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Its para-substituted aromatic structure gives p-Toluidine a useful balance of reactivity and selectivity in chemical synthesis.
Manufacturers rely on p-Toluidine as a versatile building block for developing high-value colorants and specialized organic compounds.
Reliable purity allows p-Toluidine to deliver controlled conversion and reproducible results in demanding production processes.
CAS Number: 106-49-0
EC Number: 203-403-1
Molecular Formula: C₇H₉N
Molecular Weight: 107.15 g/mol
Synonyms: 4-Methylaniline, 4-Aminotoluene, 4-Methylbenzenamine, 4-Toluidine, 1-Amino-4-methylbenzene, 1-Methyl-4-aminobenzene, p-Aminotoluene, p-Methylaniline, p-Tolylamine, Tolylamine, 4-amino-1-methylbenzene, Benzenamine 4-methyl-, C.I. Azoic Coupling Component 107, C.I. 37107, MFCD00007906, BRN 471281, RTECS XU3150000, CCRIS 4068, HSDB 959, EINECS 203-403-1, CAS 106-49-0
p-Toluidine has the molecular formula C₇H₉N and a molar mass of approximately 107.16 g/mol.
The structure of p-Toluidine contains an amino group and a methyl group positioned opposite each other on a benzene ring.
Also known as 4-methylaniline, p-Toluidine represents the para isomer of toluidine.
The symmetrical substitution pattern distinguishes p-Toluidine from o-toluidine and m-toluidine.
p-Toluidine normally appears as a colorless to pale-yellow crystalline solid.
Exposure to air and light can gradually darken the appearance of p-Toluidine.
The melting point of p-Toluidine lies near 43–45°C, allowing the material to melt in warm environments.
With a boiling point close to 200°C, p-Toluidine remains less volatile than many low-molecular-weight aromatic amines.
Water dissolves only a limited amount of p-Toluidine under ordinary conditions.
Alcohol, ether and several other organic solvents dissolve p-Toluidine more readily.
p-Toluidine behaves as a weak organic base because of its aromatic amino group.
Acids react with p-Toluidine to form corresponding p-toluidinium salts.
Industrial production of p-Toluidine commonly involves the catalytic reduction of p-nitrotoluene.
Hydrogenation converts the nitro group of p-nitrotoluene into the amino group found in p-Toluidine.
Another production route separates p-Toluidine from mixtures containing different toluidine isomers.
Purification methods help manufacturers obtain p-Toluidine with a controlled isomer composition.
p-Toluidine functions primarily as a versatile intermediate in organic synthesis.
Chemical manufacturers use p-Toluidine in the production of dyes, pigments, pharmaceuticals and agrochemical intermediates.
Diazotization converts p-Toluidine into a diazonium compound suitable for further reactions.
Coupling reactions involving diazotized p-Toluidine can produce a variety of azo colorants.
Dye manufacturers value p-Toluidine for introducing a methyl-substituted aromatic unit into molecular structures.
The amino group of p-Toluidine enables reactions that generate numerous colored organic compounds.
Acylation of p-Toluidine produces amide derivatives with different chemical and physical properties.
Alkylation reactions can transform p-Toluidine into secondary or tertiary aromatic amines.
p-Toluidine can react with aldehydes and ketones to produce imine derivatives.
Researchers use p-Toluidine as a starting material for synthesizing heterocyclic and functional aromatic compounds.
Selected pharmaceutical manufacturing routes employ p-Toluidine as an intermediate rather than as a final active ingredient.
Agrochemical synthesis may use p-Toluidine to construct substituted aromatic intermediates.
Rubber and polymer industries can use derivatives prepared from p-Toluidine as functional additives.
Some resin and coating formulations employ compounds manufactured from p-Toluidine.
Reaction temperature, catalyst selection and raw-material purity influence the conversion of p-Toluidine.
Controlled processing helps prevent unwanted discoloration and by-product formation in products containing p-Toluidine.
High-purity p-Toluidine is preferred for applications requiring consistent color and reaction performance.
Commercial grades of p-Toluidine may differ in purity, moisture content and isomer concentration.
Gas chromatography can determine the purity and isomer distribution of p-Toluidine.
Infrared spectroscopy and mass spectrometry can support the identification of p-Toluidine.
