Diallylamine: Characteristics, Preparation and Industrial Applications of Diallyl Substituted Amines

Diallylamine, also known as diallylamine and N,N-diallylamine, is a secondary alkylated derivative of allylamine. Its molecular formula is C₆H₁₁N, its simplified structural formula is (CH₂=CH-CH₂)₂NH, CAS number 124-02-7, and molar mass 97.16 g·mol⁻¹. As a bifunctional organic amine containing two allyl double bonds and one secondary amino group, it combines the high reactivity of allyl groups with the basic characteristics of secondary amines. Compared with primary allyl amines, the alkalinity after alkyl substitution is slightly weakened but the chemical stability is improved. At the same time, the double double bond structure gives it better polymerization and cross-linking capabilities. It has become a key intermediate in the fields of organic synthesis, polymer materials, water treatment, etc., filling the performance gap between monoallylamine and triallylamine.
1. Core psychological properties: unique properties endowed by the double substitution structure

The performance of diallylamine originates from the synergistic effect of the two allyl groups in the molecule and the secondary amino group (-NH-), which is significantly different from primary allylamine and allylamine hydrochloride. Its structural characteristics determine its uniqueness in reaction selectivity, stability and application scenarios.

In terms of physical properties, diallylamine is a colorless and transparent liquid at room temperature, with a mild ammonia smell, and its irritation is significantly lower than that of primary allylamine. Its melting point is -88°C, boiling point 111-112°C, relative density (20°C) 0.788, refractive index nD²⁰ 1.440-1.443, vapor pressure (25°C) about 2.67 kPa, easy to volatilize but less volatile than allyl ammonia. This compound is easily soluble in most polar and non-polar solvents such as water, ethanol, ether, acetone, etc. The aqueous solution is weakly alkaline, with a pKa value of about 10.4 (25°C). It is more alkaline than triallylamine but weaker than allylamine, and can react with acids to form corresponding ammonium salts (such as diallylamine hydrochloride). Its vapor and air can form an explosive mixture, with an explosion limit of 1.1%-9.1% (volume fraction). It is a flammable liquid and requires strict control of fire sources. The purity of industrial-grade products is usually ≥98%, and the purity of high-end products can reach more than 99.5%. The impurities are mainly trace amounts of monoallylamine, triallylamine and moisture.

In terms of chemical properties, the synergistic effect of the bisallyl structure and the secondary amino group makes the reactivity more diverse. First, the characteristic reactions of amino groups: as secondary amines, they can be protonated with acids to form stable ammonium salts, condensation reactions with aldehydes and ketones to form imines, acylation reactions with acid chlorides and acid anhydrides to produce diallyl amides, alkylation reactions with halogenated hydrocarbons to produce triallylamine (side reactions need to be controlled), and can also participate in nucleophilic substitutions and oxidation reactions (oxidation products are mostly imines or amides); second, the reaction of biallyl double bonds: two allyl double bonds. The bonds can simultaneously participate in addition and polymerization reactions. Homopolymerization can generate polydiallylamine, and copolymerization with acrylonitrile, acrylate, etc. can form functional polymers. Double bonds can also undergo cycloaddition and hydrogenation reactions, and the double-double bond structure makes the polymerization cross-linking efficiency much higher than that of monoallylamine. The third is a special synergistic reaction: two allyl groups in the molecule can undergo a cyclization reaction under catalytic conditions to generate pyrrole heterocyclic compounds, providing an efficient path for heterocyclic synthesis. In addition, its stability is better than that of allyl ammonia, and it is not easy to self-polymerize at room temperature, but it is prone to polymerization under high temperature, strong light or catalysts, and a polymerization inhibitor (such as hydroquinone) needs to be added for storage.

2. Preparation process: optimization of alkylation reaction based on allylamine

The core of the preparation of diallylamine is the selective monoalkylation of allylamine. The key is to control the reaction conditions to suppress incomplete monosubstitution (residual allylamine) and excessive alkylation (generating triallylamine). In industry, a mature process has been formed based on the amination of allyl halides, supplemented by catalytic dehydrogenation. Laboratory preparation focuses on product purity and reaction selectivity.

(1) Industrial scale preparation process

1. Allyl halide amination method: Using allyl amino and allyl chloride (or allyl bromide) as raw materials, an alkylation reaction occurs under the action of an alkaline catalyst (such as sodium hydroxide, sodium carbonate) to generate diallylamine. The reaction requires strict control of the molar ratio of raw materials (allylamine: allyl chloride = 1.2:1), reaction temperature (40-60°C) and pressure (0.2-0.4 MPa), and the generation of triallylamine is inhibited by excess allylamine. After the reaction is completed, excess raw materials are removed by distillation, and the by-products (monoallylamine and triallylamine) are separated by distillation to finally obtain the finished product with a yield of more than 85%. The raw materials of this process are easily available and the reaction conditions are mild. It is currently a mainstream method in the industry. Domestic companies have achieved large-scale release of 10,000-ton production capacity by optimizing the reactor structure and distillation process.

