N-methyl-4-nitroaniline(C7H8N2O2，MNA) appears as brownish-yellow prisms with violet reflex (from ethanol) or yellow powder with a melting point of 152 °C. N-methyl-4-nitroaniline is easily soluble in acetone and benzene, slightly soluble in ethanol, and insoluble in water.N-methyl-4-nitroaniline is an ingredient of insensitive munitions (IM) compounds that serves as a plasticizer and helps reduce unwanted detonations. As its use becomes widespread, N-methyl-4-nitroaniline waste streams will be generated, necessitating viable treatment options[1].

Fig 1. Chemical structure formula and three-dimensional structure of N-Methyl-4-nitroaniline

N-methyl-4-nitroaniline is representative of a class of energetic materials that contain both a nitro group and amino group; it also has a methyl substituent on the amine group.The hydrogen bonding ability of an amine group is responsible for the conformation and crystal structure of many organic and biomolecules and is important in energetic materials. N-methyl-4-nitroaniline is an especially interesting compound since there is an interplay between hydrophilic and hydrophobic functional groups when dissolved in water. By studying the hydration structure of N-methyl-4-nitroaniline, one can obtain an understanding of the effect of the methylamino and nitro groups when they are connected to aromatic ring in the para position[2]. N-methyl-4-nitroaniline is an attractive candidate for  its appealing capability to retain the nitrogen oxides, good thermal stability, and facile synthesis from abundant and inexpensive starting materials[3,4].N-Methyl-4-nitroaniline is used as an additive to lower the melting temperature of energetic materials in the synthesis of insensitive explosives. Although the biotransformation of N-Methyl-4-nitroaniline under anaerobic condition has been reported, its aerobic microbial degradation has not been documented yet. A soil microcosms study showed the efficient aerobic degradation of N-Methyl-4-nitroaniline by the inhabitant soil microorganisms[5-6]. N-methyl-4-nitroaniline is a stabilizer for gunpowder, a desensitizing agent for molten cast explosive TNAZ, a widely used organic intermediate, and N-methyl-4-nitroaniline can be used as a reference substance by its polarizing properties.

Preparation:N-methyl-4-nitroaniline is prepared from p-nitroacetanilide, methyl iodide and ethanol. After mixing acetone, p-nitroacetanilide and potassium hydroxide, the mixture was heated to reflux, and the acetone solution of methyl iodide was added dropwise. After the addition was completed, the reflux was continued for 4 hours. After standing overnight, the acetone was recovered, and crystals were precipitated. The crystals were washed by cooling, and then washed with ethanol to obtain N-methyl-4-nitroacetanilide. Then, it was mixed with ethanol and hydrochloric acid, and heated under reflux for 8 hours. The ethyl acetate and ethanol were recovered, diluted with water, washed with acidity, and dried to obtain a crude product. The crude product was dissolved in acetone, filtered, and the precipitated crystals recovered as acetone were the N-methyl-4-nitroaniline.

References

[1] Olivares C I , Wang J , Silva Luna C D , et al. Continuous treatment of the insensitive munitions compound N-methyl-p-nitro aniline (MNA) in an upflow anaerobic sludge blanket (UASB) bioreactor[J]. Chemosphere, 2016, 144:1116-1122.

[2] Boddu V M , Abburi K , Maloney S W , et al. Physicochemical properties of an insensitive munitions compound, N-methyl-4-nitroaniline (MNA)[J]. Journal of Hazardous Materials, 2008, 155(1-2):288-294.

[3] Tang QF, Fan XZ, Li JZ, Bi FQ, Fu XL, Zhai LJ (2016).Experimental and theoretical studies on stability of new stabilizers for N-methyl-P-nitroaniline derivative in CMDB propellants. J Hazard Mater 327:187–196.

[4] Trache D, Tarchoun AF (2018b) Stabilizers for nitrate esterbased energetic materials and their mechanism of action: a state-of-the-art review. J Mater Sci 53:100–123.