Synthesis Process of 2,2,6,6-Tetramethyl-4-piperidinamine via Catalytic Amination

Basic Information of 2,2,6,6-Tetramethyl-4-piperidinamine:

Common Names: 2,2,6,6-Tetramethyl-4-piperidinamine; Tetramethylpiperidinamine; 4-Amino-2,2,6,6-tetramethylpiperidine; 2,2,6,6-Tetramethyl-4-aminopiperidine.

CAS No.: 36768-62-4

Chromatographic Purity: ≥99.0%

Molecular Formula: C9H20N2

Molecular Weight: 156.27

Flash Point: 71°C (160°F)

Density: 0.912 g/mL at 25 °C (lit.)

Primary Function: 2,2,6,6-Tetramethyl-4-piperidinamine is a crucial intermediate used in the synthesis of a series of high-performance hindered amine light stabilizers (HALS).

Overview of Synthesis Methods

Tetramethylpiperidinylamine, also known as TEMP, is a key raw material in the chemical industry, primarily used in the production of monomeric and polymeric hindered amine light stabilizers. The primary methods for producing this compound are the electrochemical method and the catalytic amination method.

In the electrochemical method, aluminum is used as the cathode material and lead as the anode. An aqueous solution of alkali metal phosphate serves as the electrolyte in the cathode compartment, while a 20% sulfuric acid solution is used in the anode compartment. Using 2,2,6,6-tetramethyl-4-piperidinone (referred to as tetramethylpiperidinone or triacetone amine, TAA) as the starting material, tetramethylpiperidinamine is produced under electro-reduction conditions. This method offers a high yield, exceeding 93%, but the acidic electrolyte used can cause significant corrosion to the equipment.

Currently, the catalytic amination method is the most widely used process in industrial production. This method employs tetramethylpiperidinone and ammonia as reactants, using metal catalysts or supported metal catalysts under hydrogenation conditions to drive the reaction. When using nickel (Ni) or cobalt (Co) as catalysts, the reaction temperature typically exceeds 100°C. Although this method is energy-intensive, it effectively produces Tetramethylpiperidinylamine, though by-products like tetra-methylpiperidinol are also formed, requiring subsequent purification steps such as distillation. To enhance the selectivity of the reaction, researchers are continually exploring novel catalysts. Examples include nitrogen-doped carbon-supported cobalt catalysts and chromium-containing copper-based binary catalysts supported on γ-Al₂O₃, which can achieve a selectivity of up to 81.9% for tetramethylpiperidinamine. However, the preparation processes for these novel catalysts are complex and costly.

Reaction Mechanism and Key Factors

In the catalytic amination reaction, the conversion of tetramethylpiperidinone with ammonia proceeds via an imine intermediate stage. The efficiency of this stage directly impacts the yield of the final product. Modifying the catalyst type can, to some extent, promote the hydrogenation reduction of the imine intermediate, thereby improving the yield. The pH of the reaction system is a critical factor influencing this conversion step. Research indicates that adjusting the pH can not only promote the formation of the imine intermediate but also enhance the selectivity and yield of the desired Tetramethylpiperidinylamine.

Experimental Procedure

The experimental section typically utilizes the following main instruments and reagents: 25-28% ammonia solution as the primary raw material, Raney nickel catalyst, and sodium hydroxide (NaOH) flakes. Product analysis is performed using instruments such as the TRACE GC 2000/TRACE MS gas chromatography-mass spectrometry system and a 1790F flame ionization detector (FID).

The synthesis of tetramethylpiperidinamine is carried out in a sealed autoclave. The process involves first adding water, a specific concentration of ammonia solution, tetramethylpiperidinone, and a predetermined amount of Raney nickel catalyst into the reactor. The air inside the reactor is displaced with nitrogen to remove oxygen. Subsequently, under thorough stirring and heating to the set temperature, hydrogen is introduced until the preset pressure is reached. During the reaction, hydrogen is replenished as needed based on pressure changes until the reaction is complete. After cooling andstress relief distillation to remove water and light impurities, the catalyst is recovered and recycled, yielding the final product, Tetramethylpiperidinylamine.