2. Allyl alcohol catalytic amination method: Using allyl alcohol and ammonia as raw materials, under the action of a metal oxide catalyst (such as Al₂O₃-ZrO₂ composite catalyst), diallylamine is generated through a multi-step reaction of dehydration, amination, and alkylation. The reaction temperature is controlled at 280-350°C and the pressure is 1.5-2.5 MPa. By adjusting the proportion of catalyst active components, the diallylamine selectivity can be increased to more than 80%. This process has a high atom utilization rate, and the by-product is mainly water. It is more environmentally friendly than the halide amination method, but the catalyst is prone to carbon deposition and deactivation, and needs to be regenerated regularly. It is suitable for production capacity layouts with strict environmental protection requirements.

(2) Laboratory and new preparation technology

Laboratory preparation focuses on precise control of by-products, and usually uses the "step-by-step amination + precise distillation" strategy: take the purified allyl ammonia, slowly add allyl chloride dropwise under ice-water bath cooling, add an appropriate amount of triethylamine as an acid binding agent (to absorb the generated hydrogen chloride), after the dropwise addition is completed, raise the temperature to 50°C to react for 2 hours, wash with alkali, separate liquids, dry with anhydrous magnesium sulfate, and then rectify under reduced pressure (vacuum degree -0.095 MPa, distillation range 60-62°C) to obtain diallylamine with a purity of ≥99%, meeting experimental needs.

New green processes are gradually breaking through traditional bottlenecks: the first is the catalytic dehydrogenation method, which uses dipropylamine as raw material and selectively dehydrogenates under the action of Pd/C catalyst to produce diallylamine. The reaction temperature is 180-220°C, the selectivity can reach more than 90%, the raw material cost is low and the by-products are few, and pilot mass production has been achieved; the second is the microwave-assisted synthesis method, which uses microwave radiation to accelerate olefins. For the reaction of propyl ammonia and allyl chloride, the reaction time is shortened from 4 hours in the traditional process to 30 minutes, the yield is increased to 88%, and the energy consumption is reduced by 40%. It is currently in the laboratory amplification stage; the third is the membrane separation coupling process, which combines the reaction with membrane separation to separate the generated diallyl ammonia in real time, suppress excessive alkylation, and further increase the product selectivity to 86%.

3. Application fields: Dual functional groups enable multi-scenario upgrades

Diallylamine relies on the high-efficiency polymerization ability of diallyl double bonds and the reactivity of secondary amines. Its applications cover the fields of polymer materials, water treatment, pharmaceuticals and pesticides, organic synthesis, etc. The global annual consumption is about 35,000 tons. With the development of high-end functional materials and environmental protection industries, the demand maintains an average annual growth rate of more than 8%, forming a complementary application pattern with allylamine and allylamine hydrochloride.

(1) Field of polymer materials: core cross-linking and functional monomers

This field is the core application scenario of diallylamine, accounting for more than 50% of total consumption. The first is to prepare a cationic polymer: it homopolymerizes itself to form polydiallylamine. This polymer has a high density of cationic sites, excellent water solubility, and its flocculation performance and antibacterial properties are much better than polyallylamine. It can be used as a water treatment flocculant and a papermaking retention aid. , sludge dewatering agent, which can effectively remove anionic pollutants, color and bacteria in water, and the dosage is only 1/4 of traditional flocculants; the second is copolymerization modification: copolymerized with acrylamide, acrylic acid and other monomers to form a cross-linked polymer, which is used to prepare water-based In coatings, ink resins, and medical polymer materials, the double-double bond structure can significantly improve the mechanical strength, heat resistance, and corrosion resistance of the polymer. For example, the product after copolymerization with acrylamide can be used as an oilfield water-blocking agent to adapt to high-temperature and high-pressure reservoir environments; The third is as a cross-linking agent: used to modify epoxy resin and polyurethane resin. It forms a dense three-dimensional cross-linked network through the synergistic reaction of double bonds and amino groups to improve the aging resistance and adhesion of the material. It is used in high-end scenarios such as aerospace and electronic packaging.

(2) Water treatment field: high-efficiency cationic flocculant raw materials

In the field of water treatment, diallylamine is the core raw material for preparing high-end cationic flocculants. Its homopolymers and copolymers can be widely used in the treatment of municipal sewage and industrial wastewater (such as printing and dyeing wastewater, papermaking wastewater, and electroplating wastewater). Compared with allylamine hydrochloride polymer, polydiallylamine has a higher cation density, stronger adsorption capacity for anionic pollutants, and stable performance in a wide pH range (3-11). It can effectively remove COD, color, heavy metal ions and suspended particles in wastewater. It also has sterilization and disinfection functions, reducing the amount of subsequent disinfectants and reducing treatment costs. At present, the demand for polydiallylamine in the domestic municipal sewage treatment field is growing significantly, driving the expansion of diallylamine production capacity.

