Eco-Friendly Solution: DBU Phenolate (CAS 57671-19-9) in Green Chemistry

Introduction

In the world of chemistry, where reactions often involve hazardous substances and complex processes, the pursuit of sustainable and environmentally friendly solutions has never been more critical. One such solution that has garnered significant attention in recent years is DBU Phenolate (CAS 57671-19-9). This compound, a derivative of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), has emerged as a powerful catalyst in green chemistry, offering a safer, more efficient, and eco-friendly alternative to traditional catalysts.

But what exactly is DBU Phenolate, and why is it so important in the context of green chemistry? To answer this question, we need to delve into the world of catalysis, explore the properties of DBU Phenolate, and understand how it can help reduce the environmental impact of chemical processes. In this article, we will take a comprehensive look at DBU Phenolate, from its molecular structure to its applications in various industries. We’ll also examine the latest research and developments in the field, drawing on both domestic and international literature to provide a well-rounded perspective.

So, buckle up and get ready for a journey into the fascinating world of DBU Phenolate, where chemistry meets sustainability, and innovation leads the way to a greener future!

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What is DBU Phenolate?

Chemical Structure and Properties

DBU Phenolate, formally known as 1,8-diazabicyclo[5.4.0]undec-7-en-1-yl phenoxide, is a versatile organic compound with a unique molecular structure. It consists of a DBU core, which is a bicyclic amine, and a phenolate group, which is the deprotonated form of phenol. The combination of these two components gives DBU Phenolate its remarkable catalytic properties.

• Molecular Formula: C₁₃H₁₅N₂O
• Molecular Weight: 213.27 g/mol
• CAS Number: 57671-19-9
• Appearance: White to off-white solid
• Melting Point: 150-152°C
• Solubility: Soluble in polar organic solvents such as ethanol, acetone, and DMSO; insoluble in water

The DBU moiety is a strong base, with a pKa value of around 18.6, making it one of the most basic organic compounds available. This high basicity allows DBU Phenolate to act as an effective nucleophile and base in various chemical reactions. The phenolate group, on the other hand, provides additional stability and reactivity, making DBU Phenolate a highly efficient catalyst in a wide range of transformations.

Synthesis of DBU Phenolate

The synthesis of DBU Phenolate is relatively straightforward and can be achieved through the reaction of DBU with phenol in the presence of a base. The reaction proceeds via a simple neutralization process, where the phenolic hydroxyl group is deprotonated by the strong base, resulting in the formation of the phenolate ion. This ion then coordinates with the DBU molecule, forming the final product.

The general synthetic route can be summarized as follows:

1. Preparation of Phenolate Ion: Phenol is dissolved in a polar solvent, and a strong base (such as potassium hydroxide or sodium hydride) is added to deprotonate the phenolic hydroxyl group.

2. Formation of DBU Phenolate: The phenolate ion is then reacted with DBU, leading to the formation of the DBU Phenolate complex.

This synthesis is not only simple but also scalable, making it suitable for industrial applications. Moreover, the use of readily available starting materials and mild reaction conditions makes DBU Phenolate an attractive option for green chemistry initiatives.

Physical and Chemical Properties

Property	Value
Molecular Formula	C₁₃H₁₅N₂O
Molecular Weight	213.27 g/mol
CAS Number	57671-19-9
Appearance	White to off-white solid
Melting Point	150-152°C
Boiling Point	Decomposes before boiling
Density	1.12 g/cm³ (at 25°C)
Solubility	Soluble in polar organic solvents; insoluble in water
pKa (DBU)	18.6
Refractive Index	1.58 (at 20°C)

These physical and chemical properties make DBU Phenolate an ideal candidate for use in various catalytic reactions, particularly those involving acid-base chemistry, nucleophilic substitution, and elimination reactions.

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Applications of DBU Phenolate in Green Chemistry

Catalysis in Organic Synthesis

One of the most significant applications of DBU Phenolate is in organic synthesis, where it serves as a highly efficient catalyst for a variety of reactions. Its strong basicity and nucleophilicity make it particularly useful in reactions that require a strong base or nucleophile, such as Michael additions, aldol condensations, and Knoevenagel condensations.

Michael Addition

The Michael addition is a classic carbon-carbon bond-forming reaction that involves the conjugate addition of a nucleophile to an α,β-unsaturated carbonyl compound. DBU Phenolate is an excellent catalyst for this reaction due to its ability to activate both the nucleophile and the electrophile. For example, in the Michael addition of malonates to chalcones, DBU Phenolate has been shown to significantly accelerate the reaction rate while providing excellent yields and selectivity.

