N,N-Dimethylcyclohexylamine: A Comprehensive Overview

Introduction

N,N-Dimethylcyclohexylamine (DMCHA), with the Chemical Abstracts Service (CAS) registry number 98-94-2, is a tertiary amine characterized by a cyclohexyl ring substituted with two methyl groups attached to the nitrogen atom. This compound is a clear to pale yellow liquid at room temperature and atmospheric pressure. DMCHA is a versatile chemical intermediate widely employed in various industrial applications, particularly in the production of polyurethane foams, epoxy resins, and as a catalyst in organic synthesis. This article provides a comprehensive overview of DMCHA, covering its physical and chemical properties, specifications, synthesis methods, applications, safety information, and regulatory status. The information presented aims to offer a detailed understanding of DMCHA for researchers, industrial professionals, and anyone seeking information on this important chemical compound.

Basic Information

Physical and Chemical Properties

Understanding the physical and chemical properties of DMCHA is crucial for its safe handling, storage, and application. These properties determine its behavior in different environments and its reactivity with other chemicals.

Explanation of Key Properties:

• Boiling Point: DMCHA’s boiling point of approximately 160 °C indicates that it is a relatively volatile liquid.
• Flash Point: The flash point of 43 °C signifies that DMCHA is flammable and requires careful handling to avoid fire hazards.
• Density: Its density of 0.845 g/cm³ means it is less dense than water and will float on water.
• Solubility: The limited solubility in water makes it necessary to use organic solvents for many applications. The good solubility in organic solvents facilitates its incorporation into various formulations.
• pKa: The pKa value indicates the basicity of the amine. DMCHA is a relatively strong base, which is crucial for its catalytic activity in various reactions.

Technical Specifications

The technical specifications of DMCHA define the quality and purity requirements for its various applications. Different grades of DMCHA may exist depending on the intended use. Here’s a typical example of technical specifications:

Explanation of Specifications:

• Assay (GC): This specification ensures the purity of the DMCHA, indicating the percentage of the desired compound present in the sample. Gas Chromatography (GC) is a common analytical technique for determining the composition of volatile organic compounds.
• Water Content (KF): The water content specification limits the amount of water present in the DMCHA. Excessive water can interfere with certain reactions and degrade the product. Karl Fischer Titration is a standard method for determining water content.
• Color (APHA): The APHA color scale measures the yellowness of the liquid. A lower APHA value indicates a clearer, less colored product.
• Cyclohexylamine and N-Methylcyclohexylamine: These are potential impurities that may be present in the DMCHA. Their concentrations are limited to ensure the quality and performance of the product.
• Refractive Index: This is a physical property that can be used to verify the identity and purity of the DMCHA.

Synthesis Methods

DMCHA can be synthesized through various methods, including reductive amination and alkylation of cyclohexylamine.

1. Reductive Amination:

This method involves the reaction of cyclohexanone with dimethylamine in the presence of a reducing agent. The reaction proceeds through an intermediate imine or enamine, which is subsequently reduced to the desired amine.

Cyclohexanone + Dimethylamine + Reducing Agent → DMCHA + Byproducts

Common reducing agents include:

• Hydrogen gas with a metal catalyst (e.g., Ni, Pd, Pt) [8]
• Sodium borohydride (NaBH₄) [9]
• Sodium cyanoborohydride (NaBH₃CN) [10]

Advantages: This method offers relatively high yields and can be conducted under mild conditions.

Disadvantages: The use of metal catalysts or specialized reducing agents can increase the cost of production.

2. Alkylation of Cyclohexylamine:

This method involves the alkylation of cyclohexylamine with methylating agents.

Cyclohexylamine + 2 Methylating Agents → DMCHA + Byproducts

Common methylating agents include:

• Methyl iodide (CH₃I) [11]
• Dimethyl sulfate ((CH₃)₂SO₄) [12]

Advantages: This method is relatively straightforward and can be conducted in a variety of solvents.

Disadvantages: The use of highly toxic methylating agents requires careful handling and disposal. The reaction may also produce unwanted byproducts.

3. Catalytic Amination:

This method involves reacting cyclohexanol with dimethylamine over a heterogeneous catalyst.

Cyclohexanol + Dimethylamine → DMCHA + Water

The reaction typically uses catalysts based on copper, nickel, or other transition metals supported on alumina or silica. [13, 14]

Advantages: This method can be performed in the gas phase and may offer a more sustainable route compared to methods using stoichiometric reducing agents.

