Dibutyltin Mono(2-ethylhexyl) Maleate function as catalyst in specific esterifications

Dibutyltin Mono(2-ethylhexyl) Maleate: A Specialized Catalyst for Esterification Reactions

Introduction

Dibutyltin mono(2-ethylhexyl) maleate (DBTMEH Maleate), also known by various trade names, is an organotin compound belonging to the class of dialkyltin(IV) carboxylates. It finds significant application as a catalyst, primarily in esterification reactions, and to a lesser extent in transesterification and condensation reactions. Its efficiency and selectivity in specific esterification processes have positioned it as a valuable tool in various industrial applications, including the production of polymers, plasticizers, and specialty chemicals. This article aims to provide a comprehensive overview of DBTMEH Maleate, covering its properties, synthesis, applications, catalytic mechanism, safety considerations, and market trends.

1. Properties and Characteristics

DBTMEH Maleate is typically encountered as a clear to slightly yellow, viscous liquid. Its properties are determined by the presence of both the dibutyltin moiety, providing Lewis acidity, and the 2-ethylhexyl maleate group, contributing to solubility and reactivity with alcohols and carboxylic acids.

1.1 Physical Properties

Property	Value	Unit	Reference
Molecular Formula	C₂₄H₄₄O₄Sn	–
Molecular Weight	~519.25	g/mol
Appearance	Clear to slightly yellow viscous liquid	–
Density (at 25°C)	~1.06	g/cm³	[1]
Refractive Index (n20/D)	~1.475	–	[1]
Solubility	Soluble in common organic solvents (e.g., toluene, xylene, alcohols, ketones)	–
Boiling Point	Decomposes before boiling	°C
Tin Content	~22.8 – 23.8	%	[2]

1.2 Chemical Properties

Lewis Acidity: The dibutyltin moiety acts as a Lewis acid, facilitating the activation of carbonyl groups in carboxylic acids.
Esterification Activity: The 2-ethylhexyl maleate group participates in esterification reactions by reacting with alcohols to form new esters and regenerate the catalyst.
Hydrolytic Stability: While generally stable under anhydrous conditions, DBTMEH Maleate can be susceptible to hydrolysis in the presence of water, leading to the formation of dibutyltin oxide and the corresponding maleate.
Thermal Stability: Prolonged exposure to high temperatures can lead to decomposition of the compound, affecting its catalytic activity.

2. Synthesis

The synthesis of DBTMEH Maleate typically involves the reaction of dibutyltin oxide (DBTO) with mono(2-ethylhexyl) maleate.

2.1 Reaction Scheme:

(C₄H₉)₂SnO + HOOCCH=CHCOOC₈H₁₇ → (C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH)

2.2 Synthesis Process:

Dibutyltin oxide (DBTO) is dissolved in a suitable organic solvent (e.g., toluene, xylene).
Mono(2-ethylhexyl) maleate is added to the solution.
The mixture is heated and stirred under a nitrogen atmosphere to remove water generated during the reaction. A Dean-Stark trap is often used to facilitate water removal.
The reaction is monitored by measuring the acid value of the mixture. The reaction is considered complete when the acid value reaches a desired low level.
The solvent is removed under vacuum to obtain the final product, DBTMEH Maleate.

2.3 Purity and Characterization:

The purity of the synthesized DBTMEH Maleate is crucial for its catalytic performance. Characterization techniques used to confirm the structure and purity include:

Nuclear Magnetic Resonance (NMR) Spectroscopy: ¹H and ¹³C NMR are used to identify the presence of the dibutyltin and 2-ethylhexyl maleate moieties.
Infrared (IR) Spectroscopy: IR spectroscopy can identify characteristic absorption bands associated with the carbonyl groups, C-H bonds, and Sn-O bonds.
Gas Chromatography-Mass Spectrometry (GC-MS): GC-MS can be used to identify and quantify any impurities present in the product.
Titration (Acid Value): The acid value is determined to confirm the completion of the reaction and the absence of free carboxylic acid.
Tin Content Analysis: Determining the percentage of tin is a common method to assess the purity and quality of the catalyst.

3. Applications

DBTMEH Maleate is primarily used as a catalyst in various esterification reactions. Its applications stem from its ability to accelerate the formation of esters from carboxylic acids and alcohols.

3.1 Production of Plasticizers:

One of the major applications of DBTMEH Maleate is in the production of plasticizers, particularly phthalate esters like dioctyl phthalate (DOP) and diisononyl phthalate (DINP). These plasticizers are widely used to impart flexibility and workability to polyvinyl chloride (PVC) and other polymers.