Aldol Condensation

The aldol condensation is another important reaction in organic synthesis, involving the condensation of an aldehyde or ketone with an enolate to form a β-hydroxy ketone or aldehyde. DBU Phenolate acts as a base to generate the enolate, which then reacts with the carbonyl compound to form the desired product. This reaction is widely used in the synthesis of natural products and pharmaceuticals, and DBU Phenolate has proven to be a highly effective catalyst, offering improved yields and shorter reaction times compared to traditional bases.

Knoevenagel Condensation

The Knoevenagel condensation is a reaction between an aldehyde or ketone and a methylene-active compound, such as malonates or cyanoacetates, to form α,β-unsaturated compounds. DBU Phenolate is an excellent catalyst for this reaction, as it can activate both the carbonyl compound and the methylene-active compound, leading to faster reaction rates and higher yields. Additionally, DBU Phenolate has been shown to be compatible with a wide range of substrates, making it a versatile choice for this type of reaction.

Polymerization Reactions

DBU Phenolate has also found applications in polymerization reactions, particularly in the ring-opening polymerization (ROP) of cyclic esters and lactones. These reactions are important for the production of biodegradable polymers, which are increasingly sought after in the field of green chemistry.

Ring-Opening Polymerization of Lactones

Lactones are cyclic esters that can undergo ring-opening polymerization to form polyesters, which are widely used in packaging, textiles, and biomedical applications. DBU Phenolate is an effective initiator for the ROP of lactones, such as ε-caprolactone and δ-valerolactone, due to its ability to form a stable carbanion intermediate that propagates the polymer chain. This reaction is typically carried out under mild conditions, making it an attractive option for industrial-scale production of biodegradable polymers.

Controlled Radical Polymerization

DBU Phenolate has also been used as a catalyst in controlled radical polymerization (CRP) reactions, such as atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. These reactions allow for precise control over the molecular weight and architecture of the resulting polymers, making them valuable for applications in coatings, adhesives, and drug delivery systems. DBU Phenolate’s ability to stabilize radicals and promote chain growth makes it a promising catalyst for CRP, offering improved efficiency and reduced environmental impact compared to traditional initiators.

Cross-Coupling Reactions

Cross-coupling reactions are essential in the synthesis of complex organic molecules, such as pharmaceuticals and fine chemicals. DBU Phenolate has been shown to be an effective catalyst in several types of cross-coupling reactions, including Suzuki-Miyaura coupling, Heck coupling, and Sonogashira coupling.

Suzuki-Miyaura Coupling

The Suzuki-Miyaura coupling is a palladium-catalyzed cross-coupling reaction between an aryl halide and an arylboronic acid to form a biaryl compound. DBU Phenolate has been used as a ligand in this reaction, where it forms a stable complex with palladium, enhancing the catalytic activity and selectivity. This modification has led to improved yields and shorter reaction times, making DBU Phenolate a valuable tool in the optimization of Suzuki-Miyaura couplings.

Heck Coupling

The Heck coupling is a palladium-catalyzed reaction between an aryl halide and an alkene to form a substituted alkene. DBU Phenolate has been used as a base in this reaction, where it facilitates the oxidative addition of palladium to the aryl halide. This results in faster reaction rates and higher yields, particularly for challenging substrates. Additionally, DBU Phenolate’s compatibility with a wide range of solvents and reaction conditions makes it a versatile choice for Heck coupling reactions.

Sonogashira Coupling

The Sonogashira coupling is a palladium-catalyzed reaction between an aryl halide and an alkynyl halide to form a substituted alkyne. DBU Phenolate has been used as a base in this reaction, where it promotes the transmetalation step, leading to faster reaction rates and higher yields. This reaction is particularly useful in the synthesis of conjugated polymers and organic semiconductors, where the formation of alkynes is crucial.

Environmental Benefits

One of the key advantages of using DBU Phenolate in green chemistry is its environmental benefits. Unlike many traditional catalysts, DBU Phenolate is non-toxic, non-corrosive, and easily recyclable, making it a safer and more sustainable option for industrial applications. Additionally, DBU Phenolate can be used in aqueous media, reducing the need for organic solvents and minimizing waste generation.

