N,N-Dimethylcyclohexylamine: A Comprehensive Overview of Structure, Properties, and Catalytic Applications

Introduction

N,N-Dimethylcyclohexylamine (DMCHA) is a tertiary amine widely employed as a catalyst in various industrial processes, notably in the production of polyurethane foams and coatings. Its cyclic structure and dialkyl substitution on the nitrogen atom impart unique characteristics that contribute to its catalytic activity and selectivity. This article provides a detailed overview of DMCHA, exploring its chemical properties, synthesis methods, applications, and a comparative analysis with other amine catalysts. The structure of this article will follow a similar pattern to that of a Baidu Baike entry, ensuring a clear and organized presentation of information.

1. Chemical Information

• IUPAC Name: N,N-Dimethylcyclohexanamine
• Common Name: N,N-Dimethylcyclohexylamine; DMCHA
• CAS Registry Number: 98-94-2
• Molecular Formula: C₈H₁₇N
• Molecular Weight: 127.23 g/mol
• Structural Formula:

    CH3
     |
  N--C6H11
     |
    CH3

2. Physical and Chemical Properties

3. Synthesis Methods

DMCHA can be synthesized through several methods, including:

• Reductive Amination of Cyclohexanone: This involves reacting cyclohexanone with dimethylamine in the presence of a reducing agent, such as hydrogen and a metal catalyst (e.g., nickel, palladium).

  C6H10O + (CH3)2NH + H2  --[Catalyst]--> C8H17N + H2O

• Alkylation of Cyclohexylamine: This method involves the alkylation of cyclohexylamine with methyl halides (e.g., methyl chloride, methyl iodide) or dimethyl sulfate. This reaction typically requires a base to neutralize the liberated acid.

  C6H11NH2 + 2 CH3X --[Base]--> C8H17N + 2 HX  (X = Cl, I)

• Direct Amination of Cyclohexanol: Cyclohexanol can be directly aminated with dimethylamine over a suitable catalyst at elevated temperatures. This method is considered greener as it avoids the use of stoichiometric reducing agents or alkylating agents.

  C6H11OH + (CH3)2NH  --[Catalyst]--> C8H17N + H2O

The choice of synthesis method depends on factors such as cost, availability of starting materials, and desired purity of the product.

4. Applications

DMCHA finds widespread use in various industrial applications, primarily as a catalyst:

• Polyurethane Foam Production: DMCHA is a crucial catalyst in the production of polyurethane foams, both rigid and flexible. It accelerates the reaction between polyols and isocyanates, leading to the formation of the urethane linkage. It also promotes the blowing reaction, which generates carbon dioxide to create the cellular structure of the foam.

• Polyurethane Coatings and Elastomers: Similar to foam production, DMCHA is used to catalyze the reactions involved in the synthesis of polyurethane coatings and elastomers. It helps control the reaction rate and ensures proper crosslinking, resulting in desired mechanical properties.

• Epoxy Resin Curing: DMCHA can act as a curing agent or accelerator for epoxy resins. It initiates the ring-opening polymerization of the epoxy groups, leading to the formation of a crosslinked polymer network.

• Polymerization Reactions: DMCHA can be employed as a catalyst in various other polymerization reactions, including Michael additions and transesterifications.

• Pharmaceutical Intermediates: DMCHA serves as a building block or intermediate in the synthesis of various pharmaceutical compounds.

• Neutralizing Agent: In some applications, DMCHA is used as a neutralizing agent for acidic compounds.

5. Mechanism of Catalysis

The catalytic activity of DMCHA is based on its ability to act as a nucleophile and a base. In polyurethane chemistry, for instance, it facilitates both the urethane (gelation) and urea (blowing) reactions.

• Urethane Reaction (Gelation): DMCHA activates the hydroxyl group of the polyol by abstracting a proton, making it more nucleophilic and accelerating its reaction with the isocyanate group.

  R-OH + DMCHA  <-->  R-O⁻...H⁺-DMCHA
  R-O⁻...H⁺-DMCHA + R'-NCO  --> R-O-C(O)-NH-R' + DMCHA

• Urea Reaction (Blowing): DMCHA also catalyzes the reaction between isocyanate and water to form carbon dioxide, which acts as the blowing agent. The mechanism involves the formation of an unstable carbamic acid intermediate, which then decomposes to yield carbon dioxide and an amine.

  R-NCO + H2O  -->  R-NH-COOH
  R-NH-COOH + DMCHA  -->  R-NH-COO⁻...H⁺-DMCHA
  R-NH-COO⁻...H⁺-DMCHA --> R-NH2 + CO2 + DMCHA

The efficiency of DMCHA as a catalyst depends on its concentration, the reaction temperature, and the specific reactants involved.

6. Safety Information

• Toxicity: DMCHA is considered moderately toxic. Inhalation, ingestion, or skin absorption can cause irritation and other adverse health effects.
• Flammability: DMCHA is flammable, with a relatively low flash point. Proper handling and storage procedures should be followed to prevent fire hazards.
• Handling and Storage: DMCHA should be handled in well-ventilated areas, and appropriate personal protective equipment (PPE) should be worn, including gloves, safety glasses, and a respirator if necessary. It should be stored in tightly closed containers in a cool, dry, and well-ventilated place away from heat, sparks, and open flames.
• First Aid: In case of contact with skin or eyes, flush with plenty of water for at least 15 minutes. If inhaled, move to fresh air. If ingested, do not induce vomiting and seek medical attention immediately.

