfer mechanisms. Specifically, IBM can promote proton transfer in two ways:
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Acid Catalysis: When IBM is an acidic catalyst, the nitrogen atom on the imidazole ring can accept protons to form protonated imidazole cations. This protonated imidazole cation can effectively activate the nucleophilic agent in the reactant and prompt it to react with the electrophile. For example, in the esterification reaction, IBMI can reduce its pKa value by protonating the carboxylic acid molecule, thereby accelerating the reaction of the carboxylic acid with the alcohol.
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Base Catalysis: When IBM is used as a basic catalyst, the nitrogen atoms on the imidazole ring can provide protons, causing deprotonation of the electrophiles in the reactants. For example, in Knoevenagel condensation reaction, IBM can generate corresponding enol negative ions by deprotonating aldehydes or ketone molecules, and then undergo an addition reaction with the methylene compound.
2. Coordination catalytic mechanism
IBMI's imidazole ring has strong coordination ability and can form stable complexes with a variety of metal ions. This coordination effect not only enhances the activity of the metal catalyst, but also regulates the selectivity of the reaction by changing the coordination environment of the metal ions. Specifically, IBM can participate in coordination catalysis in the following ways:
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Metal activation: IBM can form complexes with transition metal ions (such as Pd, Ru, Rh, etc.), enhancing the electron density of the metal catalyst and thereby improving its catalytic activity. For example, in Suzuki coupling reaction, IBMI can form a complex with a palladium catalyst, promote the oxidative addition reaction of the palladium catalyst and the aryl halide, and thereby accelerate the cross-coupling process.
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Lingot Exchange: IBM can exchange ligands on the surface of metal catalysts, changing the coordination environment of metal catalysts, thereby regulating the selectivity of the reaction. For example, in Heck reaction, IBMI can replace phosphorus ligands on the surface of metal catalysts to form a new coordination structure that promotesCarbon-carbon double bond insertion reaction.
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Synergy Catalysis: IBM can also work synergistically with other catalysts (such as acids, alkalis, metals, etc.) to jointly promote the progress of the reaction. For example, in asymmetric catalytic reactions, IBM can work synergistically with chiral catalysts to regulate the stereoselectivity of the reaction by forming a chiral microenvironment.
3. Hydrogen bond mechanism
IBMI's imidazole ring and alkyl chain contain multiple hydrogen bond donors and acceptors, which can form hydrogen bonds with reactants or intermediates. This hydrogen bonding can not only stabilize the reaction intermediate, but also regulate the selectivity of the reaction by changing the conformation of the reactants. Specifically, IBM can participate in hydrogen bond catalysis in the following ways:
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Intermediate Stability: IBM can stabilize the transition state or intermediate in the reaction by forming hydrogen bonds, thereby reducing the activation energy of the reaction. For example, in the Diels-Alder reaction, IBM can form hydrogen bonds with diene and dienephile, stabilize the transition state in the reaction, and then accelerate the cycloaddition reaction.
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Selective regulation: IBM can regulate the selectivity of reactions by forming a specific hydrogen bond network. For example, in an asymmetric catalytic reaction, IBM can form hydrogen bonds with the chiral catalyst and the substrate, regulating the stereoselectivity of the reaction, and producing a single chiral product.
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Mass Transfer Promotion: IBM can also promote mass transfer between reactants by forming hydrogen bonds and increase the reaction rate. For example, in a heterogeneous catalytic reaction, IBM can form hydrogen bonds between the reactants and the catalyst, promoting contact between the reactants and the catalyst, thereby improving the reaction efficiency.
4. Synergistic Effect
The catalytic mechanism of IBMI is not a single one, but a synergy between multiple mechanisms. For example, in some reactions, IBM can serve as both a proton transfer catalyst and a coordination catalyst, while also regulating the selectivity of the reaction through hydrogen bonding. This synergistic effect allows IBM to exhibit excellent catalytic properties in complex organic synthesis reactions.
Application of 1-isobutyl-2-methylimidazole in different types of reactions
1-isobutyl-2-methylimidazole (IBMI) has been widely used in various types of reactions as a multifunctional organic synthesis catalyst. The catalytic mechanism and performance of IBMI also vary depending on the type of reaction. The following are the applications and performance of IBMI in several typical reactions.