Moreover, DBU Phenolate’s ability to promote reactions under mild conditions helps to reduce energy consumption and greenhouse gas emissions. For example, in the ring-opening polymerization of lactones, DBU Phenolate allows for the production of biodegradable polymers at room temperature, eliminating the need for high temperatures and pressures. This not only reduces the environmental footprint of the process but also lowers production costs, making it a win-win solution for both industry and the environment.

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Case Studies and Industrial Applications

Biodegradable Polymers

One of the most exciting applications of DBU Phenolate is in the production of biodegradable polymers, which are increasingly being used as alternatives to conventional plastics. These polymers, such as polycaprolactone (PCL) and poly(lactic acid) (PLA), are derived from renewable resources and can degrade naturally in the environment, reducing plastic waste and pollution.

Polycaprolactone (PCL)

Polycaprolactone is a biodegradable polyester that is widely used in medical devices, drug delivery systems, and packaging materials. DBU Phenolate has been shown to be an effective initiator for the ring-opening polymerization of ε-caprolactone, leading to the formation of PCL with controlled molecular weight and narrow polydispersity. This reaction is typically carried out under mild conditions, making it an attractive option for industrial-scale production of PCL.

Poly(lactic acid) (PLA)

Poly(lactic acid) is another biodegradable polymer that is derived from lactic acid, which can be produced from renewable resources such as corn starch. DBU Phenolate has been used as a catalyst in the polymerization of lactic acid, where it promotes the formation of PLA with high molecular weight and good mechanical properties. This reaction is typically carried out in the presence of a co-catalyst, such as tin(II) octoate, which enhances the catalytic activity of DBU Phenolate.

Pharmaceutical Synthesis

DBU Phenolate has also found applications in the synthesis of pharmaceuticals, where it is used as a catalyst in various reactions, including cross-coupling reactions, Michael additions, and aldol condensations. These reactions are essential for the production of active pharmaceutical ingredients (APIs) and intermediates, and DBU Phenolate’s ability to promote these reactions under mild conditions makes it a valuable tool in the pharmaceutical industry.

Synthesis of Celecoxib

Celecoxib is a nonsteroidal anti-inflammatory drug (NSAID) that is used to treat pain and inflammation. The synthesis of celecoxib involves a series of cross-coupling reactions, including a Suzuki-Miyaura coupling and a Heck coupling. DBU Phenolate has been used as a ligand in these reactions, where it enhances the catalytic activity of palladium and improves the yield and selectivity of the product. This modification has led to a more efficient and environmentally friendly synthesis of celecoxib, reducing the amount of waste generated during the process.

Synthesis of Atorvastatin

Atorvastatin is a statin drug that is used to lower cholesterol levels in patients with hypercholesterolemia. The synthesis of atorvastatin involves a Michael addition reaction, where DBU Phenolate acts as a base to facilitate the reaction. This reaction is typically carried out under mild conditions, making it a safer and more sustainable option compared to traditional methods that require harsh conditions and toxic reagents.

Fine Chemicals and Agrochemicals

DBU Phenolate has also been used in the synthesis of fine chemicals and agrochemicals, where it serves as a catalyst in various reactions, including cross-coupling reactions, Michael additions, and aldol condensations. These reactions are essential for the production of intermediates and active ingredients used in the manufacture of dyes, pigments, and pesticides.

Synthesis of Pyrethroid Insecticides

Pyrethroid insecticides are widely used in agriculture to control pests. The synthesis of pyrethroids involves a series of cross-coupling reactions, including a Heck coupling and a Sonogashira coupling. DBU Phenolate has been used as a base in these reactions, where it promotes the transmetalation step and improves the yield and selectivity of the product. This modification has led to a more efficient and environmentally friendly synthesis of pyrethroid insecticides, reducing the amount of waste generated during the process.

Synthesis of Dyes and Pigments

Dyes and pigments are essential for the coloring of textiles, paints, and plastics. The synthesis of these compounds often involves cross-coupling reactions, such as the Suzuki-Miyaura coupling and the Heck coupling. DBU Phenolate has been used as a ligand in these reactions, where it enhances the catalytic activity of palladium and improves the yield and selectivity of the product. This modification has led to a more efficient and environmentally friendly synthesis of dyes and pigments, reducing the amount of waste generated during the process.

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Challenges and Future Directions

While DBU Phenolate has shown great promise in green chemistry, there are still some challenges that need to be addressed. One of the main challenges is the recycling and recovery of DBU Phenolate, as it can be expensive to produce on a large scale. However, recent advances in catalyst recycling technologies have shown that DBU Phenolate can be recovered and reused in subsequent reactions, reducing the overall cost and environmental impact of the process.

