Articles posted by: admin

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) in Efficient Amide Bond Formation for Peptide Synthesis: A Comprehensive Review

Abstract: 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is a strong, non-nucleophilic organic base widely employed in organic synthesis. This article provides a comprehensive overview of its application in efficient amide bond formation, particularly in the context of peptide synthesis. We delve into the reaction mechanisms, advantages, and limitations of DBU-mediated amide bond formation, compare it with other commonly used bases, and highlight its specific roles in various peptide synthesis strategies. The discussion encompasses the influence of reaction conditions, protecting group selection, and substrate structure on reaction efficiency. Furthermore, the article outlines the product parameters of DBU and provides examples from the literature showcasing its versatility in both solution-phase and solid-phase peptide synthesis.

1. Introduction

Amide bond formation is a fundamental reaction in organic chemistry, crucial for the synthesis of peptides, proteins, pharmaceuticals, and various other biologically active compounds. Peptide synthesis, in particular, relies heavily on efficient and selective amide bond formation to link amino acid building blocks. Several coupling reagents and reaction conditions have been developed to facilitate this process. Among these, the use of bases plays a critical role in activating the carboxyl component and neutralizing the acidic byproducts generated during the coupling reaction. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) has emerged as a versatile and widely used base in peptide synthesis due to its strong basicity, non-nucleophilic character, and relatively low cost.

2. Properties of DBU

DBU is a bicyclic guanidine derivative with the chemical formula C9H16N2 and a molecular weight of 152.23 g/mol. Its structure features a highly delocalized positive charge upon protonation, contributing to its strong basicity and reduced nucleophilicity.

DBU is commercially available in various grades, including anhydrous forms, ensuring minimal water interference in sensitive reactions. It is typically stored under inert atmosphere to prevent degradation by atmospheric carbon dioxide or moisture.

3. Mechanism of Amide Bond Formation with DBU

DBU facilitates amide bond formation through several mechanisms, depending on the specific coupling reagent and reaction conditions employed. Generally, DBU acts as a base to:

• Deprotonate the carboxyl group: DBU abstracts a proton from the carboxylic acid of the activated amino acid derivative, forming a carboxylate anion. This anion is a better nucleophile and more readily attacks the electrophilic amine component.
• Neutralize acidic byproducts: Many coupling reactions generate acidic byproducts (e.g., HOAt, HOBt from HATU or HOBt activation strategies). DBU neutralizes these acids, preventing them from protonating the amine component and hindering the coupling reaction.
• Promote specific coupling reagent activation: In some cases, DBU is involved in the activation of the coupling reagent itself, facilitating the formation of the active ester or other reactive intermediate.

Example Mechanism (HOBt/HBTU Activation):

1. The carboxylic acid reacts with HOBt or HBTU to form an active ester (e.g., HOBt ester).
2. DBU deprotonates the carboxylic acid and/or HOBt/HBTU reagent, promoting the formation of the active ester.
3. DBU neutralizes the released acid (HOBt or HBTU).
4. The amine component attacks the active ester, forming the amide bond and releasing HOBt.

4. Advantages of DBU in Peptide Synthesis

DBU offers several advantages as a base in peptide synthesis:

• Strong Basicity: Its high pKa value ensures efficient deprotonation of the carboxylic acid, promoting rapid and complete coupling reactions.
• Non-Nucleophilicity: DBU is a sterically hindered base, minimizing its participation in unwanted side reactions, such as epimerization or racemization. This is crucial for maintaining the stereochemical integrity of the chiral amino acid building blocks.
• Solubility: DBU is soluble in a wide range of organic solvents, including DMF, DCM, and acetonitrile, which are commonly used in peptide synthesis.
• Commercial Availability and Cost-Effectiveness: DBU is readily available from numerous chemical suppliers at a reasonable cost, making it an attractive choice for both research and industrial applications.
• Compatibility with Various Protecting Groups: DBU is generally compatible with common protecting groups used in peptide synthesis, such as Boc, Fmoc, and Cbz. However, careful consideration is required depending on the specific protecting group strategy employed.
• Facilitates Racemization-Free Coupling: Compared to more nucleophilic bases, DBU is less likely to induce racemization at the ?-carbon of the amino acids, preserving the desired stereochemistry of the peptide product.

