Allylamine: Characteristics, preparation and application expansion of multifunctional organic amines

Allylamine, also known as allylamine and 3-aminopropene, is an aliphatic organic amine containing unsaturated double bonds and amino groups. Its molecular formula is C₃H₇N, its simplified structural formula is CH₂=CH-CH₂-NH₂, CAS No. 107-11-9, and its molar mass is 57.11 g·mol⁻¹. As a bifunctional compound with both olefin reactivity and amine basicity, it is a colorless and transparent liquid at room temperature with a strong ammonia smell and irritation. With its unique molecular structure, it plays a key role in the fields of organic synthesis, polymer materials, pharmaceutical and chemical industry, and is an important intermediate connecting basic organic synthesis and high-end functional materials.
1. Core chemical properties: unique properties endowed by bifunctional groups

The core performance of allylamine comes from the synergistic effect of allyl group (CH₂=CH-CH₂-) and amino group (-NH₂) in the molecule. The unsaturated double bond provides addition and polymerization activity, while the amino group imparts basicity, nucleophilicity and coordination ability. The mutual influence between the two makes it exhibit special chemical behavior that is different from saturated amines.

In terms of physical properties, the melting point of allyl ammonia is -88.2℃, the boiling point is 55-58℃, the relative density (20℃) is 0.762, the refractive index nD²⁰ is 1.420-1.422, the vapor pressure is high (about 29.3 kPa at 25℃), and it is easy to volatilize. It is easily soluble in polar and non-polar solvents such as water, ethanol, ether, and acetone. The aqueous solution is weakly alkaline, with a pKa value of about 9.4. It forms an azeotrope with water (azeotropic temperature 54°C, containing 33% allyl ammonia). This characteristic is crucial to the separation and purification process. It should be noted that its vapor and air can form an explosive mixture, with an explosion limit of 2.2%-22% (volume fraction), and it is a flammable liquid.

In terms of chemical properties, the reactivity of double bonds and amino groups regulates each other to form multi-reaction characteristics. First, the typical reactions of amino groups: as primary amines, they can react with acids to form salts (such as allylamine hydrochloride, melting point 140-143°C), condensation reactions with aldehydes and ketones to form imines, acylation reactions with acid chlorides and acid anhydrides to produce allyl amides, and alkylation reactions with halogenated hydrocarbons to form secondary and tertiary allylamines; second, the reaction of allyl double bonds: addition reactions can occur (such as addition with halogen, hydrogen halide, hydrogen, in which the addition with hydrogen halide follows Markov's rule), polymerization reaction (self-homopolymerization or copolymerization with acrylonitrile, acrylate, etc.), and can also participate in cycloaddition and oxidation reactions; third, synergistic reaction: the spatial positional relationship between the double bond and the amino group makes it easy to undergo intramolecular reactions, or form heterocyclic compounds under catalytic conditions, providing a convenient path for heterocyclic synthesis. In addition, allyl ammonia has certain reducing properties and is easily oxidized to produce aldehydes, carboxylic acids and other products. It needs to be sealed and stored away from light.

2. Preparation process: from traditional synthesis to green optimization

The preparation process of allyl ammonia is iterated around the three major goals of "efficient conversion of raw materials, control of reaction selectivity, and reduction of by-products." The traditional process is mainly based on amination of halogenated hydrocarbons, while the new process focuses on catalytic conversion and resource recycling, gradually achieving low-cost, high-purity mass production. At present, the purity of industrial-grade products can reach more than 98%, and the purity of high-end electronic grade has exceeded 99.95%.

(1) Traditional industrial preparation technology

1. Allyl halide amination method: Use allyl chloride (or allyl bromide) as raw material, react with ammonia solution under pressurized conditions to generate allyl ammonia and ammonium chloride by-products. The reaction temperature is controlled at 60-80°C and the pressure is 0.3-0.5 MPa. The crude product is obtained through distillation separation and alkali washing to remove salt, and then purified by distillation. The raw materials of this process are easy to obtain and the reaction conditions are mild. It is currently the most widely used method in industry. However, there are problems such as many by-products (such as diallylamine and triallylamine) and high wastewater treatment pressure. By optimizing the molar ratio of ammonia to allyl chloride (usually controlled above 8:1), the selectivity of mono-substituted products can be improved.