7. Environmental Considerations

DMCHA is considered to have some environmental impact. Its volatility can contribute to air pollution, and its release into aquatic environments can be harmful to aquatic organisms. Proper waste disposal methods should be employed to minimize its environmental impact. Research is ongoing to develop more environmentally friendly alternatives to DMCHA in various applications.

8. Quality Control and Specifications

These specifications ensure that the DMCHA meets the required standards for its intended applications.

9. Comparison with Other Amine Catalysts

DMCHA is just one of many amine catalysts used in various industries. Comparing its properties and performance with other common amine catalysts helps understand its advantages and disadvantages.

Explanation of the Table:

• Structure: Provides a simplified representation of the chemical structure of each amine catalyst.
• pKa: The pKa value is an indicator of the basicity of the amine. Higher pKa values generally correspond to stronger bases.
• Relative Activity in Polyurethane Foam: This column indicates the relative catalytic activity of each amine in polyurethane foam production. The activity is classified as low, moderate, or high. Gel catalysts primarily promote the urethane reaction (gelation), while blow catalysts primarily promote the urea reaction (blowing).
• Advantages: Highlights the key benefits of using each specific amine catalyst.
• Disadvantages: Lists the potential drawbacks or limitations associated with each amine catalyst.

Detailed Comparison Points:

• Basicity (pKa): The basicity of the amine catalyst is a critical factor influencing its catalytic activity. More basic amines tend to be more effective catalysts, but they can also be more prone to side reactions. DMCHA has a moderate pKa value, providing a good balance of activity and selectivity.

• Gel vs. Blow Catalysis: In polyurethane foam production, it’s essential to balance the gel (urethane formation) and blow (CO2 generation) reactions. DMCHA provides a moderate balance of both, making it a versatile catalyst. Some amines, like TEDA, are primarily gel catalysts, while others, like BDMAEE, are primarily blow catalysts.

• Odor: The odor of amine catalysts can be a concern, especially in consumer applications. DMCHA has a relatively low odor compared to some other amines, such as TEDA.

• Emissions (VOCs): Many amine catalysts are volatile organic compounds (VOCs) and can contribute to air pollution. Reactive catalysts, like DMAE, which incorporate into the polymer matrix, can help reduce emissions.

• Discoloration: Some amine catalysts can cause discoloration in polyurethane foams or coatings. DMCHA is less prone to causing discoloration compared to some other amines.

• Reactivity and Side Reactions: Highly reactive amines can lead to unwanted side reactions, such as chain termination or premature gelation. DMCHA’s moderate reactivity helps minimize these issues.

• Cost: The cost of amine catalysts can vary depending on their availability and synthesis complexity. DMCHA is generally considered a cost-effective catalyst.

10. Future Trends and Research Directions

Research is ongoing to develop more sustainable and environmentally friendly alternatives to traditional amine catalysts like DMCHA. Some key areas of focus include:

• Reactive Amine Catalysts: Developing amine catalysts that incorporate into the polymer matrix, reducing VOC emissions.
• Bio-based Amine Catalysts: Exploring the use of amine catalysts derived from renewable resources.
• Metal-Based Catalysts: Investigating the use of metal-based catalysts as alternatives to amine catalysts.
• Encapsulated Catalysts: Developing encapsulated amine catalysts to improve their handling, reduce odor, and control their release.
• Optimized Catalyst Blends: Designing optimized blends of amine catalysts to achieve specific performance characteristics in polyurethane foams and other applications.

These research efforts aim to address the environmental and health concerns associated with traditional amine catalysts while maintaining or improving their catalytic performance.

Conclusion

N,N-Dimethylcyclohexylamine (DMCHA) is a versatile tertiary amine widely used as a catalyst in polyurethane foam production, coatings, and other industrial applications. Its moderate basicity, balanced gel and blow catalysis, and relatively low odor make it a valuable component in various formulations. While DMCHA has proven to be an effective catalyst, ongoing research is focused on developing more sustainable and environmentally friendly alternatives to address concerns about VOC emissions and potential health effects. The continued development of new catalyst technologies will play a crucial role in shaping the future of polyurethane chemistry and other industries that rely on amine catalysts.

Literature Sources (References)

[1] Sigma-Aldrich product safety data sheet for N,N-Dimethylcyclohexylamine. (Replace with actual link and accessed date if applicable – external links are not allowed)

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

[3] Riddick, J. A.; Bunger, W. B.; Sakano, T. K. Organic Solvents: Physical Properties and Methods of Purification, 4th ed.; Wiley-Interscience: New York, 1986.

[4] Randall, D.; Lee, S. The Polyurethanes Book. John Wiley & Sons: 2002.

[5] Ulrich, H. Introduction to Industrial Polymers. Hanser Publishers: 1993.

[6] Oertel, G. Polyurethane Handbook. Hanser Publishers: 1994.

[7] Woods, G. The ICI Polyurethanes Book. John Wiley & Sons: 1990.

[8] Chattopadhyay, D. K.; Webster, D. C. Progress in Polymer Science 2009, 34, 1068-1133. (Example of a Journal Article)

[9] European Chemicals Agency (ECHA) Registration dossier for N,N-Dimethylcyclohexylamine. (Replace with actual link and accessed date if applicable – external links are not allowed)

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