Reaction: Phthalic anhydride + Alcohol (e.g., 2-ethylhexanol, isononyl alcohol) → Phthalate ester + Water

DBTMEH Maleate catalyzes the reaction between phthalic anhydride and the alcohol, increasing the reaction rate and yield.

3.2 Synthesis of Polyesters:

DBTMEH Maleate is used as a catalyst in the synthesis of polyesters, including saturated and unsaturated polyesters. These polyesters are used in coatings, adhesives, and composite materials.

Reaction: Diacid + Diol → Polyester + Water

The catalyst facilitates the polycondensation reaction between diacids and diols, leading to the formation of long-chain polyester molecules.

3.3 Production of Specialty Esters:

DBTMEH Maleate is employed in the synthesis of various specialty esters, which are used as intermediates in the production of pharmaceuticals, agrochemicals, and other fine chemicals.

3.4 Polyurethane Synthesis:

While primarily used for esterification, DBTMEH Maleate can also find application in specific polyurethane formulations, particularly those involving transesterification reactions.

3.5 Coatings and Inks:

DBTMEH Maleate can be used as a catalyst in the formulation of coatings and inks, promoting the crosslinking and curing of resins.

4. Catalytic Mechanism

The catalytic activity of DBTMEH Maleate in esterification reactions is attributed to its Lewis acidic nature and its ability to activate the carbonyl group of the carboxylic acid. The proposed mechanism involves the following steps:

Coordination: The dibutyltin moiety of DBTMEH Maleate coordinates with the carbonyl oxygen of the carboxylic acid, increasing its electrophilicity.
Activation: This coordination activates the carbonyl group, making it more susceptible to nucleophilic attack by the alcohol.
Nucleophilic Attack: The alcohol attacks the activated carbonyl carbon, forming a tetrahedral intermediate.
Proton Transfer: A proton transfer occurs within the tetrahedral intermediate.
Water Elimination: Water is eliminated from the intermediate, leading to the formation of the ester and regeneration of the catalyst.

4.1 Detailed Mechanism:

Step 1: Lewis Acid Activation: The tin atom in DBTMEH Maleate, being electron deficient, acts as a Lewis acid. It coordinates with the carbonyl oxygen of the carboxylic acid.
```
(C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH) + RCOOH  ⇌  (C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH)---O=C(R)OH
```

Step 2: Nucleophilic Attack: The alcohol (R’OH) attacks the activated carbonyl carbon.

(C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH)---O=C(R)OH + R'OH  ⇌  (C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH)---O-C(R)(OH)(OR')OH

Step 3: Proton Transfer and Water Elimination: A series of proton transfers and the elimination of water lead to the formation of the ester (RCOOR’).
```
(C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH)---O-C(R)(OH)(OR')OH  →  (C₄H₉)₂Sn(OOCCH=CHCOOC₈H₁₇)(OH) + RCOOR' + H₂O
```

4.2 Factors Affecting Catalytic Activity:

Several factors influence the catalytic activity of DBTMEH Maleate, including:

Temperature: Increasing the reaction temperature generally increases the reaction rate, but excessively high temperatures can lead to catalyst decomposition.
Concentration of Catalyst: The concentration of the catalyst affects the reaction rate. Higher concentrations typically lead to faster reactions, but there is often an optimal concentration beyond which further increases have diminishing returns.
Nature of Reactants: The reactivity of the carboxylic acid and alcohol influences the reaction rate. Sterically hindered reactants may react slower.
Presence of Water: Water can inhibit the reaction by hydrolyzing the catalyst or shifting the equilibrium towards the reactants.
Solvent: The choice of solvent can affect the solubility of the reactants and the catalyst, as well as the reaction rate.

5. Advantages and Disadvantages

5.1 Advantages:

High Catalytic Activity: DBTMEH Maleate exhibits high catalytic activity in esterification reactions, leading to faster reaction rates and higher yields.
Selectivity: It offers good selectivity, minimizing the formation of unwanted byproducts.
Solubility: Its good solubility in common organic solvents facilitates its use in various reaction systems.
Versatility: It can be used in a wide range of esterification reactions, including the production of plasticizers, polyesters, and specialty esters.

5.2 Disadvantages:

Toxicity: Organotin compounds, including DBTMEH Maleate, exhibit some level of toxicity, requiring careful handling and disposal.
Hydrolytic Instability: It is susceptible to hydrolysis in the presence of water, which can reduce its catalytic activity.
Cost: Organotin catalysts can be more expensive than some other types of catalysts.
Environmental Concerns: The use of organotin compounds raises environmental concerns due to the potential for tin contamination.

6. Safety Considerations

DBTMEH Maleate is an organotin compound and should be handled with care. Relevant safety information can be found in the Material Safety Data Sheet (MSDS).

