Author(s)

Tomoko Matsumoto¹, Ayaka Yamauchi², Jun Ishikawa², Guan-Hong Jin², Jin Matsumoto², Yoshiyuki Fueda³, Masahide Yasuda^2*

¹Center for Collaborative Research and Community Cooperation, University of Miyazaki, Miyazaki, Japan.
²Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki, Miyazaki, Japan.
³Fuji Silysia Chemical Ltd., Miyazaki, Japan.

Nitroaromatics are usually prepared using a mixed acid of nitric acid with strong acids. However, the use of strong acids caused dangerous work-up and the disposal of large amounts of acid-waste. Therefore, much effort has been made on the improvement of nitration process without strong acids. We examined solid-phase aromatic nitration with Mg(NO₃)₂ on silica gel in order to establish the nitration process without strong acids. The nitration of 1,2- and 1,3-, 1,4-dimethoxybenzenes and 4-methylanisole with Mg(NO₃)₂ proceeded by heating on silica gel at 150°C for 4 - 5 h to produce the nitroaromatics. The nitration of 1,3,5-trimethoxybenzene produced the nitrated dimer, 2,4,6,2’, 4’,6’-hexamethoxy-3-nitrobiphenyl, which was not isolated in other solid-phase nitration. In the cases of naphthalene derivatives, the α-nitrated compounds were obtained. In the cases of p-cresol and 2-naphthol, the esterification occurred at the hydroxyl group to give 4-tolyl nitrate and 2-naphthyl nitrate, respectively. It is synthetic interest to note that nitrate esters were isolated in solid phase. Thus Mg(NO₃)₂-SiO₂ composite was mild reagent for solid-phase nitration. Acidity of Mg(NO₃)₂-SiO₂ composite was determined to be pH 0.96 by the measurement of absorption spectra on a micro spectrophotometer using meso-tetra(p-cyanophenyl)porphyrin as a pH-indicator. Mg(NO₃)₂-SiO₂ composite made acidic conditions. Therefore, it was suggested that Mg(NO₃)₂ reacted with proton on silica gel to form the NO⁺₂. Thus, electron-rich aromatic hydrocarbons led the efficient nitration through electrophilic attack of NO⁺₂. After the nitration, acidic Mg(NO₃)₂-SiO₂ composite could be turned into neutrality by exposing wet conditions and disposed safely since the composite did not involve harmful elements. Thus the solid-phase nitration using Mg(NO₃)₂-SiO₂ composite will provide safety and environmentally conscious chemical process.

Aromatic Nitration, Silica Gel, Mg(NO₃)₂, Solid State

Matsumoto, T. , Yamauchi, A. , Ishikawa, J. , Jin, G. , Matsumoto, J. , Fueda, Y. and Yasuda, M. (2017) Solid-Phase Aromatic Nitration with Mg(NO₃)₂ on Silica Gel. International Journal of Organic Chemistry, 7, 1-11. doi: 10.4236/ijoc.2017.71001.