In synthetic routes that require both a primary aromatic amine and a methylated benzylic secondary amine on the same monomer, 3-amino-N-methylbenzylamine (IUPAC 3-(methylaminomethyl)aniline, CAS 18759-96-1) is specified as a low-molecular-weight diamine intermediate. Its molecular formula is C₈H₁₂N₂, molecular weight 136.19 g/mol, and exact mass 136.1000 g/mol. The SMILES string is CNCC1=CC(=CC=C1)N, and the InChI is InChI=1S/C8H12N2/c1-10-6-7-3-2-4-8(9)5-7/h2-5,10H,6,9H2,1H3. The molecule contains a meta-substituted primary aromatic amine and an N-methyl secondary aliphatic amine linked through a benzylic methylene group.

Research grades are supplied in 1 g to 100 g catalog quantities, while bulk technical lots are sold under CAS-specific product codes in 200 L nitrogen-purged steel or HDPE drums and 1000 L IBCs. No uniform industry model number exists for this substance; grade differentiation is based on assay, water content, color, isomer purity, and residual solvents. Discharge from cold storage may require warming to 35–40 °C because the material can become viscous at 2–8 °C.

What specification limits and analytical methods are used for lot acceptance?

Because no single ISO or ASTM product standard covers this substance, acceptance criteria are derived from supplier certificates of analysis and harmonized with the methods listed below. The following table is representative for technical-grade material and must be checked against the specific lot certificate.

The gas chromatography assay is reported as area percent and does not detect non-volatile salts or water. For pharmaceutical campaigns, sulfated ash, chloride, and nitrite are tested separately because trace nitrite can react with the secondary amine. Pharmaceutical-grade lots may also specify residual solvents by headspace GC according to USP <467> or an equivalent pharmacopeial method, because methanol, ethanol, or toluene may remain from the reductive amination route. In epoxy and polyurethane applications, water content above 0.5% w/w shifts stoichiometry by consuming isocyanate or by opening epoxide rings through hydrolysis side reactions.

In epoxy-amine thermoset formulation, the reactive amino hydrogen count determines the amine hydrogen equivalent weight. The molecule contains 3 active amino hydrogens: 2 on the primary aromatic amine and 1 on the secondary N-methyl amine. The calculated AHEW is therefore 136.19 g/mol ÷ 3 = 45.40 g/eq. For a conventional bisphenol A diglycidyl ether resin with an epoxide equivalent weight of 188 g/eq, as determined by ASTM D1652, the stoichiometric loading is (45.40 × 100) ÷ 188 = 24.1 phr.

The cure profile is not uniform across the three N–H sites. The secondary aliphatic amine is more nucleophilic than the aromatic amine and can react earlier in the exotherm or catalyze epoxy homopolymerization; the aromatic amino hydrogens require higher thermal input and contribute to final crosslink density. Thermal screening should be conducted by differential scanning calorimetry under ISO 11357-2, and the cured glass transition should be measured according to ASTM E1356 or equivalent dynamic mechanical methods. Because the aliphatic and aromatic amine sites have different reaction rates, the practical AHEW in low-temperature cure may be higher than the theoretical value, and stoichiometric adjustments should be based on laminate or casting trials.

In polyurethane systems, the secondary amino hydrogen reacts with aliphatic or aromatic isocyanates such as isophorone diisocyanate or hexamethylene diisocyanate to form substituted urea. The aromatic amine remains less reactive toward isocyanate at low temperature, allowing staged chain extension and post-cure adhesion development. Yellowness relative to aliphatic-only amine curatives can be quantified by ASTM E313; water in the hardener must be kept below 0.5% because 1 mol water consumes 2 isocyanate equivalents and generates carbon dioxide, causing foaming and off-ratio networks.

Pharmaceutical Intermediate Handling and Nitrosamine Risk Control

In pharmaceutical synthesis, the compound is used as a bifunctional aniline–benzylamine building block. The primary aromatic amine undergoes diazotization, Sandmeyer halogenation, amide coupling, and palladium-catalyzed aryl amination; the secondary N-methylbenzylamine participates in acylation, sulfonylation, reductive amination, and urea formation. N-methylation suppresses overalkylation at the benzylic nitrogen and leaves a single side-chain N–H for controlled derivatization. In dye intermediate use, the aromatic amine can be diazotized and coupled to naphthols or pyrazolones; the N-methylbenzylamine side chain increases the molecular weight and alters hydrophilicity of the resulting azo dye.