Sealed and light-resistant containers help maintain the appearance and quality of p-Toluidine.
Storage away from excessive heat, oxidizing agents and strong acids helps preserve p-Toluidine.
Temperature-controlled handling may be necessary because p-Toluidine can solidify near normal room temperature.
Industrial transfer systems may gently warm p-Toluidine to maintain a pumpable liquid form.
Uses of p-Toluidine:
p-Toluidine is an essential intermediate in the manufacture of numerous acid dyes and azo dyes, including Acid Blue 25, Acid Green 25, Fuchsin Basic, Pigment Red 122, and azo coupling products; the amino group undergoes diazotisation to give p-diazoniotoluene, which couples with various phenols, naphthols, and amines to give commercial azo dyes with excellent colour development stability and colour fastness.
p-Toluidine is used in the Sandmeyer reaction to produce p-chlorotoluene (diazotisation followed by CuCl replacement) — the major industrial starting material for herbicide trifluralin, fenvalerate insecticide, and growth regulators paclobutrazol and uniconazole; it is also converted to 4-bromotoluene (via Sandmeyer with CuBr), 4-fluorotoluene (via Balz-Schiemann fluorination), and 4-aminobenzotrifluoride (via diazotisation-fluorination).
p-Toluidine is used as a pharmaceutical intermediate in the synthesis of the core framework of numerous drug molecules including indomethacin (anti-inflammatory), and in the preparation of dye intermediates such as 4-aminotoluene-3-sulfonic acid, 5-amino-2-methylbenzenesulfonic acid, and 2-(4-aminophenyl)-6-methyl-1,3-benzothiazole-7-sulfonic acid.
p-Toluidine is used in agrochemical production as a building block for herbicides and fungicides, including synthesis intermediates for 3,5-dinitrotoluene, 4-methyl-2-nitroaniline, and related nitrotoluene herbicide precursors; it is also used in the production of permethrin-type pyrethroid insecticides via 1R-cis-permethrinic acid intermediates.
p-Toluidine is used in the rubber chemicals industry as a precursor to antioxidants, vulcanisation accelerators, and 1-(4-methylphenyl)piperazine; it is used as a component of accelerators for cyanoacrylate (instant) adhesives; it forms bidentate Schiff base ligands via condensation with salicylaldehyde, used in coordination chemistry and metal complex catalysis.
p-Toluidine undergoes oxidative coupling with catecholamines to form orange water-soluble dyes, making it useful as a colorimetric reagent for flow injection-spectrophotometric determination of catecholamine drugs; it is also used as a reagent for the detection of lignin, nitrites, and phloroglucinol in analytical chemistry.
p-Toluidine is used as a monomer in the synthesis of water-soluble poly(p-toluidine) and other conducting polymers, which have been investigated as corrosion inhibitors for iron in acid solutions; it is also used in the preparation of aromatic azo compounds, liquid crystal building blocks, and functional materials.
Benefits and Advantages of p-Toluidine:
The para-isomer of toluidine is the commercially most important and most selectively synthesised isomer; it is available at ≥99% purity with specification limits of ≤0.05% ortho-, ≤0.35% meta-isomer, and ≤0.10% low and high boilers, enabling highly controlled downstream synthesis chemistry not achievable with mixed isomers.
The primary amine group of p-toluidine is a versatile bifunctional handle: it undergoes diazotisation (→ diazonium salt → Sandmeyer halogenation, azo coupling, fluorination), acylation (→ acetamides, sulfonamides), condensation (→ imines, Schiff bases), and alkylation reactions, while the para-methyl group can be further oxidised or halogenated, providing two independent sites of reactivity in one molecule.
p-Toluidine is a high-production-volume chemical with established global supply chains, TSCA-listed, REACH-registered, and available in multi-tonne quantities from multiple producers, providing supply security for regulated industries including pharmaceuticals and agrochemicals.
p-Toluidine has well-characterised physical and chemical properties (pKa 5.08, logP 1.39, solubility in dilute acids due to salt formation), enabling predictable process chemistry in both aqueous and organic media across a wide pH range important for dye and pharmaceutical manufacturing.