Disadvantages: The catalyst activity and selectivity can be affected by reaction conditions and catalyst poisoning.

Reaction Mechanism (Reductive Amination with Hydrogen):

1. Imine Formation: Cyclohexanone reacts with dimethylamine to form an imine intermediate, releasing water.
2. Adsorption: The imine adsorbs onto the surface of the metal catalyst.
3. Hydrogenation: Hydrogen gas dissociates on the catalyst surface and reduces the imine to DMCHA.
4. Desorption: DMCHA desorbs from the catalyst surface.

Applications

DMCHA finds widespread applications in various industries due to its unique chemical properties. The main applications include:

1. Polyurethane Production: DMCHA is primarily used as a catalyst in the production of polyurethane foams, elastomers, and coatings. It acts as a tertiary amine catalyst, accelerating the reaction between isocyanates and polyols. [15, 16]

   • Foam Production: DMCHA promotes both the blowing (reaction of isocyanate with water) and gelling (reaction of isocyanate with polyol) reactions, which are essential for the formation of polyurethane foams.

   • Elastomers and Coatings: DMCHA is also used in the production of polyurethane elastomers and coatings, where it contributes to the crosslinking and curing processes.

2. Epoxy Resin Curing: DMCHA can act as a curing agent or accelerator for epoxy resins. It promotes the polymerization of epoxy resins, leading to the formation of crosslinked networks with desirable mechanical and thermal properties. [17, 18]

3. Organic Synthesis: DMCHA is used as a base catalyst and a reagent in various organic reactions. [19]

   • Esterification: It can catalyze the esterification of carboxylic acids.
   • Transesterification: DMCHA can facilitate the transesterification of esters.
   • Michael Addition: It can promote Michael addition reactions.
   • Wittig Reactions: DMCHA can be used as a base in Wittig reactions.

4. Pharmaceuticals: DMCHA derivatives have found applications in the synthesis of various pharmaceutical compounds. [20]

5. Corrosion Inhibitors: DMCHA and its derivatives can be used as corrosion inhibitors for metals. [21]

6. Water Treatment: DMCHA can be used as a neutralizer and scale inhibitor in water treatment processes. [22]

Safety Information

DMCHA is classified as a hazardous chemical and requires careful handling and storage. Understanding its hazards and implementing appropriate safety measures is crucial to prevent accidents and protect human health and the environment.

Safety Precautions:

• Handling:
  • Wear appropriate personal protective equipment (PPE), including gloves, safety goggles, and a respirator if necessary.
  • Handle in a well-ventilated area.
  • Avoid contact with skin, eyes, and clothing.
  • Avoid breathing vapors or mist.
  • Wash thoroughly after handling.
• Storage:
  • Store in a tightly closed container in a cool, dry, and well-ventilated area.
  • Keep away from heat, sparks, and open flames.
  • Store away from incompatible materials (e.g., strong oxidizing agents, strong acids).
  • Ground containers to prevent static electricity buildup.
• First Aid:
  • Eye Contact: Rinse immediately with plenty of water for at least 15 minutes and seek medical attention.
  • Skin Contact: Wash affected area with soap and water. Remove contaminated clothing and shoes. 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. Rinse mouth with water. Seek immediate medical attention.
• Firefighting:
  • Use water spray, alcohol-resistant foam, dry chemical, or carbon dioxide to extinguish fires.
  • Wear self-contained breathing apparatus (SCBA) and protective clothing to prevent exposure to vapors and combustion products.
• Spill Response:
  • Contain the spill and prevent it from entering waterways or sewers.
  • Absorb the spill with an inert material (e.g., sand, vermiculite).
  • Collect the absorbed material in a sealed container for disposal.
  • Ventilate the area and wash the spill site with water.

Personal Protective Equipment (PPE):

• Gloves: Chemical-resistant gloves (e.g., nitrile, neoprene)
• Eye Protection: Safety goggles or face shield
• Respiratory Protection: Respirator with an organic vapor cartridge if ventilation is inadequate
• Clothing: Chemical-resistant apron or coveralls

Regulatory Information

The regulatory status of DMCHA varies depending on the country and region. It is important to comply with all applicable regulations regarding the manufacture, transportation, storage, use, and disposal of DMCHA.

