H₃PW₁₂O₄₀ synergized with MCM-41 for the catalytic nitration of benzene with NO₂ to nitrobenzene

Abstract

Developing a new environmentally friendly process for benzene nitration to nitrobenzene has been highly desirable for a long time. In this work, NO 2 was used as a nitration agent to replace traditional nitric acid, and different mesoporous SiO 2 and their supported heteropoly acid (salt) were employed to catalyze benzene nitration to nitrobenzene. Several typical catalysts were characterized using XRD, BET and FT-IR, and the acid amounts of the various catalysts were determined. The effects of various factors such as different catalysts, the molar ratio of benzene to NO 2 , reaction temperature, reaction time, HPW loading, the acid amounts of the catalyst and the reuse of the catalyst on the nitration reaction have also been systematically examined. The results indicate that the supported HPW/MCM-41 catalysts exhibit a remarkably synergistic catalytic performance on the nitration reaction of benzene to nitrobenzene. In particular, the 50%HPW/MCM-41 catalyst gives the best results with 73.4% benzene conversion and 98.8% selectivity to nitrobenzene under the optimal reaction conditions. Moreover, the mesoporous structure of MCM-41 was retained under the high loading of HPW. The possible reaction mechanism for the nitration reaction of benzene with NO 2 over HPW/MCM-41 is suggested in the present work. This method provides a promising strategy for the preparation of nitro-aromatic compounds from a catalytic nitration reaction by using NO 2 as the nitration reagent.

Metal salts with highly electronegative cations as efficient catalysts for the liquid-phase nitration of benzene by NO2 to nitrobenzene

“…When the temperature was further increased to 110°C, the conversion increased slightly to 96.0% and the selectivity slightly decreased to 98%. The reason for the decrease in selectivity is that a higher temperature accelerates the side reaction of the conversion of nitrobenzene to dinitrobenzene [16]. Both metadinitrobenzene and para-dinitrobenzene were formed at 110°C.…”

“…However, all of these still require the use of high concentrations of nitric acid as the nitrating agent. In the past few years, several new nitration agents such as NO 2 [16], N 2 O 5 [17,18], nitrate salts [19], Zn(NO 3 ) 2 $2N 2 O 4 [20] and nitronium tetrafluoroborate [21] have been used as an alternative to nitric acid. Among these nitration agents, NO 2 has attracted a great deal of attention because it is "acid-free" and is readily available [22][23][24][25].…”

Solvent-Free, Low-Temperature, Highly Efficient Catalytic Nitration of Toluene with NO2 Promoted by Molecular Oxygen over Immobilized AlCl3–SiO2

“…In the past few years, some solid acid catalysts had gained considerable attention due to easy separation and recycle from reaction system, high thermal stability, and ecofriendly for the development of green chemical process . In the aromatics nitration reactions, some solid acid catalysts exhibited good catalytic performance, which mainly included FeCl 3 –SiO 2 , MCM-41, H 3 PW 12 O 40 /MCM-41, β-zeolite, , NaZSM-5, H 3 PO 4 /MoO 3 /SiO 2 , sulfated SnO 2 , Cs 2.5 H 0.5 PMoO 40 /SiO 2 , MoO 3 /SiO 2 , H 3 PO 4 /ZSM-5, WO 3 /ZrO 2 and NaHSO 4 /SiO 2 , CuFe 0.8 Al 1.2 O 4 , and H 4 SiW 12 O 40 /ZrO 2 , etc.…”

“…In addition, in regard to nitrating agent, some researchers had reported that NO 2 (N 2 O 4 ), ,, N 2 O 5 , , nitrate or nitrite salts (Fe­(NO 3 ) 3 ·9H 2 O, NaNO 3 , Bi­(NO 3 ) 3 , AgNO 3 , NH 4 NO 3 or NaNO 2 ), − and acetyl nitrate or liquid Ag 0.51 K 0.42 Na 0.07 NO 3 instead of nitric acid were employed in the nitration process. However, compared to other nitrating agents, NO 2 as nitrating agent looks more attractive because it can provide more moderate reaction conditions .…”

The application of nitrogen oxides in industrial preparations of nitro compounds

“…Nitration reactions to form C‐N bonds have been widely used for the preparation of nitro compounds in numerous areas of applied research . Owing to the widespread presence of nitro compounds in pharmaceuticals, natural products, organic intermediates, catalysts, and high energy density materials, the application of this process has been exceptionally broad. However, based on the principles of green chemistry, most industrial nitration processes are less environmentally‐friendly because they use nitric acid, nitrates, and nitrous esters as nitrating agents .…”