Features of p-Toluidine:
p-Toluidine is a colourless solid (white lustrous plates or flakes) that turns tan to brown on exposure to air and light; it has an aromatic odour; melting point 41–46°C (freezing point 43–44.5°C); boiling point 200°C; density 0.973 g/mL at 25°C (specific gravity 1.05); refractive index 1.5636; vapour pressure 0.26 mmHg at 25°C (0.66 mmHg at 38°C); vapour density 3.7–3.9 vs air; autoignition temperature 480°C.
p-Toluidine has limited water solubility (0.75 g/100 mL at 20°C; 1.1 g/100 mL by alternate source; slightly soluble — 1 part in 135 parts water by lit.) and is sensitive to air and light (store in the dark, well-closed containers); it is freely soluble in ethanol, pyridine, diethyl ether, acetone, carbon tetrachloride, methanol, carbon disulfide, and oils; it dissolves well in dilute acids forming ammonium salts; pH 7.8 (7 g/L solution).
Key physicochemical parameters: pKa 5.08 at 25°C; logP 1.39–1.44 (pH 7.4–7.5); dielectric constant 4.98; Henry's Law constant 2.9 mol/(m³·Pa) at 25°C; Cp(gas) 1.18 J/(g·K) at 25°C; ionisation potential 7.50 eV; flash point 87°C (c.c.); explosive limits 1.1–6.6% v/v; ITSL 0.03 µg/m³; electrostatic charges may be generated during flow and agitation of the solid — use bonded and earthed equipment.
p-Toluidine is a confirmed animal carcinogen (ACGIH A3; NCI mouse liver carcinoma study — significant increases in liver carcinomas in CD-1 mice at high doses); methemoglobin formation is the principal acute toxicological mechanism; absorption occurs significantly through the skin — classified with skin notation (ACGIH, EU); hemoglobin adducts detectable in blood (used as biomarkers for aromatic amine exposure in smokers and nonsmokers).
Chemical Properties of p-Toluidine:
p-Toluidine has IUPAC name 4-methylaniline (or 1-amino-4-methylbenzene; Benzenamine, 4-methyl-), linear formula CH₃C₆H₄NH₂, SMILES Cc1ccc(N)cc1, InChI=1S/C7H9N/c1-6-2-4-7(8)5-3-6/h2-5H,8H2,1H3, InChIKey RZXMPPFPUUCFRN-UHFFFAOYSA-N; Beilstein/REAXYS 471281; MDL MFCD00007906; RTECS XU3150000.
p-Toluidine is a primary aromatic amine and weak base (pKa 5.08); it neutralises acids to form ammonium salts in exothermic reactions; it undergoes diazotisation with NaNO₂/HCl at 0–5°C to give p-diazoniotoluene, which undergoes Sandmeyer reactions (→ halides), Balz-Schiemann (→ fluoride), Gomberg-Bachmann (→ biaryl), and azo coupling; it undergoes electrophilic aromatic substitution at the ring (positions 2 and 3, ortho and meta to NH₂) favoured by the amine activating group.
p-Toluidine is produced from 4-nitrotoluene by reduction with iron/HCl, catalytic hydrogenation (Fe or Pd/C), or sodium sulfide reduction; purification methods include crystallisation from water (charcoal), ethanol, benzene, petroleum ether, or ethanol/water (1:4); the compound can be sublimed at 30°C under vacuum; the oxalate, sulfate, or acetyl derivatives are used for further purification.
p-Toluidine is incompatible with strong oxidising agents (chlorates, nitrates, peroxides, permanganates, perchlorates, halogens), strong acids, strong bases, isocyanates, halogenated organics, phenols (acidic), epoxides, anhydrides, acid halides, and hydrides (produce flammable H₂); hypergolic reaction with red fuming nitric acid; decomposes on heating with evolution of toxic NOₓ; attacks some forms of plastic.
Production of p-Toluidine:
p-Toluidine is produced industrially from 4-nitrotoluene by three main routes: (1) iron/hydrochloric acid reduction (Béchamp reduction) at ~90–100°C — the classic method; (2) catalytic hydrogenation over Raney nickel, Fe/Pd, or Pd/C catalyst at elevated pressure; (3) sodium sulfide or sodium sulfide nonahydrate reduction for specialty grades; after reduction, p-toluidine is separated from ortho and meta isomers by fractional distillation and crystallisation from ethanol/water or water.
