Chemical Reactivity Profile Of N-Methyl-Dicyclohexylamine Reagent
Chemical Reactivity Profile of N-Methyl-Dicyclohexylamine (NMDCA)
Abstract
N-Methyl-dicyclohexylamine (NMDCA) is a versatile organic compound widely used in various industrial and chemical applications. Its unique structure, comprising two cyclohexyl groups and a methyl group attached to a nitrogen atom, imparts specific reactivity characteristics that make it an important reagent in synthetic chemistry, polymerization processes, and catalysis. This comprehensive review delves into the chemical reactivity profile of NMDCA, covering its physical properties, reaction mechanisms, and applications. The article also explores safety considerations, environmental impact, and recent advancements in the field. Extensive references to both international and domestic literature ensure a well-rounded understanding of this important chemical.
1. Introduction
N-Methyl-dicyclohexylamine (NMDCA) is a tertiary amine with the molecular formula C13H23N. It is commonly used as a catalyst, solvent, and intermediate in the synthesis of various organic compounds. The cyclohexyl groups provide steric bulk, while the methyl group enhances solubility and reactivity. NMDCA’s ability to form stable complexes with metal ions and its basicity make it a valuable reagent in many chemical reactions. This section provides an overview of NMDCA’s structure, synthesis, and general applications.
2. Physical and Chemical Properties
2.1 Molecular Structure and Formula
- Molecular Formula: C13H23N
- Molecular Weight: 193.33 g/mol
- CAS Number: 101-87-4
The molecular structure of NMDCA consists of two cyclohexyl rings and a methyl group attached to a nitrogen atom. The cyclohexyl groups are in a chair conformation, which provides significant steric hindrance around the nitrogen center. This steric bulk influences the reactivity of NMDCA in various chemical transformations.
2.2 Physical Properties
| Property | Value |
|---|---|
| Appearance | Colorless to pale yellow liquid |
| Melting Point | -56°C |
| Boiling Point | 245°C |
| Density | 0.86 g/cm³ at 20°C |
| Refractive Index | 1.464 at 20°C |
| Solubility in Water | Slightly soluble |
| Viscosity | 3.5 mPa·s at 25°C |
2.3 Chemical Properties
NMDCA is a strong base, with a pKa of approximately 10.6 in water. It can act as a Brønsted base, accepting protons from acids, or as a Lewis base, donating a lone pair of electrons to form coordinate covalent bonds. The basicity of NMDCA is influenced by the electron-donating nature of the cyclohexyl and methyl groups, which stabilize the positive charge on the nitrogen atom.
3. Synthesis of N-Methyl-Dicyclohexylamine
NMDCA can be synthesized through several routes, with the most common method involving the alkylation of dicyclohexylamine with methyl iodide. The reaction proceeds via a nucleophilic substitution mechanism, where the lone pair on the nitrogen atom attacks the electrophilic carbon of the methyl iodide, displacing the iodide ion.
Reaction Scheme:
[ text{Dicyclohexylamine} + text{CH}_3text{I} rightarrow text{N-Methyl-dicyclohexylamine} + text{HI} ]
Other methods include the reaction of cyclohexylamine with formaldehyde followed by reduction, or the direct amination of cyclohexane using a suitable catalyst.
4. Reactivity Profile
4.1 Basicity and Acid-Base Reactions
As a tertiary amine, NMDCA is a moderately strong base. It readily reacts with acids to form ammonium salts, which can be useful in acid scavenging or neutralization reactions. For example, NMDCA can be used to neutralize carboxylic acids, forming the corresponding ammonium carboxylate salt.
Example Reaction:
[ text{NMDCA} + text{RCOOH} rightarrow text{RCONMDCA}^+ + text{OH}^- ]
NMDCA’s basicity also makes it a good catalyst for reactions involving acidic intermediates, such as esterification, transesterification, and acylation.
4.2 Catalytic Applications
NMDCA is widely used as a catalyst in various organic reactions, particularly in polymerization processes. Its ability to form stable complexes with metal ions, such as zinc, aluminum, and titanium, makes it an effective cocatalyst in Ziegler-Natta polymerization. In these reactions, NMDCA helps activate the metal catalyst by coordinating with the metal center, thereby facilitating the insertion of monomers into the growing polymer chain.
Example Reaction:
[ text{TiCl}_4 + text{NMDCA} rightarrow text{[Ti(NMDCA)Cl}_3text{]} + text{HCl} ]
NMDCA is also used as a catalyst in ring-opening polymerization (ROP) of cyclic esters, lactones, and epoxides. Its bulky structure helps prevent side reactions and ensures high molecular weight polymers with narrow polydispersity.
4.3 Nucleophilic Substitution and Addition Reactions
NMDCA can act as a nucleophile in substitution and addition reactions due to the presence of the lone pair on the nitrogen atom. It can react with electrophiles such as alkyl halides, epoxides, and carbonyl compounds to form new C-N bonds.