(3) Pharmaceutical and pesticide fields: active intermediates and raw materials for synthesis

In the pharmaceutical field, diallylamine is used to synthesize intermediates such as antifungal drugs, antiviral drugs, and antitumor drugs. Active groups are introduced through aminoacylation and double-bond cyclization reactions. The prepared heterocyclic compounds have an efficient inhibitory effect on fungi and viruses. For example, the diallyl amide compounds derived from it can be used as protease inhibitor intermediates for the synthesis of anti-hepatitis B virus drugs; in the development of anti-tumor drugs, the diallyl structure can be modified into a targeting group to improve the selectivity of the drug to tumor cells.

In the field of pesticides, it is used to prepare high-efficiency and low-toxic fungicides, insecticides and herbicides. The quaternary ammonium salt compounds derived from it have a killing effect on aphids, red spider mites and other pests. The heterocyclic derivatives can inhibit plant fungal diseases (such as cucumber downy mildew, tomato gray mold), and have good environmental degradability, which is in line with the development trend of green pesticides. At the same time, it can be used as a raw material for pesticide emulsifiers to improve the dispersion and stability of pesticides.

(4) Organic synthesis and other fields

In organic synthesis, diallylamine, as a secondary amine intermediate, can be used to prepare compounds such as triallylamine, diallylurea, and diallylisocyanate. These products are core raw materials for polyurethane cross-linking agents, antibacterial agents, and fluorescent materials. They can also be used as ligands to form complex catalysts with metal ions (such as Pd²⁺, Pt²⁺) for olefin polymerization and hydrogenation reactions to improve catalytic activity and selectivity. In addition, in the field of surface modification, it can be used for surface treatment of metal and fiber substrates. A modified layer is formed through double bond polymerization. The amino group imparts hydrophilicity and antibacterial properties to the substrate. It is suitable for medical fibers, food packaging materials and other scenarios.

4. Safety, environmental protection and industry development trends

(1) Safety control and environmental protection requirements

Diallylamine is a hazardous chemical (UN number 2359, hazardous category 3 flammable liquid, category 8 corrosive substance), which is mildly irritating. It can cause redness, swelling and stinging after contact with skin and eyes. Inhalation of high-concentration vapor may cause dizziness, nausea and other discomforts. Its vapor is flammable and can cause combustion and explosion when exposed to open flames or high temperatures. Storage and operation must strictly follow safety regulations: store in a cool and ventilated explosion-proof warehouse, away from fire sources, oxidants, and acids, equipped with explosion-proof electrical, flammable gas alarm systems and emergency sprinkler devices, and add hydroquinone inhibitor to prevent self-aggregation; wear protective clothing during operation Acid and alkali resistant protective clothing, protective glasses, gas masks, keep well ventilated, and avoid direct contact with skin and mucous membranes; when leaking, use sand to adsorb and collect, waste water will be discharged after neutralization treatment (pH adjusted to 6-8), and waste gas will be discharged after being treated in a dilute acid absorption tower to meet standards.

In terms of environmental protection, industrial production needs to strengthen by-product recovery and wastewater treatment: the chloride by-product produced by the halide amination method can be recycled as industrial salt, and excess allyl ammonia is recovered and recycled through distillation; the amination reaction wastewater is deamination and biochemical treatment to reduce the ammonia nitrogen and COD content; the carbon deposits generated during the catalyst regeneration process can be recycled as fuel. The overall environmental protection pressure is lower than that of allyl ammonia production, which meets the requirements of green chemical industry development.

(2) Industry development trends

The diallylamine industry is evolving towards high-end, green and collaborative directions, forming an industrial chain linkage with the allylamine series products. At the technical level, the research and development of high-end pharmaceutical grade and electronic grade products has become the core competitiveness. Through the upgrade of membrane separation and precision distillation technology, the purity has been increased to more than 99.8%, and the metal ion content has been controlled to ≤0.5 ppm, meeting the needs of the biomedicine and electronic materials fields. In terms of green production, new processes such as catalytic dehydrogenation and microwave-assisted synthesis will gradually replace the traditional halogenated amination method, reduce environmental protection costs and energy consumption, and promote raw material utilization to more than 92%.

At the application level, with the development of new energy, environmental protection, and high-end manufacturing industries, its applications in high-end water treatment flocculants, medical polymer materials, electronic packaging resins and other fields will be further expanded, and the added value of derivative products will continue to increase; in terms of market structure, global production capacity is mainly concentrated in China, Europe and the United States. Domestic companies have achieved import substitution of industrial-grade products through technological breakthroughs, and some companies have deployed high-end product production capacity. In the future, they will rely on the synergy of the industrial chain to seize the global high-end market share.

As the core secondary amine derivative of the allylamine series, diallylamine effectively makes up for the performance shortcomings of monoallylamine and triallylamine by virtue of the synergistic advantages of bifunctional groups. Driven by technological innovation and green manufacturing, it will play a more important role in environmental protection, medicine, high-end materials and other fields, promoting the industrial upgrading and application boundary expansion of the entire allylamine series compounds.