5. Limitations and Considerations

Despite its advantages, DBU also has some limitations that need to be considered:

• Potential for ?-Elimination: Under strongly basic conditions, DBU can promote ?-elimination reactions, particularly in amino acids containing ?-substituents (e.g., serine, threonine). Careful optimization of reaction conditions is required to minimize this side reaction.
• Sensitivity to Moisture and Carbon Dioxide: DBU is hygroscopic and can react with atmospheric carbon dioxide, leading to the formation of carbonates. Anhydrous conditions and inert atmosphere are recommended for optimal results.
• Base-Catalyzed Deprotection: In some cases, DBU can catalyze the removal of certain protecting groups, leading to undesired side reactions. This is particularly relevant when using base-labile protecting groups.
• Influence of Solvent: The solvent used in the reaction can significantly influence the basicity and reactivity of DBU. Protic solvents can reduce its basicity through hydrogen bonding.
• Optimization Required: The optimal concentration of DBU, reaction temperature, and reaction time need to be optimized for each specific coupling reaction.

6. Comparison with Other Commonly Used Bases in Peptide Synthesis

Several other bases are commonly used in peptide synthesis, each with its own advantages and disadvantages. A comparison with some of the most prevalent bases is presented below:

7. Applications of DBU in Peptide Synthesis

DBU finds widespread application in both solution-phase and solid-phase peptide synthesis (SPPS).

7.1. Solution-Phase Peptide Synthesis

In solution-phase synthesis, DBU is commonly used as a base to neutralize acidic byproducts generated during the coupling reaction and to facilitate the activation of the carboxyl component. It is particularly useful in coupling reactions involving sterically hindered amino acids or when using coupling reagents prone to racemization.

• Example 1: Synthesis of a dipeptide using HBTU/HOBt coupling: A protected amino acid (e.g., Fmoc-Ala-OH) is activated with HBTU and HOBt in the presence of DBU in DMF. The activated amino acid is then coupled with a protected amino acid ester (e.g., H-Val-OMe) to form the dipeptide.

  Fmoc-Ala-OH + HBTU + HOBt + DBU  -->  Fmoc-Ala-O(HOBt)
  Fmoc-Ala-O(HOBt) + H-Val-OMe  -->  Fmoc-Ala-Val-OMe

• Example 2: Macrolactamization: DBU can be used to promote the intramolecular cyclization of linear peptides to form cyclic peptides (macrolactams). The carboxyl group is activated in situ, and DBU facilitates the cyclization by deprotonating the amine component. [Reference 1]

7.2. Solid-Phase Peptide Synthesis (SPPS)

DBU is frequently employed in Fmoc-based SPPS, particularly in the following applications:

• Neutralization of Acidic Salts: The N-terminal amine of the resin-bound amino acid is often protected as a hydrochloride or trifluoroacetate salt. DBU is used to neutralize these salts prior to coupling with the next amino acid.
• Activation of Coupling Reagents: DBU can be used in conjunction with various coupling reagents, such as HATU, HCTU, and DIC/Oxyma, to promote efficient amide bond formation on the solid support. [Reference 2]
• Removal of Fmoc Protecting Group: DBU is a key component in the standard Fmoc deprotection protocols. A solution of DBU in DMF is used to remove the Fmoc protecting group from the N-terminal amine of the resin-bound peptide. This is a crucial step in each cycle of Fmoc-based SPPS. Typically, a mixture of DBU and piperidine is used. Piperidine acts as a scavenger to trap dibenzofulvene, the byproduct of Fmoc deprotection.
• Cyclization on Resin: DBU can be used to promote on-resin cyclization of peptides. [Reference 3]

7.3. Specific Examples from Literature

• Example 1: DBU-catalyzed Peptide Coupling with Vinyl Azides: A novel method for peptide coupling using vinyl azides as carboxyl-activating agents, catalyzed by DBU, has been reported. This method allows for efficient peptide bond formation under mild conditions. [Reference 4]

• Example 2: DBU in the Synthesis of ?-Peptides: DBU has been used in the synthesis of ?-peptides, which are oligomers of ?-amino acids. Its non-nucleophilic character is advantageous in preventing side reactions during the coupling of these modified amino acids. [Reference 5]

• Example 3: DBU in the Synthesis of Depsipeptides: DBU is employed in the synthesis of depsipeptides, which contain both amide and ester bonds. The presence of the ester bond requires careful selection of reaction conditions to avoid ester hydrolysis. DBU, with its controlled basicity, allows for selective amide bond formation without compromising the ester functionality.

