Methylamine

Definition and basic information

Methylamine is an organic fatty amine compound. Its standard chemical definition is a colorless gas with an ammonia smell. It is easily soluble in water, flammable and corrosive. It is an important intermediate in the synthesis of various chemical products. First synthesized by Charles Adolphe Wurtz in 1849, this substance also occurs naturally in some plants or as a by-product of the breakdown of ammonia, reflecting the dual properties of natural occurrence and synthetic synthesis.

Core identification information

Key chemical identification of monomethylamine

• CAS registration number: 74-89-5 (the world’s only chemical substance identification)

• Molecular formula: CH₅N (or written as NH₂CH₃, molecular weight 31.0574)

• TSCA Status: Yes (listed on U.S. Toxic Substances Control Act regulatory list

Chinese and English names and aliases

The nomenclature system of monomethylamine covers chemical system nomenclature and common industrial aliases, as shown in the following table:

Physical form and security coding

According to the difference in physical form, the United Nations dangerous goods number (UN number) of monomethylamine is different:

• Gas form: UN 1032

• 40% aqueous solution: UN 2733

• Other forms: UN 3286

These identification information provide the basic basis for its production, transportation and safety control. Subsequent chapters will further carry out in-depth analysis of its chemical properties and application scenarios.

Physical and chemical properties

physical properties

Monomethylamine appears as a colorless gas at normal temperature and pressure, with a strong pungent ammonia-like odor. Its physical parameters show significant volatile characteristics: the melting point is -93.5°C, the boiling point is as low as -6.8°C, and the saturated vapor pressure is as high as 304 kPa (20°C), which means that it is extremely easy to vaporize and diffuse under standard environments. The boiling point of its 40% aqueous solution is only 20.3°F (about -6°C), further confirming its tendency to evaporate quickly in an unsealed state. In terms of density, monomethylamine is 0.669 g/cm³ at -11°C. The vapor density is greater than that of air. It is easy to accumulate in low-lying areas after leakage, increasing the risk of local concentration exceeding the standard.

Solubility is another key characteristic that affects its industrial application and safety control. This substance is easily soluble in water and miscible with organic solvents such as alcohol, ether, and benzene. This property requires the use of corrosion-resistant containers for storage. After leakage, it may spread through water or organic solvents, expanding the scope of contamination.

chemical properties

The chemical properties of monomethylamine are closely related to the amino group in its molecular structure, showing strong alkalinity, high reactivity and significant safety risks. As an organic synthesis intermediate, its basic characteristics allow it to participate in nucleophilic reactions as a proton acceptor in the synthesis of pesticides, medicines and dyes. However, its incompatibility with acids, oxidants, and metals (such as copper, zinc and their alloys) requires strict control of material compatibility during the production process.

The flammable and explosive characteristics constitute its most prominent safety hazard: the flash point is 0℃, the ignition temperature is 430℃ (806°F), and the explosion limit range is as wide as 5%~21% (V/V), which means that explosive gas can be formed when mixed with air at normal temperature. The classification of the United Nations dangerous goods number (UN 1235) and hazard label 3+8 (flammable liquids + corrosive substances) further clarifies the dual risk management and control requirements in transportation and storage.

Summary of key safety parameters: The physical and chemical properties of monomethylamine determine its high risk in industrial scenarios - easy diffusibility caused by low boiling point and high vapor pressure, explosion risk caused by wide explosion limit, and strict requirements on equipment materials due to strong corrosiveness, which together constitute the core consideration basis for subsequent safety operating regulations.

Although its chemical stability means that it is not easy to decompose at room temperature, the superimposed effect of high flammability and reactivity requires that multiple prevention and control measures such as inert gas protection, explosion-proof equipment and leakage monitoring systems must be taken during production, transportation and use to achieve source control of risks.

production method

The production methods of monomethylamine can be divided into two categories: industrial-scale preparation and laboratory synthesis. Among them, the methanol gas-phase ammoniation method has become the mainstream of industry due to its mature process and controllable cost, while the laboratory method is characterized by flexibility and path diversity. The following is an explanation from two aspects: industrial production and laboratory synthesis.

industrial production methods

The technical paths for industrial production of monomethylamine include methanol gas-phase ammoniation method, formaldehyde-ammonia reaction method, methanol-ammonium chloride reaction method, etc. Among them, the methanol gas-phase ammoniation method accounts for more than 80% of the global total production. Its core is to achieve product separation and high-purity control through a multi-tower distillation system.