4-Nitrotoluene is itself produced by mixed acid (HNO₃/H₂SO₄) nitration of toluene, which gives a mixture of 2-nitrotoluene (~59%), 4-nitrotoluene (~38%), and 3-nitrotoluene (~3–4%); 4-nitrotoluene is separated by distillation/crystallisation from the nitration mixture; it is subsequently reduced to p-toluidine with purity ≥99% GC after purification.
Commercial p-toluidine is available at ≥99% purity (GC) as white crystalline powder; specification limits: freezing point ≥43°C; ortho-toluidine ≤0.05% GC; meta-toluidine ≤0.35% GC; low boilers ≤0.10% GC; high boilers ≤0.10% GC; global production is approximately 5,000 tonnes per year, with major production in China, Germany, India, and the USA.
p-Toluidine Material Safety Data Sheet (MSDS):
Handling of p-Toluidine:
p-Toluidine is a toxic substance (Hazard Class 6.1) that is toxic by all routes (inhalation, skin absorption, ingestion) and causes methemoglobin formation, cyanosis, and anaemia; skin absorption is a major exposure route — classified with a skin notation; strict hygiene is mandatory: use local exhaust ventilation or full respiratory protection; wear complete protective clothing including gloves, goggles, and, where necessary, SCBA.
Prevent dispersion of dust; do not eat, drink, or smoke during handling; remove and wash contaminated clothing immediately — do NOT take working clothes home; p-toluidine turns dark on exposure to air and light — store in well-closed containers in the dark; electrostatic charges may form during flow and agitation — use bonded and earthed equipment; store away from drains and sewers.
p-Toluidine SDS:
Stability and Reactivity of p-Toluidine:
Chemical stability:
p-Toluidine is stable under recommended storage conditions (below 30°C, well-closed, in the dark, away from air and light).
p-Toluidine is sensitive to air and light (undergoes oxidative darkening); it is incompatible with strong oxidising agents and strong acids.
Reactivity:
p-Toluidine reacts vigorously with strong oxidising agents — contact may cause fires or explosions; it neutralises acids exothermically forming ammonium salts.
On heating and burning, p-toluidine decomposes with evolution of very toxic nitrogen oxides (NOₓ); hypergolic reaction with red fuming nitric acid.
Conditions to avoid:
Air and light exposure (oxidative darkening; store in dark, well-closed containers).
Sources of ignition above flash point 87°C (combustible vapours above 87°C form explosive mixtures).
Contact with strong oxidising agents (peroxides, chlorates, permanganates, halogens, nitric acid).
Release to drains and environment (very toxic to aquatic life).
Incompatible materials:
Strong oxidising agents (chlorates, nitrates, peroxides, permanganates, perchlorates, halogens).
Strong acids, strong bases, epoxides, acid anhydrides, acid halides.
Isocyanates, halogenated organics, phenols (acidic).
Strong reducing agents (hydrides — produce flammable H₂).
Red fuming nitric acid (hypergolic).
Hazardous decomposition products:
Nitrogen oxides (NOₓ) — very toxic — upon heating and combustion.
Carbon monoxide (CO) and carbon dioxide (CO₂).
Aniline-type thermal decomposition products.
Handling and Storage of p-Toluidine:
Handling:
Use local exhaust ventilation or complete protective clothing including SCBA.
Wear protective gloves (nitrile or neoprene), safety goggles, and chemical-resistant protective clothing.
Prevent dispersion of dust; avoid all skin contact (major absorption route); do not eat, drink, or smoke in work areas.
Use bonded and earthed equipment to prevent static charge build-up during handling of solid or melt.
Do NOT let the chemical enter the environment.
Storage:
Store below 30°C in well-closed containers in the dark; provision to contain effluent from fire extinguishing.
Separate from strong oxidants, strong acids, food, and feedstuffs.
Ventilation along the floor; store in an area without drain or sewer access.
Keep in the dark; tightly closed; away from air and light.
Packaging: appropriate containers for toxic class 6.1 materials.
Transport: UN 3451 (Toluidines, solid); Hazard Class 6.1; Labels: Poisonous materials.
First Aid Measures for p-Toluidine:
Inhalation:
Immediately remove the affected person to fresh air; artificial respiration may be needed if breathing has stopped; refer immediately for medical attention.
