N-Methylallylamine Hydrochloride: Properties, Preparation and Applications

N-Allylmethylamine Hydrochloride, also known as N-allylmethylamine hydrochloride, is an important organic amine salt derivative formed by N-methylallylamine and hydrochloric acid. Compared with free N-methylallylamine, it has stronger chemical stability, better water solubility, and improved reaction controllability, showing unique application value in fine chemicals, pharmaceutical synthesis, water treatment and other fields. This article combines its structural characteristics to systematically and carefully elaborate on basic information, physical and chemical properties, preparation processes, application scenarios, and safety protection.
1. Basic information

N-methylallylamine hydrochloride is a secondary amine hydrochloride derivative. The core chemical information is as follows:

- Alias: N-allylmethylamine hydrochloride, methylallylamine hydrochloride

- CAS number: Temporarily refer to the properties of similar secondary amine hydrochlorides (if there is no exclusive general CAS number, the actual measurement shall prevail)

- Molecular formula: C₄H₁₀ClN

- Molecular weight: 107.58

- Chemical structure: CH₂=CHCH₂NH₂⁺CH₃·Cl⁻ (retain the carbon-carbon double bond, and the amino group is protonated to form a hydrochloride)

- Exact mass: 107.04990

- PSA (Polar Surface Area): 26.02000 (significantly higher than free amine, due to enhanced polarity of protonated amino group)

- LogP (oil-water partition coefficient): 0.23±0.10 (enhanced water solubility, weakened fat solubility)

2. Physical and chemical properties

N-Methylallylamine hydrochloride is a typical organic amine salt solid, and its physical and chemical properties are significantly different from those of free amines, as follows:

- Appearance and form: It is white to light yellow crystalline powder or crystal at room temperature, with no obvious odor. The higher the purity, the closer the color is to white. It is easy to absorb moisture and agglomerate, so it needs to be sealed and stored in a moisture-proof manner.

- Density: The bulk density of solid is about 1.12-1.18 g/cm³, which is much higher than that of free liquid.

- Melting point and boiling point: Melting point is about 102-108°C (fluctuates with purity). It easily decomposes when heated above 180°C. It has no clear boiling point. It may be accompanied by double bond polymerization and hydrochloric acid removal reaction at high temperatures.

- Solubility: Very soluble in water, the aqueous solution is weakly acidic (pH value 3-5, 1% aqueous solution); slightly soluble in polar organic solvents such as ethanol and isopropyl alcohol, insoluble in non-polar solvents such as ether and petroleum ether, and its water solubility advantage is significantly better than that of free amines.

- Stability: It is stable under dry conditions at room temperature and is not easily oxidized or deteriorated; it easily dissolves and slowly hydrolyzes after absorbing moisture. It may decompose when in contact with strong oxidants and strong alkali, releasing free amines and chlorides.

- Chemical activity: It retains the carbon-carbon double bond in the molecule and can participate in polymerization, addition and other reactions; the protonated amino group can react with a base to form free N-methylallylamine, providing the possibility of controlled transformation.

3. Preparation method

The preparation of N-methylallylamine hydrochloride uses high-purity N-methylallylamine (free amine) as raw material and is produced through a salt-forming reaction with hydrochloric acid. The process route is simple and controllable, and is easy to produce on a large scale. The core is to control the reaction conditions to avoid double bond side reactions. The specific steps are as follows:

1. Raw material pretreatment

Select N-methylallylamine with a purity of ≥97.5% as the substrate to remove trace amounts of water and distillation residue; use 36%-38% industrial-grade concentrated hydrochloric acid as the hydrochloric acid, which needs to be left to stand at low temperature to remove impurities, or diluted to 20% dilute hydrochloric acid before use to reduce the intensity of the local reaction and avoid excessive heat generation. At the same time, prepare ice salt water, explosion-proof mixing equipment and sealed reaction vessels to adapt to the flammable and corrosive characteristics of the raw materials.

2. Salt formation reaction

Add N-methylallylamine to a dry three-necked flask, place it in an ice-salt water bath and cool it to 0-10°C, and turn on explosion-proof stirring. Slowly add diluted hydrochloric acid (or concentrated hydrochloric acid, the dropping rate must be strictly controlled), keeping the temperature of the reaction system no more than 15°C. During the dropping process, the solution is gradually turbid and solids are precipitated. Continue dropping until the pH value of the system is stable at 3-4 (to ensure complete salt formation and avoid residual free amines). After the dropwise addition is completed, continue stirring for 1-2 hours, and let it stand for 30 minutes at room temperature to allow the crystals to fully grow.

3. Purification and refinement

Perform suction filtration of the reaction solution, collect the precipitated solid crude product, and wash it 2-3 times with a small amount of absolute ethanol to remove hydrogen chloride and unreacted raw materials adsorbed on the surface. Place the washed crude product in a vacuum drying oven, control the temperature to 40-50°C (lower than the melting point to prevent softening and decomposition of the crystals), and dry at a vacuum level of -0.08~-0.1MPa for 4-6 hours until a constant weight is obtained. The pure white crystalline N-methylallylamine hydrochloride is obtained. After high-performance liquid chromatography, the purity can reach more than 98.5%, which meets the needs of fine chemicals and pharmaceutical synthesis.

4. Key points of process optimization

The reaction temperature is a key control factor. Too high a temperature can easily lead to the polymerization of carbon-carbon double bonds and reduce the yield. The hydrochloric acid dripping rate needs to match the stirring rate to avoid side reactions such as excessive protonation of amino groups or hydrochloric acid removal caused by excessive local hydrochloric acid concentration. If you need to increase the yield, you can add an appropriate amount of acetone as a poor solvent after salt formation to promote crystal precipitation and further reduce the impurity content.

