yellow crystalline needles or powder
3-Methyl-4-nitropyridine N-Oxide (POM) is an efficient nonlinear optical organic material having a high nonlinear coefficient and achieving the parametric emission process within the desired spectral range (1–2 μm). POM crystallizes in the orthorhombic class, space group P212121, and point group 222. It is a positive biaxial crystal. It melts at 136°C and the nonlinear coefficient is deff=10 pm/V[1]. This compound exhibits a negative-linear-compressibility (NLC) region as well as exceptionally large positive thermal expansion. The initial compression of the weak supramolecular network in the molecular POM crystal is analogous to the hydrostatic responses of the framework crystals with much stronger cohesion forces. 3-Methyl-4-nitropyridine N-Oxide is a commercial NLO material for pico- and femtosecond optics in the near-IR range[2].
Nitration of picoline-N-oxide in the fourth position yields 3-Methyl-4-nitropyridine N-Oxide. Initially, Picoline-N-oxide (50 g) was melted at 38C and mixed with sulfuric acid (250 ml) in cold condition. Later, nitration of this mixture was done at room temperature by addition of sodium nitrate (70 g) and the solution was continuously stirred until all the solid particles dissolves. Temperature was increased slowly to 70C by keeping it in an oil bath and solution was stirred continuously for 2 h at this temperature. To ensure complete nitration, the solution was maintained about 95–100C for 12 h with continuous stirring. The reaction mixture was taken out from the oil bath and cooled. It is then poured over crushed ice and neutralized with ammonia solution till the pH reaches about 7–8. On cooling, bright yellow crystalline 3-Methyl-4-nitropyridine N-Oxide powder was obtained. It was washed and dried in vacuum[1].
[1] Boomadevi, S. , H. P. Mittal , and R. Dhansekaran . "Synthesis, crystal growth and characterization of 3-methyl 4-nitropyridine 1-oxide (POM) single crystals."Journal of Crystal Growth 261.1(2004):55-62.
[2] Cai, Weizhao , et al. "Anomalous compression of a weakly CHO bonded nonlinear optical molecular crystal." Journal of Materials Chemistry C 2.32(2014).
