Zinc Chloride Catalyzed Regioselective Nitration of Aromatic Hydrocarbons Using Tetrachlorosilane-Sodium Nitrate Homogeneous System (original) (raw)
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Frontiers in chemistry, 2024
Electrophilic aromatic nitrations are used for the preparation of a variety of synthetic products including dyes, agrochemicals, high energy materials, fine chemicals and pharmaceuticals. Traditional nitration methods use highly acidic and corrosive mixed acid systems which present a number of drawbacks. Aside from being hazardous and waste-producing, these methods also often result in poor yields, mostly due to low regioselectivity, and limited functional group tolerance. As a consequence, there is a need for effective and environmentally benign methods for electrophilic aromatic nitrations. In this work, the major aim was to develop reaction protocols that are more environmentally benign while also considering safety issues. The reactions were carried out in dilute aqueous nitric acid, and a broad range of experimental variables, such as acid concentration, temperature, time, and activation method, were investigated. Mesitylene and m-xylene were used as test substrates for the optimization. While the optimized reactions generally occurred at room temperature without any activation under additional solvent-free conditions, slight adjustments in acid concentration, stoichiometric equivalents, and volume were necessary for certain substrates, in addition to the activation. The substrate scope of the process was also investigated using both activated and deactivated aromatics. The concentration of the acid was lowered when possible to improve upon the safety of the process and avoid over-nitration. With some substrates we compared traditional and nontraditional activation methods such as ultrasonic irradiation, microwave and high pressure, respectively, to achieve satisfactory yields and improve upon the greenness of the reaction while maintaining short reaction times.
Current Chemistry Letters, 2014
Regioselective nitration of phenols using Sr(NO 3) 2 or benzyltriphenylphosphonium nitrate in the presence of H 2 SO 4-silica had been realized under solvent free conditions. The reaction proceeds through the formation of nitronium ion, which attack the phenol ring preferential at ortho position in presence of Sr(NO 3) 2 , forming mono nitrophenol. Para-orientation relative to hydroxyl group and mononitration of phenolic compounds was observed in the case of benzyltriphenylphosphonium nitrate. Some of the major advantages of this method are mild reaction conditions, high efficiency and regioselectivity of nitration and complementarity with other reported methods. In addition, benzyltriphenylphosphonium nitrate as nitrating reagent can be easily recycled.
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A green and facile methodology for the synthesis of nitrile has been established from the corresponding aldehydes and hydroxylamine hydrochloride on silica-gel in hot condition. The protocol is equally effective for aliphatic as well as aromatic aldehydes, and has wide range of functional group tolerance. In addition, this methodology is solvent-free, inexpensive, environmental friendly and involves simple work-up process.