Development of a system for clean and regioselective mononitration of aromatic compounds involving a microporous solid, dinitrogen tetroxide and air

Abstract

Nitration of aromatic compounds using a zeolite as a solid inorganic catalyst and a combination of dinitrogen tetroxide and oxygen or air as the nitrating reagent, in open or sealed systems, leads to high yields and significant para selectivities for halogenobenzenes and other aromatics in a relatively clean process. The material used as catalyst has a strong influence on the reaction.

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.…”

Regioselective Electrophilic Aromatic Substitution Reactions over Reusable Zeolites

“…Therefore, we decided to study nitration using dinitrogen tetroxide and oxygen in the presence of zeolites to see if we could develop a process that would be mild, high-yielding and para-selective. [53,54]. a Hβ (1 g), 5 (10 mmol), 1,2-dichloroethane (30 ml) and N 2 O 4 (ca.…”

Regioselective dinitration of simple aromatics over zeolite Hβ/nitric acid/acid anhydride systems

“…[5][6][7][8][9][10][11] We have reported the successful use of zeolites in various electrophilic aromatic substitution reactions. [12][13][14] We have shown that the zeolites can be used in greener para-regioselective reactions including nitration, [15][16][17][18][19][20][21] alkylation, 22,23 acylation, 24,25 halogenation 26,27 and methanesulfonylation 28 reactions.…”