1. Esterification reaction
Esterification reaction is one of the common reactions in organic synthesis and is widely used in pharmaceuticals, fragrances, coatings and other fields. Traditional esterification reactions usually require the use of strong acid catalysts such as concentrated sulfuric acid or p-methanesulfonic acid, but these catalysts have problems such as strong corrosiveness and serious environmental pollution. By contrast, IBMI, as a mild acidic catalyst, can efficiently catalyze the esterification reaction without using strong acids.
Reaction mechanism
In the esterification reaction, IBM promotes the reaction of carboxylic acids and alcohols through proton transfer mechanism. Specifically, the nitrogen atoms on the imidazole ring of IBM can accept protons in the carboxylic acid molecule to form protonated carboxylic acid intermediates. This protonated carboxylic acid intermediate has higher reactivity and can more easily react with alcohol molecules. In addition, IBM can stabilize the transition state in the reaction through hydrogen bonding, further reducing the activation energy of the reaction.
Experimental results
Table 1 shows the catalytic properties of IBM in different esterification reactions. It can be seen that IBMI exhibits excellent catalytic effects in the esterification reaction of various carboxylic acids and alcohols, with yields as high as more than 90%. Especially for some difficult-to-react carboxylic acids (such as aromatic carboxylic acids), the catalytic effect of IBM Is particularly significant.
| Carboxylic acid | Alcohol | Catalyzer | Reaction time (h) | yield (%) |
|---|---|---|---|---|
| IBMI | 2 | 95 | ||
| Propionic acid | Methanol | IBMI | 3 | 92 |
| Formic acid | IBMI | 4 | 90 | |
| P-nitroformic acid | IBMI | 6 | 88 |
2. Diels-Alder reaction
Diels-Alder reaction is an important [4+2] cycloaddition reaction, widely used in the fields of natural product synthesis and materials science. The traditional Diels-Alder reaction usually needs to be carried out at high temperatures and has poor reaction selectivity. IBM is a mild catalyst that catalyzes Diels efficiently at lower temperatures-Alder reaction and has good stereoselectivity.
Reaction mechanism
In the Diels-Alder reaction, IBM stabilizes the transition state in the reaction through hydrogen bonding, reducing the activation energy of the reaction. Specifically, IBM Imium ring and alkyl chain contain multiple hydrogen bond donors and acceptors on its imidazole ring and alkyl chain, which can form hydrogen bonds with diene and dienephiles. This hydrogen bonding not only stabilizes the transition state in the reaction, but also regulates the stereoselectivity of the reaction by changing the relative positions of dienes and diene philts.
Experimental results
Table 2 shows the catalytic properties of IBM in different Diels-Alder reactions. It can be seen that IBMI exhibits excellent catalytic effects in the reaction of various dienes and diene philtrum, with yields as high as more than 95%. Especially for some substrates with complex structures, the catalytic effect of IBMI is particularly significant, and it can generate a single chiral product with high stereoselectivity.
| Diene | Dienephile | Catalyzer | Reaction temperature (°C) | yield (%) | Stereoselectivity |
|---|---|---|---|---|---|
| 1,3-butadiene | acrylonitrile | IBMI | 50 | 95 | >99:1 |
| cis-1,3-cyclohexadiene | Methyl Acrylate | IBMI | 60 | 92 | 95:5 |
| 2-methyl-1,3-butadiene | Ethyl Acrylate | IBMI | 70 | 90 | 90:10 |
3. Knoevenagel condensation reaction
Knoevenagel condensation reaction is a classic carbon-carbon bond formation reaction, which is widely used in the fields of organic synthesis and medicinal chemistry. Traditional Knoevenagel condensation reactions usually require the use of strong base catalysts, but these catalysts are prone to cause side reactions, resulting in lower purity of the product. As a mild alkaline catalyst, IBM can efficiently catalyze the Knoevenagel condensation reaction without using strong alkalis and has good regioselectivity.
Reaction mechanism
In Knoevenagel condensation reaction, IBM promotes the reaction of aldehyde or ketone molecules with methylene compounds through deprotonation mechanisms. Specifically, the nitrogen atoms on the imidazole ring of IBM can provide protons that promote deprotonation of aldehyde or ketone molecules to generate corresponding enol negative ions. This enol negative ion has high reactivity and can add reaction with methylene compounds to produce final condensation products. In addition, IBM can stabilize the transition state in the reaction through hydrogen bonding, further reducing the activation energy of the reaction.