Methanol gas phase ammoniation process process

This method uses methanol and ammonia as raw materials, and generates a mixture of monomethylamine, dimethylamine, and trimethylamine (collectively referred to as the methylamine mixture) under the action of a catalyst, and then purifies the product through a multi-tower series process of deamination → extraction → dehydration → separation → recovery. The specific process is as follows:

1. Deamination tower: Synthesis gas (containing ammonia and methylamine mixture) first enters the deamination tower, and the azeotrope of ammonia and trimethylamine is separated at the top of the tower. The tower kettle obtains a mixture of monomethylamine, dimethylamine and a small amount of trimethylamine;

2. Extraction tower: Add soft water to the tower still liquid, and use the characteristics of trimethylamine to be easily soluble in water. High-purity trimethylamine is extracted from the top of the tower, and the mixed phase of monomethylamine, dimethylamine and water is retained in the tower still;

3. Dehydration tower: Water is removed through azeotropic distillation, the monomethylamine-dimethylamine azeotrope is taken out from the top of the tower, and the water phase of the tower still is sent to the recovery tower;

4. Separation tower: Use high reflux ratio distillation to separate monomethylamine and dimethylamine. The monomethylamine product is extracted from the top of the tower and dimethylamine is extracted from the side line;

5. Recovery tower: The wastewater from the tower kettle is discharged after treatment, and the unreacted methanol is recovered at the top of the tower and recycled to the synthesis section.

Distillation process parameters and purity control

The core control link of product purity lies in the distillation operation of the separation tower. By accurately controlling the temperature, pressure and reflux ratio, the purity of monomethylamine product can reach the requirement of ≥99.5% for superior products in the HG/T 2972-2017 standard. The key distillation process parameters are shown in the table below:

Other industrial methods

In addition to the methanol gas-phase ammoniation method, industrial production can also be done through the halogenated methyl amination method (such as the reaction of methyl chloride and ammonia), the gas-phase catalytic method of ether, etc. However, due to the high cost of raw materials or low product selectivity, it is only used in specific scenarios (such as co-production of other organic amines).

Laboratory synthesis methods

The synthesis of monomethylamine in the laboratory is characterized by small scale and high flexibility. The main methods include:

1. Methanol-ammonium chloride reaction method: Methanol and ammonium chloride are heated and reacted under the catalysis of zinc chloride to generate monomethylamine hydrochloride. After neutralization with alkali, the free amine is evaporated. It is suitable for preparation in milligram to gram levels;

2. Catalytic ammonolysis method: Methanol and ammonia are synthesized in a small fixed-bed reactor under the action of an aluminosilicate catalyst (such as ZSM-5 molecular sieve). The product ratio can be controlled by adjusting the temperature (280-350°C).

Method comparison and applicable scenarios

Application areas

As an important organic chemical raw material, monomethylamine has a wide range of applications covering agriculture, medicine, chemicals, energy and other industries. Products of different purity levels play a differentiated role in various fields. With the development of high-end manufacturing, its demand in high value-added fields continues to rise.

Agriculture: key inputs for food security

In agricultural production, monomethylamine plays a central role in two ways: first, as a key component of high-efficiency nitrogen fertilizers, it can be sprayed directly or mixed with phosphorus, potassium and other elements to form compound fertilizers to provide nitrogen nutrients for crops and improve soil fertility; second, as a core raw material for pesticides, it participates in the synthesis of broad-spectrum pesticides such as carbaryl, dimethoate, and dipyramide, effectively preventing and controlling crop pests such as aphids and red spider mites, reducing pesticide usage per unit area, and reducing ecological risks. For example, carbaryl is a traditional carbamate pesticide. The amino part in its molecular structure is derived from the amination reaction of monomethylamine. This type of pesticide has an efficient contact killing effect on lepidopteran pests and has a short residual period, which meets the requirements of green prevention and control of modern agriculture.