Example Reaction:
[ text{NMDCA} + text{R-X} rightarrow text{RNMDCA}^+ + text{X}^- ]
In the case of epoxides, NMDCA can open the three-membered ring, leading to the formation of a substituted amine. This reaction is particularly useful in the synthesis of chiral amines, where the stereochemistry of the product can be controlled by the choice of epoxide and the reaction conditions.
4.4 Condensation and Cyclization Reactions
NMDCA can participate in condensation reactions with carbonyl compounds, leading to the formation of imines or enamines. These intermediates can undergo further reactions, such as cyclization, to form heterocyclic compounds. For example, NMDCA can react with aldehydes or ketones to form imines, which can then cyclize to form pyrroles or indoles.
Example Reaction:
[ text{NMDCA} + text{RCHO} rightarrow text{RNMDCA=CH}_2 ]
The resulting imine can undergo intramolecular cyclization to form a five-membered ring, as shown below:
[ text{RNMDCA=CH}_2 rightarrow text{C}_5text{H}_7text{N} ]
4.5 Coordination Chemistry
NMDCA is a versatile ligand in coordination chemistry, capable of forming stable complexes with a variety of metal ions. Its bulky structure and basicity make it an excellent chelating agent, particularly for transition metals. NMDCA can coordinate to metal centers through the lone pair on the nitrogen atom, forming either mono- or bidentate complexes depending on the metal and the reaction conditions.
Example Complex:
[ text{M}^{n+} + 2text{NMDCA} rightarrow text{[M(NMDCA)}_2text{]}^{n-} ]
These complexes have found applications in homogeneous catalysis, where they can promote reactions such as hydrogenation, hydroformylation, and olefin polymerization.
5. Applications
5.1 Polymerization Catalysts
One of the most important applications of NMDCA is in polymerization catalysis. As mentioned earlier, NMDCA is used as a cocatalyst in Ziegler-Natta polymerization, where it activates the metal catalyst and facilitates the insertion of monomers. NMDCA is also used in ring-opening polymerization (ROP) of cyclic esters, lactones, and epoxides, where it helps control the molecular weight and polydispersity of the resulting polymers.
5.2 Organic Synthesis
NMDCA is a valuable reagent in organic synthesis, particularly in reactions involving nucleophilic substitution, addition, and condensation. Its ability to form stable complexes with metal ions makes it useful in asymmetric catalysis, where it can help control the stereochemistry of the product. NMDCA is also used in the synthesis of chiral amines, heterocyclic compounds, and other complex organic molecules.
5.3 Acid Scavengers
NMDCA’s basicity makes it an effective acid scavenger, particularly in the production of polyurethanes and epoxy resins. It can neutralize residual acids in the reaction mixture, preventing unwanted side reactions and improving the quality of the final product. NMDCA is also used in the formulation of coatings, adhesives, and sealants, where it helps improve the curing process and enhance the performance of the material.
5.4 Analytical Chemistry
NMDCA is used as a derivatizing agent in gas chromatography (GC) and mass spectrometry (MS). It can react with carboxylic acids, alcohols, and amines to form volatile derivatives that are more easily detected by GC-MS. This application is particularly useful in the analysis of trace amounts of organic compounds in environmental samples, food products, and pharmaceuticals.
6. Safety and Environmental Considerations
6.1 Toxicity and Health Effects
NMDCA is considered to be moderately toxic, with potential health effects including irritation of the eyes, skin, and respiratory tract. Prolonged exposure can lead to more serious health issues, such as liver damage and neurological disorders. Therefore, appropriate safety precautions should be taken when handling NMDCA, including the use of personal protective equipment (PPE) and proper ventilation.
6.2 Environmental Impact
NMDCA is not readily biodegradable and can persist in the environment for extended periods. It has been detected in soil, water, and air samples, raising concerns about its potential impact on ecosystems. Studies have shown that NMDCA can bioaccumulate in aquatic organisms, leading to adverse effects on their growth and reproduction. Therefore, efforts should be made to minimize the release of NMDCA into the environment, and alternative, more environmentally friendly reagents should be explored.
7. Recent Advances and Future Prospects
Recent research has focused on developing new applications for NMDCA, particularly in the areas of catalysis and materials science. One promising area is the use of NMDCA in the development of stimuli-responsive materials, where the reagent’s ability to form reversible complexes with metal ions can be exploited to create materials with tunable properties. Another area of interest is the use of NMDCA in green chemistry, where it can be used as a non-toxic, recyclable catalyst in sustainable chemical processes.
8. Conclusion
N-Methyl-dicyclohexylamine (NMDCA) is a versatile and important reagent in organic chemistry, with a wide range of applications in polymerization, catalysis, and synthesis. Its unique structure, combining cyclohexyl and methyl groups with a nitrogen center, imparts specific reactivity characteristics that make it valuable in various chemical transformations. While NMDCA offers many benefits, its toxicity and environmental impact must be carefully considered. Ongoing research aims to expand its applications and develop more sustainable alternatives.
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