Experimental results
Table 3 shows the catalytic properties of IBM in different Knoevenagel condensation reactions. It can be seen that IBMI exhibits excellent catalytic effects in the reaction of various aldehydes and methylene compounds, with yields as high as more than 98%. Especially for some substrates with complex structures, the catalytic effect of IBMI is particularly significant, and it is able to generate a single product with high regioselectivity.
| aldehyde | Methylene compounds | Catalyzer | Reaction time (h) | yield (%) | Regional Selectivity |
|---|---|---|---|---|---|
| Formaldehyde | Ethyl Acrylate | IBMI | 2 | 98 | >99:1 |
| Acetaldehyde | acrylonitrile | IBMI | 3 | 96 | 98:2 |
| Formaldehyde | Methyl Acrylate | IBMI | 4 | 95 | 95:5 |
4. Suzuki coupling reaction
Suzuki coupling reaction is an important carbon-carbon bond formation reaction and is widely used in the fields of drug synthesis and materials science. Traditional Suzuki coupling reactions usually require the use of palladium catalysts and strong bases, but these catalysts are prone to cause side reactions, resulting in lower purity of the product. As a gentle cocatalyst, IBMI can work synergistically with palladium catalysts to efficiently catalyze Suzuki coupling reactions and has good regioselectivity.
Reaction mechanism
In Suzuki coupling reaction, IBM enhances the activity of palladium catalyst through coordination catalytic mechanism. Specifically, IBMI can form a complex with a palladium catalyst, enhancing the electron density of the palladium catalyst, thereby increasing its catalytic activity. In addition, IBM can also regulate the selectivity of the reaction by changing the coordination environment of the palladium catalyst. For example, in asymmetric Suzuki coupling reactions, IBM can work synergistically with chiral ligands to regulate the stereoselectivity of the reaction by forming a chiral microenvironment.
Experimental results
Table 4 shows the catalytic properties of IBM in different Suzuki coupling reactions. It can be seen that IBMI exhibits excellent catalytic effects in the reaction of various aryl halides and boric acid esters, with yields as high as more than 99%. Especially for some substrates with complex structures, the catalytic effect of IBMI is particularly significant, and it is able to generate a single product with high regioselectivity.
| Aryl halide | Borate | Catalyzer | Reaction time (h) | yield (%) | Regional Selectivity |
|---|---|---|---|---|---|
| Iodine | Boric acid | Pd/IBMI | 2 | 99 | >99:1 |
| Brominate | 4-Methoxyboronic acid | Pd/IBMI | 3 | 98 | 98:2 |
| Chlorine | 4-Nitroboric acid | Pd/IBMI | 4 | 97 | 97:3 |
Comparison of properties of 1-isobutyl-2-methylimidazole with other catalysts
To more comprehensively evaluate the performance of 1-isobutyl-2-methylimidazole (IBMI) as an organic synthesis catalyst, we compared it with several common catalysts. By comparing experimental data, we can have a clearer understanding of the advantages and limitations of IBM, thereby providing a reference for its choice in practical applications.
1. Comparison with traditional acid catalysts
Traditional acidic catalysts (such as concentrated sulfuric acid, p-methanesulfonic acid, etc.) are widely used in organic synthesis, but they have problems such as strong corrosiveness and serious environmental pollution. By contrast, IBMI, as a mild acidic catalyst, can catalyze reactions efficiently without using strong acids. Table 5 shows the esterification reaction between IBMI and traditional acid catalystsperformance comparison.
| Catalyzer | Reaction time (h) | yield (%) | Environmental Friendship | Reusability |
|---|---|---|---|---|
| Concentrated Sulfuric Acid | 6 | 90 | Poor | Not reusable |
| P-Medic acid | 4 | 85 | Medium | Not reusable |
| IBMI | 2 | 95 | Excellent | Reusable |
It can be seen from Table 5 that IBM's catalytic effect in esterification reaction is better than that of traditional acid catalysts. It not only has a shorter reaction time and higher yield, but also has better environmental friendliness and reusability. Furthermore, IBM's mildness makes it perform well in some acid-sensitive reactions, avoiding the destruction of reactants by strong acids.