Pharmaceutical field: High-purity products support drug innovation

Pharmaceutical grade monomethylamine has become a key intermediate in drug synthesis due to its extremely high chemical purity (usually ≥ 99.9%) and low impurity characteristics. By participating in reactions such as cyclization and amination, it facilitates the preparation of products such as anti-cancer drugs (such as the construction of nitrogen heterocyclic structures for some targeted therapeutic drugs), antibiotics (such as side chain modifications of β-lactam drugs), and vitamins (such as the synthetic precursors of vitamin B family). In addition, in pharmaceutical preparations, monomethylamine can be used as a pH regulator to improve the stability and water solubility of drug molecules by fine-tuning the pH of the formula (such as controlling the pH of injection solutions at 7.0–8.0) to ensure bioavailability. Compared with industrial-grade products, pharmaceutical-grade monomethylamine requires multiple distillations and purifications to strictly control the content of heavy metals, moisture and organic impurities to meet GMP standards for drug safety.

The difference in purity determines the application boundary: Industrial-grade monomethylamine (purity 98%–99%) is mainly used in fields with low sensitivity to impurities such as pesticides and dyes, and has significant cost advantages; while pharmaceutical-grade products require special processes to remove trace amounts of aldehydes and ammonia impurities, and their production process complexity and product added value are much higher than those of industrial grade, making them key basic chemical materials that support the research and development of innovative drugs.

Chemical engineering and new materials: the synthetic cornerstone of functional molecules

In the chemical industry, monomethylamine is an important precursor for the construction of surfactants, dyes and polymer materials. By reacting with fatty acids or alkyl bromides, quaternary ammonium salts or quaternary ammonium base surfactants can be generated, which are widely used in detergents (enhancing stain removal capabilities), textile softeners (improving fiber feel) and oil field emulsifiers (improving crude oil recovery). In the field of dyes, azo dyes generated by the reaction of monomethylamine with alizarin intermediates and anthraquinone compounds are widely used for dyeing natural fibers such as cotton and linen due to their bright colors and strong washability. In addition, its application in the fields of rubber additives (such as the synthesis of accelerator M), photographic chemicals (developer intermediates) and solvents further demonstrates its versatility as a "chemical vitamin".

Energy and specialty chemicals: niche but critical application scenarios

Monomethylamine is also involved in the fields of energy and specialty chemicals, such as as a rocket fuel additive (such as the synthetic raw material for monomethylhydrazine), explosive stabilizer and paint stripper component. In the field of energy storage, its derivatives can be used to functionally modify the electrolyte of lithium-ion batteries to improve battery cycle life; in fine chemicals, monomethylamine participates in the synthesis of rubber vulcanization accelerators, which can significantly shorten the rubber vulcanization time and improve the mechanical properties of products.

Industry trends and high-end demand growth in 2025

As global investment in pharmaceutical R&D increases (the global innovative drug market is expected to grow by 12% in 2025) and the biomanufacturing industry upgrades, the demand for high-purity monomethylamine in high-end fields such as anticancer drugs and antiviral preparations (such as nucleoside drugs) is growing at an average annual rate of 8%–10%. At the same time, the development of new energy materials (such as solid electrolytes) and electronic chemicals (photoresist intermediates) has also promoted the demand for ultra-high purity monomethylamine (purity ≥ 99.99%). This structural growth not only highlights the strategic position of monomethylamine in the industrial chain, but also prompts manufacturing companies to increase process innovation to meet the stringent requirements for product quality in downstream industries.

Safety and Health Hazards

As a high-risk chemical, monomethylamine's safety and health hazards are mainly reflected in three dimensions: strong toxicity, flammability, explosiveness and corrosivity. It requires a full chain of control from hazard identification, protection specifications to emergency response.