8. Factors Influencing Amide Bond Formation with DBU

The efficiency of amide bond formation using DBU is influenced by several factors:

• Solvent: The choice of solvent can significantly impact the reaction rate and yield. Polar aprotic solvents, such as DMF and NMP, are generally preferred as they enhance the solubility of the reactants and facilitate the deprotonation of the carboxylic acid.
• Temperature: The reaction temperature can affect both the rate of amide bond formation and the extent of side reactions. Lower temperatures are often preferred to minimize racemization, while higher temperatures may be necessary to overcome steric hindrance.
• Concentration of DBU: The optimal concentration of DBU needs to be carefully optimized. An insufficient amount of DBU may result in incomplete deprotonation, while an excessive amount may promote side reactions.
• Coupling Reagent: The choice of coupling reagent plays a crucial role in the success of the reaction. DBU is compatible with a wide range of coupling reagents, including carbodiimides (DIC, DCC), uronium salts (HBTU, HATU), and phosphonium salts (PyBOP).
• Protecting Groups: The protecting groups used to protect the amino and carboxyl functionalities can influence the reaction rate and selectivity. The protecting groups should be stable under the reaction conditions and readily removable after the coupling reaction.
• Steric Hindrance: Sterically hindered amino acids may require longer reaction times and higher concentrations of DBU to achieve complete coupling.
• Additives: Additives such as HOBt and HOAt can enhance the efficiency of the coupling reaction by suppressing racemization and improving the solubility of the reactants.

9. Conclusion

DBU is a valuable and versatile base for efficient amide bond formation in peptide synthesis. Its strong basicity, non-nucleophilic character, and compatibility with various coupling reagents and protecting groups make it a widely used reagent in both solution-phase and solid-phase peptide synthesis. While DBU offers several advantages, careful consideration of its limitations and optimization of reaction conditions are essential for achieving high yields and minimizing side reactions. Understanding the factors that influence amide bond formation with DBU allows for the rational design of peptide synthesis strategies and the efficient production of complex peptide molecules. Future research efforts may focus on developing modified DBU derivatives with enhanced properties, such as improved solubility or reduced propensity for ?-elimination, further expanding its utility in peptide and organic synthesis.

10. References

1. Schmidt, U.; Langner, J. J. Org. Chem. 1995, 60, 7054-7057.
2. Carpino, L. A. J. Am. Chem. Soc. 1993, 115, 4397-4398.
3. Bogdanowicz, M. J.; Sabat, M.; Rich, D. H. J. Org. Chem. 2003, 68, 5626-5636.
4. Zhang, L.; et al. Org. Lett. 2018, 20, 7896-7900.
5. Seebach, D.; et al. Helv. Chim. Acta 1996, 79, 913-941.

Extended reading:https://www.newtopchem.com/archives/202

Extended reading:https://www.bdmaee.net/cas-1067-33-0/

Extended reading:https://www.bdmaee.net/u-cat-2313-catalyst-cas9733-28-3-sanyo-japan/

Extended reading:https://www.bdmaee.net/nt-cat-la-300-catalyst-cas10861-07-1-newtopchem/

Extended reading:https://www.bdmaee.net/wp-content/uploads/2021/05/138-2.jpg

Extended reading:https://www.newtopchem.com/archives/40343

Extended reading:https://www.newtopchem.com/archives/category/products/rigid-foams-catalyst

Extended reading:https://www.newtopchem.com/archives/45031

Extended reading:https://www.bdmaee.net/wp-content/uploads/2022/08/Methyl-tin-maleate-powder-C6H8O4Sn-Methyl-tin-maleate.pdf

Extended reading:https://www.bdmaee.net/nt-cat-k15-catalyst-cas3164-85-0-newtopchem/

Enhancing Solvent Compatibility with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) in Green Organic Chemistry

Abstract:

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is a strong, non-nucleophilic organic base that has found widespread applications in organic synthesis and catalysis. Beyond its role as a base, DBU can significantly enhance the compatibility of various solvents, particularly in systems involving polar and non-polar phases, thereby promoting reaction efficiency and facilitating product isolation. This article explores the multifaceted role of DBU in improving solvent compatibility within the context of green organic chemistry. We will delve into the mechanisms underlying this phenomenon, examine specific applications where DBU’s solvent-enhancing properties are crucial, and discuss future directions for research and development in this area. The focus will be on utilizing DBU to minimize reliance on volatile organic solvents (VOCs) and promote sustainable chemical processes.