Process-scale campaigns commonly isolate the compound as the free base; amine salts are used only when a subsequent aqueous workup requires water solubility. Glass-lined or stainless steel 316L reactors are specified, and copper-containing alloys are excluded because of amine complexation and color body formation. If the aromatic amine is to be diazotized, the secondary methylamine must be protected or the pH and temperature controlled to avoid side reactions. Published data for this specific configuration is limited; pilot-scale experiments should establish the required pH and nitrite stoichiometry for each route.

Because the molecule contains a secondary N-methyl amine, it falls within the scope of nitrosamine risk assessments under ICH M7(R2) and regional regulatory guidance. Exposure to nitrite at low pH can produce the corresponding N-nitroso derivative. Manufacturing controls for pharmaceutical use therefore avoid nitrite or nitrous acid in the same vessel, maintain aqueous workup pH above 5, and use dedicated equipment or validated cleaning where nitrite is handled upstream. The aromatic amine also carries a primary-amine structural alert; residual levels in drug substances should be assessed under ICH M7(R2) and purge calculations, rather than assumed to be fully removed by recrystallization.

When the Meta Isomer Is Compared with 4-Amino-N-methylbenzylamine and N-Methylbenzylamine

Relative to N-methylbenzylamine (CAS 103-67-3), the title compound is not a monofunctional secondary amine but a difunctional aromatic-aliphatic diamine. N-methylbenzylamine has 1 reactive amino hydrogen and no aromatic amine; it is therefore limited to salt formation, single-site derivatization, and catalysis. The title compound has 3 reactive amino hydrogens and can be incorporated into polymer backbones or derivatized at the aromatic ring and the benzylic nitrogen. This changes its regulatory profile, storage behavior, and process hazard because primary aromatic amines are more readily oxidized and may present a genotoxic impurity burden in pharmaceutical routes.

Relative to 3-aminobenzylamine (CAS 4403-69-4), N-methylation reduces the side-chain functionality from 2 active hydrogens to 1. The calculated AHEW increases from 30.54 g/eq to 45.40 g/eq, and the maximum number of covalent bonds available at the aliphatic nitrogen is reduced from 2 to 1. In reductive amination, acylation, and urea synthesis, this suppresses overalkylation and simplifies impurity profiles. The secondary amine is also more basic than the primary aliphatic amine in 3-aminobenzylamine, with an approximate conjugate acid pKa near 9.5 versus 9.3 for the benzylamine nitrogen, while the aromatic amine pKa remains in the 4.5–5.0 range depending on solvent and ionic strength.

Relative to 4-amino-N-methylbenzylamine, the meta substitution pattern changes the geometry of the aromatic core. In polyamide and polyimide syntheses, meta-linked diamine monomers introduce a kinked chain path that reduces crystallinity, often lowers the glass transition and melt transition relative to para-linked counterparts, and increases solubility in polar aprotic solvents. These thermal transitions should be measured by ISO 11357-2 or ASTM E1356 for each polymer composition because the observed effect depends on the comonomer and molecular weight. Compared with N,N-dimethyl-3-aminobenzylamine, the title compound retains the side-chain N–H required for covalent incorporation; the dimethyl analogue is a tertiary amine and can only function as a catalyst or salt former unless quaternized.

The ortho-substituted analogue is not commonly offered at bulk scale because intramolecular hydrogen bonding between the ortho amino group and the benzylic nitrogen can alter amine reactivity and reduce shelf stability; meta substitution avoids this interaction and provides a more predictable cure profile in step-growth polymer systems.

Storage stability and incompatibilities are governed by the two amine sites. The secondary amine can absorb carbon dioxide from ambient air, forming carbamate species; repeated opening of containers under humid air also increases water content and can produce a surface crust or haze. The product is therefore stored under a nitrogen blanket in closed, grounded containers at 2–8 °C for long-term retention; open handling in areas above 60% relative humidity should be avoided unless the material is used immediately in aqueous or moisture-tolerant chemistry. Transfer equipment should use stainless steel 316L, PTFE, or glass-lined wetted surfaces; copper, brass, zinc, and mild steel are avoided because they can promote color formation and metal contamination. The compound is incompatible with strong oxidizing agents, acid chlorides, anhydrides, isocyanates, peroxides, nitrous acid, and nitrite-generating acidic solutions. For moisture-sensitive polyurethane or organometallic steps, pre-drying with activated 4A molecular sieves under inert gas is required before use.

Distillation of the product should be preceded by removal of dissolved carbon dioxide; otherwise the carbamate may decompose during heating and release carbon dioxide or form high-boiling residues. The product has limited public toxicological data, so industrial handling should follow amine-specific occupational exposure limits and use local exhaust ventilation, nitrile or butyl rubber gloves, and full chemical goggles. Waste streams should be collected separately and neutralized with dilute acid under controlled pH before disposal according to local regulations.