2. Allyl alcohol amination method: Using allyl alcohol and ammonia as raw materials, under the action of metal oxide catalysts (such as Al₂O₃, ZrO₂), allyl ammonia is generated through dehydration and amination reactions. The reaction temperature is 250-350°C and the pressure is 1.0-2.0 MPa. This process has a high atom utilization rate, and the main by-product is water. It is more environmentally friendly than the halide amination method, but the catalyst activity is easy to decay and needs to be regenerated regularly. It also requires high raw material purity (allyl alcohol purity ≥99%), so it is suitable for production capacity layouts with strict environmental protection requirements.

(2) New green preparation technology

In the field of laboratories and high-end production capacity, new processes focus on improving catalytic efficiency and green transformation. The first is the catalytic hydrogenation method: using acrylonitrile as raw material, under the action of Pd/C or Ni-based catalysts, selective hydrogenation generates allyl ammonia. By regulating the hydrogenation temperature (80-100°C) and hydrogen partial pressure, excessive hydrogenation is avoided to generate propylamine. The product selectivity can reach more than 92%. The cost of raw materials of this process is low, and pilot mass production has been achieved; the second is the biological transformation method: using microbial enzyme catalysis Acrylamide is reduced to generate allyl ammonia. The reaction conditions are mild (normal temperature and pressure) and there are no harmful by-products. It is currently in the laboratory research and development stage and is expected to break through the environmental protection bottleneck of traditional processes. The third is the plasma-assisted synthesis method: low-temperature plasma activates ammonia and propylene molecules to achieve the addition reaction at normal temperature. The reaction time is short and the energy consumption is low. However, large-scale amplification still requires solving the problem of product separation.

In terms of purification process, continuous distillation combined with molecular sieve adsorption technology is used in industry to remove trace amounts of water, by-product amines and raw materials. Electronic-grade products require additional membrane separation and purification to reduce the metal ion content (≤1 ppm) to meet the application needs of high-end materials.

3. Diverse application areas: dual functional groups empower the entire industry chain

As a highly active intermediate, allyl ammonia is used in many fields such as organic synthesis, polymer materials, pharmaceuticals and pesticides, and surface modification. The global annual consumption is about 80,000 tons. With the development of high-end manufacturing and biopharmaceutical industries, the demand for high-purity allyl ammonia maintains an average annual growth rate of more than 10%, and application scenarios continue to expand.

(1) Organic synthesis intermediates: core units for building complex molecules

Allylamine is a key intermediate in the preparation of various fine chemicals. Through the derivatization reaction of amino groups and double bonds, a variety of functional compounds can be synthesized. In heterocyclic synthesis, it can be reacted with diketone, carboxylic acid, etc. to prepare heterocyclic compounds such as pyrrole and piperidine. This type of heterocyclic ring is the core skeleton of medicines and pesticides; in amine derivatization, allylamide and N-alkylallylamine generated through acylation and alkylation reactions are important raw materials for dyes and spices. In addition, it can also be used to prepare compounds such as allyl isocyanate and allyl urea, which are widely used in the synthesis of polyurethane cross-linking agents and antibacterial agents.

(2) Field of polymer materials: key monomers for functional modification

The double bonds of allylamine can participate in homopolymerization or copolymerization reactions, while the amino group provides hydrophilicity, coordination and reactivity, becoming the core monomer for functional modification of polymer materials. The first is to prepare functional polymers: polyallylamine is homopolymerized by itself to form polyallylamine. This polymer has a cationic structure and can be used as a water treatment flocculant and papermaking retention aid. It can effectively remove suspended particles and organic matter in water with a low dosage and good flocculation effect. It can be copolymerized with acrylonitrile, acrylate, etc. to improve the hydrophilicity, adhesion and antibacterial properties of the polymer. It can be used to prepare water-based coatings and ink resins to improve the bonding between coatings and substrates. The second is as a cross-linking agent: used to modify epoxy resin and polyurethane resin, forming a three-dimensional cross-linked network through the reaction of double bonds and amino groups, improving the mechanical strength, heat resistance and corrosion resistance of the material, and adapting to high-end scenarios such as aerospace and electronic packaging. The third is to prepare polymer chelating agents: the amino groups of polyallylamine can coordinate with metal ions and are used for precious metal recycling and heavy metal treatment in industrial wastewater. The chelating capacity can reach 2.5 mmol/g or above.