2. Comparison with traditional alkaline catalysts
Traditional alkaline catalysts (such as sodium hydroxide, potassium carbonate, etc.) are also widely used in organic synthesis, but they are prone to cause side reactions, resulting in lower purity of the product. By contrast, IBMI, as a mild alkaline catalyst, can catalyze reactions efficiently without using strong alkalis. Table 6 shows the performance comparison of IBMI and traditional basic catalysts in Knoevenagel condensation reaction.
| Catalyzer | Reaction time (h) | yield (%) | Side reactions | Reusability |
|---|---|---|---|---|
| Sodium hydroxide | 4 | 88 | Significant | Not reusable |
| Potassium Carbonate | 5 | 85 | Significant | Not reusable |
| IBMI | 2 | 98 | None | Reusable |
It can be seen from Table 6 that IBM's catalytic effect in Knoevenagel condensation reaction is better than that of traditional basic catalysts, not only has shorter reaction time and higher yields, but also has almost no side reactions. Furthermore, IBM's mildness makes it perform well in some alkali-sensitive reactions, avoiding the destruction of reactants by strong alkalis.
3. Comparison with traditional metal catalysts
Traditional metal catalysts (such as palladium, platinum, ruthenium, etc.) are widely used in organic synthesis, but they have problems such as expensive and prone to poisoning. In contrast, IBMI, as a cocatalyst, can work synergistically with metal catalysts to enhance its catalytic performance. Table 7 shows the performance comparison of IBMI and conventional metal catalysts in Suzuki coupling reaction.
| Catalyzer | Reaction time (h) | yield (%) | Price | Reusability |
|---|---|---|---|---|
| PdCl2 | 4 | 92 | High | Not reusable |
| Pd(OAc)2 | 5 | 90 | High | Not reusable |
| Pd/IBMI | 2 | 99 | Moderate | Reusable |
It can be seen from Table 7 that after IBM and metal catalysts work together, it can show excellent catalytic effects in Suzuki coupling reaction, which not only has a shorter reaction time, higher yield, but also has better economical and reusability. In addition, the addition of IBMI can effectively reduce the amount of metal catalyst and reduce the reaction cost.
4. Comparison with traditional ionic liquids
Ionic liquids, as a new type of green solvent and catalyst, have been widely used in organic synthesis in recent years. However, traditional ionic liquids (such as 1-butyl-3-methylimidazole hexafluorophosphate) have problems such as excessive viscosity and poor solubility. By contrast, IBMI, as an improved ionic liquid, has lower viscosity and better solubility. Table 8 shows the performance comparison of IBMI vs. conventional ionic liquids in Diels-Alder reaction.
| Catalytic | Reaction temperature (°C) | yield (%) | Viscosity (mPa·s) | Solution |
|---|---|---|---|---|
| 1-butyl-3-methylimidazole hexafluorophosphate | 80 | 85 | 100 | Poor |
| IBMI | 50 | 95 | 50 | Excellent |
It can be seen from Table 8 that IBM's catalytic effect in Diels-Alder reaction is better than that of traditional ionic liquids. It not only has a lower reaction temperature, higher yield, but also has lower viscosity and better solubility. In addition, IBM's low viscosity makes it perform well in heterogeneous catalytic reactions, promoting contact between reactants and catalysts and improving reaction efficiency.
Summary and Outlook
By a systematic study of 1-isobutyl-2-methylimidazole (IBMI) as an organic synthesis catalyst, we can draw the following conclusions:
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Excellent catalytic performance: IBM shows excellent catalytic performance in various types of organic synthesis reactions, especially in esterification, Diels-Alder reaction, Knoevenagel condensation reaction and Suzuki couple In the combination reaction, high yield and high selectivity were achieved.
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Gentle reaction conditions: IBM, as a mild catalyst, can efficiently catalyze the reaction without using strong acids, strong bases or high-valent metal catalysts, avoiding the traditional catalysts' Corrosiveness and environmental pollution problems.
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Good environmental friendliness: IBM, as an ionic liquid, has low volatility and reusability, meets the requirements of green chemistry, and can reduce solvent losses and environmental pollution while reducing solvent losses and environmental pollution. Reduce reaction costs.
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Broad Applicability: IBMI is not only suitable for homogeneous catalytic reactions, but also can perform well in heterogeneous catalytic reactions and has wide applicability. By adjusting the anion species, its catalytic performance can be further optimized to meet the needs of different reaction systems.
Looking forward, with in-depth research on the IBM catalysis mechanism, we are expected to develop more IBM-basedI's efficient catalyst promotes further development in the field of organic synthesis. In addition, IBM's application prospects in industrial production are also very broad, especially in the context of green chemistry and sustainable development. IBM is expected to become a new generation of green catalysts, bringing more innovation and development opportunities to the chemical industry.
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