Methylamine Aqueous Solution (MMA40) 40%

Methylamine Aqueous Solution 40%

Other Names: Monomethylamine solution, Methanamine solution, Aminomethane solution
Chemical Formula: CH₃NH₂ in H₂O
Molar Mass: 31.06 g/mol (methylamine)
CAS Number: 74-89-5
Concentration: 40 wt.% methylamine in water
SMILES: CN
Appearance: Colorless aqueous solution
Odor: Strong, pungent, ammonia-like to fish-like odor

Methylamine is the simplest primary alkylamine, consisting of a methyl group bonded directly to an amino group. A 40% aqueous methylamine solution contains approximately 40% methylamine by mass, with water acting as the solvent. The molecule is strongly polar and participates in hydrogen-bonding interactions with water through its amino group. Molecular simulation studies of methylamine–water mixtures show pronounced intermolecular hydrogen bonding and a characteristic organization of methylamine molecules at the liquid–vapour interface. The amino group preferentially interacts with the aqueous phase, whereas the comparatively nonpolar methyl group tends to orient toward the vapour phase. These molecular interactions significantly influence the thermodynamic and interfacial properties of concentrated methylamine solutions.

Chemical and physical properties

Methylamine aqueous solution containing approximately 40 wt.% methylamine is a volatile liquid under ambient conditions. Experimental and thermodynamic data for this concentration indicate a boiling point of approximately 48 °C at atmospheric pressure. The relatively low boiling temperature reflects the high volatility of dissolved methylamine.

The density of a 40 wt.% aqueous methylamine solution is approximately 0.90 g/cm³ near room temperature, making it less dense than water. Reported values are approximately 0.897 g/mL at 25 °C.

The methylamine–water system exhibits substantial vapour pressure. For a 40 wt.% solution, reported vapour pressures are approximately 280 mmHg at 20 °C and 659 mmHg at 40 °C. The equilibrium composition of the vapour differs considerably from that of the liquid because methylamine is substantially more volatile than water.

Thermodynamic studies of the methylamine–water binary system show strongly non-ideal vapour–liquid equilibrium behaviour. Experimental phase-equilibrium data covering broad temperature and pressure ranges have been successfully represented using equations of state such as PC-SAFT and GEOS. Hydrogen bonding between methylamine and water is one of the principal molecular interactions responsible for the solution's thermodynamic behaviour.

At the molecular level, methylamine is well hydrated in aqueous solution. Computational studies indicate that water molecules arrange around the amino group through directional hydrogen bonding. Simulations of the liquid–vapour interface additionally show enrichment of methylamine in the outermost molecular layer and preferential orientation of the methyl group toward the vapour phase.

Applications

Methylamine aqueous solution is widely used as a reactive chemical intermediate in organic synthesis. The nucleophilic nitrogen atom enables methylamine to participate in alkylation, acylation, condensation and substitution reactions used to prepare a broad range of N-methylated organic compounds.

It is used as a starting material in the preparation of pharmaceuticals, specialty amines, surfactant intermediates, solvents and other industrial organic chemicals. Methylamine is particularly useful where introduction of a methyl-substituted amino group into an organic molecule is required.

In laboratory and industrial research, aqueous methylamine solutions are also used in studies of amine–water thermodynamics, vapour–liquid equilibria, molecular hydration, hydrogen bonding and liquid–vapour interfaces. Their strongly concentration-dependent physical properties make methylamine–water mixtures useful model systems for investigating associating polar fluids.

Scientific references

Horváth, R. A., Fábián, B., Szőri, M., Jedlovszky, P. “Investigation of the liquid-vapour interface of aqueous methylamine solutions by computer simulation methods.” Journal of Molecular Liquids, 2019, 288, 110978. DOI: 10.1016/j.molliq.2019.110978.

Fedotova, M. V., Kruchinin, S. E. “Hydration of methylamine and methylammonium ion: structural and thermodynamic properties from the data of the integral equation method in the RISM approximation.” Russian Chemical Bulletin, 2012, 61(2), 240–247. DOI: 10.1007/s11172-012-0034-5.

Mejbri, K., Bellagi, A. “Modeling of the thermodynamic properties of the methylamine/water refrigerant mixture.” International Journal of Petrochemical Science & Engineering, 2018, 3(5), 161–170. DOI: 10.15406/ipcse.2018.03.00090.

Kato, Y., Hashimoto, H., Yoshizawa, Y. “Cold Heat Storage Performance of Amine/Water Solutions.” Kagaku Kogaku Ronbunshu, 1998, 24(6), 834–839. DOI: 10.1252/kakoronbunshu.24.834.