Symptoms: blue lips, fingernails and skin (cyanosis, methemoglobinemia), confusion, dizziness, headache, shortness of breath, weakness, nausea, unconsciousness — specific treatment for methemoglobinemia (methylene blue, ascorbic acid) must be immediately available.
Skin contact:
MAY BE ABSORBED THROUGH SKIN — remove contaminated clothing immediately; rinse and wash skin thoroughly with water and soap for at least 15 minutes.
Refer immediately for medical attention even if no symptoms — absorption may have occurred.
Eye contact:
Remove contact lenses if easily possible; rinse immediately with plenty of water for at least 15 minutes.
Refer immediately for medical attention.
Ingestion:
Rinse the mouth with water; refer immediately for medical attention — do NOT induce vomiting without medical advice.
Symptoms: blue lips, fingernails and skin, dizziness, headache, laboured breathing — systemic methemoglobin formation.
Firefighting Measures for p-Toluidine:
Suitable extinguishing media:
Water spray, foam, powder, or carbon dioxide (CO₂).
Specific hazards:
p-Toluidine is a combustible solid/liquid (flash point 87°C); above 87°C explosive vapour/air mixtures form; combustion produces very toxic NOₓ fumes; no open flames above 87°C — use closed systems and ventilation.
NFPA: Health 3 / Fire 2 / Reactivity 0.
Protective equipment for firefighters:
SCBA and complete protective clothing; keep drums cool by water spray in case of fire.
Firefighting procedures:
Prevent contaminated firefighting water from entering drains or water courses; provision to contain effluent from fire extinguishing required at storage facility.
Accidental Release Measures for p-Toluidine:
Personal precautions:
Complete protective clothing including SCBA — p-toluidine is toxic by skin absorption.
Do NOT let the chemical enter the environment; sweep spilled substance into sealable containers; if appropriate, moisten first to prevent dusting.
Environmental precautions:
p-Toluidine is very toxic to aquatic organisms (H400); do NOT let chemical enter drains, sewers, or water courses; notify local health and environmental authorities.
Clean-up methods:
Carefully collect spilled material into sealed containers avoiding dust generation; if appropriate, moisten first to prevent dusting.
Dispose according to local regulations for toxic chemicals; controlled incineration with NOₓ scrubbing.
Exposure Controls / Personal Protective Equipment for p-Toluidine:
Engineering controls:
Local exhaust ventilation at point of use; use closed systems above 87°C; ventilation along the floor (vapours heavier than air); general room ventilation.
Eye protection:
Safety goggles; face shield for bulk handling.
Hand protection:
Protective gloves (nitrile, neoprene, or butyl rubber — minimum 0.4 mm tested to EN 374); regular inspection and replacement.
Skin and body protection:
Complete protective clothing; impervious chemical-resistant suit; solvent-resistant boots; do NOT take working clothes home.
Respiratory protection:
Combination cartridge (organic vapour + P2 particulate) for routine handling; positive-pressure full-face SCBA where high concentrations or dust may occur.
Hygiene measures:
Strict hygiene — p-toluidine is absorbed through skin; wash hands and any exposed skin thoroughly before breaks and at end of workday; do not eat, drink, or smoke in work areas; periodic medical examination recommended; specific treatment must be available (methylene blue for methemoglobinemia); BEI (Biological Exposure Index) issued by ACGIH.