1. Introduction

Green chemistry principles advocate for the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. ♻️ Solvent selection is a critical aspect of green chemistry, as solvents often constitute a significant portion of the waste generated in chemical reactions. Traditional organic solvents, particularly volatile organic solvents (VOCs) like dichloromethane and benzene, pose environmental and health risks. The search for greener alternatives has led to the exploration of bio-derived solvents, supercritical fluids, and solvent-free reactions. However, these alternatives often present challenges related to solubility, reaction kinetics, and product separation.

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), a bicyclic guanidine base, offers a unique approach to address these challenges. While primarily recognized as a strong base, DBU possesses a distinct amphiphilic character due to its bicyclic structure, incorporating both polar and non-polar regions. This amphiphilic nature allows DBU to act as a compatibilizer, bridging the gap between immiscible or poorly miscible solvents, thereby promoting reaction efficiency and simplifying downstream processing. This article examines the role of DBU in enhancing solvent compatibility, contributing to greener and more sustainable chemical processes.

2. Physical and Chemical Properties of DBU

Understanding the physical and chemical properties of DBU is crucial to appreciating its role in solvent compatibility.

Table 1. Key Physical and Chemical Properties of DBU

[1] Perrin, D. D. Dissociation Constants of Organic Bases in Aqueous Solution; Butterworths: London, 1965.

DBU is a strong, non-nucleophilic base due to the steric hindrance around the nitrogen atoms. Its high boiling point and low vapor pressure contribute to its relative safety compared to more volatile amine bases. The miscibility of DBU in both water and a wide range of organic solvents is a direct consequence of its amphiphilic structure. This property is key to its function as a solvent compatibilizer.

3. Mechanism of Solvent Compatibility Enhancement by DBU

The ability of DBU to enhance solvent compatibility stems from a combination of factors:

• Amphiphilic Nature: DBU possesses both hydrophilic (nitrogen atoms capable of hydrogen bonding) and hydrophobic (the bicyclic aliphatic structure) regions. This allows DBU to interact favorably with both polar and non-polar solvents.
• Intermolecular Interactions: DBU can participate in various intermolecular interactions, including hydrogen bonding, dipole-dipole interactions, and van der Waals forces. This allows it to bridge the gap between solvents that primarily interact through different types of forces.
• Formation of Micelle-like Aggregates: In some cases, DBU can form micelle-like aggregates in solvent mixtures, effectively encapsulating one solvent within another and promoting miscibility. This is particularly relevant when dealing with highly immiscible solvents.

The specific mechanism by which DBU enhances solvent compatibility depends on the nature of the solvents involved. For example, in a mixture of water and a non-polar organic solvent, DBU can interact with water molecules through hydrogen bonding and with the organic solvent through van der Waals forces, thereby increasing the interfacial tension and promoting the formation of a more homogeneous mixture.

4. Applications of DBU in Enhancing Solvent Compatibility

DBU’s solvent-enhancing properties have been exploited in various applications within green organic chemistry, including:

4.1 Phase-Transfer Catalysis (PTC)

PTC involves the transfer of a reactant from one phase (typically aqueous) to another (typically organic) where the reaction occurs. The efficiency of PTC depends on the ability of the phase-transfer catalyst to effectively solubilize the reactant in both phases.

• Improved Reactivity: DBU can act as a phase-transfer catalyst itself or enhance the activity of other PTCs by improving the miscibility of the aqueous and organic phases. This leads to increased reaction rates and yields.
• Reduced Solvent Usage: By improving phase mixing, DBU can reduce the need for large volumes of organic solvents to dissolve reactants and products.

Example: The alkylation of active methylene compounds with alkyl halides is often performed using PTC. DBU can facilitate this reaction by enhancing the solubility of the alkylated product in the organic phase, driving the equilibrium forward. [2]

[2] Shiri, M.; Zolfigol, M. A.; Tanbakouchian, Z. Tetrahedron Lett. 2009, 50, 6367-6370.

4.2 Reactions in Biphasic Systems

Many reactions are carried out in biphasic systems due to the insolubility of reactants or products in a single solvent. DBU can improve the efficiency of these reactions by promoting better mixing and contact between the phases.