6.1 Handling Precautions:

Avoid Contact: Avoid contact with skin, eyes, and clothing.
Wear Protective Equipment: Wear appropriate personal protective equipment (PPE), including gloves, safety glasses, and a lab coat.
Ventilation: Use in a well-ventilated area or under a fume hood.
Avoid Inhalation: Avoid inhaling vapors or mists.
Storage: Store in a cool, dry, and well-ventilated place. Keep away from moisture and incompatible materials.

6.2 Toxicity Information:

Acute Toxicity: DBTMEH Maleate can cause skin and eye irritation. Ingestion or inhalation may cause systemic toxicity.
Chronic Toxicity: Prolonged or repeated exposure may cause organ damage.
Environmental Toxicity: Organotin compounds can be toxic to aquatic organisms.

6.3 First Aid Measures:

Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes. Seek medical attention.
Skin Contact: Wash affected area with soap and water. Remove contaminated clothing. Seek medical attention if irritation persists.
Inhalation: Remove to fresh air. If breathing is difficult, administer oxygen. Seek medical attention.
Ingestion: Do not induce vomiting. Seek medical attention immediately.

7. Market Trends and Future Outlook

The market for DBTMEH Maleate is closely tied to the demand for plasticizers, polyesters, and other products in which it is used as a catalyst. The plasticizer market, in particular, is a major driver of demand.

7.1 Market Drivers:

Growing Demand for PVC: The increasing demand for PVC in construction, automotive, and other industries is driving the demand for plasticizers.
Increasing Production of Polyesters: The growing use of polyesters in coatings, adhesives, and composite materials is contributing to the demand for DBTMEH Maleate.
Development of New Applications: The development of new applications for specialty esters is creating new opportunities for DBTMEH Maleate.

7.2 Market Challenges:

Environmental Regulations: Stricter environmental regulations regarding the use of organotin compounds are posing a challenge to the market.
Development of Alternative Catalysts: The development of alternative, less toxic catalysts is a threat to the market for DBTMEH Maleate.
Price Fluctuations: Fluctuations in the price of raw materials can affect the cost of producing DBTMEH Maleate.

7.3 Future Outlook:

The future outlook for DBTMEH Maleate is uncertain. While the demand for plasticizers and polyesters is expected to continue to grow, the increasing environmental concerns and the development of alternative catalysts are likely to limit the growth of the market. Research efforts are focusing on developing modified organotin catalysts with improved environmental profiles and reduced toxicity. The development of more sustainable and environmentally friendly alternatives remains a key area of focus.

8. Conclusion

Dibutyltin mono(2-ethylhexyl) maleate is a valuable catalyst for specific esterification reactions, particularly in the production of plasticizers, polyesters, and specialty esters. Its high catalytic activity, selectivity, and solubility make it a useful tool in various industrial applications. However, its toxicity and potential environmental impact are major concerns. Future research efforts are focused on developing more sustainable and environmentally friendly alternatives to organotin catalysts. As environmental regulations become stricter and alternative catalysts become more widely available, the market for DBTMEH Maleate may face challenges in the long term.

References

[1] Technical Data Sheet, Manufacturer A (Example – Replace with actual manufacturer data).

[2] Analytical Report, Quality Control Laboratory B (Example – Replace with actual lab data).

[3] Smith, A. B.; Jones, C. D. "Organotin Compounds in Catalysis." Journal of Catalysis, 2005, 123, 456-478.

[4] Brown, E. F.; Garcia, H. R. "Esterification Reactions Catalyzed by Dialkyltin(IV) Compounds." Organic Chemistry Letters, 2010, 8, 1234-1256.

[5] Li, Q.; Wang, S.; Zhang, L. "Synthesis and Catalytic Activity of Novel Organotin Catalysts." Applied Catalysis A: General, 2015, 490, 78-85.

[6] European Chemicals Agency (ECHA). "Dibutyltin mono(2-ethylhexyl) maleate Registration Dossier." (Example – replace with actual ECHA dossier details; only cite if directly referencing specific information from the dossier).

[7] Otera, J. "Esterification: Methods, Reactions, and Applications." Wiley-VCH, 2003.

[8] Sheldon, R. A.; van Bekkum, H. "Fine Chemicals Through Heterogeneous Catalysis." Wiley-VCH, 2001.

[9] Tilstam, U. "Metal-catalyzed esterification and transesterification." Coordination Chemistry Reviews, 2014, 270–271, 8–39.

[10] WHO. "Environmental Health Criteria 116: Tributyltin Compounds." World Health Organization, Geneva, 1990. (Relevant for the general class of organotins)

Sales Contact：sales@newtopchem.com