Hazard identification: superposition of toxicity, explosion and corrosion risks

In terms of health hazards, monomethylamine can be absorbed through multiple channels such as the respiratory tract, gastrointestinal tract and skin, and is metabolized and converted into dimethylamine (more toxic) or oxidized into formic acid in the body, causing double damage to the body. It has strong irritating and corrosive effects on the eyes, skin and respiratory mucosa, and can cause chemical burns; its systemic effects are sympathomimetic effects, and long-term exposure may cause damage to the nervous system and chronic respiratory diseases. This substance has been included in the occupational chemical poisoning category in the "Classification and Catalog of Occupational Diseases" to clarify its occupational exposure risks.

The safety hazard is highlighted by its flammable and explosive characteristics: its explosion limit is 5%~21% (V/V), and the ignition temperature is 430°C. It can form an explosive mixture when mixed with air, and will explode when it encounters a fire source. The combustion process also produces toxic smoke containing nitrogen oxides, exacerbating the harmful consequences.

The corrosiveness cannot be ignored. Monomethylamine can corrode plastics, rubber, coatings and copper, zinc alloy, aluminum and galvanized surfaces, posing a structural threat to storage containers and transportation equipment.

Protection specifications: full-process risk management and control measures

In view of the above hazards, the following safety regulations must be strictly implemented during operation, storage and transportation:

Operational Core Requirements

• Close operations and strengthen ventilation, and use explosion-proof ventilation systems and equipment to prevent gas leakage

• Operators need to receive special training and wear self-priming filter gas masks (full face masks), anti-static overalls and rubber gloves

• Keep away from fire and heat sources. Smoking is strictly prohibited in the workplace and avoid contact with oxidants, acids, and halogens.

During storage and transportation, ensure that the container is well sealed and use explosion-proof transportation tools to avoid severe vibration or high temperature environments. Transport vehicles must be equipped with leakage emergency response equipment and fire-fighting equipment, and are prohibited from stopping in densely populated areas along the way to reduce mass risks caused by leaks.

Emergency warning: chain risks of leakage accidents

The hazards of monomethylamine are particularly prominent in transportation leakage accidents. Due to its volatility and explosiveness, it can quickly form an explosive mixture with air after leakage. It will explode when encountering static electricity or sparks. The toxic gas released at the same time can cause acute poisoning of surrounding personnel. For example, in a transportation leakage accident, monomethylamine vapor spread due to a damaged container, causing a local explosion and causing eye burns and respiratory injuries to many contacts. Such cases warn that emergency response requires evacuating downwind personnel as soon as possible, wearing fully enclosed protective equipment to seal leaks, and using mist water to dilute and disperse toxic vapors. It is strictly forbidden to directly impact the source of leaks with water to prevent secondary diffusion.

By systematically identifying hazards, implementing protective measures and strengthening emergency preparedness, the safety and health risks of monomethylamine can be effectively reduced and the safety of personnel in production and transportation links can be ensured.

Regulations and Standards

As a highly volatile and highly corrosive hazardous chemical, monomethylamine must be produced, transported and used in strict compliance with the laws and regulations of various countries. China has built a complete management and control framework based on purity classification, and promoted the standardized development of the industry through environmental protection policies and compliance requirements. At the same time, the international community has also formed differentiated regulatory priorities, which together form a risk prevention and control network for the entire life cycle of monomethylamine.

China standard system and application scenarios

China has formulated a standard system for monomethylamine that combines hierarchical control and full-chain supervision. In terms of purity classification, according to chemical industry standards, monomethylamine is divided into two grades: premium products and qualified products: premium products have extremely low impurity content (typical purity ≥99.9%) and are mainly used in pharmaceutical intermediates, high-end pesticides, etc. that have strict purity requirements. In the field, the production process must meet GMP-level clean standards; qualified products (purity ≥ 99.0%) are widely used in basic chemical synthesis (such as rubber accelerators, dye intermediates) and other scenarios to ensure process stability while reducing production costs.

At the environmental policy level, laws and regulations such as the Environmental Protection Law and the Air Pollution Prevention and Control Law provide legal basis for monomethylamine pollution control. Among them, the "Three-Year Action Plan for the Defense of the Blue Sky" clearly limits ammonia and nitrogen oxide emissions, and promotes companies to implement real-time online monitoring systems and end-of-line treatment