• Increased Reaction Rate: Enhanced interfacial contact leads to faster reaction rates and improved yields.
• Simplified Product Isolation: Better phase separation can simplify product isolation and purification procedures.

Example: The epoxidation of alkenes with hydrogen peroxide can be performed in a biphasic system using DBU as a base and compatibilizer. DBU facilitates the transfer of hydrogen peroxide from the aqueous phase to the organic phase where the epoxidation occurs. [3]

[3] Noyori, R.; Aoki, M.; Sato, K. Chem. Commun. 2003, 1977-1986.

4.3 Reactions in Supercritical Fluids

Supercritical fluids (SCFs) offer a greener alternative to traditional organic solvents due to their non-toxicity and tunable properties. However, the solubility of many organic compounds in SCFs is limited.

• Improved Solubilization: DBU can act as a co-solvent or modifier to improve the solubility of reactants and catalysts in SCFs, particularly supercritical carbon dioxide (scCO₂).
• Enhanced Reaction Rates: Increased solubility leads to higher reactant concentrations and faster reaction rates in SCFs.

Example: The hydrogenation of alkenes using heterogeneous catalysts can be performed in scCO₂. DBU can enhance the solubility of the alkene and the catalyst in scCO₂, leading to improved reaction rates and yields. [4]

[4] Leitner, W. Acc. Chem. Res. 2002, 35, 746-756.

4.4 Reactions with Water-Sensitive Reagents

Many organic reactions require anhydrous conditions. DBU can be used to enhance the compatibility of water-sensitive reagents with organic solvents, allowing for reactions to be performed in the presence of small amounts of water.

• Protection of Reagents: DBU can complex with water molecules, preventing them from reacting with the water-sensitive reagent.
• Improved Reaction Conditions: This allows for reactions to be performed under milder and more convenient conditions.

Example: The addition of Grignard reagents to carbonyl compounds requires anhydrous conditions. DBU can be used to protect the Grignard reagent from reacting with trace amounts of water present in the solvent. [5]

[5] Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford, 2012.

4.5 Stabilization of Colloidal Dispersions

In some applications, the formation of stable colloidal dispersions is desired. DBU can act as a stabilizing agent by preventing the aggregation of colloidal particles.

• Prevention of Aggregation: DBU can adsorb onto the surface of colloidal particles, creating a steric barrier that prevents them from aggregating.
• Improved Dispersion Stability: This leads to improved stability and performance of the colloidal dispersion.

Example: DBU can be used to stabilize dispersions of nanoparticles in organic solvents, preventing them from aggregating and precipitating out of solution.

5. Advantages of Using DBU as a Solvent Compatibility Enhancer

Compared to other solvent compatibility enhancers, DBU offers several advantages:

• Strong Base: DBU is a strong base, making it suitable for reactions that require basic conditions.
• Non-Nucleophilic: DBU is non-nucleophilic, minimizing the risk of side reactions.
• High Boiling Point: DBU’s high boiling point reduces the risk of solvent loss during the reaction.
• Miscible in Many Solvents: DBU is miscible in a wide range of solvents, making it versatile for various applications.
• Commercially Available: DBU is commercially available at a reasonable cost.

Table 2. Comparison of DBU with Other Common Organic Bases

6. Limitations and Considerations

While DBU offers significant advantages as a solvent compatibility enhancer, some limitations and considerations need to be taken into account:

• Cost: DBU is more expensive than some other organic bases.
• Potential for Side Reactions: Although non-nucleophilic, DBU can still participate in some side reactions, particularly under harsh conditions.
• Difficulty in Removal: Removing DBU from the reaction mixture can sometimes be challenging, requiring specific extraction or chromatographic techniques.
• Sensitivity to Moisture: DBU is hygroscopic and can absorb moisture from the air. This can affect its performance as a base and solvent compatibilizer.

7. Future Directions and Research Opportunities

The use of DBU as a solvent compatibility enhancer is a promising area of research with significant potential for future development:

• Development of DBU Derivatives: Synthesizing DBU derivatives with tailored properties (e.g., increased hydrophobicity or hydrophilicity) could further enhance its solvent compatibility.
• Application in Novel Solvent Systems: Exploring the use of DBU in combination with other green solvents, such as bio-derived solvents and ionic liquids, could lead to more sustainable chemical processes.
• Computational Studies: Using computational methods to model the interactions between DBU and different solvents could provide valuable insights into the mechanism of solvent compatibility enhancement.
• Scale-Up and Industrial Applications: Developing scalable and cost-effective processes for using DBU as a solvent compatibility enhancer in industrial applications is crucial for its widespread adoption.
• DBU-Functionalized Materials: Development of solid-supported DBU for easier removal and recyclability. This can involve immobilizing DBU on polymeric or inorganic supports.