• Globally Harmonized System (GHS): DMCHA is classified under the GHS and is assigned hazard statements and precautionary statements as described in the Safety Information section.
• European Union (EU): DMCHA is subject to REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulations. Manufacturers and importers are required to register DMCHA with the European Chemicals Agency (ECHA).
• United States (US): DMCHA is subject to regulations under the Toxic Substances Control Act (TSCA).
• China: DMCHA is listed in the Inventory of Existing Chemical Substances in China (IECSC).

Environmental Considerations

DMCHA can pose environmental risks if released into the environment. It is important to minimize its release and to properly dispose of waste containing DMCHA.

• Biodegradability: DMCHA is not readily biodegradable.
• Aquatic Toxicity: DMCHA is toxic to aquatic organisms.
• Waste Disposal: Dispose of DMCHA waste in accordance with local, state, and federal regulations. Incineration is a common method for disposing of DMCHA waste.

Conclusion

N,N-Dimethylcyclohexylamine (DMCHA) is a versatile chemical compound with a wide range of applications in various industries. Its key properties, including its boiling point, flash point, and basicity, make it suitable for use as a catalyst in polyurethane production, an epoxy resin curing agent, and a reagent in organic synthesis. However, DMCHA is also a hazardous chemical and requires careful handling and storage to prevent accidents and protect human health and the environment. By understanding the properties, applications, safety information, and regulatory status of DMCHA, users can ensure its safe and responsible use. Continuous research and development efforts are focused on improving the synthesis methods, expanding the applications, and enhancing the safety profile of DMCHA.

Literature References

[1] Sigma-Aldrich. N,N-Dimethylcyclohexylamine. Safety Data Sheet.

[2] Alfa Aesar. N,N-Dimethylcyclohexylamine. Safety Data Sheet.

[3] Yaws, C.L. The Yaws Handbook of Vapor Pressure: Antoine Coefficients. Gulf Professional Publishing, 2015.

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

[5] Perrin, D.D. Dissociation Constants of Organic Bases in Aqueous Solution. IUPAC Chemical Data Series, Butterworths, London, 1965.

[6] Daubert, T.E.; Danner, R.P. Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Hemisphere Publishing Corp, 1989.

[7] Bretherick, L. Bretherick’s Handbook of Reactive Chemical Hazards. Butterworth-Heinemann, 2016.

[8] Smith, M. B., & March, J. March’s Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. John Wiley & Sons, 2007.

[9] Hutchins, R. O., et al. "Sodium Borohydride in Trifluoroacetic Acid: A Mild and Selective Reagent for the Reduction of Imines to Amines." The Journal of Organic Chemistry, 1975, 40(26), 3734-3736.

[10] Borch, R. F., Bernstein, M. D., & Durst, H. D. "Cyanohydridoborate Anion as a Selective Reducing Agent." Journal of the American Chemical Society, 1971, 93(12), 2897-2904.

[11] Vogel, A.I. Vogel’s Textbook of Practical Organic Chemistry. Longman, 1989.

[12] Furniss, B.S., et al. Vogel’s Textbook of Practical Organic Chemistry, 5th Edition. Longman Scientific & Technical, 1989.

[13] Shimizu, K.-I., et al. "Catalytic Amination of Alcohols with Ammonia over Metal Oxides." Catalysis Surveys from Asia, 2011, 15(3-4), 109-123.

[14] Opanasenko, M. V., et al. "Selective Amination of Alcohols with Ammonia over Supported Copper Catalysts." Journal of Catalysis, 2014, 311, 106-116.

[15] Oertel, G. Polyurethane Handbook. Hanser Gardner Publications, 1994.

[16] Rand, L.; Reegen, S.L. "Amine Catalysts in Urethane Chemistry." Advances in Urethane Science and Technology, 1971, 3, 1-52.

[17] Ellis, B. Chemistry and Technology of Epoxy Resins. Springer Science & Business Media, 1993.

[18] Lee, H.; Neville, K. Handbook of Epoxy Resins. McGraw-Hill, 1967.

[19] Carey, F.A.; Sundberg, R.J. Advanced Organic Chemistry: Part B: Reactions and Synthesis. Springer Science & Business Media, 2007.

[20] Lednicer, D. Organic Chemistry of Drug Synthesis. John Wiley & Sons, 2007.

[21] Roberge, P.R. Handbook of Corrosion Engineering. McGraw-Hill, 1999.

[22] Nalco Chemical Company. The Nalco Water Handbook. McGraw-Hill, 1988.