p-Toluidine Identifiers:
CAS Number: 106-49-0
EC Number: 203-403-1
MDL Number: MFCD00007906
PubChem Substance ID: 24854162
Beilstein/REAXYS: 471281
RTECS: XU3150000
ChEBI: not listed in file
NACRES: NA.22
UNSPSC: 12352100
IUPAC Name: 4-methylaniline (Benzenamine, 4-methyl-)
Linear Formula: CH₃C₆H₄NH₂ (C₇H₉N)
Molecular Formula: C₇H₉N
Molecular Weight: 107.15 g/mol
SMILES: Cc1ccc(N)cc1
InChI: InChI=1S/C7H9N/c1-6-2-4-7(8)5-3-6/h2-5H,8H2,1H3
InChIKey: RZXMPPFPUUCFRN-UHFFFAOYSA-N
pKa: 5.08 (25°C)
LogP: 1.39–1.44 (pH 7.4–7.5)
Dielectric constant: 4.98
Henry's Law constant: 2.9 mol/(m³·Pa) at 25°C
Ionisation potential: 7.50 eV
GHS Signal Word: Danger
GHS Hazard Statements: H301, H311, H317, H319, H331, H373, H400, H411 (also H302, H332 in some notifications)
GHS Precautionary Statements: P260, P264, P270, P272, P273, P280, P301+P310, P302+P352, P304+P340, P305+P351+P338, P311, P312, P314, P333+P313, P363, P391, P405, P501
NFPA 704: Health 3 / Fire 2 / Reactivity 0
UN Number: UN 3451 (Toluidines, solid)
Hazard Class: 6.1
Packing Group: II
RIDADR: UN 3451 6.1/PG 2
WGK Germany: 2
Risk Statements: R23/24/25, R36, R40, R43, R50
Storage Class: 6.1A
HS Code: 38220000
TSCA: Listed
EINECS: 203-403-1
ITSL: 0.03 µg/m³ (annual average)
TLV-TWA (ACGIH): 2 ppm (skin); A3 carcinogen; BEI issued
EU-OEL: 1 ppm TWA (4.46 mg/m³); STEL 2 ppm (8.92 mg/m³); skin notation
MAK: skin absorption (H); skin sensitisation (SH); carcinogen category 3
Rabbit oral LD50: 336 mg/kg
Rabbit dermal LD50: 890 mg/kg
Autoignition: 480°C
Explosive limits: 1.1–6.6% v/v
Properties of p-Toluidine:
Physical state: Solid (crystalline) at ambient temperature; liquid above 41–46°C
Appearance: Colourless to white lustrous plates or flakes (turns tan to brown in air and light)
Odour: Aromatic
Molecular formula: C₇H₉N
Molecular weight: 107.15 g/mol
Melting point: 41–46°C (lit.); 43–44.5°C (typical)
Boiling point: 200°C
Flash point: 87°C (c.c.); 188–192°F
Autoignition temperature: 480°C
Explosive limits: 1.1–6.6% v/v
Density: 0.973 g/mL at 25°C; relative density 1.05
Vapour density: 3.7–3.9 (air = 1)
Vapour pressure: 0.26 mmHg (25°C); 0.66 mmHg (38°C)
Refractive index: 1.5636
Water solubility: 0.75–1.1 g/100 mL at 20°C; pH 7.8 (7 g/L)
Organic solvent solubility: Freely soluble in ethanol, pyridine, ether, acetone, CCl₄, methanol, CS₂, oils; soluble in dilute acids
pKa: 5.08 (25°C)
LogP: 1.39–1.44
GHS Classification: Danger — H301, H311, H317, H319, H331, H373, H400, H411
Sensitivity: Air and light sensitive
Storage: Below 30°C; in the dark; well-closed; away from drains
p-Toluidine Properties — Specifications:
Product name: p-Toluidine (4-Methylaniline)
CAS Number: 106-49-0
EC Number: 203-403-1
Molecular Formula: C₇H₉N
Molecular Weight: 107.15 g/mol
Purity (GC): ≥99% (≥99.6% high purity grade)
Specification limits: Freezing point ≥43°C; o-toluidine ≤0.05% GC; m-toluidine ≤0.35% GC; low boilers ≤0.10% GC; high boilers ≤0.10% GC
Appearance: White to off-white crystalline powder or flakes (turns dark on exposure to air and light)
Melting point: 41–46°C
Boiling point: 200°C
Density: 0.973 g/mL at 25°C
Storage: Below 30°C; tightly closed; in the dark; away from air, light, oxidants, and acids
Sensitivity: Air and light sensitive — protect from air exposure and UV light
Shelf life: 36 months under proper storage
Documents: CoA (Certificate of Analysis), MSDS/SDS available
Names of p-Toluidine:
p-Toluidine
4-Methylaniline
4-Aminotoluene
4-Methylbenzenamine
4-Toluidine
1-Amino-4-methylbenzene
1-Methyl-4-aminobenzene
p-Aminotoluene
p-Methylaniline
p-Tolylamine
Tolylamine
4-amino-1-methylbenzene
Benzenamine 4-methyl-
C.I. Azoic Coupling Component 107
C.I. 37107
MFCD00007906
BRN 471281
RTECS XU3150000
CCRIS 4068
HSDB 959
CAS 106-49-0
UN 3451