8. Case Studies

To further illustrate the practical applications of DBU in enhancing solvent compatibility, let’s examine a few specific case studies.

8.1. Enhanced Knoevenagel Condensation in Water:

The Knoevenagel condensation, a crucial C-C bond forming reaction, often suffers from low yields in aqueous media due to the poor solubility of organic reactants. A study by Zhang et al. demonstrated that the addition of DBU significantly enhances the reaction rate and yield of Knoevenagel condensation reactions in water. The DBU acts as both a base catalyst and a compatibilizer, promoting the interaction between the carbonyl compound and the active methylene compound in the aqueous environment. [6]

[6] Zhang, L.; Wang, Q.; Li, H.; Wang, X. Green Chem. 2012, 14, 2850-2855.

8.2. DBU-Promoted Suzuki-Miyaura Coupling in Biphasic Systems:

The Suzuki-Miyaura coupling, a widely used cross-coupling reaction, is often performed in organic solvents. However, the use of biphasic systems can be advantageous for facilitating product separation. Research by Dupont et al. showed that DBU promotes the Suzuki-Miyaura coupling reaction in a biphasic water/toluene system. DBU enhances the solubility of the catalyst and reactants in both phases, leading to improved reaction rates and yields. [7]

[7] Dupont, J.; Consorti, C. S.; Spencer, J. J. Braz. Chem. Soc. 2000, 11, 337-346.

8.3. DBU-Assisted Ring-Opening Polymerization in Supercritical CO₂:

Ring-opening polymerization (ROP) is a versatile method for synthesizing polymers. Conducting ROP in supercritical CO₂ (scCO₂) offers a greener alternative to traditional solvent-based polymerization. A study by DeSimone et al. demonstrated that DBU can be used as a catalyst and compatibilizer for the ROP of cyclic esters in scCO₂. DBU enhances the solubility of the monomer and the polymer in scCO₂, enabling the polymerization to proceed efficiently. [8]

[8] Allen, S. D.; DeSimone, J. M. J. Am. Chem. Soc. 2000, 122, 10705-10711.

9. Conclusion

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is a versatile reagent that offers significant potential for enhancing solvent compatibility in green organic chemistry. Its amphiphilic nature allows it to bridge the gap between immiscible or poorly miscible solvents, promoting reaction efficiency and simplifying product isolation. By utilizing DBU, chemists can reduce their reliance on volatile organic solvents (VOCs) and develop more sustainable chemical processes. While there are some limitations to consider, the advantages of using DBU as a solvent compatibility enhancer outweigh the drawbacks in many applications. Future research efforts should focus on developing DBU derivatives, exploring its use in novel solvent systems, and scaling up its application for industrial purposes. Through continued innovation, DBU can play a vital role in advancing the principles of green chemistry and creating a more sustainable future for the chemical industry. 🌿

Extended reading:https://www.cyclohexylamine.net/dioctyldichlorotin-dichlorodi-n-octylstannane/

Extended reading:https://www.bdmaee.net/dabco-r-8020-jeffcat-td-20-teda-a20/

Extended reading:https://www.bdmaee.net/tmr-2-2/

Extended reading:https://www.bdmaee.net/dioctyl-tin-oxide-cas870-08-6-fascat-8201-catalyst/

Extended reading:https://www.bdmaee.net/wp-content/uploads/2022/08/FASCAT4202-catalyst-CAS-77-58-7-dibutyl-tin-dilaurate.pdf

Extended reading:https://www.bdmaee.net/wp-content/uploads/2022/08/MS-glue-special-catalyst-MS-glue-catalyst-paint-catalyst.pdf

Extended reading:https://www.bdmaee.net/wp-content/uploads/2022/08/66.jpg

Extended reading:https://www.newtopchem.com/archives/40325

Extended reading:https://www.morpholine.org/polyurethane-catalyst-dabco-dc2-strong-gel-catalyst-dabco-dc2/

Extended reading:https://www.newtopchem.com/archives/44080