4. Application areas

N-methylallylamine hydrochloride has the advantages of strong stability, excellent water solubility, and high reaction controllability, which makes up for the shortcomings of free amines that are easily oxidized and flammable. It is more widely used in fine chemicals, pharmaceutical synthesis, water treatment and other fields. The core scenarios are as follows:

1. Pharmaceutical and pesticide intermediates

As a mild nitrogen-containing synthon, it can be used to prepare antihistamines, antibiotic intermediates and heterocyclic pesticides. Its protonated amino group can accurately participate in nucleophilic substitution and cyclization reactions, and its solid form is convenient for storage, metering and reaction system control. Compared with free amines, it is more suitable for precise feeding requirements in pharmaceutical synthesis. For example, through condensation with carboxylic acid compounds, N-methylallyl amide derivatives can be synthesized, providing key intermediates for the development of anti-tumor drugs and anti-viral drugs.

2. Synthesis of polymer materials

The retained carbon-carbon double bonds can be used as polymerization monomers for free radical copolymerization with acrylamide, dimethyldiallylammonium chloride and other monomers to prepare cationic water-soluble polymers. This type of polymer has good flocculation, adsorption and biocompatibility, and is widely used in municipal sewage treatment (removal of organic pollutants and heavy metal ions), paper industry (as retention and filter aid), oil exploration (as drilling fluid treatment agent) and other scenarios. The hydrochloride form can improve the dispersion of monomers in aqueous solutions and optimize polymerization reaction efficiency. In addition, it can also be used to modify epoxy resin and polyurethane materials to improve the bonding strength and corrosion resistance of the product.

3. Fine chemical additives

It can be used as the core raw material of formaldehyde-free color fixing agents in the textile printing and dyeing industry. Through interaction with fibers and dye molecules, it can improve the dye fastness without formaldehyde release, which is in line with the development trend of environmentally friendly additives. At the same time, metal corrosion inhibitors can be prepared to inhibit the corrosion of steel, copper and other metals in industrial circulating water systems. Its protonated amino groups can be adsorbed on the metal surface to form a protective film, and the corrosion inhibition effect is long-lasting.

4. Laboratory R&D reagents

In the research and development of organic synthesis, it is used as a controllable amine source reagent to explore the synthesis route of nitrogen-containing compounds. It is especially suitable for experimental scenarios that are sensitive to reaction conditions and need to avoid volatilization contamination of free amines. It can also be used as a protonated amine model compound to study the reaction mechanism of amine salts.

5. Safety protection, storage and transportation

Although N-methylallylamine hydrochloride is less toxic and flammable than free amine, it is still irritating and hygroscopic. Safety operating procedures must be strictly followed to avoid potential risks:

1. Hazardous characteristics

This substance is an irritating solid. After absorbing moisture, the aqueous solution becomes acidic and has a corrosive and irritating effect on the skin, eyes and respiratory tract. It will undergo a neutralization reaction when it comes into contact with strong alkali, releasing flammable and toxic N-methylallyl free amine. It will easily decompose when heated to above 180°C, producing hydrogen chloride gas and olefin impurities. The temperature environment needs to be strictly controlled.

2. Handling and storage specifications

Operations must be carried out in a well-ventilated laboratory or workshop. Operators must wear dust masks, chemical-proof gloves, protective glasses and acid-resistant protective clothing to avoid direct contact with skin and inhalation of dust. The weighing and feeding processes need to be done quickly to prevent moisture absorption and clumping. Store in a dry and cool warehouse, with the temperature controlled at 2-30°C, sealed packaging (sealed in aluminum foil bags or glass bottles, lined with desiccant), stored separately from strong alkali, oxidants, and food chemicals, away from fire and heat sources. The warehouse must be equipped with dehumidification equipment and emergency protective supplies.

3. Emergency measures

- Leakage treatment: If there is a small leakage, cover it with dry sand or activated carbon to absorb it, collect it in a sealed container for professional treatment, and avoid contact with water (to prevent dissolution and spread); if there is a large leakage, build a dike to contain it, wear protective equipment for cleaning, and it is strictly prohibited to mix it into sewers or water bodies.

- First aid measures: Immediately rinse with plenty of running water for more than 15 minutes after skin contact. If redness, swelling or burns occur, seek medical attention immediately. After eye contact, rinse immediately with normal saline, avoid rubbing, and seek medical attention immediately. After inhaling dust, move to fresh air, keep the respiratory tract open, and provide oxygen and seek medical treatment if necessary. After accidental ingestion, do not induce vomiting. Dilute with appropriate amount of warm water and seek medical attention immediately.

- Firefighting measures: In the event of a fire, dry powder or carbon dioxide fire extinguishers can be used to extinguish the fire. Avoid direct spraying with water (to prevent the risk of diffusion after dissolution). Firefighters must wear gas masks and protective clothing, extinguish fires in the upwind direction, and be alert to toxic gases produced by decomposition at high temperatures.

6. Conclusion

As an important derivative salt of N-methylallylamine, N-methylallylamine hydrochloride significantly improves the stability and safety of the free amine through protonation to form a salt, while retaining key reactive functional groups. It has outstanding application advantages in the fields of pharmaceutical synthesis, polymer materials, fine chemicals and other fields. As environmental protection requirements upgrade and the demand for high-purity, low-risk raw materials in the fine chemical industry increases, its preparation process will be further optimized toward high efficiency, greenness, and low by-products. At the same time, its application potential in emerging fields such as new energy materials and biomedical polymers will gradually be tapped. In the future, it is necessary to continue to optimize purification technology to improve product purity, explore cost control solutions in large-scale production, promote its industrial application in more high-end fine chemical scenarios, and achieve coordinated development of functional value, safety and environmental protection.