What is N-methylaniline?

N-methylaniline is an important organic chemical intermediate widely used in pesticides, dyes, and pharmaceuticals. However, it is toxic and flammable, requiring careful handling and storage.

1. Basic Information

Chinese Name: N-Methylaniline

English Name: N-Methylaniline

CAS Number: 100-61-8

Molecular Formula: C₇H₉N

Molecular Weight: 107.15

2. Physicochemical Properties

Appearance: Colorless to reddish-brown oily liquid at room temperature; color gradually darkens upon prolonged storage or exposure to air.

Melting Point: -57°C

Boiling Point: Approximately 196°C (196.25°C)

Density: 0.989 g/mL (25°C)

Solubility: Slightly soluble in water, readily soluble in organic solvents such as ethanol, ether, and chloroform.

Flash Point: Approximately 78°C; flammable liquid.

Refractive Index: 1.5684

Vapor Pressure: 0.13 kPa (36°C)

3. Main Uses

N-Methylaniline is a key intermediate in fine chemicals, with applications covering multiple fields:

(1) Dye Industry

Used to produce cationic dyes, such as:

Cationic Brilliant Red FG, Cationic Peach Blossom

Reactive Yellow Brown KGR, Acid Blue BR, etc.

As a dye intermediate, it is used for printing and dyeing acrylic fibers, polyester fibers, and their blended fabrics.

(2) Pesticide Synthesis

It is an important raw material for the insecticide thiamethoxam (pymetrozine), used to control pests such as rice planthoppers.

Used to synthesize herbicides such as bensulfuron-methyl and methyl chlorpyrifos.

It has no cross-resistance with many pesticide varieties and has high safety.

(3) Pharmaceutical and Organic Synthesis

Used as a pharmaceutical intermediate, participating in the synthesis of certain drugs.

It can be used as a solvent, acid absorbent, and gasoline antiknock agent.

Used in industrial fields such as explosive stabilizers and rubber additives.

4. Synthesis Methods

Industrially, there are two main processes:

Method 1: Catalytic Methylation

Raw Material: Aniline + Methanol

Catalyst: Cu-Zn-Cr/Al₂O₃ modified catalyst (e.g., containing Ce, Mo)

Conditions: 200–250°C, high pressure

Characteristics: High selectivity, but complex catalyst preparation

Method Two: Gas-phase method (dual reactor) Segmented reaction controls product distribution

Can co-produce N-methylaniline and N,N-dimethylaniline

Low energy consumption, but high equipment requirements

5. Safety and Health Risks

N-Methylaniline is a highly toxic hazardous material (hazard class 6.1) requiring strict protection:

(1) Health Hazards

It can be absorbed through the skin, respiratory tract, and digestive tract.

It can cause methemoglobinemia, leading to tissue hypoxia, cyanosis, nausea, vomiting, convulsions, and in severe cases, coma or shock.

It can damage the central nervous system, liver, and kidneys; long-term exposure may lead to chronic poisoning (such as neurasthenia, anemia, hepatosplenomegaly).

(2) Fire and Explosion Hazards

It is flammable and may burn and explode when exposed to open flames, high heat, or oxidizers.

It decomposes upon heating to produce toxic gases (such as nitrogen oxides and carbon monoxide).

(3) Occupational Exposure Limits

Chinese Standards:

PC-TWA (Time-Weighted Average Permissible Concentration): 5 mg/m³

PC-STEL (Short-Term Exposure Limit): 10 mg/m³

The "skin" absorption route is indicated; comprehensive protection is required.

NIOSH/ACGIH: 5 ppm (25 mg/m³) TWA, 10 ppm STEL

(4) Storage and Emergency Handling

Store in a cool, ventilated place, away from fire and heat sources.

Do not store with oxidizers or acids.

Operate in a fume hood, wearing protective clothing, gloves, and a respirator.

Absorb any leaks with sand. For fires, use water mist, foam, or dry powder fire extinguishers.