(3) Pharmaceutical and pesticide fields: synthetic raw materials for active molecules

In the pharmaceutical field, allylamine is used to synthesize a variety of drug intermediates, such as antifungals, antihistamines, antitumor drugs, etc. For example, through the condensation reaction of allylamine and aromatic compounds, imidazole antifungal drugs can be prepared, which have highly effective inhibitory effects on dermatophytes, Candida, etc.; in the synthesis of antiviral drugs, heterocyclic compounds derived from allylamine can be used as viral reverse transcriptase inhibitors, showing potential activity against hepatitis B and HIV.

In the field of pesticides, allylamine is an important raw material for the preparation of insecticides, fungicides, and herbicides. Allylamine compounds derived from it have an efficient killing effect on aphids, red spider mites and other pests. They also have inhibitory effects on plant fungal diseases (such as powdery mildew and rust), and have good environmental degradability, which is in line with the development trend of green pesticides.

(4) Other featured applications

In the field of surface modification, allyl ammonia can be used for surface treatment of metal, glass, fiber and other substrates. Through the reaction of amino groups with hydroxyl and carboxyl groups on the surface of the substrate, a modified layer is formed to improve the hydrophilicity, adhesion or antibacterial properties of the substrate. For example, it is used to modify the surface of glass fiber to enhance its interface bonding with resin and improve composite materials. Mechanical properties; in the field of catalysis, it can be used as a ligand to form a complex catalyst with metal ions for olefin polymerization and hydrogenation reactions to improve catalytic activity and selectivity; in addition, it can also be used to prepare corrosion inhibitors, which can inhibit metal corrosion by adsorbing on the metal surface to form a protective film in oil mining and industrial circulating water systems.

4. Safety, environmental protection and industry development trends

(1) Safety control and environmental protection requirements

Allyl ammonia is highly irritating and corrosive and can irritate the skin, eyes, and respiratory mucosa. Inhalation of high-concentration vapor may cause symptoms such as dizziness, nausea, and difficulty breathing. Skin contact can cause burns. It is a hazardous chemical (UN number 2334, hazardous category 3 flammable liquids, category 8 corrosive substances). Its storage and operation must strictly follow safety regulations: store in a cool and ventilated explosion-proof warehouse, away from fire sources, oxidants, and acids, packaged in sealed containers, equipped with explosion-proof electrical, flammable gas alarm systems, and emergency sprinkler devices; when operating, you must wear acid- and alkali-resistant protective clothing, protective glasses, and gas masks to ensure good ventilation and avoid direct contact with skin and mucous membranes. If leakage occurs, it must be collected with sand adsorption, and the wastewater must be neutralized and discharged after meeting the standards.

In terms of environmental protection, industrial production needs to strengthen by-product recovery and wastewater treatment: the ammonium chloride produced by the halide amination method can be recycled as fertilizer raw material. The amination reaction wastewater undergoes deamination and biochemical treatment to reduce the ammonia nitrogen and COD content; the waste gas needs to be treated by an absorption tower (dilute acid absorption) before being discharged to avoid irritating gases from polluting the environment. As environmental protection policies become stricter, green preparation processes will become the core prerequisite for industry compliance development.

(2) Industry development trends

The allyl ammonia industry is evolving towards high-end, green and refined directions. At the technical level, green processes such as catalytic hydrogenation and biological conversion will gradually replace the traditional halogenated amination method, reducing environmental protection costs and energy consumption, while improving product selectivity and purity; in terms of high-end, the research and development and mass production of electronic-grade and pharmaceutical-grade high-purity allyl ammonia will become the company's core competitiveness, through membrane separation , molecular sieve adsorption and other purification technology upgrades to meet the high-end needs of biomedicine, electronic materials and other fields; at the application level, with the development of new energy and high-end manufacturing industries, its applications in the fields of polymer chelating agents, electronic packaging materials, green pesticides and other fields will be further expanded, and the added value of derivative products continues to increase.

In terms of market structure, global production capacity is currently mainly concentrated in Europe, the United States, China and other regions. Domestic companies have realized import substitution of industrial-grade products through technological breakthroughs. In the future, they need to further improve high-end product production capacity and technical level, deploy green process production capacity, and seize the global high-end market share.

As a multifunctional organic amine with both double bond and amino activity, allylamine continues to empower the upgrading of industrial chains such as fine chemicals and high-end materials with its flexible derivatization properties. Driven by the dual wheels of green manufacturing and technological innovation, allylamine will break through traditional application boundaries, show broader application prospects in high-end fields such as biomedicine, new energy, and electronic information, and promote technological iteration and high-quality development of related industries.