Another challenge is the compatibility of DBU Phenolate with certain substrates and reaction conditions. While DBU Phenolate is generally compatible with a wide range of substrates, there are some cases where it may not perform as well as expected. For example, in reactions involving highly acidic or basic conditions, DBU Phenolate may decompose or lose its catalytic activity. Therefore, further research is needed to optimize the performance of DBU Phenolate in these challenging conditions.

Future Research

Despite these challenges, the future of DBU Phenolate in green chemistry looks bright. Ongoing research is focused on developing new applications for DBU Phenolate, as well as improving its catalytic performance and recyclability. Some potential areas of research include:

• Development of novel DBU Phenolate derivatives: By modifying the structure of DBU Phenolate, researchers hope to create new catalysts with enhanced properties, such as higher activity, better selectivity, and greater stability.

• Integration of DBU Phenolate into continuous flow processes: Continuous flow reactors offer several advantages over batch reactors, including improved safety, higher throughput, and better control over reaction conditions. Integrating DBU Phenolate into continuous flow processes could lead to more efficient and scalable production of biodegradable polymers, pharmaceuticals, and fine chemicals.

• Exploration of DBU Phenolate in biomass conversion: With the increasing demand for renewable energy sources, there is growing interest in converting biomass into valuable chemicals and fuels. DBU Phenolate could play a key role in this area by catalyzing the conversion of lignocellulosic biomass into platform chemicals, such as levulinic acid and furfural.

Conclusion

In conclusion, DBU Phenolate (CAS 57671-19-9) is a powerful and versatile catalyst that has the potential to revolutionize green chemistry. Its unique combination of strong basicity, nucleophilicity, and stability makes it an excellent choice for a wide range of reactions, from organic synthesis to polymerization and cross-coupling. Moreover, its environmental benefits, including non-toxicity, recyclability, and compatibility with aqueous media, make it a safer and more sustainable alternative to traditional catalysts.

As research in this field continues to advance, we can expect to see even more innovative applications of DBU Phenolate in the coming years. Whether it’s in the production of biodegradable polymers, the synthesis of pharmaceuticals, or the conversion of biomass, DBU Phenolate is poised to play a key role in shaping the future of green chemistry. So, let’s embrace this eco-friendly solution and pave the way for a greener, more sustainable future!

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References

1. Zhang, Y., & Wang, X. (2020). "Recent Advances in the Use of DBU Phenolate as a Catalyst in Green Chemistry." Journal of Green Chemistry, 12(3), 456-472.
2. Smith, J. A., & Brown, L. M. (2019). "Catalytic Applications of DBU Phenolate in Polymerization Reactions." Macromolecules, 52(10), 3891-3905.
3. Lee, S. H., & Kim, J. (2018). "DBU Phenolate as a Ligand in Cross-Coupling Reactions: A Review." Chemical Reviews, 118(15), 7245-7270.
4. Chen, W., & Li, Z. (2017). "Green Chemistry Approaches to Biodegradable Polymers Using DBU Phenolate as a Catalyst." Polymer Chemistry, 8(12), 1987-2002.
5. Patel, R., & Johnson, D. (2016). "Sustainable Synthesis of Pharmaceuticals Using DBU Phenolate as a Catalyst." Organic Process Research & Development, 20(5), 987-1001.
6. Yang, T., & Liu, H. (2015). "DBU Phenolate in the Synthesis of Fine Chemicals and Agrochemicals." Tetrahedron Letters, 56(3), 289-292.
7. Wang, Q., & Zhou, Y. (2014). "Recycling and Recovery of DBU Phenolate in Catalytic Reactions." Green Chemistry Letters and Reviews, 7(4), 321-330.
8. Martinez, A., & Hernandez, C. (2013). "DBU Phenolate in Continuous Flow Processes: Opportunities and Challenges." Chemical Engineering Journal, 225, 567-575.
9. Zhang, L., & Wu, F. (2012). "DBU Phenolate in Biomass Conversion: A Promising Catalyst for Sustainable Chemistry." Bioresource Technology, 123, 345-352.
10. Kim, B., & Park, J. (2011). "Synthesis and Characterization of DBU Phenolate: A Versatile Catalyst for Green Chemistry." Journal of Organic Chemistry, 76(10), 3845-3852.

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