A Novel Method for the Nitration of Simple Aromatic Compounds

Abstract

Simple aromatic compounds such as benzene, alkylbenzenes, halogenobenzenes, and some disubstituted benzenes are nitrated in excellent yields with high regioselectivity under mild conditions using zeolite β as a catalyst and a stoichiometric quantity of nitric acid and acetic anhydride. The zeolite can be recycled, and the only byproduct is acetic acid, which can be separated easily from the nitration product by distillation; the process is inexpensive and represents an attractive method for the clean synthesis of a range of nitroaromatic compounds. For example, nitration of toluene gives a quantitative yield of mononitrotoluenes, of which 79% is 4-nitrotoluene; fluorobenzene gives a quantitative yield of mononitro compounds, of which 94% is 4-nitrofluorobenzene; and 2-fluorotoluene gives a 96% yield of mononitro products, of which 90% is the 5-nitro isomer and 10% is the 4-nitro isomer.

Mixed Oxide Supported MoO3 Catalyst: Preparation, Characterization and Activities in Nitration of o-xylene

“…With respect to this, solid acid catalysts are potentially more attractive due to their shape selective behavior, non corrosiveness, easy recovery, reusability and environmentally friendly nature. Taking in to the account of this, zeolite beta [4,5], ZSM-5 [5,6], sulfated zirconia [7], sulfuric acid supported on silica [8], clay supported metal nitrates [9], metal exchanged clays [10] etc. have been used and studied for the nitration of aromatic substrates like benzene, toluene, halo-benzene, phenol, anisole and disubstituted benzene [4][5][6][7][8][9][10]11,12].…”

“…Taking in to the account of this, zeolite beta [4,5], ZSM-5 [5,6], sulfated zirconia [7], sulfuric acid supported on silica [8], clay supported metal nitrates [9], metal exchanged clays [10] etc. have been used and studied for the nitration of aromatic substrates like benzene, toluene, halo-benzene, phenol, anisole and disubstituted benzene [4][5][6][7][8][9][10]11,12]. However, some of these catalysts were suffered with need of longer residence time, tedious workup procedures and above all, their expensiveness MoO3 based catalysts are well known and successfully tested for different applications like, trasesterification of dimethyl oxalate with phenol [13], thiophene hydrodesulfurization and 1-cyclohehene hydrogenation [14] and hydroprocessing applications [15].…”

Regioselective nitration of 2- and 4-nitrotoluenes over systems comprising nitric acid, an acid anhydride and a zeolite

“…In order to gauge the influence of various zeolites, nitration of 2-NT (35 mmol) was carried out using various quantities of both nitric acid and acetic anhydride (Scheme 1) over 2 g of zeolite HY or Hβ at 50 °C for 4 h. These zeolites were chosen because both have large pores (2-NT might have difficulty entering the pores of small or medium pore zeolites) and have shown high regioselectivity in previous nitration studies. [13][14][15][16][17][18][19][20][21][22] The results obtained are recorded in Table. Table 1 shows that no reaction took place when HY zeolite (SiO 2 /Al 2 O 3 = 5.1) was used as a catalyst; the starting material was recovered quantitatively even when a large excess of nitrating reagent was used.…”

“…Despite the increased size of the substrate compared to toluene itself, it was clear that zeolite Hβ remained significantly better than zeolite HY in terms of both activity and selectivity for 2,4-DNT production. [13][14][15][16][17][18][19][20][21][22] Therefore, zeolite Hβ was selected as the catalyst for investigation of the nitration of 4-nitrotoluene (4-NT).…”

“…11 The 2,4-:2,6-DNT ratio was improved to 14 when the reaction was carried out with nitric acid over zeolite H. 12 We have shown that zeolites and other solid catalysts can play an important role in the enhancement of regionselectivity in nitration processes [13][14][15][16][17][18][19][20][21][22] and in many other electrophilic aromatic substitution reactions. [23][24][25][26][27][28][29][30][31] For example, 2,4-DNT was successfully produced in 96% yield with a 2,4-:2,6-DNT ratio of 70:1 by simple direct dinitration of toluene over a HNO 3 /acetic anhydride (Ac 2 O)/trifluoroacetic anhydride (TFAA)/Hβ system in two steps.…”